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TRPC proteins form cation conducting channels regulated by different stimuli and are regulators of the cellular calcium homeostasis. TRPC are expressed in cardiac cells including cardiac fibroblasts (CFs) and have been implicated in the development of pathological cardiac remodeling including fibrosis. Using Ca 2+ imaging and several compound TRPC knockout mouse lines we analyzed the involvement of TRPC proteins for the angiotensin II (AngII)-induced changes in Ca 2+ homeostasis in CFs isolated from adult mice. Using qPCR we detected transcripts of all Trpc genes in CFs; Trpc1 , Trpc3 and Trpc4 being the most abundant ones. We show that the AngII-induced Ca 2+ entry but also Ca 2+ release from intracellular stores are critically dependent on the density of CFs in culture and are inversely correlated with the expression of the myofibroblast marker α-smooth muscle actin. Our Ca 2+ measurements depict that the AngII- and thrombin-induced Ca 2+ transients, and the AngII-induced Ca 2+ entry and Ca 2+ release are not affected in CFs isolated from mice lacking all seven TRPC proteins (TRPC-hepta KO) compared to control cells. However, pre-incubation with GSK7975A (10 µM), which sufficiently inhibits CRAC channels in other cells, abolished AngII-induced Ca 2+ entry. Consequently, we conclude the dispensability of the TRPC channels for the acute neurohumoral Ca 2+ signaling evoked by AngII in isolated CFs and suggest the contribution of members of the Orai channel family as molecular constituents responsible for this pathophysiologically important Ca 2+ entry pathway., Competing Interests: The authors declare no conflict of interest.

TRPC proteins form cation conducting channels regulated by different stimuli and are regulators of the cellular calcium homeostasis. TRPC are expressed in cardiac cells including cardiac fibroblasts (CFs) and have been implicated in the development of pathological cardiac remodeling including fibrosis. Using Ca2+ imaging and several compound TRPC knockout mouse lines we analyzed the involvement of TRPC proteins for the angiotensin II (AngII)-induced changes in Ca2+ homeostasis in CFs isolated from adult mice. Using qPCR we detected transcripts of all Trpc genes in CFs; Trpc1, Trpc3 and Trpc4 being the most abundant ones. We show that the AngII-induced Ca2+ entry but also Ca2+ release from intracellular stores are critically dependent on the density of CFs in culture and are inversely correlated with the expression of the myofibroblast marker α-smooth muscle actin. Our Ca2+ measurements depict that the AngII- and thrombin-induced Ca2+ transients, and the AngII-induced Ca2+ entry and Ca2+ release are not affected in CFs isolated from mice lacking all seven TRPC proteins (TRPC-hepta KO) compared to control cells. However, pre-incubation with GSK7975A (10 µM), which sufficiently inhibits CRAC channels in other cells, abolished AngII-induced Ca2+ entry. Consequently, we conclude the dispensability of the TRPC channels for the acute neurohumoral Ca2+ signaling evoked by AngII in isolated CFs and suggest the contribution of members of the Orai channel family as molecular constituents responsible for this pathophysiologically important Ca2+ entry pathway. [ABSTRACT FROM AUTHOR]

Pathological cardiac hypertrophy is an independent risk for heart failure (HF) and sudden death. Deciphering signaling pathways regulating intracellular Ca2+ homeostasis that control adaptive and pathological cardiac growth may enable identification of novel therapeutic targets. The objective of the present study is to determine the role of the store-operated calcium entry-associated regulatory factor (Saraf), encoded by the Tmem66 gene, on cardiac growth control in vitro and in vivo. Saraf is a single-pass membrane protein located at the sarco/endoplasmic reticulum and regulates intracellular calcium homeostasis. We found that Saraf expression was upregulated in the hypertrophied myocardium and was sufficient for cell growth in response to neurohumoral stimulation. Increased Saraf expression caused cell growth, which was associated with dysregulation of calcium-dependent signaling and sarcoplasmic reticulum calcium content. In vivo , Saraf augmented cardiac myocyte growth in response to angiotensin II and resulted in increased cardiac remodeling together with worsened cardiac function. Mechanistically, Saraf activated mTORC1 (mechanistic target of rapamycin complex 1) and increased protein synthesis, while mTORC1 inhibition blunted Saraf-dependent cell growth. In contrast, the hearts of Saraf knockout mice and Saraf-deficient myocytes did not show any morphological or functional alterations after neurohumoral stimulation, but Saraf depletion resulted in worsened cardiac function after acute pressure overload. SARAF knockout blunted transverse aortic constriction cardiac myocyte hypertrophy and impaired cardiac function, demonstrating a role for SARAF in compensatory myocyte growth. Collectively, these results reveal a novel link between sarcoplasmic reticulum calcium homeostasis and mTORC1 activation that is regulated by Saraf. • Saraf expression is upregulated in hypertrophied myocardium and is sufficient for pathological cell growth in myocytes • Saraf depletion results in deteriorated cardiac function after pressure overload • Saraf activates mTORC1 signaling and protein synthesis in cardiac myocytes • Saraf might link sarcoplasmic reticulum calcium homeostasis and mTORC1 activation during pathological growth [ABSTRACT FROM AUTHOR]