A role for matrix metalloproteinases in granulocyte infiltration and testicular remodelation in a seasonal breeding teleost

The testicular cystic structure and the abrupt morphological changes that the fish testis undergoes during the reproductive cycle (RC) make it an interesting model for studying the regulation of spermatogenesis, in particular the role of matrix metalloproteinases (Mmps). The gilthead seabream is a seasonal breeding teleost whose testis undergoes drastic remodeling events, especially during the post-spawning stage when a massive infiltration of a immune cell type, the acidophilic granulocytes, occurred. Bearing this in mind, we studied the gilthead seabream testis gelatinolytic activities involved in migration and tissue remodeling and its regulation by endocrine, immune and tissue stimuli. Thus, we demonstrated that the germinal epithelium of the testis showed gelatinolytic activity during spermatogenesis and post-spawning but not during resting, when only scarce interstitial cells were stained. Moreover, the precursor and mature forms of two gelatinases, Mmp2- and Mmp9-like, were active in the gonad, whose activities were up-regulated by 17β-estradiol (E2) but not by lipopolysaccharide (LPS)/bacterial DNA (VaDNA) in testicular cell suspensions. E2 and LPS/VaDNA also up-regulated a variety of cytokines and chemokines. We also cloned mmp9, mmp13, tissue inhibitors of Mmps (timp)-2a and timp2b genes and found that all of them were expressed in the gonad in a RC stage-dependent manner. Interestingly, mmps and timps were highly expressed by the testicular acidophilic granulocytes. Moreover, in these cells, the gelatinolytic activity seemed to correspond to the precursor and mature forms of putative Mmp2 and Mmp9 gelatinases, while the main gelatinolytic activity seemed to correspond to the mature form of Mmp2 in head–kidney acidophilic granulocytes. Finally, although none of the stimuli used were able to induce the gelatinolytic activity of Mmp9-like in head–kidney acidophilic granulocytes, the expression of mmp9, timp2a and timp2b were all up-regulated by LPS/VaDNA in these cells, while only mmp9 and timp2a expression increased upon stimulation with gelatin.