Rat liver perisinusoidal lipocytes (PL) cultured on uncoated plastic transform spontaneously within 6-10 d to myofibroblastlike cells (MFBIC). Parallel to the transformation the TGFa-and TGF#1-mRNA expression increased and was highest in MFBIC. Competitive radioligand binding assays demonstrated that in contrast to untransformed PL the MFBIC synthesize and secrete transforming growth factor (TGF)-a (15 fmol/cell per 24 h) and predominantly the latent form of TGFWI (0.2 fmol/cell per 24 h). Medium conditioned by MFBIC (MFBcM) significantly stimulated PL proliferation with little effect on PL proteoglycan synthesis. By transient acidification of the MFBcM, known to activate the latent form of TGFj@1, the stimulatory effect on PL proteoglycan synthesis was enhanced and furthermore PL transformation (measured by expression of iso-a smooth muscle actin and loss of retinylpalmitate) was accelerated. Preincubation of this medium with neutralizing antibodies to TGF,6 resulted in (a) the growth inhibitory effect was converted to a growth stimulation and (b) the stimulatory effect on proteoglycan synthesis was abolished.In summary our data indicate that progressive activation of PL on plastic (transformation to MFBIC) leads to an enhanced expression of the TGFa-and TGFjdl-mRNAs and secretion of the corresponding proteins. Medium conditioned by MFBIC stimulates proliferation, transformation, and PG synthesis of untransformed PL. These mechanisms are suggested to be relevant in self perpetuation of liver fibrogenesis. (J. Clin. Invest.

BackgroundDuring their transit through the female genital tract, sperm have to recognize and discriminate numerous chemical compounds. However, our current knowledge of the molecular identity of appropriate chemosensory receptor proteins in sperm is still rudimentary. Considering that members of the Tas1r family of taste receptors are able to discriminate between a broad diversity of hydrophilic chemosensory substances, the expression of taste receptors in mammalian spermatozoa was examined.Methodology/Principal FindingsThe present manuscript documents that Tas1r1 and Tas1r3, which form the functional receptor for monosodium glutamate (umami) in taste buds on the tongue, are expressed in murine and human spermatozoa, where their localization is restricted to distinct segments of the flagellum and the acrosomal cap of the sperm head. Employing a Tas1r1-deficient mCherry reporter mouse strain, we found that Tas1r1 gene deletion resulted in spermatogenic abnormalities. In addition, a significant increase in spontaneous acrosomal reaction was observed in Tas1r1 null mutant sperm whereas acrosomal secretion triggered by isolated zona pellucida or the Ca2+ ionophore A23187 was not different from wild-type spermatozoa. Remarkably, cytosolic Ca2+ levels in freshly isolated Tas1r1-deficient sperm were significantly higher compared to wild-type cells. Moreover, a significantly higher basal cAMP concentration was detected in freshly isolated Tas1r1-deficient epididymal spermatozoa, whereas upon inhibition of phosphodiesterase or sperm capacitation, the amount of cAMP was not different between both genotypes.Conclusions/SignificanceSince Ca2+ and cAMP control fundamental processes during the sequential process of fertilization, we propose that the identified taste receptors and coupled signaling cascades keep sperm in a chronically quiescent state until they arrive in the vicinity of the egg - either by constitutive receptor activity and/or by tonic receptor activation by gradients of diverse chemical compounds in different compartments of the female reproductive tract.

A TPCN1 gene–deficient mouse strain is used to show that two convergent working NAADP-dependent pathways with nonoverlapping activation and self-inactivation profiles for distinct NAADP concentrations drive acrosomal exocytosis, by which TPC1 is central for the pathway activated by low-micromolar NAADP concentrations.

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