Cellular expression of monocarboxylate transporters in the female reproductive organ of mice: implications for the genital lactate shuttle.

The present study examined the cellular localization of monocarboxylate transporters (MCTs), glucose transporters (GLUTs), and some glycolysis-related molecules in the murine female genital tract to demonstrate existence of lactate/pyruvate-dependent energy systems. MCT1, a major MCT subtype, was localized selectively in the ovarian granulosa, oviductal-ciliated cells, and vaginal epithelium; all localizations were associated with intense expressions of glycolytic enzymes. MCT1 was localized in the cell membrane of granulosa cells, including fine processes extending from cumulus cells toward oocytes. The cumulus cells and oocytes showed intense signals for lactate dehydrogenase (LDH)-A and -B, respectively. The basolateral membrane of oviductal-ciliated cells expressed MCT4 as well as MCT1, while adjacent non-ciliated cells contained an intense immunoreactivity for aldolase-C, a glycolytic enzyme. The expression of GLUTs in the ovary was generally weak with an intense expression of GLUT1 only in some vascular endothelia. The oviductal epithelium expressed GLUT1 and GLUT3, respectively, in the basolateral and apical membrane of non-ciliated cells. In the vagina, the basal layers of epithelium were immunolabeled for MCT1 with the entire length of cell membrane, and expressed abundantly both GLUT1 and LDH-A. The findings correspond well with the rich existence of lactate in the genital fluids and strongly suggest the active transport of lactate/pyruvate in the female reproductive tract, which provides favorable conditions for oocytes, sperms, and zygotes.

Histochemical demonstration of monocarboxylate transporters in mouse brown adipose tissue.

Proton-coupled monocarboxylate transporters (MCTs) are essential for the transport of lactate, ketone bodies, and other monocarboxylates through the plasma membrane. The present immunohistochemical study aimed to examine the expression of MCTs in the brown adipose tissue (BAT) of mice. An intense immunoreactivity for MCT1 was found in the plasma membrane of brown adipose cells at light and electron microscopic levels but not in white adipose cells. The expression of MCT1 in BAT was confirmed by Western blot and in situ hybridization analyses. In fetuses (E17.5) and neonates, the MCT1 mRNA expression of BAT was abundant and appeared more intense than that in adult animals. These results, together with the intense expression of CD147 (a functional partner of MCTs) and acetyl-CoA carboxylase-2 (a component of fatty acid oxidation) in perinatal periods, suggest the involvement of MCT1 in the uptake of monocarboxylates from the circulation for thermogenesis rather than lipogenesis.