Monocarboxylate transporter expression in the spontaneous hypertensive rat: effect of stroke

The expression of the monocarboxylate transporters (MCT) 1, 2, and 4 have been studied in the brains of spontaneous hypertensive (SH) rats after an ischemic insult induced by a permanent occlusion of the left middle cerebral artery (MCAO). Profound temporal changes in MCT1 expression were observed in various regions of the ipsilateral hemisphere over the period of 1 hr to 5 days after MCAO. Initially, a very rapid and transient increase in MCT1 mRNA was observed in neurons in the second layer of the cortex and in the piriform cortex at 1-3 hr. A slower but sustained increase in MCT1 mRNA expression was observed in astrocytes in the peri-infarct region beginning at 6 hr after MCAO and persisting over a period of 120 hr coinciding with their activation, migration, and involvement in scar formation. An increase in MCT1 expression in endothelial cells was seen over the same period. These increases in MCT1 expression in astrocytes and endothelial cells were accompanied by a corresponding increase in MCT1 protein. Finally at 120 hr post-MCAO, increases in MCT1, MCT2, and MCT4 expression were observed in cells within the infarct and bordering the scar, the identity of which remains to be determined. Consistent with cell death, the levels of MCT1, MCT2, and MCT4 mRNA decreased with cell death within the infarcted area but unlike MCT1, no increases in either MCT2 or 4 were observed within the remaining ipsilateral hemisphere. These studies reveal that the pattern of regulation of MCT1 expression after MCAO is similar to that observed previously for glucose transporter 1 (GLUT1) and suggest that the regulation of MCT1 mRNA expression is mediated by the hypoxia-inducible transcription factor HIF1.