The role of the mitochondrial outer membrane protein SLC25A46 in mitochondrial fission and fusion.

Mutations in SLC25A46 underlie a wide spectrum of neurodegenerative diseases associated with alterations in mitochondrial morphology. We established an SLC25A46 knock-out cell line in human fibroblasts and studied the pathogenicity of three variants (p.T142I, p.R257Q, and p.E335D). Mitochondria were fragmented in the knock-out cell line and hyperfused in all pathogenic variants. The loss of SLC25A46 led to abnormalities in the mitochondrial cristae ultrastructure that were not rescued by the expression of the variants. SLC25A46 was present in discrete puncta at mitochondrial branch points and tips of mitochondrial tubules, co-localizing with DRP1 and OPA1. Virtually, all fission/fusion events were demarcated by a SLC25A46 focus. SLC25A46 co-immunoprecipitated with the fusion machinery, and loss of function altered the oligomerization state of OPA1 and MFN2. Proximity interaction mapping identified components of the ER membrane, lipid transfer proteins, and mitochondrial outer membrane proteins, indicating that it is present at interorganellar contact sites. SLC25A46 loss of function led to altered mitochondrial lipid composition, suggesting that it may facilitate interorganellar lipid flux or play a role in membrane remodeling associated with mitochondrial fusion and fission.

Frontline Science: Proliferation of Ly6C+ monocytes during urinary tract infections is regulated by IL-6 trans-signaling.

Ly6C+ monocytes are important components of the innate immune defense against infections. These cells have been shown to proliferate in the bone marrow of mice with systemic infections. However, the proliferative capacity of Ly6C+ monocytes in infected peripheral tissues as well as the associated regulatory mechanisms remain unclear. In this study, we analyzed the proliferative capacity of Ly6C+ monocytes in the urinary bladder after infection with uropathogenic E. coli, one of the most prevalent pathogen worldwide, and in LPS-induced peritonitis. We show that Ly6C+ monocytes proliferated in the bladder after infection with uropathogenic E. coli and in the peritoneum after intraperitoneal injection of LPS. We identified IL-6, a molecule that is highly expressed in infections, as a crucial regulator of Ly6C+ monocyte proliferation. Inhibition of IL-6 via administration of antibodies against IL-6 or gp130 impeded Ly6C+ monocyte proliferation. Furthermore, repression of IL-6 trans-signaling via administration of soluble gp130 markedly reduced the proliferation of Ly6C+ monocytes. Overall, this study describes the proliferation of Ly6C+ monocytes using models of urinary tract infection and LPS-induced peritonitis. IL-6 trans-signaling was identified as the regulator of Ly6C+ monocyte proliferation.