Unexpected role of α-fetoprotein in spermatogenesis

Background

Heat shock severely affects sperm production (spermatogenesis) and results in a rapid loss of haploid germ cells, or in other words, sperm formation (spermiogenesis) is inhibited. However, the mechanisms behind the effects of heat shock on spermatogenesis are obscure.

Methodology/Principal Findings

To identify the inhibitory factor of spermiogenesis, experimental cryptorchid (EC) mice were used in this study. Here we show that α-fetoprotein (AFP) is specifically expressed in the testes of EC mice by proteome analysis. AFP was also specifically localized spermatocytes by immunohistochemical analysis and was secreted into the circulation system of EC mice by immunoblot analysis. Since spermatogenesis of an advanced mammal cannot be reproduced with in vitro, we performed the microinjection of AFP into the seminiferous tubules of normal mice to determine whether AFP inhibits spermiogenesis in vivo. AFP was directly responsible for the block in spermiogenesis of normal mice. To investigate whether AFP inhibits cell differentiation in other models, using EC mice we performed a partial hepatectomy (PH) that triggers a rapid regenerative response in the remnant liver tissue. We also found that liver regeneration is inhibited in EC mice with PH. The result suggests that AFP released into the blood of EC mice regulates liver regeneration by inhibiting the cell division of hepatocytes.

Conclusions/Significance

AFP is a well-known cancer-specific marker, but AFP has no known function in healthy human beings. Our findings indicate that AFP expressed under EC conditions plays a role as a regulatory factor in spermatogenesis and in hepatic generation.     

A role of PPARgamma in reproduction?

Synthetic molecules of the glitazone family are currently used in the treatment of type II diabetes. Glitazones also improve secondary pathologies that are frequently associated with insulin resistance such as the polycystic ovary syndrome (PCOS). Glitazones bind to the peroxysome proliferator-activated receptor gamma (PPARgamma), a nuclear receptor which is highly expressed in adipose tissue. PPARgamma also binds natural ligands such as long-chain fatty acids. Recently, several groups have shown that PPARgamma is also highly expressed in ovarian granulosa cells, and that glitazones are able to modulate in vitro granulosa cell proliferation and steroidogenesis in several species. These recent data raise new questions concerning the underlying mechanism of the effect of glitazones on PCOS. One might hypothesize, as for other < glucophage > molecules such as metformin, that it is the general improvement of glucose metabolism and insulin sensitivity by glitazones which indirectly, and via an unknown mechanism, ameliorates ovarian functionality. The data discussed here suggest now an alternative possibility, that glitazones act directly at the ovarian level. Moreover, PPARgamma also seems to play a key role in the maturation of the placenta. In particular, inactivation of PPARgamma in mice is lethal, since the foetus is unable to develop because of alterations of placental maturation. In women, the activation of PPARgamma in placenta leads to an increase of placental hormone secretion. Overall, these results raise some questions about the role of natural ligands of PPARgamma such as long chain fatty acids on female fertility and the interactions between energy metabolism and reproduction in general.     

The role of α-synuclein in the pathophysiology of alcoholism

Alcoholism has complex etiology and there is evidence for both genetic and environmental factors in its pathophysiology. Chronic, long-term alcohol abuse and alcohol dependence are associated with neuronal loss with the prefrontal cortex being particularly susceptible to neurotoxic damage. This brain region is involved in the development and persistence of alcohol addiction and neurotoxic damage is likely to exacerbate the reinforcing effects of alcohol and may hinder treatment. Understanding the mechanism of alcohol’s neurotoxic effects on the brain and the genetic risk factors associated with alcohol abuse are the focus of current research. Because of its well-established role in neurodegenerative and neuropsychological disorders, and its emerging role in the pathophysiology of addiction, here we review the genetic and epigenetic factors involved in regulating α-synuclein expression and its potential role in the pathophysiology of chronic alcohol abuse. Elucidation of the mechanisms of α-synuclein regulation may prove beneficial in understanding the role of this key synaptic protein in disease and its potential for therapeutic modulation in the treatment of substance use disorders as well as other neurodegenerative diseases.     

