The Estrogen Receptor Alpha Regulates the Sex-dependent Expression and Pronociceptive Role of Bestrophin-1 in Neuropathic Rats

Bestrophin-1, a calcium-activated chloride channel (CaCC), is involved in neuropathic pain; however, it is unclear whether it has a dimorphic role in female and male neuropathic rats. This study investigated if 17β-estradiol and estrogen receptor alpha (ERα) activation regulate bestrophin-1 activity and expression in neuropathic rats. Neuropathic pain was induced by L5-spinal nerve transection (SNT). Intrathecal administration of CaCCinh-A01 (.1-1 µg), a CaCC blocker, reversed tactile allodynia induced by SNT in female but not male rats. In contrast, T16Ainh-A01, a selective anoctamin-1 blocker, had an equal antiallodynic effect in both sexes. SNT increased bestrophin-1 protein expression in injured L5 dorsal root ganglia (DRG) in female rats but decreased bestrophin-1 protein in L5 DRG in male rats. Ovariectomy prevented the antiallodynic effect of CaCCinh-A01, but 17β-estradiol replacement restored it. The effect of CaCCinh-A01 was prevented by intrathecal administration of MPP, a selective ERα antagonist, in rats with and without prior hormonal manipulation. In female rats with neuropathy, ovariectomy prevented the increase in bestrophin-1 and ERα protein expression, while 17β-estradiol replacement allowed for an increase in both proteins in L5 DRG. Furthermore, ERα antagonism (with MPP) prevented the increase in bestrophin-1 and ERα protein expression. Finally, ERα activation with PPT, an ERα selective activator, induced the antiallodynic effect of CaCCinh-A01 in neuropathic male rats and prevented the reduction in bestrophin-1 protein expression in L5 DRG. In summary, data suggest ERα activation is necessary for bestrophin-1's pronociceptive action to maintain neuropathic pain in female rats. PERSPECTIVE: The mechanisms involved in neuropathic pain differ between male and female animals. Our data suggest that ERα is necessary for expression and function of bestrophin-1 in neuropathic female but not male rats. Data support the idea that a therapeutic approach to relieving neuropathic pain must be based on patient's gender.

Molecular cloning of the gene promoter encoding the human CaVγ2/Stargazin divergent transcript (CACNG2-DT): characterization and regulation by the cAMP-PKA/CREB signaling pathway

CaVγ2 (Stargazin or TARPγ2) is a protein expressed in various types of neurons whose function was initially associated with a decrease in the functional expression of voltage-gated presynaptic Ca2+ channels (CaV) and which is now known to promote the trafficking of the postsynaptic α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPAR) towards the cell membrane. Alterations in CaVγ2 expression has been associated with several neurological disorders, such as absence epilepsy. However, its regulation at the transcriptional level has not been intensively addressed. It has been reported that the promoter of the Cacng2 gene, encoding the rat CaVγ2, is bidirectional and regulates the transcription of a long non-coding RNA (lncRNA) in the antisense direction. Here, we investigate the proximal promoter region of the human CACNG2 gene in the antisense direction and show that this region includes two functional cAMP response elements that regulate the expression of a lncRNA called CACNG2-DT. The activity of these sites is significantly enhanced by forskolin, an adenylate cyclase activator, and inhibited by H89, a protein kinase A (PKA) antagonist. Therefore, this regulatory mechanism implies the activation of G protein-coupled receptors and downstream phosphorylation. Interestingly, we also found that the expression of CACNG2-DT may increase the levels of the CaVγ2 subunit. Together, these data provide novel information on the organization of the human CACNG2-DT gene promoter, describe modulatory domains and mechanisms that can mediate various regulatory inputs, and provide initial information on the molecular mechanisms that regulate the functional expression of the CaVγ2 protein.

