# Opposing roles for lipocalins and a CD36 family scavenger receptor in apical extracellular matrix-dependent protection of narrow tube integrity

## TL;DR

The study shows how lipocalins and a scavenger receptor affect the structure of narrow tubes in the body by influencing a protective matrix.

## Contribution

The study reveals opposing roles of a lipocalin and a scavenger receptor in maintaining narrow tube integrity through the apical extracellular matrix.

## Key findings

- Loss of LPR-1 disrupts LPR-3 assembly in the pre-cuticle aECM of narrow tubes.
- SCAV-2 restores LPR-3 localization and suppresses tube defects in lpr-1 mutants.
- LPR-1 and SCAV-2 have opposing effects on tube integrity via the aECM.

## Abstract

All exposed epithelial surfaces, including the walls of internal tubes, are lined by a lipid and glycoprotein-rich apical extracellular matrix (aECM) that helps shape and protect the apical domain. Secreted lipocalins are lipid transporters frequently found within apical compartments. We show that loss of the Caenorhabditis elegans lipocalin LPR-1 disrupts the assembly of another lipocalin, LPR-3, within the pre-cuticle aECM that protects and shapes the narrow excretory duct and pore tubes. Loss of SCAV-2, a CD36 family scavenger receptor, restored LPR-3 matrix localization and suppressed the tube shaping defects of lpr-1 and a subset of pre-cuticle mutants, but not lpr-3 mutants. SCAV-2 accumulates at duct and pore apical surfaces and functions locally within these tubes. These data demonstrate that LPR-1 and SCAV-2 have opposing effects on narrow tube integrity by altering the content and organization of the luminal aECM of the tube, possibly by acting as transporters of LPR-3 or an LPR-3 cofactor. These results have broadly relevant implications regarding the importance of lipocalins and scavenger receptors for aECM organization and integrity of the narrowest tubes in the body.

Summary: Lipocalins and SCARBs are lipid transporters that influence susceptibility to infection and disease. This study shows that lipocalin and SCARB mutations affect the organization of a protective extracellular matrix.