Myofibroblasts in the lamina propria of human seminiferous tubules are dynamic structures of heterogeneous phenotype

Myofibroblasts of the lamina propria of human seminiferous tubules were studied in testes having normal or slightly reduced spermatogenesis by means of electron microscopy, confocal laser microscopy and immunocytochemistry. Myofibroblasts are large, flat individual cells braced in a network of microfibrils and collagen fibrils in the tubular wall. They are arranged in discontinuous cell layers with interposed layers of an extracellular matrix. Myofibroblasts of the lamina propria exhibit an unique cell shape with the peripheral cytoplasm split up in two or more layers. After FITC-phalloidin staining and by means of confocal laser microscopy, actin filaments of variable orientation are visible in their cytoplasm. The thickness and preferential direction of actin filaments differ in the outer and innermost cell layers. The myofibroblasts express both antigens of smooth muscle cells (alpha-smooth muscle actin, pan-actin, desmin, GB 42, smooth muscle myosin), and of connective tissue cells (vimentin, fibroblast surface protein). The variable expression of these antigens evidenced the existence of different phenotypes of myofibroblasts. Immunoreactivity for basic fibroblast growth factor and transforming growth factor beta as well as for components of the extracellular matrix indicate that these agents may be important for the phenotypic differentiation of the lamina propria cells. The detection of CNPase-and galactocerebroside-immunoreactivity in a number of lamina propria cells and some cells of the intertubular tissue gives rise to the hypothesis that components of the testicular tissue share some structural similarities with glia cells of the nervous system. Finally, immunoreactivities for the neuronal and endothelial nitric oxide synthase, soluble guanylyl cyclase, cyclic GMP, calmodulin, calcium-dependent protein kinase II and glutamate indicate that the contractility of myofibroblasts in the lamina propria of human seminiferous tubules may be in part modulated by the NO/cGMP-system.