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Deletion of CDKAL1 affects mitochondrial ATP generation and first-phase insulin exocytosis.

ABSTRACT: BACKGROUND:A variant of the CDKAL1 gene was reported to be associated with type 2 diabetes and reduced insulin release in humans; however, the role of CDKAL1 in ? cells is largely unknown. Therefore, to determine the role of CDKAL1 in insulin release from ? cells, we studied insulin release profiles in CDKAL1 gene knockout (CDKAL1 KO) mice. PRINCIPAL FINDINGS:Total internal reflection fluorescence imaging of CDKAL1 KO ? cells showed that the number of fusion events during first-phase insulin release was reduced. However, there was no significant difference in the number of fusion events during second-phase release or high K(+)-induced release between WT and KO cells. CDKAL1 deletion resulted in a delayed and slow increase in cytosolic free Ca(2+) concentration during high glucose stimulation. Patch-clamp experiments revealed that the responsiveness of ATP-sensitive K(+) (K(ATP)) channels to glucose was blunted in KO cells. In addition, glucose-induced ATP generation was impaired. Although CDKAL1 is homologous to cyclin-dependent kinase 5 (CDK5) regulatory subunit-associated protein 1, there was no difference in the kinase activity of CDK5 between WT and CDKAL1 KO islets. CONCLUSIONS/SIGNIFICANCE:We provide the first report describing the function of CDKAL1 in ? cells. Our results indicate that CDKAL1 controls first-phase insulin exocytosis in ? cells by facilitating ATP generation, K(ATP) channel responsiveness and the subsequent activity of Ca(2+) channels through pathways other than CDK5-mediated regulation.

SUBMITTER: Ohara-Imaizumi M

PROVIDER: S-EPMC3000340 | biostudies-literature | 2010 Dec

REPOSITORIES: biostudies-literature

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Deletion of CDKAL1 affects mitochondrial ATP generation and first-phase insulin exocytosis.

Ohara-Imaizumi Mica M Yoshida Masashi M Aoyagi Kyota K Saito Taro T Okamura Tadashi T Takenaka Hitoshi H Akimoto Yoshihiro Y Nakamichi Yoko Y Takanashi-Yanobu Rieko R Nishiwaki Chiyono C Kawakami Hayato H Kato Norihiro N Hisanaga Shin-ichi S Kakei Masafumi M Nagamatsu Shinya S

PloS one 20101209 12

<h4>Background</h4>A variant of the CDKAL1 gene was reported to be associated with type 2 diabetes and reduced insulin release in humans; however, the role of CDKAL1 in β cells is largely unknown. Therefore, to determine the role of CDKAL1 in insulin release from β cells, we studied insulin release profiles in CDKAL1 gene knockout (CDKAL1 KO) mice.<h4>Principal findings</h4>Total internal reflection fluorescence imaging of CDKAL1 KO β cells showed that the number of fusion events during first-ph ...[more]

PMID: 21151568

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Project description:BACKGROUND/OBJECTIVE:The CDKAL1 gene is among the best-replicated susceptibility loci for type 2 diabetes, originally identified by genome-wide association studies in humans. To clarify a physiological importance of CDKAL1, we examined effects of a global Cdkal1-null mutation in mice and also evaluated the influence of a CDKAL1 risk allele on body mass index (BMI) in Japanese subjects. METHODS:In Cdkal1-deficient (Cdkal1?/?) mice, we performed oral glucose tolerance test, insulin tolerance test, and perfusion experiments with and without high-fat feeding. Based on the findings in mice, we tested genetic association of CDKAL1 variants with BMI, as a measure of adiposity, and type 2 diabetes in Japanese. PRINCIPAL FINDINGS:On a standard diet, Cdkal1?/? mice were modestly lighter in weight than wild-type littermates without major alterations in glucose metabolism. On a high fat diet, Cdkal1?/? mice showed significant reduction in fat accumulation (17% reduction in %intraabdominal fat, P?=?0.023 vs. wild-type littermates) with less impaired insulin sensitivity at an early stage. High fat feeding did not potentiate insulin secretion in Cdkal1?/? mice (1.0-fold), contrary to the results in wild-type littermates (1.6-fold, P<0.01). Inversely, at a later stage, Cdkal1?/? mice showed more prominent impairment of insulin sensitivity and glucose tolerance. mRNA expression analysis indicated that Scd1 might function as a critical mediator of the altered metabolism in Cdkal1?/? mice. In accordance with the findings in mice, a nominally significant (P<0.05) association between CDKAL1 rs4712523 and BMI was replicated in 2 Japanese general populations comprising 5,695 and 12,569 samples; the risk allele for type 2 diabetes was also associated with decreased BMI. CONCLUSIONS:Cdkal1 gene deletion is accompanied by modestly impaired insulin secretion and longitudinal fluctuations in insulin sensitivity during high-fat feeding in mice. CDKAL1 may affect such compensatory mechanisms regulating glucose homeostasis through interaction with diet.

