Pancreatic progenitor cell | |
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Details | |
Precursor | Foregut endoderm |
Identifiers | |
Latin | Cellula pancreaticum praecursoria |
TH | H2.00.01.0.00005 |
Anatomical terms of microanatomy |
Pancreatic progenitor cells are multipotent stem cells originating from the developing fore-gut endoderm which have the ability to differentiate into the lineage specific progenitors responsible for the developing pancreas. [1] [2]
They give rise to both the endocrine and exocrine cells. Exocrine cells constitute the acinar cells and the ductal cells. The endocrine cells constitute the beta cells which make insulin, alpha cells which secrete glucagon, delta cells which secrete somatostatin and the PP-cells which secrete pancreatic polypeptide. [3]
Pancreatic progenitor cells have been shown to arise from cells originating from the developing foregut during mammalian development. [4] [5] It has been seen in the developing embryo at stages E9.0 to E9.5 that there are a cluster of cells which give rise to the pancreas. These clusters have been characterized to show multipotent properties. [6]
The pancreas is an organ of endodermal origin. The endoderm is amongst the three germ layers that make up the developing embryo. The origination of the pancreatic tissue is from the dorsal and ventral aspects of the posterior foregut. They can be observed at E9.0 to E9.5 during embryonic development. Fusion of these buds occurs during rotation of the developing gut. The fused and developed pancreas consists of pancreatic enzyme secreting cells (exocrine cells), digestive enzyme transporting cells (ductal cells) and hormone producing cells (endocrine cells). These endocrine cells develop in discrete areas within the pancreas known as the islets.
In humans, the dorsal bud can be observed 26 days post-fertilization. However, the islet cells can only be observed at 52 days post-fertilization. The development of beta cells precedes that of the development of other endocrine cells in the islets. All islet cells can be observed in the first trimester in human. This variation in the development of islet cell subtypes is due to differential gene expression and induction pathways of progenitor cells. [7]
Genetic lineage tracing experiments have been performed by various research groups to show that the cell clusters originating from the developing foregut express a transcription factor called PDX1 (Pancreatic and duodenal homeobox 1). This transcription factor has been shown to give rise to the multipotent stem cell lineages contributing to the endocrine, exocrine and ductal cells of the pancreas. These cells have been shown to be spatially located at the tip of the branching pancreatic tree. Later these cells are shown to originate from the dorsal bud of the developing pancreas.[ citation needed ]
Pdx1 is accepted as the earliest marker for pancreatic differentiation. Pdx1 has been shown to be a marker for all pancreatic and mid-gut progenitor cells. Pdx1 expression is empirical to drive the developing pancreas after the bud stage where two buds (dorsal and lateral) of the immature pancreas develop. Notch signaling has been shown to regulate the number of exocrine and endocrine cells in the pancreas, but not without the presence of Pdx1. [8] [9] Notch signaling allows the expansion of pancreatic progenitors by the process of lateral inhibition. [10]
These cells have been shown to have 28 genes regulating the cell cycle to be upregulated, showing that they are proliferative cells having the ability to replace and give rise to multiple cell populations in the pancreas. [11] [12]
Pancreatic progenitors have been shown to arise from the early expression of the gene Mnx1/Hlxb1 (Motor Neuron and pancreas homobox 1). Mnx1 expression has been shown to be important for the development of dorsal Pdx1, hence acting as a necessary transcription factor for the specification of foregut endoderm into Pdx1 expressing pancreatic progenitors. Similarly, another set of genes Gata4 (GATA binding protein 4) and Hnf1b/Tcf2 (HNF homobox B gene) is required for the development of the ventral bud of the developing pancreas. These genes regulates the expression of Mnx1 in the ventral bud, leading to the developmental specification of the pancreatic progenitor cells expressing Pdx1. One gene Onecut1/Hnf6 (onecut domain family member 1 transcription factor) is also responsible for the timely expression of Pdx1 in both the ventral and dorsal buds. Hence the expression of this protein also contributes to the formation of these pancreatic progenitors expressing Pdx1. It is important to note here that the developing dorsal and ventral buds are characterized as endoderm, and it isn’t until the expression of Pdx1 (specification of endoderm to a stem cell multipotent state) that the endoderm to pancreatic progenitor transition occurs.
