Comparison of MMP-2 and TIMP-2 expressions in yak testes at different ages.

This study aimed to investigate the distribution and expression of matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of matrix metalloproteinase-2 (TIMP-2) in yak testes. The testes of healthy yaks at different ages: newborn [3 days], young [1 year], adult [4 years], and old [9 years] were collected for microscopic analyses using hematoxylin and eosin staining, immunohistochemistry and immunofluorescence, as well as western blot to compare the expression of MMP-2 and TIMP-2. Furthermore, the levels of MMP-2mRNA and TIMP-2mRNA was detected by real-time quantitative polymerase chain reaction (qPCR). The results of immunohistochemistry and immunofluorescence demonstrated that MMP-2 and TIMP-2 were mainly located in gonocytes of newborn, Sertoli cells of young, spermatozoa of adult and Leydig cells of old. The protein levels of MMP-2 and TIMP-2 exhibited a downward from newborn to adult, but increased again in old yaks. The analysis of qPCR showed that MMP-2 was higher in young compared with newborn or adult(**p < .01), but a lower expression was detected in adult compared with old yak testicular tissues (*p < .05). Compared with adults, TIMP-2 was significantly higher in newborn and young yaks (**p < .01), and slightly higher in old yaks (*p < .05). Hence, The location of MMP-2 and TIMP-2 in gonocytes were associated with the development of newborn yak testes. The expression of MMP-2 and TIMP-2 in Sertoli cells at young and adult yaks suggested that they provided a clue for the regulation of spermatogenesis. The positive labeling of MMP-2 and TIMP-2 in Leydig cells in old yaks suggested that both may be involved in the interstitial metabolism of the testes during this period. This study revealed the possible role of MMP-2 and TIMP-2 in testicular functionality of yaks at different ages.