Additive loss-of-function proteasome subunit mutations in CANDLE/PRAAS patients promote type I IFN production

Area of Science:

• Genetics and Immunology
• Molecular Biology
• Cellular Biology

Background:

• Chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE) is an immune-dysregulatory disease caused by mutations in proteasome subunit β 8 (PSMB8).
• CANDLE syndrome is classified as a proteasome-associated autoinflammatory syndrome (PRAAS).

Purpose of the Study:

• To identify novel genetic mutations associated with PRAAS.
• To investigate the functional consequences of these mutations on proteasome function and type I interferon production.

Main Methods:

• Genetic sequencing to identify mutations in proteasome genes (PSMA3, PSMB4, PSMB9, POMP, PSMB8).
• Functional evaluation of mutations, including transcription, protein expression, folding, assembly, and proteasome activity assays.
• siRNA-mediated knockdown in primary fibroblasts to recapitulate proteasome defects.
• Analysis of interferon (IFN) gene-expression signature in patient cells and healthy controls.

Main Results:

• Identified 8 novel mutations in PSMA3, PSMB4, PSMB9, and POMP, and 1 new mutation in PSMB8.
• Established digenic and autosomal dominant inheritance patterns for PRAAS in some patients.
• Demonstrated that identified mutations impair proteasome transcription, assembly, and activity.
• Observed a strong type I IFN gene-expression signature in patient cells, which could be induced in healthy cells by proteasome inhibition or knockdown.

Conclusions:

• The study expands the genetic landscape of PRAAS, identifying new mutations in multiple proteasome genes.
• Digenic and autosomal dominant inheritance patterns are implicated in PRAAS.
• Proteasome dysfunction resulting from these mutations directly links to increased type I interferon production, providing a mechanistic understanding of disease pathogenesis.