Phenotypic Correction of Oligodendrocytes by Concurrent Direct Reprogramming and Gene Replacement of Fibroblasts

Transcription factor-mediated direct reprogramming technologies that can convert one differentiated somatic cell to another, without an intermediate pluripotent stem cell stage, provide a new mechanism to access somatic cell types for disease modeling and possible therapeutic application. Previous efforts have focused on wild-type cells harboring transgenic reporters to signal successful reprogramming events. Outstanding questions remain of whether cells from disease backgrounds without transgenic reporters are capable of direct reprogramming and whether they phenocopy disease pathology. Here we demonstrate that fibroblasts from the shiverer mouse model of myelin disease can be directly reprogrammed to induced oligodendrocyte progenitor cells (iOPCs) by the expression of Sox10, Olig2, and Nkx6.2 without the aid of transgenic selection reporters. Shiverer mice harbor a homozygous ~20-kilobase deletion in the Myelin Basic Protein (Mbp) gene and this substantial deletion leads to abnormal oligodendrocytes resulting in hypomyelination and decreased lifespan. Shiverer iOPCs efficiently differentiated to induced oligodendrocytes (iOLs) which recapitulated the known disease phenotype of impaired axonal ensheathment and myelination capacity. Combining direct reprogramming and genetic supplementation of a minigene carrying regulatory elements and an open reading frame of MBP, restored MBP expression in differentiated iOLs and their ability to track along and ensheath microfibers in an in vitro assay of myelination capacity. Collectively these results show that iOPCs provide a rapid and accessible system to accurately model myelin disease pathology and provide promise for future therapeutic advancement for genetic myelin disorders.