miR-32 and its target SLC45A3 regulate the lipid metabolism of oligodendrocytes and myelin.

Oligodendrocytes generate large amounts of myelin by extension of their cell membranes. Though lipid is the major component of myelin, detailed lipid metabolism in the maintenance of myelin is not understood. We reported previously that miR-32 might be involved in myelin maintenance (Shin et al., 2009). Here we demonstrate a novel role for miR-32 in oligodendrocyte function and development through the regulation of SLC45A3 (solute carrier family 45, member 3) and other downstream targets such as CLDN-11. miR-32 is highly expressed in the myelin-enriched regions of the brain and mature oligodendrocytes, and it promotes myelin protein expression. We found that miR-32 directly regulates the expression of SLC45A3 by binding to the complementary sequence on the 3'UTR of cldn11 and slc45a3. As a myelin-enriched putative sugar transporter, SLC45A3 enhances intracellular glucose levels and the synthesis of long-chain fatty acids. Therefore, overexpression of SLC45A3 triggers neutral lipid accumulation. Interestingly, both overexpression and suppression of SLC45A3 reduces myelin protein expression in mature oligodendrocytes and alters oligodendrocyte morphology, indicating that tight regulation of SLC45A3 expression is necessary for the proper maintenance of myelin proteins and structure. Taken together, our data suggest that miR-32 and its downstream target SLC45A3 play important roles in myelin maintenance by modulating glucose and lipid metabolism and myelin protein expression in oligodendrocytes.