PROBLEM: Next generation sequencing studies have highlighted discrepancies in β-cells which exist between mice and men. Numerous reports have identified MAF BZIP Transcription Factor B (MAFB) to be present in human β-cells postnatally, while its expression is restricted to embryonic and neo-natal β-cells in mice
NOVEL APPROACH: Using CRISPR/Cas9-mediated gene editing, coupled with endocrine cell differentiation strategies, we dissect the contribution of MAFB to β-cell development and function specifically in humans
FINDINGS: MAFB knockout hPSCs have normal pancreatic differentiation capacity up to the progenitor stage, but favor somatostatin- and pancreatic polypeptide-positive cells at the expense of insulin- and glucagon-producing cells during endocrine cell development. Our results describe a requirement for MAFB late in the human pancreatic developmental program and identify it as a distinguishing transcription factor within islet cell subtype specification. We propose that hPSCs represent a powerful tool to model human pancreatic endocrine development and associated disease pathophysiology.
PROBLEM: In adults, increase in β-cell mass is limited due to brakes on cell replication. In contrast, proliferation is robust in neonatal β cells that are functionally immature as defined by a lower set point for glucose-stimulated insulin secretion. The temporal separation of mature, glucose-sensitive insulin secretion, and replicative potential has led to the speculation that there exists an inverse relation between the maturation state and the ability of the β cell to divide. Despite compelling evidence that these two β-cell features are negatively correlated, it has been difficult to dissect the functional state of a β cell that is either undergoing replication, or is competent to divide, primarily due to the small fraction of cells that are actively in the replicative phase of the cell cycle even in neonatal stages
NOVEL APPROACH: Here we show that β-cell proliferation and immaturity are linked by tuning expression of physiologically relevant, non-oncogenic levels of c-Myc (a cell cycle regulator)
FINDINGS: Adult β cells induced to replicate adopt gene expression and metabolic profiles resembling those of immature neonatal β that proliferate readily. We directly demonstrate that priming insulin-producing cells to enter the cell cycle promotes a functionally immature phenotype. We suggest that there exists a balance between mature functionality and the ability to expand, as the phenotypic state of the β cell reverts to a less functional one in response to proliferative cues
The Hebrok lab focuses on the generation and function of pancreatic islet cells, most prominently the insulin producing beta cells. They have established sophisticated protocols to generate functional islet cells from human stem cells and to modify gene expression in these cells with the intent to optimize beta cell function and to protect cells from immune responses. The ultimate goal is to develop next generation cells for cell therapy and disease modeling.
The lab is currently using multiple tools including transgenic mouse models in which gene expression is conditionally regulated to manipulate the activity of specific signaling pathways. The information gained from these studies is used to optimize and develop novel methods to generate functional insulin-producing β-cells from human stem cell populations such as human embryonic stem cells (hESCs) and induced pluripotentstem (iPS) cells.