Decreased ceramide underlies mitochondrial dysfunction in Charcot‐Marie‐Tooth 2F

Abstract

Charcot-Marie-Tooth (CMT) disease is the most commonly inherited neurologic disorder, but its molecular mechanisms remain unclear. One variant of CMT, 2F, is characterized by mutations in heat shock protein 27 (Hsp27). As bioactive sphingolipids have been implicated in neurodegenerative diseases, we sought to determine if their dysregulation is involved in CMT. Here, we show that Hsp27 knockout mice demonstrated decreases in ceramide in peripheral nerve tissue and that the disease-associated Hsp27 S135F mutant demonstrated decreases in mitochondrial ceramide. Given that Hsp27 is a chaperone protein, we examined its role in regulating ceramide synthases (CerSs), an enzyme family responsible for catalyzing generation of the sphingolipid ceramide. We determined that CerSs colocalized with Hsp27, and upon the presence of S135F mutants, CerS1 lost its colocalization with mitochondria suggesting that decreased mitochondrial ceramides result from reduced mitochondrial CerS localization rather than decreased CerS activity. Mitochondria in mutant cells appeared larger with increased interconnectivity. Furthermore, mutant cell lines demonstrated decreased mitochondrial respiratory function and increased autophagic flux. Mitochondrial structural and functional changes were recapitulated by blocking ceramide generation pharmacologically. These results suggest that mutant Hsp27 decreases mitochondrial ceramide levels, producing structural and functional changes in mitochondria leading to neuronal degeneration.-Schwartz, N. U., Linzer, R. W., Truman, J.-P., Gurevich, M., Hannun, Y. A., Senkal, C. E., Obeid, L. M. Decreased ceramide underlies mitochondrial dysfunction in Charcot-Marie-Tooth 2F.

Neuromuscular Diseases Due to Chaperone Mutations: A Review and Some New Results

“…As the retrograde transport of p75NTD was affected to a lower extent, a primary impairment in mitochondrial function, rather than a cytoskeletal defect, was suggested to underlie the altered mitochondrial transport in this model [360]. One mechanism for this was identified by Schwartz et al, who showed that an abnormal interaction of mutant HSPB1 with ceramide synthase led to decreased mitochondrial ceramide content and impaired respiration [362].…”

“…The role of mitochondrial defects in the downstream pathomehcanism of HSPB1 mutations gained additional support from recent studies [360,362]. In the experiments of Kalmar and colleagues on cultured motor neurons, the expression of HSPB1 mutants, most remarkably p.S135F, decreased mitochondrial membrane potential in neurites and impaired complex I activity [360].…”

Myeloperoxidase and Septic Conditions Disrupt Sphingolipid Homeostasis in Murine Brain Capillaries In Vivo and Immortalized Human Brain Endothelial Cells In Vitro

“…It is plausible that decreased CERS1 mRNA expression ( Figure 6C) and a concomitant downregulation of Hsp27/CERS1-dependent pathways could account for decreased mitochondrial Cer levels. If occurring (not addressed experimentally in this study), a reduction in mitochondrial Cer concentrations likely induces structural and functional changes in mitochondria as observed in a model of Charcot-Marie-Tooth disease, the most commonly inherited neurological disorder [63].…”

Advances in determining signaling mechanisms of ceramide and role in disease

“…In addition, C16-ceramide has been proposed to disrupt FAO and electron transport through inactivation of complexes II and IV of the respiratory chain (20,21). Interestingly, the absence of ceramides can also disrupt mitochondrial respiration, suggesting that ceramide homeostasis may be important for normal mitochondrial function (22).…”