Abstract P2105: Store-Operated Channels Mediate Metabolic Adaptations In Activated Fibroblast During Cardiac Fibrosis

Abstract

Endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) are associated with developing fibrotic disorders in multiple organs, including the heart. Many ER resident chaperones require calcium (Ca2+) as a co-factor to mediate protein folding. Store-operated Ca2+ entry (SOCE) mediated by the Orai1 channels primarily maintains the ER- Ca2+ homeostasis. However, the role of the Orai1 channels in the modulation of ER-stress/UPR and downstream cellular processes that lead to cardiac fibrosis is not entirely understood. To investigate the role of Orai1 channels on the ER-stress/UPR signaling we utilized a multilayered approach that includes both genetic and pharmacological inhibition of Orai and a combination of long-term real-time cell imaging combined with genetically encoded sensors for several metabolites signaling. Our results showed that Orai1 expression was upregulated in the fibrotic mouse heart. Transcriptome analysis of fibrotic tissue from a fibroblast-specific Orai1 knock-out mouse model revealed the dysregulation of many genes associated with cell metabolism and collagen turnover. Pharmacological inhibition of Orai1 channel activity in cultured cardiac fibroblast decreased ER-Ca2+ and mitochondrial Ca2+ levels and was sufficient to trigger ER-stress/UPR and promote mitochondrial dysfunction. Like the in vivo fibrotic model, comparative transcriptome and pathway analysis between cells treated with Orai1 blocker (YM-58483, 48 hours) and controls identified dysregulated metabolic pathways and ER-stress/UPR signaling. Bioenergetic analysis showed that Orai1 inhibition induced an overall decrease in oxygen consumption rate (OCR), and mitochondrial membrane potential and reduced cellular ATP levels. Accordingly, we found that Orai1 loss-of-function increased glycolysis and reduced fatty acid oxidation (FAO), substantially reducing fibroblast fuel flexibility. This is a remarkable novel function of Orai1 channels because perturbations in fibroblast metabolic dynamic are the initial steps in the injury response. Our results suggest that Orai1 could be a novel target for developing treatments for fibrosis.