The variable number of genes shows the multiple routes of induction of the developing endoderm, intrinsically within the endoderm (for example, notch signaling) or from the adjacent cardiac mesoderm (Sonic hedgehog protein inhibition by Fibroblast growth factor). [13] [14]
The differential of pancreatic progenitors from hepatic progenitors is also notable, as Hhex1 (Hematopoietically expressed homeobox gene) is responsible for the origination of pancreatic progenitor cells. In the absence of Hhex, (in Hhex double negative mice) the liver develops but not the pancreas, showing that Hhex allows for divergent specification of a pancreatic progenitor rather than allow the formation of a hepatic progenitor. [15] [16]
Pancreatic progenitor cells have the ability to differentiate into both endocrine and exocrine precursors. [17]
The endocrine precursors are a committed group of progenitors that develop into all of the endocrine cells in the pancreas. Endocrine lineages develop into Delta cells, PP-cells, Epsilon cells, Beta cells and Alpha cells. Alpha cells produce glucagon and beta cells produce insulin. Insulin and glucagon antagonistically regulate the glucose homeostasis in the mammalian body. PP-cells produce pancreatic polypeptide which is a regulator of endocrine and exocrine secretions in the pancreas and gut. Delta cells which produce somatostatin which is a growth hormone inhibiting hormone and has important function in the regulation of hormone production from the anterior pituitary gland. Epsilon cells produce Ghrelin (hunger hormone) which is a neuropeptide that acts on the hypothalamic center of the brain, where it couples with GHSR (growth hormone secretagogue receptors) and mediates hunger. [18]
The exocrine progenitor cell develop into precursor cells expressing amylase. These cells then can be identified in tissue to be secretory in nature and contribute to the production of pancreatic enzymes. [19]
The ductal progenitors are a group of precursors that develop into ductal cells in the pancreas. These cells line the ducts and also originate from pancreatic progenitors. [20] [21]
The endodermal progenitors are shown to express Hnf6 and Hnf1b, hence are Hnf6+/Hnf1b+ cells. Due to the suppression of Sonic hedgehog signaling, pancreatic progenitor cells develop and give rise to multiple cell lineages. Pancreatic progenitor cells are Nkx2.2+/Nkx6.1+/P48+ cells. [22]
Endocrine progenitor cells develop from Pancreatic Progenitor cells under the influence of Ngn3 (neurogenin 3). This cell fate commitment is due to the expression of Sox9 (Sry-related HMB box transcription factor 9) and suppression of Notch signaling. Pancreatic Progenitor cells are hence Ngn3+/NeuroD+/IA1+/Isl1+/Pax6+ cells. These cells then develop into Beta cell pro-precursors under the influence of Pax4. Beta cell pro-precursors are MafB+/Pdx1+/Nkx2.2+ cells. These beta cell pro-precursors are determined to form beta cell precursors expressing Pax1. [23] Finally, beta-cell precursors mature into mature adult beta cells which are Pdx1+/Nkx2.2+/Nkx6.1+/Pax6+/NeuroD+/MafA+. [24]
Endocrine progenitor cells also develop into delta cell pro-precursors expressing Pax4 and Pax6. They then form Som+ delta cell precursor cells. These delta cell precursors mature into delta cells which are Brn+/Pax6+. [25]
Additionally endocrine progenitor cells also form Nkx2.2+ PP cell pro-precursors, which then are determined to form PP+ (Pancreatic polypeptide) precursor cells and later PP-cells. Endocrine progenitors are also responsible for forming epsilon cells. [26]
These progenitor cells develop from pancreatic progenitor cells and are P48+ cells. These cells develop into amylase+/P48+ mature exocrine cells. [27]
These cells express Hnf6 and originate from pancreatic progenitor cells. They are peculiar as their morphology and characteristics is similar to that of the pancreatic progenitor cell. Ductal cell precursors express Hnf6 before developing into the mature ductal cell of the pancreas. [28]
The regenerative potential of the adult pancreas has been a pivotal point for debate. Many research groups including prominent research scientists in the field have been unable to decide the true presence or absence of these cells and their function in pancreatic regeneration as their name would suggest. This is due to the fact that their regenerative potential in an experimental setting is lost. However new studies show that growth factors of the TGF-beta superfamily may be involved in regeneration of pancreatic cells. Pancreatic mesenchymal stem cells isolated from ductal digests have also been shown to have a regenerative potential under the effect of certain growth factors. [29] [30] They have also been shown to give rise to cells of at least two different germ layers. However this may be misinterpreted as an endocrine precursor rather than a pancreatic progenitor cell. This is due to a study performed by Zulweski and co-workers, who showed the presence of neural stem cell specific markers in the pancreatic duct of rats. However these cells did not show staining for CK19 (cytokeratin 19) a ductal cell marker. [31]
