👤 Aleena Defreitas

Lipid processing in the retinal pigment epithelium (RPE) is important for maintaining the health and function of the neural retina and the RPE itself. One mode of en mass lipid transport from the RPE is apolipoprotein B-containing lipoproteins (Blps), the assembly of which is regulated by microsomal triglyceride transfer protein (MTP). To gain an initial understanding of how the loss of MTP and, thereby, Blp secretion alters other lipid processing pathways in the RPE, we measured the expression of proteins associated with β-oxidation and lipid droplets in mice lacking MTP expression in the RPE (RPEΔMttp) and age-matched controls. Expression of perilipin 2, a lipid droplet-associated protein, nearly doubled in the RPE of RPEΔMttp, and its localization with neutral lipids also increased. Meanwhile, expression of CPT1A, which mediates the transport of fatty acids into the mitochondria for β-oxidation, was unaffected. These results suggest that the loss of Blp assembly alters intracellular lipid storage patterns. Future studies will examine the effects of the loss of RPE-specific MTP expression and Blp secretion on additional lipid processing pathways. Show less

The most common form of neuronal ceroid lipofuscinosis (NCL) is juvenile CLN3 disease (JNCL), a currently incurable neurodegenerative disorder caused by mutations in the CLN3 gene. Based on our previous work and on the premise that CLN3 affects the trafficking of the cation-independent mannose-6 phosphate receptor and its ligand NPC2, we hypothesised that dysfunction of CLN3 leads to the aberrant accumulation of cholesterol in the late endosomes/lysosomes (LE/Lys) of JNCL patients' brains. An immunopurification strategy was used to isolate intact LE/Lys from frozen autopsy brain samples. LE/Lys isolated from samples of JNCL patients were compared with age-matched unaffected controls and Niemann-Pick Type C (NPC) disease patients. Indeed, mutations in NPC1 or NPC2 result in the accumulation of cholesterol in LE/Lys of NPC disease samples, thus providing a positive control. The lipid and protein content of LE/Lys was then analysed using lipidomics and proteomics, respectively. Lipid and protein profiles of LE/Lys isolated from JNCL patients were profoundly altered compared to controls. Importantly, cholesterol accumulated in LE/Lys of JNCL samples to a comparable extent than in NPC samples. Lipid profiles of LE/Lys were similar in JNCL and NPC patients, except for levels of bis(monoacylglycero)phosphate (BMP). Protein profiles detected in LE/Lys of JNCL and NPC patients appeared identical, except for levels of NPC1. Our results support that JNCL is a lysosomal cholesterol storage disorder. Our findings also support that JNCL and NPC disease share pathogenic pathways leading to aberrant lysosomal accumulation of lipids and proteins, and thus suggest that the treatments available for NPC disease may be beneficial to JNCL patients. This work opens new avenues for further mechanistic studies in model systems of JNCL and possible therapeutic interventions for this disorder. San Francisco Foundation. Show less