bims-mecmid Biomed News
on Membrane communication in mitochondrial dynamics
Issue of 2022‒01‒02
five papers selected by
Mauricio Cardenas Rodriguez
University of Padova

  1. Cell Rep. 2021 Dec 28. pii: S2211-1247(21)01651-X. [Epub ahead of print]37(13): 110155
      During somatic reprogramming, cellular energy metabolism fundamentally switches from predominantly mitochondrial oxidative phosphorylation toward glycolysis. This metabolic reprogramming, also called the Warburg effect, is critical for the induction of pluripotency, but its molecular mechanisms remain poorly defined. Notably, SIRT2 is consistently downregulated during the reprogramming process and regulates glycolytic switch. Here, we report that downregulation of SIRT2 increases acetylation of mitogen-activated protein kinase (MAPK) kinase-1 (MEK1) at Lys175, resulting in activation of extracellular signal-regulated kinases (ERKs) and subsequent activation of the pro-fission factor dynamin-related protein 1 (DRP1). In parallel, downregulation of SIRT2 hyperacetylates the serine/threonine protein kinase AKT1 at Lys20 in a non-canonical way, activating DRP1 and metabolic reprogramming. Together, our study identified two axes, SIRT2-MEK1-ERK-DRP1 and SIRT2-AKT1-DRP1, that critically link mitochondrial dynamics and oxidative phosphorylation to the somatic reprogramming process. These upstream signals, together with SIRT2's role in glycolytic switching, may underlie the Warburg effect observed in human somatic cell reprogramming.
    Keywords:  AKT1; DRP1; MEK1-ERK axis; OXPHOS; SIRT2; Warburg-like effect; human somatic cell reprogramming; induced pluripotent stem cells; metabolic reprogramming; mitochondrial remodeling
  2. Redox Biol. 2021 Dec 20. pii: S2213-2317(21)00376-1. [Epub ahead of print]49 102216
      Mitochondria play an essential role in pathophysiology of both inflammatory and neuropathic pain (NP), but the mechanisms are not yet clear. Dynamin-related protein 1 (Drp1) is broadly expressed in the central nervous system and plays a role in the induction of mitochondrial fission process. Spared nerve injury (SNI), due to the dysfunction of the neurons within the spinal dorsal horn (SDH), is the most common NP model. We explored the neuroprotective role of Drp1 within SDH in SNI. SNI mice showed pain behavior and anxiety-like behavior, which was associated with elevation of Drp1, as well as increased density of mitochondria in SDH. Ultrastructural analysis showed SNI induced damaged mitochondria into smaller perimeter and area, tending to be circular. Characteristics of vacuole in the mitochondria further showed SNI induced the increased number of vacuole, widened vac-perimeter and vac-area. Stable overexpression of Drp1 via AAV under the control of the Drp1 promoter by intraspinal injection (Drp1 OE) attenuated abnormal gait and alleviated pain hypersensitivity of SNI mice. Mitochondrial ultrastructure analysis showed that the increased density of mitochondria induced by SNI was recovered by Drp1 OE which, however, did not change mitochondrial morphology and vacuole parameters within SDH. Contrary to Drp1 OE, down-regulation of Drp1 in the SDH by AAV-Drp1 shRNA (Drp1 RNAi) did not alter painful behavior induced by SNI. Ultrastructural analysis showed the treatment by combination of SNI and Drp1 RNAi (SNI + Drp1 RNAi) amplified the damages of mitochondria with the decreased distribution density, increased perimeter and area, as well as larger circularity tending to be more circular. Vacuole data showed SNI + Drp1 RNAi increased vacuole density, perimeter and area within the SDH mitochondria. Our results illustrate that mitochondria within the SDH are sensitive to NP, and targeted mitochondrial Drp1 overexpression attenuates pain hypersensitivity. Drp1 offers a novel therapeutic target for pain treatment.
