Protein O-carboxylmethylation in relation to male gamete production and function

Vitamin B12 suppresses GADD153, prevents apoptosis and regulates the testicular function in methotrexate treated rat testis

Methotrexate (MTX) is an anti-neoplastic drug that also causes testicular damage. Vitamin B12 (Vit B12) is a water soluble vitamin that is required for normal metabolism. We investigated Vit B12 as a possible protective agent against testicular damage caused by MTX treatment. We divided rats into four groups: control group, Vit B12 group treated with Vit B12 daily for 15 days, MTX group treated with MTX on day 8, MTX + Vit B12 group treated with MTX on day 8 + Vit B12 for 15 days. Serum levels of follicle stimulating hormone (FSH), luteinizing hormone (LH) and testosterone were measured. We also measured proliferating cell nuclear antigen (PCNA), connexin43 (Cx43) and the growth arrest- and DNA damage-inducible gene, 153 (GADD153), using immunohistochemical staining. Apoptosis was assessed using TUNEL staining. The MTX group exhibited degeneration of seminiferous tubules; decreased serum testosterone, LH and FSH levels; fewer PCNA positive cells; increased Cx43 expression; and increased GADD153 and TUNEL stained cells compared to the control group. These pathologic findings were substantially reversed In the MTX + Vit B12 group. MTX caused increased endoplasmic reticulum stress and apoptosis via GADD153. Consequently, Vit B12 potentially is a protective agent against damage caused by MTX.

Changes in Carboxy Methylation and Tyrosine Phosphorylation of Protein Phosphatase PP2A Are Associated with Epididymal Sperm Maturation and Motility

Mammalian sperm contain the serine/threonine phosphatases PP1γ2 and PP2A. The role of sperm PP1γ2 is relatively well studied. Here we confirm the presence of PP2A in sperm and show that it undergoes marked changes in methylation (leucine 309), tyrosine phosphorylation (tyrosine 307) and catalytic activity during epididymal sperm maturation. Spermatozoa isolated from proximal caput, distal caput and caudal regions of the epididymis contain equal immuno-reactive amounts of PP2A. Using demethyl sensitive antibodies we show that PP2A is methylated at its carboxy terminus in sperm from the distal caput and caudal regions but not in sperm from the proximal caput region of the epididymis. The methylation status of PP2A was confirmed by isolation of PP2A with microcystin agarose followed by alkali treatment, which causes hydrolysis of protein carboxy methyl esters. Tyrosine phosphorylation of sperm PP2A varied inversely with methylation. That is, PP2A was tyrosine phosphorylated when it was demethylated but not when methylated. PP2A demethylation and its reciprocal tyrosine phosphorylation were also affected by treatment of sperm with L-homocysteine and adenosine, which are known to elevate intracellular S-adenosylhomocysteine, a feedback inhibitor of methyltransferases. Catalytic activity of PP2A declined during epididymal sperm maturation. Inhibition of PP2A by okadaic acid or by incubation of caudal epididymal spermatozoa with L-homocysteine and adenosine resulted in increase of sperm motility parameters including percent motility, velocity, and lateral head amplitude. Demethylation or pharmacological inhibition of PP2A also leads to an increase in phosphorylation of glycogen synthase kinase-3 (GSK3). Our results show for the first time that changes in PP2A activity due to methylation and tyrosine phosphorylation occur in sperm and that these changes may play an important role in the regulation of sperm function.