Basis for abnormal desquamation and permeability barrier dysfunction in RXLI

Area of Science:

• Dermatology
• Biochemistry
• Molecular Biology

Background:

• Mutations in the steroid sulfatase (SSase) gene cause recessive X-linked ichthyosis (RXLI).
• SSase deficiency leads to cholesterol sulfate (CSO4) accumulation in the epidermis, causing scaling and barrier defects.
• Previous research highlighted SSase and CSO4's roles in skin differentiation, barrier maintenance, and desquamation.

Purpose of the Study:

• To investigate the precise localization and function of SSase in the stratum corneum (SC).
• To elucidate the molecular mechanisms underlying RXLI pathogenesis, focusing on CSO4 accumulation and its effects.
• To explore the contribution of calcium ions (Ca++) to RXLI pathology.

Main Methods:

• Immunohistochemical analysis to determine SSase localization within lamellar bodies (LB) and SC.
• Biochemical assays to assess SSase activity and CSO4 levels in SC interstices.
• Analysis of corneodesmosome (CD) integrity and corneocyte cohesion in RXLI models.

Main Results:

• SSase is concentrated in lamellar bodies and secreted into SC interstices, where it degrades CSO4.
• Excess CSO4 causes nonlamellar phase separation in SC interstices, leading to barrier dysfunction.
• Elevated CSO4 inhibits serine protease activity, delaying CD degradation and causing corneocyte retention.
• Increased SC interstitial Ca++ may also contribute to corneocyte retention by enhancing CD and interlamellar cohesion.

Conclusions:

• SSase's role in degrading CSO4 is crucial for normal epidermal differentiation, barrier function, and desquamation.
• RXLI pathogenesis involves both CSO4-induced lipid abnormalities and impaired desquamation due to delayed CD degradation.
• Understanding SSase and CSO4's functions provides insights into epidermal homeostasis and RXLI treatment strategies.