Rictor/mTORC2 involves mitochondrial function in ES cells derived cardiomyocytes via mitochondrial Connexin 43

Abstract

Rictor is a key component of the mammalian target of rapamycin complex 2 (mTORC2) and is required for Akt phosphorylation (Ser473). Our previous study shows that knockdown of Rictor prevents cardiomyocyte differentiation from mouse embryonic stem (ES) cells and induces abnormal electrophysiology of ES cell-derived cardiomyocytes (ESC-CMs). Besides, knockdown of Rictor causes down-expression of connexin 43 (Cx43), the predominant gap junction protein, that is located in both the sarcolemma and mitochondria in cardiomyocytes. Mitochondrial Cx43 (mtCx43) plays a crucial role in mitochondrial function. In this study, we used the model of cardiomyocyte differentiation from mouse ES cells to elucidate the mechanisms for the mitochondrial damage in ESC-CMs after knockdown of Rictor. We showed swollen and ruptured mitochondria were observed after knockdown of Rictor under transmission electron microscope. ATP production and mitochondrial transmembrane potential were significantly decreased in Rictor-knockdown cells. Furthermore, knockdown of Rictor inhibited the activities of mitochondrial respiratory chain complex. The above-mentioned changes were linked to inhibiting the translocation of Cx43 into mitochondria by knockdown of Rictor. We revealed that knockdown of Rictor inactivated the mTOR/Akt signalling pathway and subsequently decreased HDAC6 expression, resulted in Hsp90 hyper-acetylation caused by HDAC6 inhibition, thus, inhibited the formation of Hsp90-Cx43-TOM20 complex. In conclusion, the mitochondrial Cx43 participates in shRNA-Rictor-induced mitochondrial function damage in the ESC-CMs.

Impaired ERK MAPK activation in mature osteoblasts enhances bone formation via the mTOR pathway

“…Mechanistically, impaired ERK signaling in committed osteoblasts enhances osteoblast differentiation via an increase in mitochondria-mediated metabolic demands, activation of mTORC2-SGK1 signaling axis, thereby promoting bone formation (Fig 6I). This corresponds to previous reports showing that mTORC2 activation is required for mitochondrial function and homeostasis (Wang, Shao et al, 2020) and that both glycolysis and oxidative phosphorylation by mitochondria are required to meet the energy demands needed for bone formation by osteoblasts (Lee et al, 2017). However, despite previous studies showing the importance of SGK1 in osteogenic trans-differentiation of vascular smooth muscle cells (Voelkl et al, 2018) and energy metabolism in different cellular types and functions (Mason, Cockfield et al, 2021), our findings suggest that while ERK-mTORC2-SGK1 signaling axis is required for osteogenesis and production of pro-angiogenic and -osteogenic factors, it is dispensable for mitochondrial function.…”

mTORC2/RICTOR exerts differential levels of metabolic control in human embryonic, mesenchymal and neural stem cells

“…Stem cells, including pluripotent stem cells and adult stem cells, possess the remarkable capability of being able to self-renew while at the same time having potential to differentiate into different cell lineages and functionally distinct cell types. Human embryonic stem cells (hESCs) can differentiate into all adult stem cell types, including human mesenchymal stem cells (hMSCs) and human neural stem cells (hNSCs), but can also give rise to all terminally differentiated cell types (Wang et al, 2021a ). Through the continuous replenishment of differentiated cells, stem cells support tissue homeostasis and respond to tissue injuries.…”

Secretion of miRNA-326-3p by senescent adipose exacerbates myocardial metabolism in diabetic mice

“…Although mTORC2 is associated with cell metabolism [ 55 , 56 ] yet its role in cardiomyocytes remains to be explored. Given that Rictor is at the heart of the mTORC2 complex, we speculate based on previous work that loss of Rictor in STZ murine cardiomyocytes likely results in attenuation of metabolite influx into mitochondria [ 57 ], blocked connexin 43 localization to mitochondria [ 58 ], and mitochondrial dysfunction [ 59 ]. There are two distinct mTOR complexes, mTORC1 and mTORC2, that function very differently.…”