Interaction between Retinoschisin and Norrin: Physical or Functional Relationship?

ABSTRACT Background Retinoschisis and Norrie disease are X-linked recessive retinal disorders caused by mutations in RS1 and NDP genes respectively. Both are likely to be monogenic and no locus heterogeneity has been reported. However, there are reports showing overlapping clinical features of Norrie disease and retinoschisis in a NDP knock-out mouse model and also the involvement of both the genes in retinoschisis patients. Yet, the exact molecular mechanism and relationship between the two disorders have still not been understood. Objective In this study, we aim to investigate the association between retinoschisin (RS1) and norrin (NDP) using in vitro and in silico approaches. Method Specific protein-protein interaction between RS1 and NDP was determined in human retina by co-immunoprecipitation assay and immunoblotting. The immunoprecipitated complexes of RS1 and NDP were analyzed using MALDI-TOF mass spectrometry to validate the findings. STRING database was used to explore the functional relationship. Results Co-immunoprecipitation and immunoblotting demonstrated lack of a direct interaction between RS1 and NDP. This was further substantiated by analyzing the immunoprecipitation complexes using MALDI-TOF mass spectrometry. STRING did not reveal any direct functional association between the two proteins. Conclusion While literature suggest the existence of digenic involvement of RS1 and NDP in the pathophysiology of retinoschisis and Norrie disease, our data provides evidence for lack of a physical interaction between the two proteins. However, we cannot exclude the possibility of an indirect functional association as our analyses point to MAP kinase signaling pathway, which is presumed to be the link between them.