Sphingolipid signalling mediates mitochondrial dysfunctions and reduced chronological lifespan in the yeast model of Niemann‐Pick type C1

Abstract

Summary The Niemann-Pick type C is a rare metabolic disease with a severe neurodegenerative phenotype characterized by an accumulation of high amounts of lipids (cholesterol and sphingolipids) in the late endosomal/lysosomal network. It is caused by loss-of-function point mutations in either NPC1 or NPC2, which seem to mediate proper intracellular lipid transport through endocytic pathway. In this study, we show that yeast cells lacking Ncr1p, an orthologue of mammalian NPC1, exhibited a higher sensitivity to hydrogen peroxide and a shortened chronological lifespan. These phenotypes were associated with increased levels of oxidative stress markers, decreased levels of antioxidant defenses and mitochondrial dysfunctions. Moreover, we report that Ncr1p deficient cells displayed high levels of long chain bases (LCB), and that Sch9p-phospho-T570 and Sch9p levels increased in ncr1Δ cells through a mechanism regulated by Pkh1p, a LCB-activated protein kinase. Notably, deletion of PKH1 or SCH9 suppressed ncr1Δ phenotypes but downregulation of de novo sphingolipid biosynthesis had no protective effect, suggesting that LCBs accumulation may result from an increased turnover of complex sphingolipids. These results suggest that sphingolipid signaling through Pkh1p-Sch9p mediate mitochondrial dysfunction, oxidative stress sensitivity and shortened chronological lifespan in the yeast model of Niemann-Pick type C disease.

Sphingolipids and mitochondrial function in budding yeast

“…Given the reports that indicate that transient Hog1p activation promotes mitochondrial function [65-68], and prolonged Hog1p activation is detrimental [64, 69], these results also imply that Hog1p phosphorylation is a delicate event in order to preserve mitochondrial function in yeast. The role of the TORC1/Sch9p axis is not restricted to the Δisc1 mutant genetic background, as Sch9p was also shown to be crucial in regulating mitochondrial function in a yeast model for Niemann Pick type C1 [77, 78]. Hence, Sch9p acts as a critical switch in the regulation of mitochondrial function in yeast; whether Hog1p is the sole downstream target in the regulation of mitochondrial function in response to SL remains to be elucidated.…”

“…However, the specific mechanisms that lead to neurodegeneration during Niemann Pick type C1 are not fully elucidated. Interestingly, Δncr1 mutants not only exhibit hallmarks of oxidative stress and mitochondrial dysfunction, they also accumulate LCBs [77]. In addition, these LCBs are proposed to be crucial in regulating mitochondrial function in Δncr1 mutants [77].…”

“…Additional indications concerning a central signal transducing role for Sch9p in regulating mitochondrial function originates from Δisc1 -like phenotypical observations in a yeast model for Niemann-Pick type C1 disease based on Δncr1 mutants [77, 78]. Niemann Pick type C1 is a lipid storage disorder characterized by neurodegeneration [79] and is caused by mutations in NPC1 in 95 % of all cases [80-82].…”

“…These Δncr1 mutants exhibit increased sensitivity to oxidative stress and decreased CLS, characterized by increased levels of oxidative stress markers. Additionally, these mutant cells are unable to grow on a non-fermentative carbon source, show decreased mitochondrial membrane potential ( Δψ m ) and mitochondrial fragmentation [77]. In line with mammalian Niemann Pick type C1 cells [84], accumulation of LCBs is observed in the yeast Δncr1 mutants caused by an increased turnover of complex SLs.…”

“…In contrast, in Δisc1 mutants Sch9p phosphorylation is independent of Pkh1p [26]. Furthermore, Δncr1Δsch9 cells exhibit restored SL levels [77]. Such results indicate that the role of Sch9 as central signal transducer in the regulation of mitochondrial function is not restricted to the Δisc1 mutant genetic background.…”