Gene therapy targeting oligodendrocytes provides therapeutic benefit in a leukodystrophy model

<span class="paragraphSection"><div class="boxTitle">Abstract</div>Pelizaeus-Merzbacher-like disease or hypomyelinating leukodystrophy-2 is an autosomal recessively inherited leukodystrophy with childhood onset resulting from mutations in the gene encoding the gap junction protein connexin 47 (Cx47, encoded by <span style="font-style:italic;">GJC2</span>). Cx47 is expressed specifically in oligodendrocytes and is crucial for gap junctional communication throughout the central nervous system. Previous studies confirmed that a cell autonomous loss-of-function mechanism underlies hypomyelinating leukodystrophy-2 and that transgenic oligodendrocyte-specific expression of another connexin, Cx32 (<span style="font-style:italic;">GJB1</span>), can restore gap junctions in oligodendrocytes to achieve correction of the pathology in a disease model. To develop an oligodendrocyte-targeted gene therapy, we cloned the <span style="font-style:italic;">GJC2</span>/Cx47 gene under the myelin basic protein promoter and used an adeno-associated viral vector (AAV.MBP.Cx47myc) to deliver the gene to postnatal Day 10 mice via a single intracerebral injection in the internal capsule area. Lasting Cx47 expression specifically in oligodendrocytes was detected in Cx47 single knockout and Cx32/Cx47 double knockout mice up to 12 weeks post-injection, including the corpus callosum and the internal capsule but also in more distant areas of the cerebrum and in the spinal cord. Application of this oligodendrocyte-targeted somatic gene therapy at postnatal Day 10 in groups of double knockout mice, a well characterized model of hypomyelinating leukodystrophy-2, resulted in significant improvement in motor performance and coordination at 1 month of age in treated compared to mock-treated mice, as well as prolonged survival. Furthermore, immunofluorescence and morphological analysis revealed improvement in demyelination, oligodendrocyte apoptosis, inflammation, and astrogliosis, all typical features of this leukodystrophy model in both brain and spinal cord. Functional dye transfer analysis confirmed the re-establishment of oligodendrocyte gap junctional connectivity in treated as opposed to untreated mice. These results provide a significant advance in the development of oligodendrocyte-cell specific gene therapy. Adeno-associated viral vectors can be used to target therapeutic expression of a myelin gene to oligodendrocytes. We show evidence for the first somatic gene therapy approach to treat hypomyelinating leukodystrophy-2 preclinically, providing a potential treatment for this and similar forms of leukodystrophies.</span>

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