Novel Aspects of cAMP-Response Element Modulator (CREM) Role in Spermatogenesis and Male Fertility

Spermatogenesis is a very complex process with an intricate transcriptional regulation. The transition from the diploid to the haploid state requires the involvement of specialized genes in meiosis, among other specific functions for the formation of the spermatozoon. The transcription factor cAMP-response element modulator (CREM) is a key modulator that triggers the differentiation of the germ cell into the spermatozoon through the modification of gene expression. CREM has multiple repressor and activator isoforms whose expression is tissue-cell-type specific and tightly regulated by various factors at the transcriptional, post-transcriptional and post-translational level. The activator isoform CREMτ controls the expression of several relevant genes in post-meiotic stages of spermatogenesis. In addition, exposure to xenobiotics negatively affects CREMτ expression, which is linked to male infertility. On the other hand, antioxidants could have a positive effect on CREMτ expression and improve sperm parameters in idiopathically infertile men. Therefore, CREM expression could be used as a biomarker to detect and even counteract male infertility. This review examines the importance of CREM as a transcription factor for sperm production and its relevance in male fertility, infertility and the response to environmental xenobiotics that may affect CREMτ expression and the downstream regulation that alters male fertility. Also, some health disorders in which CREM expression is altered are discussed.

Bestrophin-1 Participates in Neuropathic Pain Induced by Spinal Nerve Transection but not Spinal Nerve Ligation

Previous studies have reported that L5/L6 spinal nerve ligation (SNL), but not L5 spinal nerve transection (SNT), enhances anoctamin-1 in injured and uninjured dorsal root ganglia (DRG) of rats suggesting some differences in function of the type of nerve injury. The role of bestrophin-1 in these conditions is unknown. The aim of this study was to investigate the role of bestrophin-1 in rats subjected to L5 SNT and L5/L6 SNL. SNT up-regulated bestrophin-1 protein expression in injured L5 and uninjured L4 DRG at day 7, whereas it enhanced GAP43 mainly in injured, but also in uninjured DRG. In contrast, SNL enhanced GAP43 at day 1 and 7, while bestrophin-1 expression increased only at day 1 after nerve injury. Accordingly, intrathecal injection of the bestrophin-1 blocker CaCC_inh-A01 (1-10 µg) reverted SNT- or SNL-induced tactile allodynia in a concentration-dependent manner. Intrathecal injection of CaCC_inh-A01 (10 µg) prevented SNT-induced upregulation of bestrophin-1 and GAP43 at day 7. In contrast, CaCC_inh-A01 did not affect SNL-induced up-regulation of GAP43 nor bestrophin-1. Bestrophin-1 was mainly expressed in small- and medium-size neurons in naïve rats, while SNT increased bestrophin-1 immunoreactivity in CGRP+, but not in IB4+ neuronal cells in DRG. Intrathecal injection of bestrophin-1 plasmid (pCMVBest) induced tactile allodynia and increased bestrophin-1 expression in DRG and spinal cord in naïve rats. CaCC_inh-A01 reversed bestrophin-1 overexpression-induced tactile allodynia and restored bestrophin-1 expression. Our data suggest that bestrophin-1 plays a relevant role in neuropathic pain induced by SNT, but not by SNL. PERSPECTIVE: SNT, but not SNL, up-regulates bestrophin-1 and GAP43 protein expression in injured L5 and uninjured L4 DRG. SNT increases bestrophin-1 immunoreactivity in CGRP+ neurons in DRG. Bestrophin-1 overexpression induces allodynia. CaCCinh-A01 reduces allodynia and restores bestrophin-1 expression. Our data suggest bestrophin-1 is differentially regulated depending on the neuropathic pain model.

