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Regulation of mitochondrial Ca2+ uniporter expression and calcium signalling by lncRNA Tug1 in cardiomyocytes

ABSTRACT: Cardiomyocyte Ca2+ is buffered by mitochondria via the mitochondrial calcium uniporter (MCU) complex. The MCU complex consists of pore-forming proteins including the mitochondrial calcium uniporter (MCU), and regulatory proteins such as mitochondrial calcium uptake proteins 1 and 2 (MICU1/2). The stoichiometry of these proteins influences the sensitivity to Ca2+ and activity of the complex. However, the factors that regulate their gene expression remain incompletely understood. Long non-coding RNAs (lncRNAs) regulate gene expression through various mechanisms, and we recently found that the lncRNA Tug1 affected the expression of MCU-associated genes. To further explore this, we knocked down Tug1 (Tug1 KD) in H9c2 rat cardiomyocytes using antisense LNA oligo. This led to increased MCU protein expression yet this did not enhance a marker of mitochondrial Ca2+ uptake. RNA-seq revealed that Tug1 KD increased Mcu and led to differential expression of genes and pathways related to Ca2+ regulation in the heart. To understand the effect of this on Ca2+ signalling, we measured phosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and its downstream target cAMP Response Element-Binding protein (CREB), a transcription factor known to promote Mcu gene expression. Tug1 KD attenuated the increase in CAMKII and CREB phosphorylation in response to ionomycin, a Ca2+ ionophore. Inhibition of CaMKII, but not CREB, partially prevented the Tug1 KD mediated increase in Mcu. Together, these data suggest that Tug1 modulates MCU expression via a mechanism that may involve CAMKII and CREB. The Tug1 mediated regulation of MCU on mitochondrial Ca2+ uptake, may have functional consequences for cellular Ca2+ handling which could have implications for cardiac disease.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE237787 | GEO | 2023/07/22

REPOSITORIES: GEO

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Project description:Chronic low-grade inflammation is a hallmark of aging, but its etiology is not well understood. Mitochondrial dysfunction has been linked to both cellular senescence and age-related inflammation or inflammaging but fundamental mechanisms underlying these links are unclear. We analyzed age-related gene expression in different human tissues and discovered that in blood, the mRNA expression of Mitochondrial Calcium Uniporter (MCU) and its regulatory subunit MICU1 correlated inversely with age. MCU is the pore-forming subunit of a Ca2+-selective ion channel complex residing in the mitochondrial inner membrane and is the main conduit for Ca2+-influx into the mitochondrial matrix. Based on these findings we tested the simple hypothesis that mitochondrial Ca2+ uptake capacity of macrophages decreases with age. We found a significant reduction in the mitochondrial Ca2+-uptake capacity of macrophages derived from aged (80-90 weeks) mice. Notably, these macrophages display amplified cytosolic Ca2+ elevations and increased inflammatory output. To test the salience of mitochondrial calcium uptake in regulating macrophage inflammatory output, we deleted Mcu selectively in macrophages. The Mcu-/- macrophages of young mice (<25 weeks) express more inflammatory genes at baseline and show a hyper-inflammatory response when stimulated. We show that reduced mitochondrial Ca2+ amplifies cytosolic Ca2+ oscillations and potentiates downstream NFkB activation, which is central to inflammation. The regulation of inflammatory response by mitochondrial Ca2+ uptake is also seen readily in human macrophages. The siRNA-mediated knockdown of MCU in human blood derived macrophages recapitulates the phenomenon – the mitochondrial Ca2+-uptake is greatly reduced, cytosolic Ca2+ elevations are more pronounced, and the macrophages are hyper-inflammatory. Our findings pinpoint the MCU complex as a keystone molecular apparatus that links age-related changes in mitochondrial physiology to macrophage-mediated inflammation. Resident macrophages are intrinsic to every organ system and the steady erosion of their mitochondrial Ca2+-uptake capacity may play a germinal or exacerbating role in many age-related neurodegenerative, cardiometabolic, renal and musculoskeletal diseases that afflict us.

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Regulation of mitochondrial Ca2+ uniporter expression and calcium signalling by lncRNA Tug1 in cardiomyocytes

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