# Differential roles of lysosomal cholesterol transporters in the development of C. elegans NMJs

## TL;DR

This study shows how two cholesterol transporters in worms control synapse development differently, highlighting the importance of cholesterol balance in neurons.

## Contribution

The paper reveals distinct roles of NCR-1 and NCR-2 in regulating neuronal cholesterol homeostasis and synaptogenesis in C. elegans.

## Key findings

- NCR-1 promotes cholesterol absorption and synapse development, while its deficiency reduces synapses and worsens under low cholesterol.
- NCR-2 increases cholesterol and sphingomyelin use, impeding synapse formation, and its deficiency increases synapses regardless of cholesterol levels.
- Modulating sphingomyelin metabolism can alter synaptic phenotypes in NCR-2 mutants.

## Abstract

Neuronal cholesterol homeostasis during synapse development is controlled by two NPC1 homologs in C. elegans: NCR-1 absorbs cholesterol and promotes synaptogenesis, whereas NCR-2 uses cholesterol and hinders synaptogenesis.

Cholesterol homeostasis in neurons is critical for synapse formation and maintenance. Neurons with impaired cholesterol uptake undergo progressive synapse loss and eventual degeneration. To investigate the molecular mechanisms of neuronal cholesterol homeostasis and its role during synapse development, we studied motor neurons of Caenorhabditis elegans because these neurons rely on dietary cholesterol. Combining lipidomic analysis, we discovered that NCR-1, a lysosomal cholesterol transporter, promotes cholesterol absorption and synapse development. Loss of ncr-1 causes smaller synapses, and low cholesterol exacerbates the deficits. Moreover, NCR-1 deficiency hinders the increase in synapses under high cholesterol. Unexpectedly, NCR-2, the NCR-1 homolog, increases the use of cholesterol and sphingomyelins and impedes synapse formation. NCR-2 deficiency causes an increase in synapses regardless of cholesterol concentration. Inhibiting the degradation or synthesis of sphingomyelins can induce or suppress the synaptic phenotypes in ncr-2 mutants. Our findings indicate that neuronal cholesterol homeostasis is differentially controlled by two lysosomal cholesterol transporters and highlight the importance of neuronal cholesterol homeostasis in synapse development.