Gene Therapy Rescues Neural Deficits in CNTNAP1 Mutant Mice

Hypomyelinating Neuropathy-3 (CHN3) is a rare neurological disorder characterized by the onset of neurogenic muscle impairment that occurs in utero. The disorder results from homozygous or compound heterozygous mutations in the CNTNAP1 gene located on chromosome 17q21. CNTNAP1 encodes Contactin-associated protein 1 (Caspr), a crucial component of the paranodal junctions in myelinated neurons, which play a critical role in maintaining the integrity of myelinated axons and facilitate saltatory conduction. Mutations in CNTNAP1 have been implicated in a spectrum of neurological disorders, characterized by disrupted nerve conduction and motor function due to axonal and myelin anomalies. Symptoms can include delayed motor development, muscle weakness, poor muscle tone, impaired muscle coordination, absence of reflexes, and difficulty in walking or crawling. In some cases, infants may experience respiratory problems or difficulty in swallowing. The exact cause of CHN3 is related to mutations in genes involved in the process of myelin formation, but the precise mechanisms by which these mutations lead to the symptoms of the disorder are not fully understood. To this account, a new study published in Cell Reports conducted by Cheng Chang, Lacey Sell, Assistant Professor Qian Shi, and led by Professor Manzoor Bhat from the University of Texas Health Science Center San Antonio, the researchers investigated the effects of CNTNAP1 mutations on nerve conduction and motor function, and explored the potential of gene therapy in rescuing these deficits. The study focused on two key mutant mouse models, Cntnap1C324R and Cntnap1R765C, which mimic human CNTNAP1 mutations. The authors used CRISPR-Cas9 technology to introduce specific point mutations into the mouse Cntnap1 gene to create two mutant lines, Cntnap1C324R and Cntnap1R765C, corresponding to the human CNTNAP1C323R and CNTNAP1R764C mutations. This genetic manipulation aimed to replicate the human disease in mice for detailed study. They evaluated the mutant mice for any signs of neurological dysfunction and compared to wild-type controls. The team found both Cntnap1C324R and Cntnap1R765C mutants exhibited significant weight loss, reduced nerve conduction velocities, and progressive motor impairments, including difficulty in maintaining balance and coordination. These phenotypes mirrored the clinical manifestations of CNTNAP1-related neuropathies in humans, establishing the validity of the mouse models for further investigation. Moreover, the authors provided compelling evidence of the detrimental impact of CNTNAP1 mutations on the paranodal structure and function. They found that mutations lead to hypomyelination and notable ultrastructural defects at the paranodes, including everted myelin loops and disrupted axo-glial junctions. These structural alterations compromise the electrical insulation of axons and impede nerve signal propagation, elucidating the basis for the observed neurological deficits. A critical finding of the research by Professor Manzoor Bhat and team is the altered stability and localization of the mutant Cntnap1 proteins. Both C324R and R765C mutants exhibit reduced protein stability and are aberrantly retained within the neuronal soma, failing to reach the paranodal regions where they are functionally required. The mislocalization is likely caused by improper folding or trafficking of the mutant proteins, underscoring the importance of precise protein processing and transport in neuronal function. Perhaps the most promising aspect of the authors’ findings is the demonstration that neuronal expression of wild-type Cntnap1 can rescue the neurological phenotypes in the mutant mice. This finding confirms the loss-of-function nature of the CNTNAP1 mutations and opens up new avenues for gene therapy. It may be possible to restore normal paranodal structure, nerve conduction, and motor function, offering hope for therapeutic interventions in humans suffering from CNTNAP1-related neuropathies by reintroducing the functional gene into affected neurons. In a nutshell, the study led by Professor Manzoor Bhat and his colleagues provided critical understanding into the pathogenic mechanisms of CNTNAP1 mutations and highlighted the potential of gene therapy for treating associated neurological disorders. The research also demonstrated the importance of timely intervention and suggest that future research should focus on optimizing gene delivery methods, assessing long-term efficacy and safety, and exploring combinatory therapeutic approaches.