Molecular mechanism of the ichthyosis pathology of Chanarin–Dorfman syndrome: Stimulation of PNPLA1-catalyzed ω-O-acylceramide production by ABHD5

Abstract

Background: ABHD5 mutations cause Chanarin-Dorfman syndrome accompanied by ichthyosis. v-O-Acylceramide (acylceramide) is essential for skin permeability barrier formation. Acylceramide production is impaired in Abhd5 knockout mice. The transacylase PNPLA1 catalyzes the final step of acylceramide production: transfer of linoleic acid in triglyceride to v-hydroxyceramide.Objective: We aimed to elucidate the role of ABHD5 in acylceramide production and the molecular mechanism of the ichthyosis symptoms of Chanarin-Dorfman syndrome. Methods: We investigated how ABHD5 influences acylceramide production using an acylceramideproducing cell system. The effects of ABHD5 and PNPLA1 expression on the morphology of lipid droplets were examined by indirect immunofluorescent microscopy and immunoelectron microscopy. Results: When ABHD5 was expressed in the acylceramide-producing cell system, acylceramide synthesis by PNPLA1 was enhanced. Dispersed localization of PNPLA1 was observed by immunofluorescent microscopy in HeLa cells under lipid droplet-forming conditions. Co-expression with ABHD5 caused PNPLA1 to localize on the lipid droplet membranes or their periphery. This staining pattern was observed in cells where PNPLA1 and ABHD5 were expressed at low levels. In contrast, lipid droplets disappeared in cells where PNPLA1 and ABHD5 were highly expressed. Immunoelectron microscopic analyses suggested that lipid droplets underwent morphological changes, transforming into vesicles or becoming incorporated into the endoplasmic reticulum. ABHD5 mutations found in Chanarin-Dorfman syndrome patients reduced ABHD5's ability to promote PNPLA1-dependent acylceramide production. Conclusion: ABHD5 enhances PNPLA1-catalyzed acylceramide production. We speculate that ABHD5 retains triglycerides in the endoplasmic reticulum, and presents them to PNPLA1 to promote substrate recognition.

Updating Phospholipase A2 Biology

“…Global or keratinocyte-specific deletion of PNPLA1 hampers epidermal ω- O -acylceramide formation, thereby severely impairing skin barrier function leading to neonatal death due to excessive dehydration. The enzymatic activity of PNPLA1 is enhanced by ABHD5, which may present triglycerides to PNPLA1 to facilitate substrate recognition [ 172 , 173 ], providing a mechanism whereby ABHD5 mutations cause Chanarin-Dorfman syndrome accompanied by ichthyosis with impaired ω- O -acylceramide formation. The role of PNPLA1 in ω- O -acylceramide biosynthesis has been described in detail in a recent review [ 174 ].…”

The Lipolysome—A Highly Complex and Dynamic Protein Network Orchestrating Cytoplasmic Triacylglycerol Degradation

“…Recently, two studies demonstrated that ABHD5 also binds and activates PNPLA1, a close relative of ATGL, predominantly expressed in skin keratinocytes. ABHD5 may activate a transacylase activity of PNPLA1 that could be essential for the formation of epidermal ω-O-acylceramides [34,35]. Another identified ABHD5 interaction partner is PNPLA3 (also designated as adiponutrin) [36].…”

Acylceramide is a key player in skin barrier function: insight into the molecular mechanisms of skin barrier formation and ichthyosis pathogenesis

“…ABHD5 was reported to enhance acylceramide synthesis by PNPLA1 [44,45]. Without ABHD5, PNPLA1 localizes dispersedly under lipid droplet-forming conditions, but ABHD5 co-expression takes PNPLA1 to the membranes or periphery of lipid droplets [44,45].…”