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Loss of furin in β cells induces an mTORC1-ATF4 anabolic pathway that leads to β cell dysfunction

ABSTRACT: ABSTRACT: Furin is a proprotein convertase (PC) responsible for proteolytic activation of a wide array of precursor proteins within the secretory pathway. It maps to the PRC1 locus, a type 2 diabetes susceptibility locus, yet its specific role in pancreatic β cells is largely unknown. The aim of this study was to determine the role of furin in glucose homeostasis. We show that furin is highly expressed in human islets, while PCs that potentially could provide redundancy are expressed at considerably lower levels. β cell-specific furin knockout (βfurKO) mice are glucose intolerant, due to smaller islets with lower insulin content and abnormal dense core secretory granule morphology. RNA expression analysis and differential proteomics on βfurKO islets revealed activation of Activating Transcription Factor 4 (ATF4), which was mediated by mammalian target of rapamycin C1 (mTORC1). βfurKO cells show impaired cleavage of the accessory V-ATPase subunit Ac45, and by blocking this pump in β cells the mTORC1 pathway is activated. Furthermore, βfurKO cells show lack of insulin receptor cleavage and impaired response to insulin. Taken together, these results suggest a model of mTORC1-ATF4 hyperactivation in β cells lacking furin, which causes β cell dysfunction. METHOD: Data obtained for the β cell specific knockout (RIP-Cre+/- furin flox/flox) and control (furin flox/flox) samples were compared to investigate the effect of furin loss on the mRNA profile of islets. Although this method does not directly provide furin targets, the notion of differential gene expression might elucidate affected cellular processes, potentially leading to upstream furin substrates.

ORGANISM(S): Mus musculus

PROVIDER: GSE150312 | GEO | 2020/05/12

REPOSITORIES: GEO

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Project description:Purpose: FURIN is a member of the proprotein convertase subtilisin/kexin (PCSK) family of serine endoproteases important in converting immature proproteins into their functional form. While FURIN is important in various aspects of the immune response such as in CD4+ T cells, FURIN´s role in CD8+ T cells is unclear. Here, we isolated naive CD8+ T cells from conditional T cell specific Furin KO (Cd4-Cre-Furinflox/flox) and WT (Furinflox/flox) mice and studied the genome-wide gene expression pattern upon in vitro anti-CD3/anti-CD28 activation (plate-bound, 5µg/ml each) using RNA sequencing. We also used recombinant TGFB1 (0.5ng/ml) or IL12 (10ng/ml) in the same experimental setting to study their impact on the CD8+ T cell transcriptome. Methods: Total RNA was isolated from the stimulated CD8+ T cells and the RNA-sequencing data was produced by the Functional Genomics Unit of the HiLIFE Genome Analysis Infrastructure (University of Helsinki, Helsinki, Finland) using Illumina NextSeq High Output 1x75 bp. Data processing pipeline was built on Snakemake wrappers, and used STAR to quantify features from quality and adapter trimmed reads in gene level. Prior the normalisation and differential gene expression analysis with DESeq2, the matrix of raw gene counts was prefiltered to keep only rows that have at least 10 reads in total. Result tables were annotated with biomaRt. Results: Snakemake preprocessing pipeline measured 55573 genes against GRCm38, ENSEMBL release 97. 17714 of them was used for statistical testing. Full result tables for each treatment were ranked by p-value and the normalized DESeq2 abundances in samples were included. The genes with BH-adjusted p-value <0.05 was considered differentially expressed. Conclusions: Our study revealed that the abscence of FURIN influences the expression of several genes in activated CD8+ T cells. Additionally, although FURIN-deficient CD8+ T cells can respond to exogenous TGFB1 and IL12, administrating these cytokines further increases the number of differentially expressed genes between Furin KO and WT CD8+ T cells.

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Loss of furin in β cells induces an mTORC1-ATF4 anabolic pathway that leads to β cell dysfunction

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