Characterization of the promoter region of the murine Catsper2 gene

CATSPER2 (Cation channel sperm-associated protein 2) protein, which is part of the calcium CATSPER channel located in the membrane of the flagellar principal piece of the sperm cell, is only expressed in the testis during spermatogenesis. Deletions or mutations in the Catsper2 gene are associated with the deafness-infertility syndrome (DIS) and non-syndromic male infertility. However, the mechanisms by which Catsper2 is regulated are unknown. Here, we report the characterization of the promoter region of murine Catsper2 and the role of CTCF and CREMτ in its transcription. We report that the promoter region has transcriptional activity in both directions, as determined by observing luciferase activity in mouse Sertoli and GC-1 spg transfected cells. WGBS data analysis indicated that a CpG island identified in silico is non-methylated; Chromatin immunoprecipitation (ChIP)-seq data analysis revealed that histone marks H3K4me3 and H3K36me3 are present in the promoter and body of the Catsper2 gene respectively, indicating that Catsper2 is subject to epigenetic regulation. In addition, the murine Catsper2 core promoter was delimited to a region between -54/+189 relative to the transcription start site (TSS), where three CTCF and one CRE binding site were predicted. The functionality of these sites was determined by mutation of the CTCF sites and deletion of the CRE site. Finally, ChIP assays confirmed that CREMτ and CTCF bind to the Catsper2 minimal promoter region. This study represents the first functional analysis of the murine Catsper2 promoter region and the mechanisms that regulate its expression.

Seroprevalence of Trypanosoma cruzi in Eight Blood Banks in Mexico

BACKGROUND

The true prevalence of Chagas disease in Mexico is unknown. However, it has been estimated that 1.1-4 million people are infected with Trypanosoma cruzi, which represents a potential risk for transmission of the disease via contaminated blood.

AIM OF THE STUDY

To determine the Chagas disease seroprevalence in donors from eight blood banks in the north of Mexico City, and the northeast of the State of Mexico.

STUDY DESIGN AND METHODS

Serum samples from blood donors (n = 515,038) were tested to detect the presence of anti-Trypanosoma cruzi antibodies in eight blood banks. The serologic screening test was performed in each of the blood banks. To confirm the seropositive blood donors, only two out of the eight blood banks used a test with a different principle with the aim of identifying anti-Trypanosoma cruzi antibodies. All tests were validated by the Mexican Institute for Epidemiological Diagnosis and Reference.

RESULTS

One thousand two hundred and ten blood donors were seropositive for Trypanosoma cruzi, which represents a 0.23% seroprevalence (95% CI 0.22-0.25%). Of the seropositive blood donors, 97.03 % resided in the northeast area of the State of Mexico, Mexico City, and southern part of the State of Hidalgo.

CONCLUSIONS

Active transmission of Chagas disease may be occurring in non-endemic regions in the northeast of the State of Mexico.

Down Regulation of Catsper1 Expression by Calmodulin Inhibitor (Calmidazolium): Possible Implications for Fertility

The CatSper channel localizes exclusively in the flagella of sperm cells. The Catsper1 protein, together with three pore units, is essential for the CatSper Channel formation, which produces flagellum hyperactivation and confers sperm fertility. Catsper1 expression is dependent on Sox transcription factors, which can recognize in vitro at least three Sox binding sites on the promoter. Sox transcription factors have calmodulin-binding domains for nuclear importation. Calmodulin (CaM) is affected by the specific inhibitor calmidazolium (CMZ), which prevents the nuclear transport of Sox factors. In this work, we assess the regulation of the Catsper1 promoter in vivo by Sox factors in the murine testis and evaluate the effects of the inhibitor calmidazolium on the expression of the Casper genes, and the motility and fertility of the sperm. Catsper1 promoter has significant transcriptional activity in vivo; on the contrary, three Sox site mutants in the Catsper1 promoter reduced transcriptional activity in the testis. CaM inhibition affects Sox factor nuclear transport and has notable implications in the expression and production of Catsper1, as well as in the motility and fertility capability of sperm. The molecular mechanism described here might conform to the basis of a male contraceptive strategy acting at the transcriptional level by affecting the production of the CatSper channel, a fundamental piece of male fertility.

