Comparative genomic hybridization analysis of sperm DNA apoptosis after exposure to heat shock

A DNA disc chip assay based on comparative genomic hybridization (CGH) was developed to measure sperm DNA integrity. The objective was to correlate DNA integrity of heat-treated sperm with the sperm capacitation index (CI) determined from the sperm penetration assay.

Basic semen and kinematic parameters were measured (N = 6). Sperm were washed in two-layer colloid suspensions and split portions incubated at either 3 degrees C (control) or 40 degrees C for 4 h. Single-stranded DNA of heated sperm were stained in SYBR Gold and hybridized to bisbenzimide (Hoechst 33342) stained control DNA in a membrane disc. Fluorescent intensities of the discs were measured and correlation analyses with sperm parameters performed.

Sperm CI was positively correlated (R = 0.737) with sperm DNA integrity. Two populations of sperm could be discerned: low capacitating sperm that initiated apoptosis and high capacitating sperm unaffected by heat shock treatment. The remaining parameters were not related to sperm DNA stability.

Fragile DNA were found in a population of sperm associated with poor capacitation characteristics and apoptosis was observed after heat treatment. The results suggested that sperm dysfunction might be due to apoptotic sperm DNA resulting from an elevated temperature in the surroundings. The data suggested that the second population of high capacitating sperm induced chaperones such as heat shock proteins hsp 70 to protect against apoptosis.