Disruptive lysosomal-metabolic signaling and neurodevelopmental deficits that precede Purkinje cell loss in a mouse model of Niemann-Pick Type-C disease

Abstract

Purkinje cell (PC) loss occurs at an early age in patients and animal models of Niemann-Pick Type C (NPC), a lysosomal storage disease caused by mutations in the Npc1 or Npc2 genes. Although degeneration of PCs occurs early in NPC, little is known about how NPC1 deficiency affects the postnatal development of PCs. Using the Npc1nmf164 mouse model, we found that NPC1 deficiency significantly affected the postnatal development of PC dendrites and synapses. The developing dendrites of Npc1nmf164 PCs were significantly deficient in mitochondria and lysosomes. Furthermore, anabolic (mTORC1) and catabolic (TFEB) signaling pathways were not only perturbed but simultaneously activated in NPC1-deficient PCs, suggesting a loss of metabolic balance. We also found that mice with conditional heterozygous deletion of the Phosphatase and Tensin Homolog Deleted on Chromosome 10 gene (Pten-cHet), an inhibitor of mTORC1, showed similar early dendritic alterations in PCs to those found in Npc1-deficient mice. However, in contrast to Npc1nmf164 mice, Pten-cHet mice exhibited the overactivation of the mTORC1 pathway but with a strong inhibition of TFEB signaling, along with no dendritic mitochondrial reductions by the end of their postnatal development. Our data suggest that disruption of the lysosomal-metabolic signaling in PCs causes dendritic and synaptic developmental deficits that precede and promote their early degeneration in NPC.

Trehalose enhances mitochondria deficits in human NPC1 mutant fibroblasts but disrupts mouse Purkinje cell dendritic growth ex vivo

“…It has been suggested that an interplay between mitophagy and mitochondrial biogenesis is necessary to prevent pathological conditions associated with mitochondria dysfunction [ 30 , 31 ]. Accumulation of fragmented and damaged mitochondria has been found in Purkinje cells from NPC1 mutant mice and in vitro NPC1 deficient cellular models where lysosomal degradation is severely impaired [ 11 , 13 , 24 ]. In this study, NPC1 mutant fibroblasts were able to increase mitochondrial length after serum starvation and reintroduction of CM, suggesting that a potential increase in lysosomal activity induced by serum starvation enhanced the fusion or biogenesis of mitochondria when CM was reintroduced.…”

“…NPC1 deficiency leads to the early degeneration of neurons in Niemann-Pick Type C disease. Given that reduced levels and fragmentation of mitochondria are found in Purkinje cells (PCs) from Npc1 nmf164 mutant mice [ 11 ], we pursued to determine the effects of TH treatment in NPC1 mutant PCs. Cerebellar slices at postnatal day 10 (P10) from wild type (WT) and Npc1 nmf164 mutant mice were used for organotypic slice cultures, and after 4 days in vitro (DIV) were fixed and immunolabeled with calbindin (CALB) and PDHE1 antibodies.…”

“…Quantifications of the percentage of the LAMP1 total volume inside CALB + PCs soma and dendrites were performed as previously reported [ 11 ]. Using the Imaris software and 40X confocal images, a 3D surface rendering was created for the CALB channel, then the total volume (sum) of CALB + dendrites was measured.…”

“…In NPC1 deficient mouse models, early post developmental demise of Purkinje cells (PCs) and ataxia are the main neuropathological and symptomatic features of the NPC disease [ 2 , 4 – 7 ]. Our laboratory and others have found that NPC1 deficiency significantly affects PCs postnatal development by impairing lysosomal metabolic signaling, dendritic growth, synaptic development, and microglia function [ 8 – 11 ]. Deficiency of NPC1 in cells causes the overactivation of the metabolic regulator mTORC1 [ 11 – 13 ], which leads to the fragmentation and dysfunction of mitochondria in in vitro cells [ 13 ] and the transient overgrowth of PC dendrites in mice during the early stages of postnatal development [ 11 ].…”

“…Our laboratory and others have found that NPC1 deficiency significantly affects PCs postnatal development by impairing lysosomal metabolic signaling, dendritic growth, synaptic development, and microglia function [ 8 – 11 ]. Deficiency of NPC1 in cells causes the overactivation of the metabolic regulator mTORC1 [ 11 – 13 ], which leads to the fragmentation and dysfunction of mitochondria in in vitro cells [ 13 ] and the transient overgrowth of PC dendrites in mice during the early stages of postnatal development [ 11 ]. This overgrowth in NPC1 deficient PCs is followed by the regression of their dendrites that is concomitant with the increased activation of the transcription factor TFEB [ 11 ].…”