Difference between revisions of "2017 Group 3 Project"

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Consequential of the clinical importance of pancreas-associated disease, such as diabetes, endocrine tumours and pancreatic cancer, the structure of the pancreas is studied extensively within medical science. Studies of the human pancreas, however, are restricted due to the inherent ethical and medical limitations present in obtaining pancreatic samples at specific and intermittent intervals. As a direct result of scarce human pancreatic samples, animal models are increasingly used in studies. Within current pancreatic research, mice are the most frequently studied animal models. As a sizeable portion of scientific knowledge concerning the cellular architecture of the human pancreas is derived from studies conducted on mice, it is thereby imperative to identify and understand the distinction between the human and mouse pancreas.  
 
Consequential of the clinical importance of pancreas-associated disease, such as diabetes, endocrine tumours and pancreatic cancer, the structure of the pancreas is studied extensively within medical science. Studies of the human pancreas, however, are restricted due to the inherent ethical and medical limitations present in obtaining pancreatic samples at specific and intermittent intervals. As a direct result of scarce human pancreatic samples, animal models are increasingly used in studies. Within current pancreatic research, mice are the most frequently studied animal models. As a sizeable portion of scientific knowledge concerning the cellular architecture of the human pancreas is derived from studies conducted on mice, it is thereby imperative to identify and understand the distinction between the human and mouse pancreas.  
  
[[File:Pancreatic_Anatomy_Comparison.png|200px|Left|Fig 1. Comparison of the macroscopic anatomy of the human pancreas (A) against the mouse pancreas (B).]]
+
[[File:Pancreatic_Anatomy_Comparison.png|400px|right|Fig 1. Comparison of the macroscopic anatomy of the human pancreas (A) against the mouse pancreas (B).]]
  
 
====Macroscopic Comparison====
 
====Macroscopic Comparison====

Revision as of 11:31, 24 May 2017

2017 Projects: Group 1 - Delta | Group 2 - Duct | Group 3 - Beta | Group 4 - Alpha

Beta Cells Title Image.png


Introduction

Background

caption

Beta cells (β cells) are one of the four major cells of the endocrine portion of the human pancreas. The human pancreas is a composite organ, which extends from the distal foregut endoderm and contains an exocrine and an endocrine portion. While the exocrine tissue consists of numerous acinar cells that discharge digestive fluid and a complementary duct complex through which the secreted fluid drains into the intestine, the endocrine portion of the pancreas comprises islets of Langerhans, or pancreatic islets (as reviewed by [1]). The islets of Langerhans constitute approximately 1-2% of the pancreas and are dispersed throughout it [2]. They contain multiple endocrine cells; alpha, beta, delta, gamma and epsilon cells, which secrete different hormones; glucagon, insulin, somatostatin, pancreatic polypeptides and ghrelin, respectively [1]. The pancreatic islets also host several endothelial cells, nerves and fibroblasts hence deeming them highly vascularised structures, which vary in size from small clusters to larger clusters containing up to several thousand islets and reaching diameters of 300-400 μm. As the majority of pancreatic islets are typically less than 160 μm in diameter, islets which exceed this diameter are considered to be responsible for the majority of the total islet mass [3].

Currently, it is predicted that adult humans have approximately 2 million islets of Langerhans, contributing to 2% of total pancreatic weight [4]. Within these pancreatic islets, approximately 60-70% of the total islet-cell population can be attributed to beta cells [5]. Beta cells, or insulin-secreting cells, are thus key cells within the pancreas and are predominately responsible for preserving normoglycaemia by neutralizing blood glucose levels with appropriate quantities of insulin secretion [6]. The hormone insulin is also synthesised and secreted by beta cells in response to other factors aside from glucose, including nervous stimuli, other hormones and multiple nutrients [4].

