TUMOR NECROSIS FACTOR-ALPHA-STIMULATED LACTATE PRODUCTION IS LINKED TO LACTATE-DEHYDROGENASE-A EXPRESSION AND ACTIVITY INCREASE IN PORCINE CULTURED SERTOLI CELLS

By using, as a model, cultured testicular immature Sertoli cells, the action of tumor necrosis factor-alpha (TNF alpha) and the site of acti on of the cytokine on lactate production were studied. TNF alpha stimu lated in a time- and dose-dependent manner (with an ED50 of 0.1 nM) Se rtoli cell lactate production. Two major sites involved in TNF alpha a ction were identified. Firstly, TNF alpha vas shown to increase the up take of glucose substrate in a time- and dose-dependent manner. The ma ximal effect was observed after 24 h of treatment, with an ED50 of 0.1 nM. Secondly, TNF alpha increased the activity of lactate dehydrogena se (LDH) A isoform, which is involved in the conversion of pyruvate in to lactate. This increase in LDH-A activity was detected at 12 h and w as maximal after 24 h of treatment with TNF alpha. The stimulatory eff ect of the cytokine on the LDH-A isoform nas observed with an ED50 of 0.05 nM. Such an increase in LDH-A activity was related to an increase in LDH-A expression, because TNF alpha stimulated LDH-A messenger RNA (size, 1.5 kilobases, determined by Northern blotting analysis). Toge ther, assuming that in the seminiferous tubules, TNF alpha is produced by spennatids that use lactate for their energetic metabolism, we sug gest that the cytokine may potentially represent a signal used by germ cells to enhance lactate production in Sertoli cells through, at leas t, a redistribution of LDH isoforms in favor of LDH-A.