Mast-cell products can stimulate fibroblast proliferation, implying that these cells are key players in fibrosis. One mast-cell product, the serine protease tryptase, is known to activate protease-activated receptor 2 (PAR2) and cause proliferation of fibroblasts. We found that recombinant tryptase, human mast-cell (HMC-1) supernatant, which contains tryptase, and the PAR2-activating peptide SLIGKV exert fibroproliferative actions in human fibroblasts. Here we report insights into this action, which after activation of PAR2 leads to increased expression of cyclooxygenase 2 (COX2), a key enzyme in the biosynthesis of prostaglandins, and consequently to enhanced prostaglandin synthesis. Subsequent cell proliferation is mediated by the prostaglandin 15-deoxy-Δ^12,14-prostaglandin J₂, which acts via the nuclear peroxisome proliferator-activated receptor γ (PPARγ). Fibroblast proliferation induced by tryptase and PAR2 agonist peptide can be blocked by antagonists of COX2 and PPARγ, implying that the proliferative effect of tryptase is PAR2-initiated but depends on COX2, 15-deoxy-Δ^12,14-prostaglandin J₂, and PPARγ. This previously uncharacterized pathway could be of relevance for human fibrotic diseases. For instance, increased numbers of activated mast cells are correlated with fibrosis in testes of infertile men. In these cases all components of the signaling pathway of tryptase were detected as well as expression of COX2. Therefore, our study describes as-yet-unknown interactions between mast cells and fibroblasts, which could be relevant for human fibrotic diseases.

Besides the hypothalamus and pituitary, melatonin action at the testicular level has been recently suggested. Therefore, we investigated in the Syrian hamster, a well-characterized seasonal breeder, melatonin action on Leydig cells, testicular expression of melatonergic receptors, and possible interactions between melatonin receptors and the previously identified testicular serotoninergic and CRH systems. In isolated Leydig cells from active testes of adult hamsters kept in a long-day (14 h light, 10 h dark) photoperiod and from regressed testes of adult animals exposed to a short-day photoperiod during 16 wk (6 h light, 18 h dark), melatonin significantly reduced human chorionic gonadotropin-stimulated production of cAMP and the main androgens: testosterone and androstane-3alpha,17beta-diol, respectively, and decreased the expression of steroidogenic acute regulatory protein, P450 side chain cleavage, 3beta-hydroxysteroid dehydrogenase and 17beta-hydroxysteroid dehydrogenase. In Leydig cells exposed to a short-day photoperiod during 16 wk, melatonin stimulated the conversion of testosterone into 5alpha-reduced androgens by inducing 5alpha-reductase isoform 1, and controlled androstane-3alpha,17beta-diol production by inhibiting 3alpha-hydroxysteroid dehydrogenase expression. Melatonin subtype (mel1a) receptors were detected in Leydig cells. Although the local serotonin system did not mediate melatonin action on androgen production, melatonergic effect on steroidogenesis involved the interaction between mel1a receptors and the inhibitory CRH system. Moreover, melatonin significantly increased CRH mRNA levels and production in hamster Leydig cells expressing CRH subtype 1 receptors. Our studies indicate that melatonin may act as a local inhibitor of human chorionic gonadotropin-stimulated cAMP and androgen production through mel1a receptors, down-regulation of steroidogenic acute regulatory protein, and key steroidogenic enzymes expression and its interaction with the local CRH system.

The pineal hormone melatonin regulates testicular function through the hypothalamic-adenohypophyseal axis. In addition, direct actions of melatonin in somatic cells of the testis have been described. Melatonin acts as a local modulator of the endocrine activity in Leydig cells. In Sertoli cells, melatonin influences cellular growth, proliferation, energy metabolism and the oxidation state, and consequently may regulate spermatogenesis. These data pinpoint melatonin as a key player in the regulation of testicular physiology (i.e., steroidogenesis, spermatogenesis) mostly in seasonal breeders. In patients with idiopathic infertility, melatonin exerts anti-proliferative and anti-inflammatory effects on testicular macrophages, and provides protective effects against oxidative stress in testicular mast cells. Consequently, melatonin is also involved in the modulation of inflammatory and oxidant/anti-oxidant states in testicular pathology. Overall, the literature data indicate that melatonin has important effects on testicular function and male reproduction.

Testicular peritubular cells are myofibroblastic cells, which represent the major cellular components of the wall of the seminiferous tubules. In men their phenotypic characteristics, including possible secretory activity and regulation, are not well known, in neither normal nor pathologically altered testes. Especially in testes of men with impaired spermatogenesis, the cytoarchitecture of the tubular wall is frequently remodeled and presents fibrotic thickening, increased innervation, and infiltration by macrophages and mast cells. The latter are two sources of TNF-α. The purpose of our study was to explore human testicular peritubular cells and mechanisms of their regulation. To this end we primarily studied cultured human testicular peritubular cells (HTPCs), isolated from adult human testes. Having established that HTPCs express TNF-α receptors 1 and 2 and respond to recombinant human TNF-α by a rapid phosphorylation of ERK1/2, we used complementary approaches, including gene array/RT-PCR studies, Western blotting/immunocytochemistry, and ELISA techniques to study phenotypic characteristics of HTPCs and actions of TNFα. We found that HTPCs express the nerve growth factor gene and TNF-α-stimulated mRNA levels and secretion of nerve growth factor in a dose- and time-dependent manner. Similarly, monocyte chemoattractant protein-1 was identified as a product of HTPCs, which was regulated by TNF-α in a concentration- and time-dependent manner. TNF-α furthermore strongly enhanced expression and/or synthesis of other inflammatory molecules, namely IL-6 and cyclooxygenase-2. Active cyclooxygenase-2 is indicated by increased prostaglandin D2 levels. In addition, intercellular adhesion molecule-1, which was not detected at protein level in the absence of TNF-α, was induced upon TNF-α stimulation. In conclusion, these results provide novel insights into the nature of human peritubular cells, which are able to secrete potent signaling molecules and are regulated by TNF-α. These results also hint to an as-yet-unknown role of peritubular cells in normal human testis and involvement in the pathomechanisms associated with impaired spermatogenesis in men.