In Vivo Role of Focal Adhesion Kinase in Regulating Pancreatic β-Cell Mass and Function Through Insulin Signaling, Actin Dynamics, and Granule Trafficking

Abstract

Focal adhesion kinase (FAK) acts as an adaptor at the focal contacts serving as a junction between the extracellular matrix and actin cytoskeleton. Actin dynamics is known as a determinant step in insulin secretion. Additionally, FAK has been shown to regulate insulin signaling. To investigate the essential physiological role of FAK in pancreatic β-cells in vivo, we generated a transgenic mouse model using rat insulin promoter (RIP)–driven Cre-loxP recombination system to specifically delete FAK in pancreatic β-cells. These RIPcre+fakfl/fl mice exhibited glucose intolerance without changes in insulin sensitivity. Reduced β-cell viability and proliferation resulting in decreased β-cell mass was observed in these mice, which was associated with attenuated insulin/Akt (also known as protein kinase B) and extracellular signal–related kinase 1/2 signaling and increased caspase 3 activation. FAK-deficient β-cells exhibited impaired insulin secretion with normal glucose sensing and preserved Ca2+ influx in response to glucose, but a reduced number of docked insulin granules and insulin exocytosis were found, which was associated with a decrease in focal proteins, paxillin and talin, and an impairment in actin depolymerization. This study is the first to show in vivo that FAK is critical for pancreatic β-cell viability and function through regulation in insulin signaling, actin dynamics, and granule trafficking.

The role of the Src Homology-2 domain containing protein B (SHB) in β cells

“…The delayed cAMP response may be attributed to FAK-regulation of phosphodiesterase activity (Serrels et al 2010), which upon elevated FAK activity promotes the local breakdown of cAMP in the sub-membrane space (Alenkvist et al 2014). Both integrins and glucose promote increased b cell FAK activity with enhanced survival, proliferation and insulin secretion as a result (Rondas et al 2011, Cai et al 2012, Rondas et al 2012, Arous et al 2013. The data of the Shb knockout islets suggest negative effects of FAK as well, operating under conditions of chronic over-activity.…”

Retinoblastoma tumor suppressor protein in pancreatic progenitors controls α- and β-cell fate

“…Experimental procedures for Ki67, insulin, and glucagon immunostaining and TUNEL assay were described previously (49). Details of staining procedures, quantitative real-time PCR, Western blotting, and chromatin immunoprecipitation analyses are provided in SI Materials and Methods.…”

“…Experimental procedures for glucose tolerance tests, insulin tolerance tests, glucose-stimulated insulin secretion, and multiple low-dose STZ-induced diabetes model were described previously (49). Full methods are provided in SI Materials and Methods.…”

Rb and p107 are required for alpha cell survival, beta cell cycle control and glucagon-like peptide-1 action

“…Antibodies for Rb, p107, E2F1, p53, p21, p27 (Santa Cruz Biotechnology, Santa Cruz, CA, USA), cyclin D1, cyclin E, cleaved caspase 3, glyceraldehyde-3-phosphate dehydrogenase, p-Akt, and proliferating cell nuclear antigen (PCNA; Cell Signaling, Beverly, MA, USA) were used [22].…”

“…Immunohistochemistry, immunofluorescence and immunoblotting Ki67, insulin and glucagon immunostaining, TUNEL assay and immunoblotting were performed as described previously [22]. Antibodies for Rb, p107, E2F1, p53, p21, p27 (Santa Cruz Biotechnology, Santa Cruz, CA, USA), cyclin D1, cyclin E, cleaved caspase 3, glyceraldehyde-3-phosphate dehydrogenase, p-Akt, and proliferating cell nuclear antigen (PCNA; Cell Signaling, Beverly, MA, USA) were used [22].…”