History

Year Historical Event
1869 The Islets of Langerhans, or Pancreatic Islets, are first discovered by German anatomist Paul Langerhans within rabbits as anatomical formations with no direct connection to the duct but are not given any function. [7] Previous to the discovery, solely recognised as an exocrine organ. [8]
1889 Joseph Von Mering and Oskar Minkowski successfully completed the first pancreatectomy in a dog. Through this, they discovered the removal of the pancreas induced diabetes in the dog thus irrevocable establighing the connection with the pancreas and diabetes. [9]
1893 Edouard Laguesse who discovered the islets in the human pancreas suggested that they were responsible for the internal secretions that regulate glycemia, and named them after their discoverer Langerhans. [10]
1907 and 1911 Lane and Bensley developed staining techniques to analyse the structure of the pancreas at a cellular level. these stains revealed at least two different granular cell types; A cells which contained granules preserved by alcohol and B cells which contained granules preserved by chrome sublimate. [9]
1914 Homans noticed that B-cells are involved in experimental diabetes and attributed the sugar regulating function to B-cells. [8]
1921 Best and Banting isolated insulin from the canine pancreas after ductal ligation. Their discovery of insulin was awarded the Nobel Prize in Medicine in 1923. [9]
1943 Dunn et al. selectively destroyed beta cells by administration of alloxan, which led to diabetes. [8]
1957-1974 morphopligical features of the islet cell types were established through multiple studies utilising electron microscopy, including the structure and apppearance of their cytoplasmic secretory granules. [10]
1966 First case of insulin independence by pancreas transplantation by William Kelly and Richard Lillehei into a 28 year old uremic woman at University of Minnesota. [11]
1972 Pictet and Rutter analysed the ultrastructural development of the pancreas by transmission electron microscopy and found both the endocrine and exocrine cells of the pancreas derived from a common progenitor; alpha cells were the first endocrine cells to differentiate. [9]
1977 Cudworth et al. made crucial step in the etiological classification of diabetes; reintroducing terms type 1 and type 2 diabetes. [12]
1990 Sharp et al. led further advances in transplantation achieving clinical insulin independance lasting 1 month through islet transplantation. [13]
2000 Shapiro et al. utilise "Edmonton protocol" where 7 patients with type 1 diabetes receive iselts and all recipients achieve insulin independence. Study utilised Immunosuppression drugs to prevent rejection. [14]
2014 Pagliuca et al. conduct first successful generation of functional human pancreatic beta cells in vitro, providing potentially an unprecedented cell source for drug discovery and cell transplantation therapy in diabetes. [15]
Continuing Research continues into stem cell therapeutics for diabetes (refer to "Current Research" below)

Structure

Among most species, pancreatic islets are generally characterised by an oval shape. Nevertheless, the distribution of cells within the endocrine portion of the pancreas is subject to variation. In most mammals, the pancreatic islet contains a core of beta cells, which is encircled by a mantle of non-beta cells. Yet, in humans and primates, cells are dispersed with greater complexity and deviate from the mammalian mantle-core arrangement to a composite of several mantle-core subunits. Due to such cellular organisation, pancreatic islets within humans and primates may be oval of clover-leaf shaped.

Islets of Langerhans are highly vascularised structures, which contain capillaries that are lined by endothelial cells comprising of mitochondria, ergastoplams, a golgi complex and a nucleus. The peripheral extensions of the cytoplasm of such endothelial cells are typically thinner and lack such organelles however contain several fenestrae, or openings. While it is not confirmed whether these fenestrae are static or whether they vary in quantity and distribution, it is predicted that they represent areas for communication and the transfer of materials between the bloodstream and the extravascular space.

The beta cell, itself, is enclosed by a continuous plasma membrane and includes, within its cytoplasm, several membrane-bound organelles such as the endoplasmic reticulum, mitochondria, a nucleus, golgi complex and secretory granules. The endoplasmic reticulum, also called the ergastoplasm, is composed of two lamellar membranes that have ribosomes attached to their exterior surface. In comparison to the mitochondria present within adjacent acinar cells, the mitochondria of the beta cells are relatively smaller in size, however they are easily identifiable by the cristae within their matrix. The golgi complex and beta granules are similarly composed of smooth membranous sacs, although the latter is sequestered from the cytoplasm by the walls of these sacs. The beta granules are additionally dispersed throughout the entire cytoplasm. The nucleus contains a double-layered nuclear membrane and also several nuclear pores, which allow continuity and interaction between the nucleoplasm and cytoplasm of the beta cell.

