Characterisation of Ppy-lineage cells clarifies the functional heterogeneity of pancreatic beta cells in mice

Takahiro Fukaishi,Michiko Saito,Tetsuya Yamada,Hirotaka Watada,Taka-Aki Matsuoka,Kenji Kohno,Takashi Sato,Motoyuki Tamaki,Yoshio Fujitani,Ayako Fukunaka,Takeshi Miyatsuka,Keiko Nakao,Akemi Hara,Yuko Nakagawa,Munehide Matsuhisa

doi:10.1007/s00125-021-05560-x

Abstract

Aims/hypothesisPancreatic polypeptide (PP) cells, which secrete PP (encoded by the Ppy gene), are a minor population of pancreatic endocrine cells. Although it has been reported that the loss of beta cell identity might be associated with beta-to-PP cell-fate conversion, at present, little is known regarding the characteristics of Ppy-lineage cells.MethodsWe used Ppy-Cre driver mice and a PP-specific monoclonal antibody to investigate the association between Ppy-lineage cells and beta cells. The molecular profiles of endocrine cells were investigated by single-cell transcriptome analysis and the glucose responsiveness of beta cells was assessed by Ca2+ imaging. Diabetic conditions were experimentally induced in mice by either streptozotocin or diphtheria toxin.ResultsPpy-lineage cells were found to contribute to the four major types of endocrine cells, including beta cells. Ppy-lineage beta cells are a minor subpopulation, accounting for 12–15% of total beta cells, and are mostly (81.2%) localised at the islet periphery. Unbiased single-cell analysis with a Ppy-lineage tracer demonstrated that beta cells are composed of seven clusters, which are categorised into two groups (i.e. Ppy-lineage and non-Ppy-lineage beta cells). These subpopulations of beta cells demonstrated distinct characteristics regarding their functionality and gene expression profiles. Ppy-lineage beta cells had a reduced glucose-stimulated Ca2+ signalling response and were increased in number in experimental diabetes models.Conclusions/interpretationOur results indicate that an unexpected degree of beta cell heterogeneity is defined by Ppy gene activation, providing valuable insight into the homeostatic regulation of pancreatic islets and future therapeutic strategies against diabetes.Data availabilityThe single-cell RNA sequence (scRNA-seq) analysis datasets generated in this study have been deposited in the Gene Expression Omnibus (GEO) under the accession number GSE166164 (www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE166164).Graphical abstract

Highlights

The islets of Langerhans consist of alpha, beta and delta cells and a fourth type of islet cell, namely, pancreatic polypeptide (PP) cells
Immunostaining analysis demonstrated that Ppy-lineage yellow fluorescent protein (YFP)+ cells contained cells that were costained for INS, GCG, SST or PP, indicating that Ppylineage cells contribute to all the four major types of endocrine cells (Fig. 1c–f)
The frequency of Ppy-lineage beta cells among total islet cells was similar between the head (14.9%) and tail (12.4%) of the pancreas, whereas the frequency of Ppylineage alpha (GCG+), delta (SST+) and PP cells differed between the two regions of the pancreas (Fig. 1g)

Summary

Introduction

The islets of Langerhans consist of alpha, beta and delta cells and a fourth type of islet cell, namely, pancreatic polypeptide (PP) cells. PP cells are located at the periphery of the islets and secrete PP [1–3], encoded by the Ppy gene. The precise physiological functions of these peptides, including their roles in glucose homeostasis, remain poorly understood. A previous study demonstrated that Ppy-lineage cells were indispensable for the differentiation of a substantial fraction of endocrine cells by the diphtheria toxin (DT)-induced ablation of Ppy-lineage cells [6]. Owing to the lack of specificity of the available PP antibody and the fidelity of the Ppy promoter used, the precise roles of Ppy-lineage cells have not yet been clarified

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