β-cell insulin receptor deficiency duringin uterodevelopment induces an islet compensatory overgrowth response

Abstract

The presence of insulin receptor (IR) on β-cells suggests that insulin has an autocrine/paracrine role in the regulation of β-cell function. It has previously been reported that the β-cell specific loss of IR (βIRKO) leads to the development of impaired glycemic regulation and β-cell death in mice. However, temporally controlled βIRKO induced during the distinct transitions of fetal pancreas development has yet to be investigated. We hypothesized that the presence of IR on β-cells during the 2nd transition phase of the fetal murine pancreas is required for maintaining normal islet development. We utilized a mouse insulin 1 promoter driven tamoxifen-inducible Cre-recombinase IR knockout (MIP-βIRKO) mouse model to investigate the loss of β-cell IR during pancreatic development at embryonic day (e) 13, a phase of endocrine proliferation and β-cell fate determination. Fetal pancreata examined at e19-20 showed significantly reduced IR levels in the β-cells of MIP-βIRKO mice. Morphologically, MIP-βIRKO pancreata exhibited significantly enlarged islet size with increased β-cell area and proliferation. MIP-βIRKO pancreata also displayed significantly increased Igf-2 protein level and Akt activity with a reduction in phospho-p53 when compared to control littermates. Islet vascular formation and Vegf-a protein level was significantly increased in MIP-βIRKO pancreata. Our results demonstrate a developmental role for the β-cell IR, whereby its loss leads to an islet compensatory overgrowth, and contributes further information towards elucidating the temporally sensitive signaling during β-cell commitment.

Critical role of β1 integrin in postnatal beta-cell function and expansion

“…Experimental MIP-CreERT + ; β1itg fl/fl ( MIPβ1KO ) mice are MIP-CreERT positive (268bp) with both β1 integrin alleles floxed by LoxP sites (β 1itg fl/fl , 280bp). MIP-CreERT-; β1itg fl/fl and MIP-CreERT +; β1itg +/+ ( Controls) mice are either MIP-CreERT negative with both β1 integrin alleles floxed or MIP-CreERT positive with wild-type β1 integrin alleles ( β1itg +/+ , 160bp) [ 30 ]. All protocols were approved by the Animal Use Subcommittee at the University of Western Ontario in accordance with the guidelines of the Canadian Council of Animal Care.…”

“…Pancreatic sections were prepared from the entire length of the pancreas and stained with primary antibodies listed in Supplementary Table 2 . Quantitative evaluations of islet number, size, and alpha-cell and beta-cell mass were performed using Image-Pro software (MediaCybernetics, Rockville, MD, USA) [ 14 , 30 ]. A minimum of 10 islets per pancreas was manually traced from 5 to 6 different mice per experimental group.…”

“…Proteins were detected using ECL™-Plus Western Blot detecting reagents (Perkin-Elmer, Wellesley, MA, USA) and imaged using the Versadoc Imaging System (Bio-Rad Laboratories). Image Lab software (Bio-Rad Laboratories) was used to quantify band intensities using densitometry, and data were normalized to total or appropriate loading controls [ 17 , 30 , 31 ].…”

Insulin regulates human pancreatic endocrine cell differentiation in vitro

“…However, the impact of loss of IR on β cell replication is still a matter of debate. Although some studies showed no or positive effects of loss of IR on murine β cell expansion [ 54 , 55 ], several other studies showed that IR deficiency reduces mouse β cell proliferation and mass [ [56] , [57] , [58] , [59] ]. Additionally, deletion of insulin inhibitory receptor (inceptor), which desensitizes IR, also enhances β cell division further supporting the direct involvement of IR signaling in β cell propagation [ 60 ].…”

Hippo pathway-mediated YAP1/TAZ inhibition is essential for proper pancreatic endocrine specification and differentiation

“…For the tamoxifen-mediated Lats1&2 deletion in adult β-cells, 6-8 weeks old mice were intraperitoneal (i.p) injected with 200 mg/kg tamoxifen (TAM, Sigma-Aldrich, T5648) for 5 consecutive days. For the early β-cell Lats1&2 deletion, female Lats1&2 fl/fl mice and male mice carrying MIP CreER ; Lats1&2 fl/fl were timed mated and after 12 days, the pregnant mice were injected with 100 mg/kg tamoxifen once [18]. PCR was used for validation of knockout alleles (S Table 2).…”