Project description:Our recent study has demonstrated that inhibition of calpain by transgenic overexpression of calpastatin reduces myocardial proinflammatory response and dysfunction in endotoxemia. However, the underlying mechanisms remain to be determined. In this study, we used cardiomyocyte-specific capn4 knockout mice to investigate whether and how calpain disrupts ATP synthase and induces mitochondrial superoxide generation during endotoxemia.Cardiomyocyte-specific capn4 knockout mice and their wild-type littermates were injected with lipopolysaccharides. Four hours later, calpain-1 protein and activity were increased in mitochondria of endotoxemic mouse hearts. Mitochondrial calpain-1 colocalized with and cleaved ATP synthase-? (ATP5A1), leading to ATP synthase disruption and a concomitant increase in mitochondrial reactive oxygen species generation during lipopolysaccharide stimulation. Deletion of capn4 or upregulation of ATP5A1 increased ATP synthase activity, prevented mitochondrial reactive oxygen species generation, and reduced proinflammatory response and myocardial dysfunction in endotoxemic mice. In cultured cardiomyocytes, lipopolysaccharide induced mitochondrial superoxide generation that was prevented by overexpression of mitochondria-targeted calpastatin or ATP5A1. Upregulation of calpain-1 specifically in mitochondria sufficiently induced superoxide generation and proinflammatory response, both of which were attenuated by ATP5A1 overexpression or mitochondria-targeted superoxide dismutase mimetics.Cardiomyocyte-specific capn4 knockout protects the heart against lipopolysaccharide-induced injury in endotoxemic mice. Lipopolysaccharides induce calpain-1 accumulation in mitochondria. Mitochondrial calpain-1 disrupts ATP synthase, leading to mitochondrial reactive oxygen species generation, which promotes proinflammatory response and myocardial dysfunction during endotoxemia. These findings uncover a novel mechanism by which calpain mediates myocardial dysfunction in sepsis.

Project description:Vascular endothelial cells (ECs) sense and transduce hemodynamic shear stress into intracellular biochemical signals, and Ca2+ signaling plays a critical role in this mechanotransduction, i.e., ECs release ATP in the caveolae in response to shear stress and, in turn, the released ATP activates P2 purinoceptors, which results in an influx into the cells of extracellular Ca2+. However, the mechanism by which the shear stress evokes ATP release remains unclear. Here, we demonstrated that cellular mitochondria play a critical role in this process. Cultured human pulmonary artery ECs were exposed to controlled levels of shear stress in a flow-loading device, and changes in the mitochondrial ATP levels were examined by real-time imaging using a fluorescence resonance energy transfer-based ATP biosensor. Immediately upon exposure of the cells to flow, mitochondrial ATP levels increased, which was both reversible and dependent on the intensity of shear stress. Inhibitors of the mitochondrial electron transport chain and ATP synthase as well as knockdown of caveolin-1, a major structural protein of the caveolae, abolished the shear stress-induced mitochondrial ATP generation, resulting in the loss of ATP release and influx of Ca2+ into the cells. These results suggest the novel role of mitochondria in transducing shear stress into ATP generation: ATP generation leads to ATP release in the caveolae, triggering purinergic Ca2+ signaling. Thus, exposure of ECs to shear stress seems to activate mitochondrial ATP generation through caveola- or caveolin-1-mediated mechanisms. NEW & NOTEWORTHY The mechanism of how vascular endothelial cells sense shear stress generated by blood flow and transduce it into functional responses remains unclear. Real-time imaging of mitochondrial ATP demonstrated the novel role of endothelial mitochondria as mechanosignaling organelles that are able to transduce shear stress into ATP generation, triggering ATP release and purinoceptor-mediated Ca2+ signaling within the cells.

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Deletion of CDKAL1 affects mitochondrial ATP generation and first-phase insulin exocytosis.

Publications

Deletion of CDKAL1 affects mitochondrial ATP generation and first-phase insulin exocytosis.

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