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The pancreatic islets are composed of discrete hormone-producing cells that orchestrate systemic glucose homeostasis. Here we identify subsets of beta cells using a single-cell transcriptomic approach. One subset of beta cells marked by high CD63 expression is enriched for the expression of mitochondrial metabolism genes and exhibits higher mitochondrial respiration compared with CD63lo beta cells. Human and murine pseudo-islets derived from CD63hi beta cells demonstrate enhanced glucose-stimulated insulin secretion compared with pseudo-islets from CD63lo beta cells. We show that CD63hi beta cells are diminished in mouse models of and in humans with type 2 diabetes. Finally, transplantation of pseudo-islets generated from CD63hi but not CD63lo beta cells into diabetic mice restores glucose homeostasis. These findings suggest that loss of a specific subset of beta cells may lead to diabetes. Strategies to reconstitute or maintain CD63hi beta cells may represent a potential anti-diabetic therapy.

Background: Zebrafish possess a remarkable regenerative capacity, which is mediated by the induction of various genes upon injury. Injury‐dependent transcription is governed by the tissue regeneration enhancer elements (TREEs). Here, we utilized leptin b (lepb), an injury‐specific factor, and its TREE to dissect heterogeneity of noncardiomyocytes (CMs) in regenerating hearts. Results: Our single‐cell RNA sequencing (scRNA‐seq) analysis demonstrated that the endothelium/endocardium(EC) is activated to induce distinct subpopulations upon injury. We demonstrated that lepb can be utilized as a regeneration‐specific marker to subset injury‐activated ECs. lepb+ ECs robustly induce pro‐regenerative factors, implicating lepb+ ECs as a signaling center to interact with other cardiac cells. Our scRNA‐seq analysis identified that lepb is also produced by subpopulation of epicardium (Epi) and epicardium‐derived cells (EPDCs). To determine whether lepb labels injury‐emerging non‐CM cells, we tested the activity of lepb‐linked regeneration enhancer (LEN) with chromatin accessibility profiles and transgenic lines. While nondetectable in uninjured hearts, LEN directs EC and Epi/EPDC expression upon injury. The endogenous LEN activity was assessed using LEN deletion lines, demonstrating that LEN deletion abolished injury‐dependent expression of lepb, but not other nearby genes. Conclusions: Our integrative analyses identify regeneration‐emerging cell‐types and factors, leading to the discovery of regenerative features of hearts. Key Findings: Integration of injury‐specific factor lepb to scRNA‐seq analysis identifies injury‐emerging non‐CM subpopulations in zebrafish hearts.lepb+ EC subgroup are characterized with the enriched expression of secreted factors lepb regeneration enhancer (LEN) can direct injury‐specific expression in the endocardium as well as the epicardium. [ABSTRACT FROM AUTHOR]

In response to cardiac damage, a mesothelial tissue layer enveloping the heart called the epicardium is activated to proliferate and accumulate at the injury site. Recent studies have implicated the epicardium in multiple aspects of cardiac repair: as a source of paracrine signals for cardiomyocyte survival or proliferation; a supply of perivascular cells and possibly other cell types such as cardiomyocytes; and as a mediator of inflammation (1-9). However, the biology and dynamism of the adult epicardium is poorly understood. To investigate this, we created a transgenic line to ablate the epicardial cell population in adult zebrafish. Here we find that genetic depletion of the epicardium after myocardial loss inhibits cardiomyocyte proliferation and delays muscle regeneration. The epicardium vigorously regenerates after its ablation, through proliferation and migration of spared epicardial cells as a sheet to cover the exposed ventricular surface in a wave from the chamber base towards its apex. By reconstituting epicardial regeneration ex vivo, we show that extirpation of the bulbous arteriosus--a distinct, smooth-muscle-rich tissue structure that distributes outflow from the ventricle--prevents epicardial regeneration. Conversely, experimental repositioning of the bulbous arteriosus by tissue recombination initiates epicardial regeneration and can govern its direction. Hedgehog (Hh) ligand is expressed in the bulbous arteriosus, and treatment with a Hh signalling antagonist arrests epicardial regeneration and blunts the epicardial response to muscle injury. Transplantation of Sonic hedgehog (Shh)-soaked beads at the ventricular base stimulates epicardial regeneration after bulbous arteriosus removal, indicating that Hh signalling can substitute for the influence of the outflow tract. Thus, the ventricular epicardiumhas pronounced regenerative capacity, regulated by the neighbouring cardiac outflow tract and Hh signalling. These findings extend our understanding of tissue interactions during regeneration and have implications for mobilizing epicardial cells for therapeutic heart repair., To assess the homeostatic properties of the epicardium, we used an inducible cell ablation system in adult zebrafish. Targeted expression of bacterial nitroreductase (NTR) depletes specific cell types via conversion [...]