Shear stress promotes mitochondrial homeostasis and attenuates TNFα‐induced mitochondrial dysfunction

Abstract

Hemodynamic blood flow‐induced laminar shear flow exerts atheroprotective responses in endothelial cells (ECs) have been intensively studied. Our earlier studies indicated that laminar shear flow attenuated cytokine‐induced inflammatory responses in ECs. However, the effects of laminar shear flow on mitochondrial homeostasis and functions in ECs and during the inflammation remain unclear. We examined the dynamic changes of mitochondrial phenotype and its regulatory proteins associated with mitochondrial functions in ECs under physiological shear flow. Cultured human ECs were subjected to a constant shear stress (12 dynes/cm2) with a parallel‐plate flow chamber system. Mitochondrial biogenesis, dynamics and function were analyzed from ECs after shear treatment. Shear‐treated ECs increased mitochondrial biogenesis as indicated by the elevated levels of mitochondrial transcription factor (TFAM), transcriptional coactivator (PGC1‐α), nuclear respiratory factor (NRF1) and mitochondrial proteins (SDHA and COX4). Shear flow triggered a time‐dependent increment of mitochondrial tubular formation (fusion). This phenomenon was coupled with an increased expression of fusion proteins (MFN2, OPA1) but decreased fission protein (FIS1). Laminar shear flow also increased the long form of OPA‐1 that promotes fusion. Consistently, an increase of phosphorylation at S637 but decrease at S616 on Drp1 and the decrease of mitochondria‐associated Drp1 were observed in ECs after flow treatment. Laminar flow increased the expression of mitochondrial antioxidant enzymes MnSOD2, Thioredoxin (TRX2), Peroxiredoxins (PRX3 and PRX5). As a consequence, ECs exposed to laminar shear flow improve mitochondrial function as revealed by a decreased mitochondrial reactive oxygen species levels (mROS), and an increase of mitochondrial membrane potential and ATP production. Furthermore, ECs exposed to TNFα decreased OPA1 and MFN2 expression and increased mitochondrial fission as revealed by the mitochondrial fragmentation. Consequently, TNFα treatment resulted in a decreased mitochondrial function in ECs. However, ECs under shear flow attenuated this TNFα‐induced decrease of OPA1 and mitochondrial dysfunction. ECs treated with TNFα decreased OPA1 and MFN2 expression, whiles under shear condition, these effects were attenuated. Our results suggest that steady laminar flow promotes endothelial function and helps to prevent the inflammation‐induced mitochondrial dysfunction in ECs. Our study further supports that laminar shear flow exerts atheroprotective role to ECs.