Putative Creatine Kinase M-Isoform in Human Sperm Is Identifiedas the 70-Kilodalton Heat Shock Protein HspA21

Abstract

We previously described a putative creatine kinase M isoform in human sperm that is developmentally regulated and expressed during late spermiogenesis, simultaneous with cytoplasmic extrusion. We have now identified this protein as the testis-expressed 70-kDa heat shock protein chaperone known as HspA2 (the human homologue of mouse Hsp70-2). We have isolated and characterized HspA2 (formerly CK-M) by amino acid sequencing and have localized it by immunocytochemistry to spermatocytes at low levels, to spermatids, and in the tail of mature sperm. The specificity of the CK-M/HspA2 antiserum to HspA2 was demonstrated on immunoblots of one- and two-dimensional SDS-PAGE. In agreement with our earlier biochemical data, immunocytochemistry of testicular tissue indicated that HspA2 is selectively expressed in mature spermatids and in sperm about to be released in the seminiferous tubuli. The identity of HspA2 has been further confirmed by cross-absorption of the mouse HSP70-2 antibody by the HspA2/CK-M fraction, and by identical immunostaining patterns of human testicular tissue using either the anti-CK-M/HspA2 or an anti-mouse Hsp70-2 antisera. During spermiogenesis, both cytoplasmic extrusion and plasma membrane remodeling, which facilitate the formation of the zona pellucida binding site, involve major intrasperm protein transport, which may be chaperoned by HspA2. Accordingly, in immature human sperm, which fail to express HspA2, there is cytoplasmic retention and lack of zona pellucida binding. The present findings provide the biological rationale for the role of the human HspA2 as an objective biochemical marker of sperm function and male fertility, which we have established in earlier clinical studies.

Is sperm hyaluronic acid binding ability predictive for clinical success of intracytoplasmic sperm injection: PICSI vs. ICSI?

“…It is well known that the proportion of immature sperm closely correlates with chromosomal disomies [Kovanci et al 2001]. The relationship between the frequencies of chromosomal aneuploidies and diminished sperm maturity is thought to reflect that cytoplasmic retention and diminished maturity in sperm are associated with a low expression of the HspA2 [Eddy 1999;Huszar et al 2000]. The relationship between sperm zona pellucida binding competence and maturity has been identified earlier.…”

“…In the semen samples there were sperm with various degrees of cytoplasmic retention, but all sperm bound to the zona pellucida were mature as characterized with the absence of any cytoplasmic retention. Diminished HspA2 chaperone activity found in developmentally immature sperm is thought to be connected with a diminished presence of DNA repair enzymes, causing DNA chain breaks and fragmentation [Dix et al 1996;Eddy 1999;Huszar et al 2000]. There is a correlation between the decreased levels of expression of the HspA2 chaperone and sperm cellular development as well as IVF success [Ergur et al 2002;Huszar et al 1992Huszar et al , 2000.…”

“…Diminished HspA2 chaperone activity found in developmentally immature sperm is thought to be connected with a diminished presence of DNA repair enzymes, causing DNA chain breaks and fragmentation [Dix et al 1996;Eddy 1999;Huszar et al 2000]. There is a correlation between the decreased levels of expression of the HspA2 chaperone and sperm cellular development as well as IVF success [Ergur et al 2002;Huszar et al 1992Huszar et al , 2000. Van Steirteghem et al [2002] found increased rates of de novo numerical and cytogenetically detectable structural chromosomal aberrations following ICSI.…”

“…There is a relationship between diminished sperm development (associated with oligozoo/asthenozoo/teratozoospermia), low levels of HspA2 expression, increased frequency of chromosomal aneuploidies, the presence of apoptotic process, and fragmented DNA [Huszar and Vigue 1993;Huszar et al 2000Huszar et al , 2003Huszar et al , 2007Yagci et al, 2010]. In vitro solid-state HAbinding facilitates the selection of individual mature sperm with low levels of chromosomal aneuploidies [Jakab et al 2005].…”

New Advances in Intracytoplasmic Sperm Injection (ICSI)

“… the heat shock protein HspA2 chaperone, involved in meiosis  creatine kinase (CK), abundant in the sperm cytoplasm Mature spermatozoa have high HspA2 (Huszar et al, 2000) and low CK . In contrast, spermatozoa with arrested maturity have low HspA2 expression, which may cause meiotic defects and probably chromosomal aneuploidies, in fact, mature spermatozoa show a reduction of more than five fold in aneupliody rate than immature ones (Jakab et al, 2005).…”