cGMP kinase I regulates glucagon release

© 2009 Leiss et al; licensee BioMed Central Ltd. Blood glucose levels are tightly controlled by the two peptide hormones glucagon and insulin. At hyperglycaemia, B-cells in the islets of Langerhans secrete insulin, whereas islet A-cells release glucagon at hypoglycaemia to stimulate e.g. glucose production in the liver. Previously, an important role for nitric oxide (NO) in the development of type-1 diabetes mellitus (insulin dependent diabetes mellitus) was reported [1]. The mechanisms are unknown whereby NO modulates islet (mal-)function. We hypothesized that NO signals via the cGMP/cGMP kinase I (cGKI) pathway to modulate the endocrine control of blood glucose levels. Glucose homeostasis was studied in the conventional cGKI knockouts (KOs) and in cGKI rescue mice (RM) [2] in comparison to age- and littermat

Heterotrimeric G-protein subunit Gαi2 contributes to agonist-sensitive apoptosis and degranulation in murine platelets

Gαi2, a heterotrimeric G-protein subunit, regulates various cell functions including ion channel activity, cell differentiation, proliferation and apoptosis. Platelet-expressed Gαi2 is decisive for the extent of tissue injury following ischemia/reperfusion. However, it is not known whether Gαi2 plays a role in the regulation of platelet apoptosis, which is characterized by caspase activation, cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) translocation to the platelet surface. Stimulators of platelet apoptosis include thrombin and collagen-related peptide (CoRP), which are further known to enhance degranulation and activation of αII bβ3-integrin and caspases. Using FACS analysis, we examined the impact of agonist treatment on activation and apoptosis in platelets drawn from mice lacking Gαi2 and their wild-type (WT) littermates. As a result, treatment with either thrombin (0.01 U/mL) or CoRP (2 μg/mL or 5 μg/mL) significantly upregulated PS-exposure and significantly decreased forward scatter, reflecting cell size, in both genotypes. Exposure to CoRP triggered a significant increase in active caspase 3, ceramide formation, surface P-selectin, and αII bβ3-integrin activation. These molecular alterations were significantly less pronounced in Gαi2-deficient platelets as compared to WT platelets. In conclusion, our data highlight a previously unreported role of Gαi2 signaling in governing platelet activation and apoptosis.Fil: Cao, Hang. Universität Tübingen; AlemaniaFil: Qadri, Syed M.. Canadian Blood Services; Canadá. McMaster University; CanadáFil: Lang, Elisabeth. Heinrich-heine-universität Düsseldorf; AlemaniaFil: Pelzl, Lisann. Universität Tübingen; AlemaniaFil: Umbach, Anja T.. Universität Tübingen; AlemaniaFil: Leiss, Veronika. Universität Tübingen; AlemaniaFil: Birnbaumer, Lutz. National Institutes of Health; Estados Unidos. Pontificia Universidad Católica Argentina "Santa María de los Buenos Aires". Instituto de Investigaciones Biomédicas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas; ArgentinaFil: Nürnberg, Bernd. Universität Tübingen; AlemaniaFil: Pieske, Burkert. Berlin Institute of Health; Alemania. Universitätsmedizin Berlin; AlemaniaFil: Voelkl, Jakob. Berlin Institute of Health; Alemania. Universitätsmedizin Berlin; AlemaniaFil: Gawaz, Meinrad. Universität Tübingen; AlemaniaFil: Bissinger, Rosi. Universität Tübingen; AlemaniaFil: Lang, Florian. Universität Tübingen; Alemania. Heinrich-heine-universität Düsseldorf; Alemani

Obesogenic and diabetogenic effects of high-calorie nutrition require adipocyte BK channels:Adipocyte BK protects from overwhelming BW gain

Elevated adipose tissue expression of the Ca2+- and voltage-activated K+ (BK) channel was identified in morbidly obese men carrying a BK gene variant supporting the hypothesis that K+ channels affect metabolic responses of fat cells to nutrients. To establish the role of endogenous BKs for fat cell maturation, storage of excess dietary fat and body-weight (BW) gain we studied a gene-targeted mouse model with a global ablation of the BK channel (BKL1/L1) and adipocyte-specific BK-deficient (adipoqBKL1/L2) mice. Global BK deficiency afforded protection from high-fat-diet (HFD) induced BW gain and excessive fat accumulation. Expansion of white adipose tissue-derived epididymal BKL1/L1 pre-adipocytes and their differentiation to lipid-filled mature adipocytes in vitro, however, were improved. Moreover, BW gain and total fat masses of usually super-obese ob/ob mice were significantly attenuated in the absence of BK together supporting a central or peripheral role for BKs in the regulatory system that controls adipose tissue and weight. Accordingly, HFD-fed adipoqBKL1/L2 mutants presented with a reduced total BW and overall body fat mass, smaller adipocytes and reduced leptin levels. Protection from pathologic weight gain in the absence of adipocyte BKs was beneficial for glucose handling and related to an increase in body core temperature due to higher levels of uncoupling protein 1 as well as low abundance of the proinflammatory interleukin-6 as a common risk factor for diabetes and metabolic abnormalities. This suggests that adipocyte BK activity is at least partially responsible for excessive BW gain under high-caloric conditions suggesting BK channels as promising drug targets for pharmacotherapy of metabolic disorders and obesity

Gα_i Proteins are Indispensable for Hearing

Background/Aims: From invertebrates to mammals, Gαi proteins act together with their common binding partner Gpsm2 to govern cell polarization and planar organization in virtually any polarized cell. Recently, we demonstrated that Gαi3-deficiency in pre-hearing murine cochleae pointed to a role of Gαi3 for asymmetric migration of the kinocilium as well as the orientation and shape of the stereociliary (“hair”) bundle, a requirement for the progression of mature hearing. We found that the lack of Gαi3 impairs stereociliary elongation and hair bundle shape in high-frequency cochlear regions, linked to elevated hearing thresholds for high-frequency sound. How these morphological defects translate into hearing phenotypes is not clear. Methods: Here, we studied global and conditional Gnai3 and Gnai2 mouse mutants deficient for either one or both Gαi proteins. Comparative analyses of global versus Foxg1-driven conditional mutants that mainly delete in the inner ear and telencephalon in combination with functional tests were applied to dissect essential and redundant functions of different Gαi isoforms and to assign specific defects to outer or inner hair cells, the auditory nerve, satellite cells or central auditory neurons. Results: Here we report that lack of Gαi3 but not of the ubiquitously expressed Gαi2 elevates hearing threshold, accompanied by impaired hair bundle elongation and shape in high-frequency cochlear regions. During the crucial reprogramming of the immature inner hair cell (IHC) synapse into a functional sensory synapse of the mature IHC deficiency for Gαi2 or Gαi3 had no impact. In contrast, double-deficiency for Gαi2 and Gαi3 isoforms results in abnormalities along the entire tonotopic axis including profound deafness associated with stereocilia defects. In these mice, postnatal IHC synapse maturation is also impaired. In addition, the analysis of conditional versus global Gαi3-deficient mice revealed that the amplitude of ABR wave IV was disproportionally elevated in comparison to ABR wave I indicating that Gαi3 is selectively involved in generation of neural gain during auditory processing. Conclusion: We propose a so far unrecognized complexity of isoform-specific and overlapping Gαi protein functions particular during final differentiation processes