Important role of methionine 145 in dimerization of bovine β-lactoglobulin

β-Lactoglobulin (LG) contains nine β-strands (strands A-I) and one α-helix. Strands A-H form a β-barrel. At neutral pH, bovine LG (BLG) forms a dimer and the dimer interface consists of AB-loops and the I-strands of two subunits. On the other hand, equine LG (ELG) is monomeric. The residues 145-153 of BLG, which compose a dimer interface, are entirely different from those of ELG. The difference in the association states between BLG and ELG can be attributed to the residues 145-153. To confirm this, we constructed a chimeric LG, ImBLG (I-strand mutated BLG), in which the residues 145-153 were replaced with those of ELG. Gel-filtration chromatography and analytical ultracentrifugation revealed that ImBLG existed as a monomer. To identify the residues important for dimerization, we constructed several revertants and investigated their association. This experiment revealed that, in addition to the interface residues (Ile147, Leu149 and Phe151), Met145 is critical for dimerization. Although Met145 does not contact with the other protomer, it seems to be important in determining the backbone conformation of the I-strand. This was supported by the fact that all Met145-containing mutants showed circular dichroism spectra similar to BLG but different from ImBLG.     

The role of ubiquitination in lysosomal trafficking of δ-opioid receptors

The δ-opioid receptor (DOR) undergoes ligand-induced downregulation by endosomal sorting complex required for transport (ESCRT)-dependent endocytic trafficking to lysosomes. In contrast to a number of other signaling receptors, the DOR can downregulate effectively when its ubiquitination is prevented. We explored the membrane trafficking basis of this behavior. First, we show that internalized DORs traverse the canonical multivesicular body (MVB) pathway and localize to intralumenal vesicles (ILVs). Second, we show that DOR ubiquitination stimulates, but is not essential for, receptor transfer to ILVs and proteolysis of the receptor endodomain. Third, we show that receptor ubiquitination plays no detectable role in the early sorting of internalized DORs out of the recycling pathway. Finally, we show that DORs undergo extensive proteolytic fragmentation in the ectodomain, even when receptor ubiquitination is prevented or ILV formation itself is blocked. Together, these results are sufficient to explain why DORs downregulate effectively in the absence of ubiquitination, and they place a discrete molecular sorting operation in the MVB pathway effectively upstream of the ESCRT. More generally, these findings support the hypothesis that mammalian cells can control the cytoplasmic accessibility of internalized signaling receptors independently from their ultimate trafficking fate.     

Pathogenic role of TGF-β in the progression of podocyte diseases

In patients with progressive podocyte diseases, such as focal segmental glomerulosclerosis and membranous nephropathy, there is enhanced expression of transforming growth factor (TGF-β) in podocytes. Biomechanical strain in these diseases may cause overexpression of TGF-β and angiotensin II (Ang II) by podocytes. Oxidative stress induced by Ang II may activate the latent TGF-β. Increased TGF-β activity by podocytes may induce not only the thickening of the glomerular basement membrane (GBM), but also podocyte apoptosis and/or detachment from the GBM, initiating the development of glomerulosclerosis. Furthermore, mesangial matrix expansion frequently occurs in podocyte diseases in association with the development of glomerulosclerosis. This review examines open questions on the pathogenic role of TGF-β that links podocyte injury to GBM thickening, podocyte loss, mesangial matrix expansion and glomerulosclerosis in podocyte diseases. It also describes paracrine regulatory mechanisms of podocyte TGF-β on mesangial cells leading to increased matrix synthesis.     

Expanding role of ubiquitination in NF-κB signaling

Best known for its role in targeting protein degradation by the proteasome, ubiquitin modification has also emerged as an important mechanism that regulates cell signaling through proteasome-independent mechanisms. The role of ubiquitin as a versatile signaling tag is characteristically illustrated in the NF-κB pathways, which regulate a variety of physiological and pathological processes in response to diverse stimuli. Here, we review the role of ubiquitination in different steps of the NF-κB signaling cascades, focusing on recent advances in understanding the mechanisms of protein kinase activation by polyubiquitin chains in different pathways that converge on NF-κB.     