Adjacent beta cells are connected to each other at distributed focal points, called desmosomes, along their plasma membrane. Between two successive desmosomes, an intercellular space exists and its size is reliant upon the respective activity of the cells. The capillaries present within the islets of Langerhans are detached from the beta cells by two basement membranes; one related to the endothelium and the other to the capillary surface. Typically, between these two basement membranes, cross-sections of fibroblasts and unmyelinated nerve fibres can be detected. In some instances, unmyelinated nerve fibres have additionally been spotted beneath the basement membrane and in close contact with the cell’s plasma membrane. Although presently unconfirmed, this is considered to indicate synapses between the nerve fibres and the beta cell [5].

Structural Comparison between Humans and Mice

Consequential of the clinical importance of pancreas-associated disease, such as diabetes, endocrine tumours and pancreatic cancer, the structure of the pancreas is studied extensively within medical science. Studies of the human pancreas, however, are restricted due to the inherent ethical and medical limitations present in obtaining pancreatic samples at specific and intermittent intervals. As a direct result of scarce human pancreatic samples, animal models are increasingly used in studies. Within current pancreatic research, mice are the most frequently studied animal models. As a sizeable portion of scientific knowledge concerning the cellular architecture of the human pancreas is derived from studies conducted on mice, it is thereby imperative to identify and understand the distinction between the human and mouse pancreas.

Fig 1. Comparison of the macroscopic anatomy of the human pancreas (A) against the mouse pancreas (B).

Macroscopic Comparison

At a macroscopic level, the human pancreas is a well-defined organ, which contains three key structural components: the head, body and tail. The left border of the superior mesenteric artery borders the head and body of the pancreas, while the midpoint of the pancreatic body and tail combined is understood as the border between the body and the tail. Reflecting a C-shape, the pancreatic head is continuous with the upper curvature of duodenum whereas the pancreatic touches the hilum of the spleen and the narrow and flat pancreatic body locates itself underneath the stomach and extends in such a manner that it crosses with the superior mesenteric artery and vein, abdominal aorta, inferior vena cava and portal vein.

Conversely, the mouse pancreas is less defined than its human counterpart and in a dendritic manner, is uniquely diffused along the mesentery of the proximal small intestine of mice (See Fig. 2.). Analogous to the human pancreas, it can also be distinguished into three key structural components. However, these are called ‘globes’ and are recognized as the duodenal, splenic and gastric lobe. Identified as the largest lobe, the splenic lobe extends between the duodenum and the spleen and is homologous to the body and the tail of the human pancreas. The second largest lobe, the duodenal lobe, is located within the mesentery that surrounds the duodenum and is homologous to the human pancreatic head. Additionally, the gastric lobe, which is the smallest observable lobe, is considered a component of the splenic lobe, from which it originally develops, and is homologous to the auricle of the human pancreas. Typically, patches of adipose, connective, and lymphatic tissue separate these three main pancreatic lobes in mice.

Microscopic Comparison

Microscopically observed, each lobe of the pancreas contains numerous lobules, which vary in size respective to the organism and measure 1-10 mm in diameter in humans and 0.5-1.5 mm in diameter in mice. Dome-resembling clusters of pyramidal acinar cells are dispersed throughout the pancreatic lobules. They secrete various digestive enzymes, which are ultimately released into the duodenum by successive movement through intercalated ducts, intralobular ducts, interlobar ducts and finally the pancreatic duct, thus forming the exocrine pancreas. The endocrine portion of the pancreas, predominately constituting Islets of Langerhans, is embedded within the exocrine tissue. The size and distribution of pancreatic islets is congruous between humans and mice. With notably irregular cross-sections, they are home to thousands of hormone-secreting endocrine cells, which may also be singularly and randomly scattered across acinar and ductal tissues. While a minimum of 5 different polypeptide endocrine cells can be identified within the islets, beta cells, which synthesize and secrete insulin, form the majority and account for 60-70% of islet cell population in humans, and 60-80% in mice. The spatial organization of beta cells has continuous focus for scientific research. In mice, the mantle component of pancreatic islets contain non-beta cells while the core component exclusively comprise beta cells. In humans, it was originally perceived that alongside a similar mantle-core pattern, beta cells additionally formed ribbon-like clusters and were scattered throughout islets in an unorganised manner. As a consequence of recent studies, however, the current scientific consensus is that human pancreatic islets form trilmainar plates, which are folded into a U- or O-shape, and within which there are two layers of alpha cells that enclose a single beta cell layer. The reason for this specific organisation is considered to be the promotion of heterologous contact between both endocrine cells. Alternatively, in mice, there is homologous contact among alpha cells within the mantle of the islet and beta cells within the core of the islet. It is proposed that this specific type of spatial arrangement promotes alpha cell stimulation of beta cell functional activity.

