Loss of spatacsin impairs cholesterol trafficking and calcium homeostasis

Abstract

Mutations in SPG11, leading to loss of spatacsin function, impair the formation of membrane tubules in lysosomes and cause the accumulation of lipids in lysosome compartment. However, the full nature of lipids accumulating in lysosomes and the physiological consequences of such accumulation are not known. Here we show that loss of spatacsin, but also downregulation of clathrin, inhibited the formation of tubules on late endosomes/lysosomes and prevented the clearance of cholesterol from this subcellular compartment. Using spatacsin-deficient cells, we evaluated the consequences of impaired cholesterol clearance from late endosomes/lysosomes. The accumulation of cholesterol in late endosomes/lysosomes led to lower cholesterol levels in the plasma membrane, enhancing the entry of extracellular calcium by store-operated calcium entry and increasing resting cytosolic calcium levels.Higher cytosolic calcium levels promoted the nuclear translocation of the master regulator of lysosomes TFEB. Downregulation of TFEB or decrease in resting calcium levels in absence of spatacsin partially corrected the formation of tubules and the accumulation of cholesterol in lysosomes, suggesting that spatacsin could be indirectly implicated in the formation of tubules. Our work reveals a homeostatic balance between cholesterol trafficking and cytosolic calcium levels and shows that loss of spatacsin impairs this homeostatic equilibrium.

ESCRT-I controls lysosomal membrane protein homeostasis and restricts MCOLN1-dependent TFEB/TFE3 signaling

“…Our data confirming the activation of TFEB and TFE3 signaling in ESCRT-I-depleted cells reinforced our hypothesis that ESCRT-I deficiency could lead to lysosomal dysfunction. TFEB activation may occur upon inhibition of cholesterol efflux from lysosomes (Boutry et al, 2019;Willett et al, 2017). Consistent with this, ESCRT-I depletion led to elevated expression of genes encoding enzymes of cholesterol biosynthesis (Fig.…”

“…Impaired cholesterol efflux from lysosomes can cause the import of extracellular calcium to the cytoplasm (Boutry et al, 2019;Tiscione et al, 2019) that may lead to TFEB nuclear translocation (Boutry et al, 2019). Hence, we tested whether preventing the lysosomal cholesterol accumulation by culturing cells in a delipidated medium (as shown in Fig.…”

Janus-faced spatacsin (SPG11): involvement in neurodevelopment and multisystem neurodegeneration

“…Additional evaluation of cellular models derived from the Spg11 knock-out mouse ( Branchu et al , 2017 ) linked the loss of spatacsin to lysosomal cholesterol accumulation, eventually leading to reduced level of cholesterol in the plasma membrane, resulting in impaired calcium homeostasis ( Boutry et al , 2019 ). Both cellular phenotypes—altered cholesterol distribution and calcium dysregulation—are known to be tightly linked to neurodegeneration ( Mattson, 2007 ; Zundorf and Reiser, 2011 ; Arenas et al , 2017 ).…”

Mouse models for hereditary spastic paraplegia uncover a role of PI4K2A in autophagic lysosome reformation

“…The latter mechanism is regulated by MTOR (mechanistic target of rapamycin kinase), which allows the recycling of lysosomes from autolysosomes after prolonged starvation [15]. It was proposed that defective ALR may alter the subcellular distribution of cholesterol and thus affect intracellular calcium homeostasis, which may impair lysosome tubulation via TFEB (transcription factor EB), the master regulator of lysosomes [16].…”