Endocrine Pancreas Development and Dysfunction Through the Lens of Single-Cell RNA-Sequencing

Abstract

A chronic inability to maintain blood glucose homeostasis leads to diabetes, which can damage multiple organs. The pancreatic islets regulate blood glucose levels through the coordinated action of islet cell-secreted hormones, with the insulin released by β-cells playing a crucial role in this process. Diabetes is caused by insufficient insulin secretion due to β-cell loss, or a pancreatic dysfunction. The restoration of a functional β-cell mass might, therefore, offer a cure. To this end, major efforts are underway to generate human β-cells de novo, in vitro, or in vivo. The efficient generation of functional β-cells requires a comprehensive knowledge of pancreas development, including the mechanisms driving cell fate decisions or endocrine cell maturation. Rapid progress in single-cell RNA sequencing (scRNA-Seq) technologies has brought a new dimension to pancreas development research. These methods can capture the transcriptomes of thousands of individual cells, including rare cell types, subtypes, and transient states. With such massive datasets, it is possible to infer the developmental trajectories of cell transitions and gene regulatory pathways. Here, we summarize recent advances in our understanding of endocrine pancreas development and function from scRNA-Seq studies on developing and adult pancreas and human endocrine differentiation models. We also discuss recent scRNA-Seq findings for the pathological pancreas in diabetes, and their implications for better treatment.

Keywords: beta cell development and maturation; diabetes; pancreas development; single-cell RNA sequencing; stem cell pancreatic differentiation.

FIGURE 1

sc-RNA-Seq insight into murine pancreatic development. (A) Three major morphogenesis transitions in pancreatic development are shown. Cell types with cell specific markers are listed in the legend below. The black arrow indicates the developmental trajectory. MP, multipotent progenitors; BP, bipotent progenitors; EP, endocrine progenitors. (B) Developmental trajectory of Pro-EP trunk and EP cells as they differentiate at e13.5–e14.5 preferably into α-cells, and at e15.5–e16.5 preferably into β-cells. Time point-specific markers are listed above the scheme.

FIGURE 2

scRNA-Seq insight into in vitro hPSC differentiation toward human pancreatic β-cells (A) and endocrine cell maturation (B). (A) (Top) Stages of differentiation protocols (arrows), which recapitulate consecutive pancreas development steps in vivo (circles). Denoted are: a length of each stage (above arrows, in days), genes commonly used to estimate differentiation efficiency (% + for stage markers out of all cells), and pathways that are inhibited (“_i”) or activated (“_a”) during each stage (below arrows). Pathways without brackets are essential for the process and applied in all commonly used protocols, while brackets indicate pathways regulated in a fraction of protocols. PSC—pluripotent stem cells, MP—multipotent progenitors, BP—bipotent progenitors, EN—endocrine lineage (endocrine progenitors and immature endocrine cells), β—β-cells, GSIS—glucose stimulated insulin secretion. (Bottom) A detailed view on the differentiation based on scRNA-Seq reveals the origin of non-β-cell specific populations that deteriorate differentiation efficiency and points to branching at which the protocols could be refined. Factors identified in scRNA-Seq studies that improve specific lineage choices are denoted. SC—stem cell-derived, EC—enterochromaffin cells. (B) Maturation of β- and α- cells including molecular changes and marker genes along the process. Dedifferentiation (reverse arrows), transdifferentation, and re-entering cell cycle are possible as physiological compensatory mechanisms, in pathology and when artificially forced by identified factors, with potential use in medicine.