Summary Table of Key Comparisons between Humans and Mice

Property Humans Mice
Macroscopic Pancreatic Structure Well-defined organ with three structural components: the head, body and tail Less-defined structure with three lobes: duodenal, splenic and gastric lobe
Diameter of Lobules 1 - 10 mm 0.5 - 1.5 mm
Beta Cells as a % of Pancreatic Cell Population 60 - 70% 60 - 80%
Microarchitecture of Islets Trilaminar islets predominate Mantle islets predominate
Contact between Alpha and Beta Cells Heterologous contact between endocrine cells as two layers of alpha cells enclose a single beta cell layer homologous contact among alpha cells within the mantle of the islet and beta cells within the core of the islet

Structural Modifications with Age

Extensive studies conducted on human pancreases from the prenatal period through to adulthood, have revealed that the anatomical architecture of pancreatic islets resemble their adult form, by the age of 2. As a direct result of this, the pancreas experiences substantial beta cell proliferation during the first 2 years after birth therefore enabling significant increases in beta cell mass and area. Increased beta cell production thus manifests as an increase in the diameter of existing pancreatic islets rather than the formation of new islets. In fact, while 10% of beta cell mass increase, during early life, can be attributed to islet development, a sizeable 90% can be linked to an increase in islet size. Although, beta cell replication continues throughout life, the replication rate notably decreases after adolescence and hereafter beta cell mass remains relatively constant between the ages of 20 – 100, as reviewed by [16].

Function

The overall function of the pancreas is to maintain glucose levels within the blood and beta cells play a specialised role within this process. The insulin gene, which provides instructions for the manufacture of the hormone insulin, is solely expressed in the endocrine portion of the pancreas within the beta cells of pancreatic islets. Insulin, a polypeptide hormone, is a key regulator of metabolism as it promotes the storage of excess glucose, amino acids and fatty acids, by acting on the liver, muscles and adipose tissue. Insulin release into the bloodstream predominantly occurs as a consequence of increased blood glucose levels. Glucose phosphorylation, by glucokinase, is currently understood to act as the glucose sensor, as it adjusts the rate of metabolic activity to the extracellular concentration of glucose. Glucose metabolism generates intracellular signals in beta cells, which subsequently initiates insulin secretion, insulin mRNA translation and insulin gene transcription.

Video elucidating the function of insulin in the human body:  

Youtube Link

Insulin Gene Expression

In the late 1980s, the 5’ flanking region of the insulin gene was identified in transgenic mice. This proved to be an extraordinary breakthrough as it allowed the general location of binding sites, for transcription factors, to be discovered. The transcription factor binding sites, which direct beta-cell-specific expression, were eventually located to be between −520 and +1 base pairs relative to the transcription initiation site. In later studies, congruous expression data was collected for the human insulin gene. Both results thus collectively indicate that there are sequences conserved between mammalian insulin genes, which lie within 350bp of the transcription start site and control the specific cell-type expressions. The enhancer region in mammalian insulin genes is located between nucleotides -340 and -91. While the transcription factors that bind onto this region principally determine the glucose-regulated expression properties of the gene, the activity of the enhancer can be additionally up-regulated and/or down-regulated by cellular activity. For example, through autocrine signalling, the insulin secreted from beta cells may increase insulin transcription in the same beta cells, by positively influencing enhancer-mediated activation [17].

Insulin Biosynthesis

In the 1950s, insulin (as show in Fig. x) became the first protein to have its structure clearly revealed. The discovery exposed insulin as a two-chain hormone and consequently triggered widespread speculation in the scientific community on the underlying mechanisms contributing to such a structure. Succeeding the discovery of single-chain precursor proteins, which occurred in 1967, insulin synthesis was finally understood to occur through several reactions with multiple single-chained precursor proteins, including preproinsulin and proinsulin.

