Mutations of the PARK2 and PINK1 genes, encoding the cytosolic E3 ubiquitin-protein ligase Parkin and the mitochondrial serine/ threonine kinase PINK1, respectively, cause autosomal recessive early-onset Parkinson's disease (PD). Parkin and PINK1 cooperate in a biochemical mitochondrial quality control pathway regulating mitochondrial morphology, dynamics and clearance. This study identifies the multifunctional PD-related mitochondrial matrix enzyme 17-β hydroxysteroid dehydrogenase type 10 (HSD17B10) as a new Parkin substrate. Parkin overproduction in cells increased mitochondrial HSD17B10 abundance by a mechanism involving ubiquitin chain extension, whereas PARK2 downregulation or deficiency caused mitochondrial HSD17B10 depletion in cells and mice. HSD17B10 levels were also found to be low in the brains of PD patients with PARK2 mutations. Confocal and Förster resonance energy transfer (FRET) microscopy revealed that HSD17B10 recruited Parkin to the translocase of the outer membrane (TOM), close to PINK1, both in functional mitochondria and after the collapse of mitochondrial membrane potential (ΔΨm). PD-causing PARK2 mutations impaired interaction with HSD17B10 and the HSD17B10-dependent mitochondrial translocation of Parkin. HSD17B10 overproduction promoted mitochondrial elongation and mitigated CCCP-induced mitochondrial degradation independently of enzymatic activity. These effects were abolished by overproduction of the fissionpromiting dynamin-related protein 1 (Drp1). By contrast, siRNA-mediated HSD17B10 silencing enhanced mitochondrial fission and mitophagy. These findings suggest that the maintenance of appropriate mitochondrial HSD17B10 levels is one of the mechanisms by which Parkin preserves mitochondrial quality. The loss of this protective mechanism may contribute to mitochondrial dysfunction and neuronal degeneration in autosomal recessive PD. Parkinson's disease (PD) is the most common neurodegenerative movement disorder. It is caused by progressive loss of the dopaminergic neurons of the substantia nigra pars compacta. It is mostly sporadic, but about 10% of cases are familial forms with Mendelian inheritance.1 Autosomal recessive forms of PD are caused by mutations of PARK2/parkin, PINK1, DJ-1 and ATP13A2. PARK2 mutations are responsible for almost 40% of cases beginning before the age of 45. Parkin is a cytosolic RING-in-between-RING ubiquitin ligase with HECT-like enzyme activity; 2 it has versatile ubiquitylation activities and various putative protein substrates with diverse functions, involved in different cellular processes.1 Genetic studies in Drosophila have shown Parkin and the mitochondrial serine/threonine kinase PINK1 to be components of a molecular pathway maintaining mitochondrial physiology. [3][4][5][6][7] In mammalian cells, PINK1 and Parkin cooperate in the clearance of dysfunctional mitochondria. The disruption of mitochondrial membrane (MM) potential (ΔΨm) by uncouplers or oxidative stress leads to PINK1 accumulation on the outer MM (OMM), the PINK1-dependent recruitment ...

To evaluate the epidermal barrier function of in vitro reconstructed epidermis, we measured the penetration of estradiol and water across human keratinocytes cultured in defined medium (DM), in the presence of proliferative fibroblasts (pF) or conditioned medium derived from pF, at the air-liquid interface on synthetic porous membrane, noncoated or coated with laminin, fibronectin, type I collagen or type IV collagen. Ultrastructural analysis showed a well-developed stratum corneum whatever the culture conditions. The permeability of reconstructed epidermis in DM on a noncoated porous membrane was 5- to 10-fold higher than human native epidermis, with both tracers. No significant change in barrier function was observed whatever the culture conditions.