Loss of lysophosphatidic acid receptor LPA1 alters oligodendrocyte differentiation and myelination in the mouse cerebral cortex

Lysophosphatidic acid (LPA) is an intercellular signaling lipid that regulates multiple cellular functions, acting through specific G-protein coupled receptors (LPA(1-6)). Our previous studies using viable Malaga variant maLPA(1)-null mice demonstrated the requirement of the LPA(1) receptor for normal proliferation, differentiation, and survival of the neuronal precursors. In the cerebral cortex LPA(1) is expressed extensively in differentiating oligodendrocytes, in parallel with myelination. Although exogenous LPA-induced effects have been investigated in myelinating cells, the in vivo contribution of LPA(1) to normal myelination remains to be demonstrated. This study identified a relevant in vivo role for LPA(1) as a regulator of cortical myelination. Immunochemical analysis in adult maLPA(1)-null mice demonstrated a reduction in the steady-state levels of the myelin proteins MBP, PLP/DM20, and CNPase in the cerebral cortex. The myelin defects were confirmed using magnetic resonance spectroscopy and electron microscopy. Stereological analysis limited the defects to adult differentiating oligodendrocytes, without variation in the NG2(+) precursor cells. Finally, a possible mechanism involving oligodendrocyte survival was demonstrated by the impaired intracellular transport of the PLP/DM20 myelin protein which was accompanied by cellular loss, suggesting stress-induced apoptosis. These findings describe a previously uncharacterized in vivo functional role for LPA(1) in the regulation of oligodendrocyte differentiation and myelination in the CNS, underlining the importance of the maLPA(1)-null mouse as a model for the study of demyelinating diseases.