Regulation of mitochondrial calcium uniporter expression and calcium-dependent cell signalling by lncRNA Tug1 in cardiomyocytes.

Cardiomyocyte calcium homeostasis is a tightly regulated process. The mitochondrial calcium uniporter (MCU) complex can buffer elevated cytosolic Ca levels and consists of pore-forming proteins including MCU, and various regulatory proteins such as mitochondrial calcium uptake proteins 1 and 2 (MICU1/2). The stoichiometry of these proteins influences the sensitivity to Ca 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 increased the expression of and associated genes. To further explore this, we performed antisense LNA knockdown of ( KD) in H9c2 rat cardiomyocytes. KD increased MCU protein expression, yet pyruvate dehydrogenase dephosphorylation, which is indicative of mitochondrial Ca uptake, was not enhanced. However, RNA-seq revealed that KD increased along with differential expression of >1000 genes including many related to Ca regulation pathways in the heart. To understand the effect of this on Ca signalling, we measured phosphorylation of Ca/calmodulin-dependent protein kinase II (CaMKII) and its downstream target cAMP Response Element-Binding protein (CREB), a transcription factor known to drive gene expression. In response a Ca stimulus, the increase in CAMKII and CREB phosphorylation was attenuated by KD. Inhibition of CaMKII, but not CREB, partially prevented the KD-mediated increase in . Together, these data suggest that modulates MCU expression via a mechanism involving CAMKII and regulates cardiomyocyte Ca signalling which could have important implications for cardiac function.