The development of a protocol involving the directed generation of pancreatic progenitors has been performed on hESCs (human embryonic stem cells). These cells showing immense potential in therapy for metabolic diseases of the pancreas like diabetes, have been programmed to pancreatic progenitors using factors mimicking the developmental cues a developing endoderm would require to form functional pancreatic tissue. [32] hESCs have are grown on matrigel and then allowed to differentiate into endoderm and later defined cells under the influence of bFGF, EGF, BMP4. [33]
The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. In vertebrates, the hypothalamus is the neural control center for all endocrine systems. In humans, the major endocrine glands are the thyroid gland, parathyroid gland, pituitary gland, pineal gland, the testes (male), ovaries (female), and the adrenal glands. The hypothalamus, pancreas, and thymus also function as endocrine glands, among other functions. Other organs, such as the kidneys, also have roles within the endocrine system by secreting certain hormones. The study of the endocrine system and its disorders is known as endocrinology.
The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e., it has both an endocrine and a digestive exocrine function. 99% of the pancreas is exocrine and 1% is endocrine. As an endocrine gland, it functions mostly to regulate blood sugar levels, secreting the hormones insulin, glucagon, somatostatin and pancreatic polypeptide. As a part of the digestive system, it functions as an exocrine gland secreting pancreatic juice into the duodenum through the pancreatic duct. This juice contains bicarbonate, which neutralizes acid entering the duodenum from the stomach; and digestive enzymes, which break down carbohydrates, proteins and fats in food entering the duodenum from the stomach.
Beta cells (β-cells) are a type of cell found in pancreatic islets that synthesize and secrete insulin and amylin. Beta cells make up 50–70% of the cells in human islets. In patients with Type 1 diabetes, beta-cell mass and function are diminished, leading to insufficient insulin secretion and hyperglycemia.
Transdifferentiation, also known as lineage reprogramming, is the process in which one mature somatic cell is transformed into another mature somatic cell without undergoing an intermediate pluripotent state or progenitor cell type. It is a type of metaplasia, which includes all cell fate switches, including the interconversion of stem cells. Current uses of transdifferentiation include disease modeling and drug discovery and in the future may include gene therapy and regenerative medicine. The term 'transdifferentiation' was originally coined by Selman and Kafatos in 1974 to describe a change in cell properties as cuticle producing cells became salt-secreting cells in silk moths undergoing metamorphosis.
The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine (hormone-producing) cells, discovered in 1869 by German pathological anatomist Paul Langerhans. The pancreatic islets constitute 1–2% of the pancreas volume and receive 10–15% of its blood flow. The pancreatic islets are arranged in density routes throughout the human pancreas, and are important in the metabolism of glucose.
Pancreatic cancer arises when cells in the pancreas, a glandular organ behind the stomach, begin to multiply out of control and form a mass. These cancerous cells have the ability to invade other parts of the body. A number of types of pancreatic cancer are known.
Maturity-onset diabetes of the young (MODY) refers to any of several hereditary forms of diabetes mellitus caused by mutations in an autosomal dominant gene disrupting insulin production. Along with neonatal diabetes, MODY is a form of the conditions known as monogenic diabetes. While the more common types of diabetes involve more complex combinations of causes involving multiple genes and environmental factors, each forms of MODY are caused by changes to a single gene (monogenic). GCK-MODY and HNF1A-MODY are the most common forms.
Epsilon cells (ε-cells) are one of the five types of endocrine cells found in regions of the pancreas called Islets of Langerhans. Epsilon cells produce the hormone ghrelin that induces hunger. They were first discovered in mice. In humans, these cells compose less than 1% of all islet cells. They are connected by tight junctions that allow impermeability to water-soluble compounds.