During insulin biosynthesis, the initial product formed instantaneously after insulin mRNA translation is preproinsulin, which contains a hydrophobic N-terminal 24 residue signal peptide. The signal peptide engages with the signal recognition particle (SRP), a ribonucleoprotein particle that is located within the cytosol, which enables the separation of the preproinsulin polypeptide chain from the cytosolic compartment into the secretory pathway. From here, the preprohormone is translocated across the membrane of the rough endoplasmic retiticulum (RER) and into its lumen, via a peptide-conducting channel. A specialized signal peptidase, situated on the surface of the RER membrane, cleaves and rapidly degrades the signal sequence. Inside the RER, several chaperone proteins, catalyse the folding of proinsulin and facilitate its manufacture of three disulfide bonds, which largely contribute to the development of its native structure.

Within a time period of ~10-20 minutes, proinsulin is rapidly transported from the RER to the Golgi apparatus. Here, proinsulin is packaged into immature secretory vesicles [REF] and cleaved to form equimolar amounts of insulin and connecting polypeptide (C-peptide) [18]. While proinsulin and insulin have a direct biological effect, C-peptide has no effect on homologous or heterologous tissue and no ability to influence the concentration or action of beta cell hormones (reviewed in [19]). Although small volumes of proinsulin and its immediate cleavage forms, C-peptide and insulin are collectively stored in the secretion granules of beta cells, insulin is the predominant hormone released after signalling.

The formation of insulin from its precursor, proinsulin, is initiated approximately 20 minutes after the synthesis of preproinsulin and typically lasts for 1-2 hours, independent of additional protein synthesis.

Notably, proinsulin and insulin share similarities with respect to many of their properties, including solubility, isoelectric point, self-associative properties and relative reactivity with insulin antiserum. The insulin moiety found within proinsulin is also highly similar to the one present in insulin itself, as indicated by nuclear magnetic resonance (NMR) imaging.

Image Proinsulin and Image insulin

Cell Biology of Insulin Biosynthesis

Congruous to other neurosecretory cells, the Golgi apparatus plays a substantial role in the formation of secretory granules in beta cells. However, its dynamic nature and the underlying mechanisms, which facilitate the transport and sorting of secretory products within it, is currently only partly understood. With further research, new models for Golgi progression are continuously proposed. Currently, a scientifically favoured model presents a form of the Golgi apparatus wherein individual cisternae, containing their secretory contents, migrate from cis to trans while small, coated vesicles transport various Golgi resident proteins and enzymes in an opposite manner from trans to cis. Relative to this model, while secretory products mature, they are kept in the same compartment and only exit from it as they dissipate into the trans Golgi network into immature secretory granules. Recent immunocyto-chemical studies have established that newly synthesized clathrin-clad granules in the trans Golgi cisternal network (TGN) are rich in proinsulin, which confirms the proposal that conversion to insulin occurs principally during the maturation of the secretory granules. The proteolytic processing of proinsulin may be prevented by energy poisons, which block their transfer into secretory vesicles. Nevertheless, once newly manufactured proinsulin has reached the trans Golgi, energy is no longer required to convert it to insulin. While proinsulin conversion may begin in the trans compartment of the Golgi apparatus, it is now confirmed that it occurs predominantly within newly manufactured secretory vesicles as they leave the Golgi region and mature biochemically in the cytosol (see Fig y.) [18]..

Development

Development of islet with age & does function change with age

Baby beta cell vs adult

Signalling

Article on signalling: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3081169/

- development and differentiation

- how the somatic cell knows to differentiate into a beta cell

- how the body communicates to the beta cell that insulin needs to be released

- how the cell knows that there is excess insulin - ie. how it switches off?

- receptors on different cells and organs

- what initiates secretion

- receptors

- hormones - secretion, breakdown

Role in Pathology

Disease

To reiterate the sections above, insulin is vital in the maintenance of glucose levels. Through signalling of liver, muscle and fat cells, insulin allows for the uptake of glucose, allowing for its use as an energy source. When the body has a sufficient amount of energy, insulin signals the liver to take up glucose and store it as glycogen. Thus in the absence of insulin or responsiveness to insulin, glucose remains in the blood stream resulting in a rise of blood-glucose levels. Refer to the video below for a visual conceptual explanation of the relationship between insulin, glucose and diabetes.

