Human lactate dehydrogenase A (LDHA) rescues mouse Ldhc-null sperm function.

By targeted disruption of the lactate dehydrogenase c (Ldhc) gene, we demonstrated that spermatozoa require Ldhc for capacitation, motility, and fertilizing capacity. Ldhc expression is restricted to the developing germ cells that, however, are apparently not compromised by the lack of the LDHC isozyme. Because LDHC is abundant in spermatozoa that utilize aerobic glycolysis for energy requirements, its main function was presumed to be the interconversion of pyruvate to lactate with the concomitant oxidation/reduction of NADH to NAD(+). We found that sperm without LDHC were still able to convert lactate to pyruvate as mediated by LDHA that is tightly bound to the fibrous sheath. It was assumed that the level of glycolysis was insufficient to power motility and the subsequent fertilizing capacity of the mutated sperm. To investigate whether LDHC possesses certain unique characteristics essential for fertility, human LDHA was introduced as a transgene to Ldhc-null mice. We report here that the exogenous LDHA rescued the phenotype of the Ldhc-null males. Sperm from the LDHA transgenic males with the Ldhc deletion (LDHA(+)/Ldhc(-/-)) are motile, capable of protein tyrosine phosphorylation, and able to fertilize, thus restoring these properties to LDHC-null sperm. However, the lactate and ATP levels in the rescued sperm did not differ significantly from sperm lacking LDHC. We suggest that it is the localization of the transgene to the sperm cytosol that is mainly responsible for restoration of sperm function and fertility.

A-MYB (MYBL1) stimulates murine testis-specific Ldhc expression via the cAMP-responsive element (CRE) site.

Generally, knowledge of the mechanism regulating gene expression in primary spermatocytes is incomplete. We have used the lactate dehydrogenase gene (Ldhc) as a model to explore these mechanisms during spermatogenesis. Its 100-bp core promoter contained two essential elements common to many genes, a GC box and a CRE site. Here we report results that support a model in which transcription factor MYBL1 acts as a coactivator directing tissue-specific expression via the CRE cis element. We hypothesize that this is a common mechanism involving activation of multiple genes in the primary spermatocyte. MYBL1 is expressed predominantly as a tissue-specific transcription factor in spermatocytes and breast epithelial cells. Our finding that LDHC expression is lost in 21-day testes of MYBL1 mutant mice supports our hypothesis. In the GC1-spg germ cell line exogenous MYBL1 induces activity 4- to 8-fold, although extracts from these cells do not show MYBL1 binding activity for the Myb consensus sequences in the Ldhc promoter by EMSA. Rather, MYBL1 stimulates expression from a synthetic promoter containing only CRE elements, suggesting MYBL1 activates the promoter by interacting with protein that binds to a CRE element. Mutation of three Myb sites does not affect Ldhc promoter activity significantly (P > 0.05). CREB-binding protein (CBP) is a coactivator that interacts with CRE-binding protein CREB. We show that the transactivation domain (TAD) in MYBL1 interacts with the KIX domain in CBP, and the TAD domain and DNA binding domain in MYBL1 each interact with the CREB N-terminal domain. MYBL1 also stimulated expression from testis-specific genes Pgk2 (phosphoglycerate kinase 2) and Pdha2 (pyruvate dehydrogenase alpha 2) promoters, each of which contains CRE promoter elements and is expressed in primary spermatocytes. We propose that MYBL1 directs germ cell-specific activation via the CRE site of certain genes that are activated specifically in the primary spermatocyte, although other, more indirect effects of MYBL1 remain a possible explanation for our results.

Egress of sperm autoantigen from seminiferous tubules maintains systemic tolerance.

Autoimmune responses to meiotic germ cell antigens (MGCA) that are expressed on sperm and testis occur in human infertility and after vasectomy. Many MGCA are also expressed as cancer/testis antigens (CTA) in human cancers, but the tolerance status of MGCA has not been investigated. MGCA are considered to be uniformly immunogenic and nontolerogenic, and the prevailing view posits that MGCA are sequestered behind the Sertoli cell barrier in seminiferous tubules. Here, we have shown that only some murine MGCA are sequestered. Nonsequestered MCGA (NS-MGCA) egressed from normal tubules, as evidenced by their ability to interact with systemically injected antibodies and form localized immune complexes outside the Sertoli cell barrier. NS-MGCA derived from cell fragments that were discarded by spermatids during spermiation. They egressed as cargo in residual bodies and maintained Treg-dependent physiological tolerance. In contrast, sequestered MGCA (S-MGCA) were undetectable in residual bodies and were nontolerogenic. Unlike postvasectomy autoantibodies, which have been shown to mainly target S-MGCA, autoantibodies produced by normal mice with transient Treg depletion that developed autoimmune orchitis exclusively targeted NS-MGCA. We conclude that spermiation, a physiological checkpoint in spermatogenesis, determines the egress and tolerogenicity of MGCA. Our findings will affect target antigen selection in testis and sperm autoimmunity and the immune responses to CTA in male cancer patients.