The role of γ-tubulin in centrosomal microtubule organization

As part of a multi-subunit ring complex, γ-tubulin has been shown to promote microtubule nucleation both in vitro and in vivo, and the structural properties of the complex suggest that it also seals the minus ends of the polymers with a conical cap. Cells depleted of γ-tubulin, however, still display many microtubules that participate in mitotic spindle assembly, suggesting that γ-tubulin is not absolutely required for microtubule nucleation in vivo, and raising questions about the function of the minus end cap. Here, we assessed the role of γ-tubulin in centrosomal microtubule organisation using three-dimensional reconstructions of γ-tubulin-depleted C. elegans embryos. We found that microtubule minus-end capping and the PCM component SPD-5 are both essential for the proper placement of microtubules in the centrosome. Our results further suggest that γ-tubulin and SPD-5 limit microtubule polymerization within the centrosome core, and we propose a model for how abnormal microtubule organization at the centrosome could indirectly affect centriole structure and daughter centriole replication.     

Pro-apoptotic role of integrin β3 in glioma cells

Malignant gliomas are the most destructive type of brain cancer. In order to gain a better understanding of the molecular mechanisms of glioma cell death and survival, we previously established an alkylating agent 1, 3-bis(2-chloroethyl)-1-nitrosourea (BCNU)-resistant variant of C6 rat glioma cells. Proteomic analysis indicated a significant down-regulation of integrin beta 3 (ITGB3) in the BCNU-resistant C6R cells. Re-expression of ITGB3 in C6R cells restored the BCNU sensitivity. In U87MG, U373MG, and T98G human glioma cells, there was a positive correlation between ITGB3 expression and the sensitivity to BCNU and etoposide, suggesting an important role of ITGB3 in glioma cell death. Over-expression of ITGB3 cDNA significantly increased the sensitivity of the human glioma cells to the anticancer drug-induced apoptosis. Nitric oxide showed an additive effect on the anticancer drug-induced glioma cell death by increasing ITGB3 expression. Subsequent dissection of signaling pathways indicated that extracellular signal-regulated kinase and unligated integrin-mediated cell death pathway may be involved in the pro-apoptotic role of ITGB3 in glioma cells. These results implicate ITGB3 in glioma cell death/survival and drug resistance.     

The role of stratifin in fibroblast–keratinocyte interaction

Stratifin is a member of 14-3-3 protein family, a highly conserved group of proteins constituted by seven isoforms. They are involved in numerous crucial intracellular functions such as cell cycle and apoptosis, regulation of signal transduction pathways, cellular trafficking, cell proliferation and differentiation, cell survival, and protein folding and processing, among others. At epidermal level, stratifin (also called 14-3-3 sigma) has been described as molecule with relevant functions. For instance, this isoform is a marker associated with keratinocyte differentiation. In this maturation process, the presence of dominant negative molecules of p53 induces a “stemness condition” of keratinocyte precursor cells and suppression of stratifin expression. In addition, the recently described keratinocyte-releasable form of stratifin is involved in dermal fibroblast MMP-1 over-expression through c-Fos and c-Jun activity. This effect is mediated, at least in part, by p38 mitogen-activated protein kinase (MAPK). Other MMP family members such as stromelysin-1 (MMP-3), stromelysin-2 (MMP-10), neutrophil collagenase (MMP-8), and membrane-type MMP-24 (MT5-MMP) are also up-regulated by stratifin. Within fibroproliferative disorder of skin, hypertrophic scar and keloids exhibit a high content of collagen, proteoglycans, and fibronectin. Thus, the MMP profile induced by stratifin is an interesting starting point to establish new therapeutic tools to control the process of wound healing. In this review, we will focus on site of synthesis and mode of action of stratifin in skin and wound healing.     

Pathogenic role of HIF-1α in prostate hyperplasia in the presence of chronic inflammation