Video to understand the connection between insulin and diabetes:  

Youtube Link

Type 1 Diabetes Type 2 Diabetes
Epidimiology Type 1 diabetes is one of the most common chronic childhood diseases. It appears two peaks occur in the presentation of type 1 diabetes; between the age of 5-7 and the other occurring near puberty. [20] Type 1 diabetes varies dramatically on a global scale with more than 350-fold variation in incidence among reporting countries. However overall occurrence seems to be least common in China, India and Venezuela and most common in Finland as well as Sweden, Norway, Portugal, Great Britain, Canada and New Zealand. [21] The number of type 2 diabetes is increasing with 80% living in low and middle income countries. It is estimated that 439 million people would have type 2 diabetes by the year 2030 [22]. The incidence varies substantially from one geographic region to the next due to environmental and lifestyle risk factors [23].
Cause Type 1 diabetes does not fit any simple inheritance pattern and is considered a complex multifactorial disease. [24] Early familial and twin studies supported the importance of both genetic and environmental risk factors. [25] Primarily lifestyle factors; physical inactivity, sedentary lifestyle, cigarette smoking and generous consumption of alcohol; obesity contributing to 55% of cases. [26]. Recent increase in occurence of type 2 diabetes may also be attributed to environmental factors as reveiwed by Olokoba et al. (2012) [27].
Symptoms Polyuria, increased thirst, unexplained weight loss, blurred vision, fasting plasma glucose of >126mg/dL (7.0mmol/L) , two hour postload plasma glucose of >200mg/dL (11.1 mmol/L) during standard oral glucose tolerance test (OGTT) [28] Polyuria, polydipsia, polyphagia and weight loss, raised fasting plasma glucose >126mg/dL (7.0mmol/L), two hour postload plasma glucose of >200mg/dL (11.1 mmol/L) during standard oral glucose tolerance test (OGTT) ( as reviewed by Olokoba et al. 2012) [27]
Pathogeneis Insert pathogenesis for Type 1 Insert pathogenesis for Type 2

Type 1 Diabetes

Type 1 diabetes results from an insulin deficiency that is caused by the loss of pancreatic beta cells, developing most commonly in the young and accounting for approximately 5-10% of the diabetic population worldwide. Type 1 diabetes is a consequence of autoimmune destruction of beta cells that generally occurs over an extended period of time. Genetic susceptibility is believed to be a prerequisite for type 1 diabetes. [29] However in a study by Barnett, Leslie & Pyke (1981), through the analysis of the concordance and discordance of diabetes occurring between 200 pairs of identical twins within different age groups it was revealed that approximately half the pairs were discordant, suggesting type 1 diabetes was not entirely genetically based. An environmental or alternative non-genetic cause was suggested as twins that were living separately between the ages of 20-39 were shown to have a greater number of discordance.[25]

File:Beta Cell Destruction.JPG
Figure 3: Beta-cell destruction by autoimmune processes

The pathogenesis of autoimmune type 1 diabetes has been extensively studied through the use of animal models; nonobese diabetic mouse and diabetes-prone BioBreeding rat. Exact mechanisms of initiation and progression remain unclear, however through the animal studies it is generally believed that beta-cell autoantigens macrophages, dendritic cells, B lymphocytes, and T lymphocytes are involved in the beta-cell specific autoimmune process. As seen in Figure 3, the beta-cell autoantigens are processed by the macrophages, dendritic cells or B cells in the pancreatic islets, and then presented to the autoreactive CD4+ T cells in the peripheral lymphoid system. These cells are consequently activated leading to the secretion of cytokines which can activate beta-cell specific cytotoxic CD8+ T cells. Activated T cells recruit at the iselts, producing cytokines which further activate macrophages and other T cells; all contributing to the destruction of pancreatic beta-cells. [30]