    Keywords:  Drp1; Mitochondria; Pain; SNI; Spinal dorsal horn
  3. Mol Neurobiol. 2021 Dec 28.
      Radiotherapy is an effective tool in the treatment of malignant brain tumors, but irradiation-induced late-onset toxicity remains a major problem. The purpose of this study was to investigate if genetic inhibition of autophagy has an impact on subcortical white matter development in the juvenile mouse brain after irradiation. Ten-day-old selective neural Atg7 knockout (KO) mice and wild-type (WT) littermates were subjected to a single 6-Gy dose of whole-brain irradiation and evaluated at 5 days after irradiation. Neural Atg7 deficiency partially prevented myelin disruption compared to the WT mice after irradiation, as indicated by myelin basic protein staining. Irradiation induced oligodendrocyte progenitor cell loss in the subcortical white matter, and Atg7 deficiency partly prevented this. There was no significant change between the KO and WT mice in the number of microglia and astrocytes in the subcortical white matter after irradiation. Transcriptome analysis showed that the GO mitochondrial gene expression pathway was significantly enriched in the differentially expressed genes between the KO and WT group after irradiation. Compared with WT mice, expression of the mitochondrial fusion protein OPA1 and phosphorylation of the mitochondrial fission protein DRP1 (P-DRP1) were dramatically decreased in KO mice under physiological conditions. The protein levels of OPA1and P-DRP1 showed no differences in WT mice between the non-irradiated group and the irradiated group but had remarkably increased levels in the KO mice after irradiation. These results indicate that inhibition of autophagy reduces irradiation-induced subcortical white matter injury not by reducing inflammation, but by increasing mitochondrial fusion and inhibiting mitochondrial fission.
    Keywords:  Astrocyte; Autophagy; Fusion and fission; Microglia; Mitochondria; White matter injury
  4. J Biochem. 2021 Dec 29. pii: mvab153. [Epub ahead of print]
      The transfer of phospholipids from the endoplasmic reticulum to mitochondria via the mitochondria-endoplasmic reticulum (ER) contact site (MERCS) is essential for maintaining mitochondrial function and integrity. Here, we identified RMDN3/PTPIP51, possessing phosphatidic acid (PA)-transfer activity, as a neighboring protein of the mitochondrial E3 ubiquitin ligase MITOL/MARCH5 by proximity-dependent biotin labeling using APEX2. We found that MITOL interacts with and ubiquitinates RMDN3. Mutational analysis identified lysine residue 89 in RMDN3 as a site of ubiquitination by MITOL. Loss of MITOL or the substitution of lysine 89 to arginine in RMDN3 significantly reduced the PA-binding activity of RMDN3, suggesting that MITOL regulates the transport of PA to mitochondria by activating RMDN3. Our findings imply that ubiquitin signaling regulates phospholipid transport at the MERCS.
    Keywords:  E3 ubiquitin ligase; MITOL; RMDN3; mitochondria-ER contact site; phospholipid
  5. Acta Histochem. 2021 Dec 24. pii: S0065-1281(21)00159-8. [Epub ahead of print]124(1): 151837
      Diabetic retinopathy (DR) is the leading clinical cause of blindness in diabetic patients. Mitophagy participates in the pathogenesis of DR. Dynamin related protein 1 (Drp1) is associated with mitophagy. Here, we investigated whether Drp1 can regulate mitophagy to affect the progression of DR. We constructed DR rat model by administration of streptozocin. Primary rat retinal endothelial cells (RECs) were treated with high glucose (HG) as a DR cell model. Drp1 was highly expressed in the retinal tissues of DR rats and HG-treated RECs. Drp1 knockdown inhibited HG-mediated increase of reactive oxygen species (ROS) levels and apoptosis in RECs. Moreover, Drp1 silencing inhibited the expression of autophagy-related proteins LC3-II/LC3-1 and Beclin-1 and reduced LC3 puncta in HG-treated RECs. The expression of mitochondrial marker Tom20 was reduced and the levels of mitophagy were increased in the HG-treated RECs, which was rescued by Drp1 silencing. Drp1 knockdown repressed LC3-II expression in HG-treated RECs, indicating that autophagy flux was inhibited. Rapamycin (autophagy activator) enhanced ROS levels and apoptosis in HG-treated RECs by activating autophagy, which was rescued by Drp1 knockdown. In conclusion, these data demonstrated that Drp1 knockdown repressed apoptosis of rat retinal endothelial cells by inhibiting mitophagy. Thus, this work suggests that targeted regulation of Drp1 may become a treatment for DR.
    Keywords:  Apoptosis; Diabetic retinopathy; Drp1; Rat retinal endothelial cells