Development and Assessment of Col4a5 Missense Mouse Model of Alport Syndrome

Background: Mutation in type IV collagen α3, α4 or α5 results in the abnormal formation and secretion of α345(IV) trimer causing Alport syndrome (AS), a progressive hereditary nephritis. Missense mutations in α5(IV) are the most frequently reported. Current symptomatic therapies are unable to prevent the progression to end-stage renal failure. Therefore, the development of novel drugs is needed but is hampered by the lack of a mouse model of missense mutant AS that enables the evaluation of drug efficacy. Methods: We previously developed a nanoluciferase-based trimer evaluation system (Cell Chem Biol 2018) and focused on the human α5(IV) G1244D mutation, whose secretion is significantly decreased and is reported to be clinically severe. We generated mutant mice using the kick-in method that can generate knock-in mice. Results: The results showed that while the α5(IV) G1244D mutation causes severe renal disease in humans it does not cause renal disease in mice, indicating a phenotypic divergence. To elucidate the cause of this species difference, we constructed an evaluation system for mouse type IV collagen trimer. We assessed clinically reported 34 missense mutations in α5(IV) and evaluated the trimer function. The results showed that the trimer secretion by the G1244D mutation in mouse α5(IV) was normal, unlike that in human. Furthermore, when the trimer secretion ability of 34 mutants was compared between human and mouse, only 15 mutations showed similar secretion. These results indicate that the trimer behavior of human and mouse mutants does not necessarily coincide. Furthermore, we are currently generating mouse models of missense mutations that cause a significant decrease in mouse trimer secretion. Phenotypic analysis will be performed to provide much-needed information for a new AS missense mouse model. Conclusion: Human and mouse α345(IV) trimer behavior diverges, necessitating a thorough assessment of each mouse mutant to produce a missense mouse model that recapitulates the clinical phenotypes of human AS missense mutant pathologies.