Type 2 Diabetes

Pancreatic beta-cell dysfunction and failure results in the prevalence of type 2 diabetes. In the normal healthy body, beta-cells are able to function at a greater capacity when glucose increases, thus producing more insulin to maintain glucose homeostasis; beta cells are able to adapt resulting in a compensatory response in insulin production. Beta-cell dysfunction is seen inType 2 diabetes as the compsenatory response results in gradual failfure of beta cells, primarily due to insulin resistance within the individual [31]

The evolution of beta-cell dysfunction is marked by 5 stages as identified by Weir & Bonner-Weir (2004) [32]:

Stage 1: Referred to as compensation; when the insulin secretion must compensate for degrees of insulin resistance for the maintenance of glucose homeostasis.

Stage 2: Where fasting levels range between 5-7.3mmol/L, representing 'beta-cell adaptation'. People progressing toward Type 2 diabetes may remain here for many years, however when beta-cell mass becomes insufficient glucose levels may rise to stage 4 rapidly.

Stage 3: Early decompensation: glucose levels rise beyond 7.3mmol/L

Stage 4: Stable decompensation: glucose levels range between 16-20mmol/L

Stage 5: Severe decompensation: extreme beta cell failure; ketosis with blood glucose levels above 22mmol/L

pubmed: 9428227 - effect of cancer on beta cells leading to diabetes http://care.diabetesjournals.org/content/27/3/824

Treatments

Insulin Therapy

Review Article https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2901025/#!po=72.5000

Pancreatic Transplantation

As there is no definite cure for diabetes, many of the current research on Beta Cells focus on developing new and better treatments for patients with diabetes. One of the most promising treatments that is still under research and experimentation is pancreatic transplantation.

1. Pancreatic Islet Transplantation [33]

This method is specifically aimed to treat patients with type-1 diabetes mellitus. The pancreatic islet is responsible for the endocrine function of the pancreas. This is isolated within the donated pancreas, and the exocrine functioning part of the pancreas is removed. The isolated pancreatic islet is then transported to the liver of the patient by the blood of the vein.

  • add more info. on the process/ procedure in details
  • what the new islet will do to the patient, changes, impacts
  • name the limitations/ dangers of this method
  • include images (from cited source)


2. Transplantation using Embryonic Pig Pancreatic Tissue [34]

Instead of using human tissue or organ for transplantation, this method uses pancreatic tissue of an embryonic pig. Pancreatic tissues are harvested at different stages of the embryonic pig development and tested to determine which was the best. Tissues of the embryonic pig on day 42, or E42, appears to be the most promising tissue for transplantation.

  • add more info. on the process/ procedure in details
  • what the new tissues will do to the patient, changes, impacts
  • name the limitations/ dangers of this method
  • include images (from cited source)

do research for: The most common form of treatment is the exogenous supply of insulin, which efficiently reduces blood glucose levels but is unable to mimic the tight glycaemic control provided by endogenous hormone production as there is no glucose-insulin feedback control. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0156204

interesting article: https://www.ncbi.nlm.nih.gov/pubmed/27904096

Good info on diabetes: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4873311/


Stem Cell Research

Another recent endeavour into a promising anti-diabetic therapeutic is within stem cell research. has also been conducted in the search for anti-diabetic therapeutics. Mitutsova et al. (2017) investigated the possible use of muscle-derived stem cells (MDSC) from adult mice to differentiate in vitro into beta cells when transplanted as undifferentiated stem cells in vivo to compensate for beta-cell deficiency. Within their study they successfully found in vitro cultured MDSC to spontaneously differentiate into insulin-expressing islet like cell clusters under the control of an insulin promoter. Differentiated clusters of beta-like cells co-expressing insuling with transcription factors were shown to secrete significant levels of insulin in response to glucose challenges. Additionally, in vivo undifferentiated MDSC injected into streptozotocin treated mice engrafted within 48 hours specifically to damaged pancreatic islets and were also shown to differentiate and express insulin within 10-12 days after injection. Also to add to the successful results, injection of MDSC into hyperglycemic diabetic mice was shown to reduce blood glucose levels for 2-4 weeks. Ultimately the study successfully showed MDSC as capable of differenctiating into mature pancreatic beta islet-like cells, both in vivo and in vitro highlighting a promising avenue in stem-cell based treated of beta-cell deficiencies. [35]

