The protein kinase C modulator bryostatin-1 therapeutically targets microglia to attenuate neuroinflammation and promote remyelination

In multiple sclerosis (MS), microglia and macrophages within the central nervous system (CNS) play an important role in determining the balance among demyelination, neurodegeneration, and myelin repair. Phagocytic and regenerative functions of these CNS innate immune cells support remyelination, whereas chronic and maladaptive inflammatory activation promotes lesion expansion and disability, particularly in the progressive forms of MS. No currently approved drugs convincingly target microglia and macrophages within the CNS, contributing to the lack of therapies aimed at promoting remyelination and slowing disease progression for individuals with MS. Here, we found that the protein kinase C (PKC)-modulating drug bryostatin-1 (bryo-1), a CNS-penetrant compound with an established human safety profile, shifts the transcriptional programs of microglia and CNS-associated macrophages from a proinflammatory phenotype to a regenerative phenotype in vitro and in vivo. Treatment of microglia with bryo-1 stimulated scavenger pathways, phagocytosis, and secretion of factors that prevented the activation of neuroinflammatory reactive astrocytes while also promoting neuroaxonal health and oligodendrocyte differentiation. In line with these findings, systemic treatment of mice with bryo-1 augmented remyelination after a focal demyelinating injury. Our results demonstrate the potential of bryo-1 and possibly a wider class of PKC modulators as myelin-regenerative and supportive agents in MS and other neurologic diseases.