Douglas A. Melton is an American medical researcher who is the Xander University Professor at Harvard University, and was an investigator at the Howard Hughes Medical Institute until 2022. Melton serves as the co-director of the Harvard Stem Cell Institute and was the first co-chairman of the Harvard University Department of Stem Cell and Regenerative Biology. Melton is the founder of several biotech companies including Gilead Sciences, Ontogeny, iPierian, and Semma Therapeutics. Melton holds membership in the National Academy of the Sciences, the American Academy of Arts and Sciences, and is a founding member of the International Society for Stem Cell Research.
HNF1 homeobox A, also known as HNF1A, is a human gene on chromosome 12. It is ubiquitously expressed in many tissues and cell types. The protein encoded by this gene is a transcription factor that is highly expressed in the liver and is involved in the regulation of the expression of several liver-specific genes. Mutations in the HNF1A gene have been known to cause diabetes. The HNF1A gene also contains one of 27 SNPs associated with increased risk of coronary artery disease.
PDX1, also known as insulin promoter factor 1, is a transcription factor in the ParaHox gene cluster. In vertebrates, Pdx1 is necessary for pancreatic development, including β-cell maturation, and duodenal differentiation. In humans this protein is encoded by the PDX1 gene, which was formerly known as IPF1. The gene was originally identified in the clawed frog Xenopus laevis and is present widely across the evolutionary diversity of bilaterian animals, although it has been lost in evolution in arthropods and nematodes. Despite the gene name being Pdx1, there is no Pdx2 gene in most animals; single-copy Pdx1 orthologs have been identified in all mammals. Coelacanth and cartilaginous fish are, so far, the only vertebrates shown to have two Pdx genes, Pdx1 and Pdx2.
Neurogenins are a family of bHLH transcription factors involved in specifying neuronal differentiation. It is one of many gene families related to the atonal gene in Drosophila. Other positive regulators of neuronal differentiation also expressed during early neural development include NeuroD and ASCL1.
Homeobox protein Nkx-2.2 is a protein that in humans is encoded by the NKX2-2 gene.
Insulitis is an inflammation of the islets of Langerhans, a collection of endocrine tissue located in the pancreas that helps regulate glucose levels, and is classified by specific targeting of immune cell infiltration in the islets of Langerhans. This immune cell infiltration can result in the destruction of insulin-producing beta cells of the islets, which plays a major role in the pathogenesis, the disease development, of type 1 and type 2 diabetes. Insulitis is present in 19% of individuals with type 1 diabetes and 28% of individuals with type 2 diabetes. It is known that genetic and environmental factors contribute to insulitis initiation, however, the exact process that causes it is unknown. Insulitis is often studied using the non-obese diabetic (NOD) mouse model of type 1 diabetes. The chemokine family of proteins may play a key role in promoting leukocytic infiltration into the pancreas prior to pancreatic beta-cell destruction.
Renal cysts and diabetes syndrome (RCAD), also known as MODY 5 or HNF1B-MODY, is a form of maturity onset diabetes of the young.
Neurogenin-3 (NGN3) is a protein that in humans is encoded by the Neurog3 gene.
Homeobox protein Nkx-6.1 is a protein that in humans is encoded by the NKX6-1 gene.
Ductal cells refer to the epithelial cell lining of the pancreatic duct that deliver enzymes from the acinar cells to the duodenum. They have the essential function of producing bicarbonate-rich (HCO3-) secretion to neutralize stomach acidity. The hormone secretin stimulates ductal cells and is responsible for maintaining the duodenal pH and preventing duodenal injury from acidic chyme. Ductal cells mix their production with acinar cells to make up the pancreatic juice.
Cystic fibrosis-related diabetes (CFRD) is diabetes specifically caused by cystic fibrosis, a genetic condition. Cystic fibrosis related diabetes mellitus (CFRD) develops with age, and the median age at diagnosis is 21 years. It is an example of type 3c diabetes - diabetes that is caused by damage to the pancreas from another disease or condition.
Islet resident macrophages are the predominant myeloid cell of the pancreatic islets of langerhans.