Current Research

current status and future research: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4019265/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989782/

working on it:

In a recent study by Lima et. al. (2016) the generation of mature and functional beta-like cells from the human exocrine pancreas was assessed for being a viable avenue for treatment of type 1 diabetes. The pivotal finding of the study was that knockdown of transcription factor ARX expression combined with over expression of transcription factor Pax4 considerably enhances the production of functional insulin secreting beta-like cells with the accompanying suppression of alpha cells.The beta-like cells produced were shown to efficiently exhibit glucose responsive insulin secretion and an immediate as well as prolonged effect in normalising blood glucose levels upon transplantation into diabetic mice. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0156204

Review Quiz

Try to attempt these questions from memory!

1

In which species does the pancreatic islet contain a core of beta cells surrounded by a mantle of non-beta cells?

Most humans and primates
Most mammals
Neither species

2

What is the name of the focal point where adjacent beta cells connect to each other along their plasma membrane?

Islets of Langerhans
Desmosomes
Rough endoplasmic reticulum

3

Which of the following statements is correct?

The proteolytic processing of proinsulin may be prevented by energy poisons, which block their transfer into secretory vesicles
Proinsulin and insulin are highly dissimilar and demonstrate large differences in solubility and isoelectric point
Type 2 diabetes is one of the most common chronic childhood diseases

4

Polydipsia is a defining symptom of which beta-cell related disease?

Pancreatitis
Type 1 Diabetes
Type 2 Diabetes
All the above

5

The correct definition of polyphagia is:

Excessive eating or appetite symptomatic of disease
The production of abnormally large volumes of dilute urine ( >2.5L per day)
Abnormally increased thirst, symptomatic of disease


Glossary

Term Definition
Adipose Bodily tissue which stores brown or white fat
Edmonton Procedure Researchers use specialised enzymes to remove islets from the pancreas of a deceased donor and transplant to patient via catheter through to small incision through to liver as treatment for type 1 diabetes.
Epidemiology The study of distribution and determinant of diseases
In vitro Performed or taking place in a test tube, culture dish, or elsewhere outside the living organism
In vivo Performed within a living organism
Islets of Langerhans A cluster of endocrine pancreatic cells, which secrete the hormones insulin and glucagon
Pancreas A large gland within organisms which has an exocrine portion that secretes digestive enzymes and an endocrine portion that secretes the hormones insuln and glucagon
Pathogenesis The manner of development of a disease
Plasma glucose The concentration of glucose in blood measured in milligram per deciliter or milimole per litre. (normal fasting is >100 mg/dL (5.55 mmol/L).
Polydipsia Abnormally increased thirst symptomatic of disease
Polyphagia Excessive eating or appetite symptomatic of disease
Polyuria The production of abnormally large volumes of dilute urine ( >2.5L per day)
Oral Glucose Tolerance Test (OGTT) Test determining the body's capacity to maintain glucose levels; results noted after overnight fasting and 4 times after administration (usually through sweet liquid) of 75g of glucose (100g for pregnant woman).
Streptozotocin A naturally occurring chemical that is particularly toxic to the insulin-producing beta cells of the pancreas in mammals

References

  1. 1.0 1.1 <pubmed>26395141</pubmed>
  2. Brissova, M. & Powers, A. C. (2008). Architecture of Pancreatic Islets. Pancreatic Beta Cell in Health and Disease (pp. 3-4).
  3. Bell, G., Seino, S., & SpringerLink. (2008). Pancreatic Beta Cell in Health and Disease.
  4. 4.0 4.1 <pubmed>14687913</pubmed>
  5. 5.0 5.1 <pubmed> 5333806 </pubmed>
  6. <pubmed>22460761</pubmed>
  7. <pubmed>6993583</pubmed>
  8. 8.0 8.1 8.2 <pubmed><4192603></pubmed>
  9. 9.0 9.1 9.2 9.3 <pubmed>19765178</pubmed>
  10. 10.0 10.1 <pubmed>26216133</pubmed>
  11. <pubmed>5338113</pubmed>
  12. <pubmed>67403</pubmed>
  13. <pubmed>2108071</pubmed>
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