Bedeutung des Hormons atriales natriuretisches Peptid (ANP) für die Regulation der Insulinsekretion und die Vitalität von pankreatischen ß-Zellen
Final Report Abstract
Background: The cardiac hormones atrial (ANP) and B-type natriuretic peptide (BNP), via their shared cGMP-forming guanylyl cyclase-A (GC-A) receptor, regulate arterial blood pressure and metabolism. Here we studied whether the role of NPs in the regulation of energy balance and glucose homeostasis involves effects on the function and vitality of pancreatic β-cells. To this aim we generated a novel genetic mouse model with conditional, β-cell-restricted deletion of GC-A (GC-Afl/fl;Rip-Cre+/-: β GC-A KO mice). Methods and Results: (A) In vitro measurements of insulin secretion in isolated pancreatic islets revealed that ANP, via GC-A, enhances stimulus-secretion coupling directly and by potentiating the effect of the incretine hormone glucagon like peptide-1 (GLP-1). The results from patch-clamp experiments underline the importance of KATP channels for the action of ANP on β-cell function. These acute in vitro effects of ANP on KATP channel activity and insulin secretion were prevented by pharmacological inhibitors of cGMP-dependent protein kinase I (PKG I), protein kinase A (PKA) and phosphodiesterase 3B (PDE3B). This points to the participation of the cGMP/PKG I and cAMP/PKA/Epac pathways in the effects of ANP on β-cell function whereby the latter seems to prevail. (B) To evaluate the relevance in vivo, we performed metabolic studies in β GC-A KO mice. Under baseline, physiological conditions fasted and fed insulin and glucose levels, glucose-induced insulin secretion (GSIS) and tolerance of oral or intraperitoneal administered glucose (oGTT, ipGTT) were not different between β GC-A KO and control littermates. Hence, although β-cells express GC- A receptors, NP/GC-A signaling seems to be dispensable for baseline or postprandial insulin release under resting, physiological conditions. (C) Because the in vitro studies with ANP were all performed with rather high peptide concentrations (10 nM; >10-100-fold over endogenous circulating ANP/BNP levels) we tested the metabolic effect of exogenous ANP injections in vivo (acutely increasing ANP plasma levels by ~10-fold). Acute ANP administration markedly reduced GSIS and oGTT in both, control and β GC-A KO littermates. Because ANP also lowered blood pressure, it is likely that hypotension (reflex)-mediated sympathetic activation blunts β-cell insulin secretion and thereby glucose tolerance counter-regulating any possible direct effect of ANP on β-cells. (D) Finally, to characterize whether endogenous NPs improve β-cell functions under pathophysiological conditions of high insulin demand, β GC-A KO mice and control littermates received a normal (ND) or a high-fat diet (60% energy from fat, HFD) starting at 5 weeks of age. The HFD induced genotype-independent increases in body weight, arterial blood pressure and left ventricular ANP and BNP mRNA expression levels. Interestingly, after 8 weeks of HFD, glucose handling (shown by oGTTs) was significantly impaired in the β GC-A KO mice but preserved in their control littermates. However, this genotypedependent difference vanished after 12 and 18 weeks of diet, with both genotypes now showing similar pathological oGTTs. Immunohistochemistry combined with quantitative real-time RT-PCR analyses of the cell cycle regulator Cyclin D2 indicated that HFD induced adaptative beta-cell proliferation in control mice, which was markedly impaired in β GC-A KO mice after 2 months of HFD. Even more, application of gene arrays revealed enhanced expression of pro-apoptotic (CEBPA, GSK3B, ACLY) and anti-proliferative genes (VEGFA) in islets from β GC-A KO mice subjected to HFD. Concordantly, incubation of cultured control islets with 0.1 and 1 nM ANP or BNP during 24h induced the expression of Cyclin D2; this effect was abolished in islets lacking GC-A in β-cells. Conclusions: Our investigations extend the current knowledge of the metabolic actions of the NP/GC-A system, showing a protective role of the cardiac hormones in the endocrine pancreas. They also remark that in vitro and in vivo observations can differ significantly and should be combined whenever possible. Specifically the results from our metabolic studies in vivo suggest that natriuretic peptides contribute to enhanced β-cell proliferation and function during early stages of increased insulin demand, i.e. in type 2 diabetes. With the recent approval and proven efficacy of EntrestoR, a combination drug containing sacubitril (which inhibits NP degradation and thereby augments the circulating levels of these cardiac hormones) and valsartan for the treatment of patients with heart failure, it became even more important to understand the pleiotropic actions of NPs and their potential therapeutic applications in cardio-metabolic diseases. From this perspective, the here presented project not only has high pathophysiological relevance but also potential therapeutical implications.
Publications
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Modulation of beta-cell function by the atrial natriuretic peptide. Acta Phsiologica 210(Suppl. 695):143; 2014 (97. Meeting of Deutsche Physiologische Gesellschaft, Mainz)
Undank S., Nakagawa H., Völker K., Gaßner B., Oberwinkler H., Krippeit-Drews P., Düfer M., Kuhn M., Drews G.
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Modulation of beta-cell function by the atrial natriuretic peptide. Diabetologia 58 (Suppl. 1):S220 2015 (51. Meeting of European Association for the Study of Diabetes (EASD), Stockholm)
Undank S., Krippeit-Drews P., Düfer M., Drews G.
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Role of atrial natriuretic peptide (ANP) in the regulation of insulin secretion and vitality of pancreatic ß cells. BMC Pharmacol Toxicol. 2015; 16(Suppl 1): A92 (7th International Conference on cGMP, Trier, 2015)
Tauscher S., Nakagawa H., Völker K., Gaßner B., Pröhl S., Kuhn M.
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Conditional, Cell-Restricted Deletion of Guanylyl Cyclase a in Pancreatic Beta Cells Reveals Protective Anp Effects in Experimental Diabetes. Endocrine Reviews, Volume 37 (Suppl), Issue 2, 2016 (Endocrine Society's 98th Annual Meeting, April 1–4, 2016 – Boston)
Tauscher S., Nakagawa H., Völker K., Kuhn, M.
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Molecular Physiology of Membrane Guanylyl Cyclase Receptors. Physiol Rev. 2016; 96:751-804
Kuhn, M.
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Atrial natriuretic peptide (ANP) affects stimulus-secretion coupling of pancreatic β-cells. Diabetes. 2017; 66:2840-2848
Undank, S., Kaiser, J., Sikimic J., Düfer, M., Krippeit-Drews, P., Drews, G.