Homo sapiens lactate dehydrogenase c (Ldhc) gene expression in cancer cells is regulated by transcription factor Sp1, CREB, and CpG island methylation.

The human testis-specific lactate dehydrogenase c gene (hLdhc) is transcribed only in cells of the germinal epithelium. Recently hLdhc was reported to express in a broad spectrum of tumors with relatively high frequency in lung cancer, melanoma, and breast cancer, and in some prostate cancers. Two melanoma cell lines that express the hLdhc gene, A375M and C81-61, were identified and were used to characterize the hLdhc promoter and explore transcriptional regulation of this gene. A 110-bp core promoter, including a conserved GC box and cyclic adenosine monophosphate-responsive element (CRE), were identified as essential for basal promoter activity. The methylation status of the CpG island (CGI) in the hLdhc core promoter sequence was analyzed in hLdhc-expressing and nonexpressing cells and human prostate tumor tissues. The CGI in 2 cell lines expressing the gene was hypomethylated whereas the DNA from cells that did not express hLdhc was hypermethylated. The role of methylation in regulating this promoter was confirmed by experimental induction of hLdhc transcription with the methylation inhibitor 5'aza-deoxycytidine. Quantitative analyses of the methylation level in the CGI were performed in prostate tumor tissues by pyrosequencing. Overall, these experiments demonstrated that hLdhc expression in cancer cells was regulated by transcription factor Sp1 and CREB and promoter CGI methylation. In addition, these findings suggest the possibility of developing a biomarker for cancer diagnosis/prognosis based on DNA methylation of the Ldhc gene.

Sustained transgene expression via citric acid-based polyester elastomers.

Polymeric scaffolds are an important tool in tissue engineering and gene delivery using porous scaffolds can be a viable approach to control tissue response. Herein we describe the use of a biodegradable polyester elastomer, poly(1,8-octanediol-co-citrate) (POC), as a substrate for plasmid immobilization and cellular transfection of colonizing cells. Plasmid (pDNA), either complexed with poly(ethyleneimine) (PEI) forming polyplexes or in its native state, was surface-immobilized onto POC scaffolds via adsorption. Polyplex-containing scaffolds showed higher loading and slower initial rates of release than naked pDNA-containing scaffolds. Seeding of HEK293 cells and porcine aortic smooth muscle cells (PASMC) onto polyplex loaded-scaffolds demonstrated cell proliferation and transfection in vitro up to 12 days, significantly longer relative to bolus transfection. In vivo, transfection was evaluated using the mouse intraperitoneal (IP) fat model. In contrast to the in vitro study, successful long-term transgene delivery was only achieved with the naked pDNA-containing scaffolds. In particular, naked pDNA-containing scaffolds promoted high levels of both luciferase and green fluorescent protein (GFP) expression in vivo for 2 weeks. The results demonstrate that POC scaffolds are a suitable material for substrate-mediated gene delivery. POC scaffolds can potentially support long-term biological cues to mediate tissue formation through non-viral gene delivery.

Regulation of murine lactate dehydrogenase C (Ldhc) gene expression.

Expression of Ldhc begins with the onset of meiosis in male germ cells and continues throughout spermatogenesis. Transcriptional regulatory mechanisms, especially in primary spermatocytes, are poorly described because of the lack of a reliable cell culture system. We constructed mouse transgenics and transfected germ cells in situ to study expression of the testis-specific isozyme of lactate dehydrogenase (LDH). From previous work, we determined that a 100-bp Ldhc core promoter contained potential cis regulatory elements, including a palindrome (-21 to +10), GC box (-70 to -65), and cAMP-responsive element (CRE) sites (-53 to -49, -39 to -35). We provide here the demonstration of a functional role for these sequences by expression of mutated transgenes in vivo. Our results reveal for the first time that mutation of the GC box does not abolish promoter activity, which remains testis-specific. Mutation of GC box or CRE sites resulted in a 73% and 74% reduction in promoter activity, respectively, in a transient transfection of germ cells in vivo by electroporation; the combination of GC box and CRE site mutations eliminates promoter activity. Therefore, we conclude that simultaneous occupancy of the GC box and CRE sites in the core promoter is necessary for full expression of Ldhc in the testis.