Intrathecal gene therapy in mouse models expressing CMT1X mutations

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• X-linked Charcot-Marie-Tooth disease (CMT1X) is caused by mutations in the gap junction beta-1 (GJB1) gene, affecting connexin32 (Cx32) protein.
• Previous studies demonstrated therapeutic potential of lentiviral vector-mediated GJB1 gene addition in a Cx32 knockout mouse model.

Purpose of the Study:

• To evaluate the efficacy of GJB1 gene addition therapy in mouse models of CMT1X harboring specific Cx32 mutations (T55I, R75W, N175D).
• To investigate whether these CMT1X mutations interfere with the therapeutic expression of wild-type Cx32.

Main Methods:

• Intrathecal delivery of lentiviral vectors carrying the GJB1 gene into Cx32 knockout mice expressing CMT1X-associated Cx32 mutants.
• Assessment of Cx32 localization, myelin integrity, motor function, and inflammatory cell infiltration.

Main Results:

• Virally delivered wild-type Cx32 successfully localized in non-compact myelin of T55I mutant mice, leading to improved motor performance and reduced demyelination and inflammation.
• The R75W and N175D mutants exhibited dominant-negative effects, hindering wild-type Cx32 expression and resulting in limited or no therapeutic benefit.
• Mutant Cx32 proteins were retained in the endoplasmic reticulum or Golgi apparatus, indicating impaired trafficking.

Conclusions:

• GJB1 gene addition therapy is effective for CMT1X caused by non-interfering mutations like T55I.
• Interfering mutations (R75W, N175D) pose a challenge to gene addition therapy, necessitating the development of alternative therapeutic strategies for these patients.