An organotypic slice culture model of chronic white matter injury with maturation arrest of oligodendrocyte progenitors

Background: CNS myelination disturbances commonly occur in chronic white matter lesions in neurodevelopmental and adult neurological disorders. Recent studies support that myelination failure can involve a disrupted cellular repair mechanism where oligodendrocyte (OL) progenitor cells (OPCs) proliferate in lesions with diffuse astrogliosis, but fail to fully differentiate to mature myelinating OLs. There are no in vitro models that reproduce these features of myelination failure. Results: Forebrain coronal slices from postnatal day (P) 0.5/1 rat pups were cultured for 1, 5, or 9 days in vitro (DIV). Slices rapidly exhibited diffuse astrogliosis and accumulation of the extracellular matrix glycosaminoglycan hyaluronan (HA), an inhibitor of OPC differentiation and re-myelination. At 1 DIV ∼1.5% of Olig2⁺ OLs displayed caspase-3 activation, which increased to ∼11.5% by 9 DIV. At 1 DIV the density of PDGFRα⁺ and PDGFRα⁺/Ki67⁺ OPCs were significantly elevated compared to 0 DIV (P < 0.01). Despite this proliferative response, at 9 DIV ∼60% of white matter OLs were late progenitors (preOLs), compared to ∼7% in the postnatal day 10 rat (P < 0.0001), consistent with preOL maturation arrest. Addition of HA to slices significantly decreased the density of MBP⁺ OLs at 9 DIV compared to controls (217 ± 16 vs. 328 ± 17 cells/mm², respectively; P = 0.0003), supporting an inhibitory role of HA in OL lineage progression in chronic lesions. Conclusions: Diffuse white matter astrogliosis and early OPC proliferation with impaired OL maturation were reproduced in this model of myelination failure. This system may be used to define mechanisms of OPC maturation arrest and myelination failure related to astrogliosis and HA accumulation.