Pancreatic islets from cyclin-dependent kinase 4/R24C (Cdk4) knockin mice have significantly increased beta cell mass and are physiologically functional, indicating that Cdk4 is a potential target for pancreatic beta cell mass regeneration in Type 1 diabetes

Abstract

Aims/hypothesis. Cyclin-dependent kinase 4 (Cdk4) is crucial for beta cell development. A mutation in the gene encoding for Cdk4, Cdk4R24C, causes this kinase to be insensitive to INK4 cell cycle inhibitors and induces beta cell hyperplasia in Cdk4R24C knockin mice. We aimed to determine whether this Cdk4R24C mutation also affects proper islet function, and whether it promotes proliferation in human islets lentivirally transduced with Cdk4R24C cDNA. Methods. Our study was conducted on wild-type and Cdk4R24C knockin mice. Pancreases were morphometrically analysed. Intraperitoneal glucose tolerance tests and intravenous insulin tolerance tests were performed on wild-type and Cdk4R24C mice. We also did in vitro islet perifusion studies and islet metabolic labelling analysis. Human islets were transduced with Cdk4R24C cDNA. Results. Pancreatic islets from Cdk4R24C knockin mice exhibit a larger insulin-producing beta cell area and a higher insulin content than islets from wild-type littermates. Insulin secretion in response to glucose is faster and reaches a higher peak in Cdk4R24C mice without leading to hypoglycaemia. Conversion of proinsulin into insulin and its intermediates is similar in Cdk4R24C and wild-type mice. Glucose utilisation and oxidation measured per islet were similar in both experimental groups. Insulin secretion was faster and enhanced in Cdk4R24C islets perifused with 16.7 mmol/l glucose, with slower decay kinetics when glucose returned to 2.8 mmol/l. Moreover, human islets expressing Cdk4R24C cDNA exhibited higher beta cell proliferation. Conclusions/interpretation. Despite their hyperplastic growth, Cdk4R24C insulin-producing islet cells behave like differentiated beta cells with regard to insulin production, insulin secretion in response to glucose, and islet glucose metabolism. Therefore Cdk4 could possibly be used to engineer a source of beta cell mass for islet transplantation.

Islet biology, the CDKN2A/B locus and type 2 diabetes risk

“…Islet morphology is normal at birth, suggesting CDK4 is not required for pancreatic development, but islets fail to expand during postnatal growth. Conversely, mice expressing the INK-resistant mutant CDK4 `R24C' have hyperplastic islets due to increased postnatal beta cell proliferation [142, 143]. Mutation of the arginine at CDK4 position 24 is oncogenic in many tissues, despite also having impaired binding to D-cyclins and reduced efficacy as an Rb kinase [144].…”

A Simple Matter of Life and Death—The Trials of Postnatal Beta-Cell Mass Regulation

“…Knockout studies have shown a very specific phenotype, with beta-cell hypoplasia and severe diabetes [191, 194, 245], whilst studies using an activating mutation in CDK4, rendering it resistant to p16, have resulted in pancreatic hyperplasia, which demonstrated normal physiology [191, 192]. Other studies have shown up to a three-fold increase in beta-cell proliferation with CDK4 overexpression [191, 193].…”

Id3 upregulates BrdU incorporation associated with a DNA damage response, not replication, in human pancreatic β-cells

“…35,75 Murine β-cells express abundant cdk-4 and cyclin D2, and genetic mouse models have shown them to be critical for β-cell proliferation and diabetes development. [76][77][78][79] In contrast, human β-cells contain high levels of the analogous enzyme cdk-6, and cyclins D1 and D3 are thought to play a role. Recently, it was reported that overexpression of cdk-6 and cyclin D1 in isolated human β-cells in vitro induced BrdU incorporation and Ki67 expression.…”