Benign prostatic hyperplasia (BPH) commonly occurs in older men with chronic prostatitis. Although BPH is frequently accompanied by inflammation, it is unclear whether inflammation underlies prostate enlargement. Recently, we reported that hypoxia‐inducible factor 1α (HIF-1α), which is known to be induced by proinflammatory cytokines, is involved in testosterone-induced prostate hyperplasia. Therefore, we hypothesized that cytokines secreted from infiltrated macrophages under inflammatory conditions stimulate prostate enlargement by up‐regulating HIF-1α. In the present study, we injected lipopolysaccharide (LPS) into rat prostates to mimic prostatitis and evaluated prostate hyperplasia 14 days later. Epithelial cells of LPS-treated prostates were found to be highly proliferative and HIF-1α levels in prostate tissues to be elevated. When prostate epithelial cells were incubated in conditioned medium from macrophages activated with LPS, they robustly expressed HIF-1α, and under these conditions IL-1β, IL-6, and TNF-α cytokines were found to mediate HIF-1α induction. In addition, HIF-1α was found to enhance the expression of Twist, which initiates epithelial–mesenchymal transition (EMT). Furthermore, profound EMT features were observed in LPS-treated rat prostates, and the natural HIF-1α inhibitors ascorbate and curcumin were found to attenuate EMT and prostate hyperplasia both in vivo and in vitro. Based on these results, we propose that HIF-1α mediates prostate enlargement under inflammatory conditions, and we suggest that HIF-1α be viewed as a promising target for blocking the transition from prostatitis to BPH.     

The revised role of TGF-β in aortic aneurysms in Marfan syndrome

BackgroundRecently, we demonstrated that losartan reduced the aortic root dilatation rate (AoDR) in adults with Marfan syndrome (MFS); however, responsiveness was diverse. The aim was to determine the role of transforming growth factor-β (TGF-β) as therapeutic biomarker for effectiveness of losartan on AoDR.MethodsBaseline plasma TGF-β levels of 22 healthy controls and 99 MFS patients, and TGF-β levels after 1 month of losartan treatment in 42 MFS patients were measured. AoDR was assessed by magnetic resonance imaging at baseline and after 3 years of follow-up.ResultsPatients with MFS had higher TGF-β levels compared with healthy controls (121 pg/ml versus 54 pg/mL, p = 0.006). After 1 month of therapy, losartan normalised the TGF-β level in 15 patients (36%); the other 27 patients (64%) showed a significant increase of TGF-β. After 3 years of losartan therapy, patients with a decrease in TGF-β had significantly higher AoDR compared with patients with increased TGF-β (1.5 mm/3 years versus 0.5 mm/3 years, p = 0.04). Patients showing a decrease in TGF-β after losartan therapy had significantly elevated baseline TGF-β levels compared with patients with increased TGF-β (189 pg/ml versus 94 pg/ml, p = 0.05).ConclusionPatients responding to losartan therapy with a reduction of the plasma TGF-β level had higher baseline TGF-β levels and a higher AoDR. Most likely, TGF-β levels may be considered to be a readout of the disease state of the aorta. We propose that increased angiotensin II is the initiator of aorta dilatation and is responsible for increased TGF-β levels in MFS. The concept of TGF-β as initiator of aortic dilatation in MFS patients should be nuanced.     

Distribution and role of calmodulin in tip growing hyphae of Saprolegnia ferax

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The role of β-alanine in the biosynthesis of nitrate byAspergillus flavus

d-Serine (0.05m) inhibited nitrification byAspergillus flavus in media containing either peptone, aspartate,a-alanine or -alanine as the sole nitrogen source. A similar inhibition was observed in an aspartate + peptone medium, but nitrate was formed in a -alanine + peptone medium in the presence of the inhibitor. Exceptionally high yields of nitrate were obtained in the -alanine + peptone medium. In replacement cultures,d-serine inhibited nitrification of aspartate but not of -alanine. Manometric studies indicated that aspartate was decarboxylated byA. flavus and that the reaction was inhibited byd-serine. In view of these results, it is suggested that aspartate is a precursor and -alanine is an intermediate in nitrification by this fungus.     

A picture of health? Unmasking the role of appearance in health

Evaluating health requires visual assessment. From the meticulous self-scrutiny of a worried woman in front of the looking glass to the doctor's reaction at the sight of a patient in the examining room, external appearance plays an important role in appraising health above and beyond clinical assessment. However, this dominance of the visual in our image-driven culture has assumed a disproportionately prominent position. Media, businesses, and health care commonly misrepresent appearance as the reality of health. Industry mongers beauty-promoting wares and services as health-protecting products, and physical appearance contributes to clinicians' imperfect heuristics. An explanation for this focus on appearance is persistence of the ancient belief that looks indicate inner character. In this article we unmask the historical origin of this belief and reveal how it contaminates contemporary approaches to health assessment and maintenance.