Increase of 5-HT levels is induced both in mouse brain and HEK-293 cells following their exposure to a non-viral tryptophan hydroxylase construct

Tryptophan hydroxylase type 2 (Tph2) is the rate-limiting enzyme for serotonin (5-HT) biosynthesis in the brain. Dysfunctional Tph2 alters 5-HT biosynthesis, leading to a deficiency of 5-HT, which could have repercussions on human behavior. In the last decade, several studies have associated polymorphisms of the TPH2 gene with suicidal behavior. Additionally, a 5-HT deficiency has been implicated in various psychiatric pathologies, including alcoholism, impulsive behavior, anxiety, and depression. Therefore, the TPH2 gene could be an ideal target for analyzing the effects of a 5-HT deficiency on brain function. The aim of this study was to use the construct pIRES-hrGFP-1a-Tph2-FLAG to treat CD1-male mice and to transfect HEK-293-cells and then to evaluate whether this treatment increases 5-HT production. 5-HT levels were enhanced 48 h post-transfection, in HEK-293 cells. Three days after the ocular administration of pIRES-hrGFP-1a-Tph2-FLAG to mice, putative 5-HT production was significantly higher than in the control in both hypothalamus and amygdala, but not in the brainstem. Further research will be needed on the possible application of this treatment for psychiatric diseases involving a Tph2 dysfunction or serotonin deficiency.

PKC- and PKA-dependent phosphorylation modulates TREK-1 function in naïve and neuropathic rats

PKC and PKA phosphorylation inhibit TREK-1 channels downstream of G_s protein-coupled receptor activation in vitro. However, the role of phosphorylation of TREK-1 in neuropathic pain is unknown. The purpose of this study was to investigate whether altered TREK-1 channel function by PKA and PKC modulators contributes to antiallodynia in neuropathic rats. Furthermore, we investigated if the in vitro described sites for PKC and PKA phosphorylation (S300 and S333, respectively) participate in the modulation of TREK-1 in naïve and neuropathic rats. L5/L6 spinal nerve ligation (SNL) induced tactile allodynia. Intrathecal injection of BL-1249 (TREK-1 activator) reversed nerve injury-induced tactile allodynia, whereas spadin (TREK-1 blocker) produced tactile allodynia in naïve rats and reversed the antiallodynic effect induced by BL-1249 in neuropathic rats. Intrathecal administration of rottlerin or Rp-cAMPs (PKC and PKA inhibitors, respectively) enhanced the antiallodynia observed with BL-1249 in neuropathic rats. In contrast, pretreatment with PdBu or forskolin (PKC and PKA activators, respectively) reduced the BL-1249-induced antiallodynia. Intrathecal injection of two high-activity TREK-1 recombinant channels, using a in vivo transfection method with lipofectamine, with mutations at PKC/PKA phosphosites (S300A and S333A) reversed tactile allodynia in neuropathic rats, with no effect in naïve rats. In contrast, transfection of two low-activity TREK-1 recombinant channels with phosphomimetic mutations at those sites (S300D and S333D) produced tactile allodynia in naïve rats and interfered with antiallodynic effects of rottlerin/BL-1249 or Rp-cAMPs/BL-1249. Data suggest that TREK-1 channel activity can be dynamically tuned in vivo by PKC/PKA to provoke allodynia and modulate its antiallodynic role in neuropathic pain.

Ophthalmic Administration of a DNA Plasmid Harboring the Murine Tph2 Gene: Evidence of Recombinant Tph2-FLAG in Brain Structures

Tryptophan hydroxylase-type 2 (Tph2) is the first rate-limiting step in the biosynthesis of serotonin (5-HT) in the brain. The ophthalmic administration (Op-Ad) is a non-invasive method that allows delivering genetic vehicles through the eye and reaches the brain. Here, the murine Tph2 gene was cloned in a non-viral vector (pIRES-hrGFP-1a), generating pIRES-hrGFP-1a-Tph2, plus the FLAG-tag. Recombinant Tph2-FLAG was detected and tested in vitro and in vivo, where 25 μg of pIRES-hrGFP-1a-Tph2-FLAG was Op-Ad to mice. The construct was capable of expressing and producing the recombinant Tph2-FLAG in vitro and in vivo. The in vivo assays showed that the construct efficiently crossed the Hemato-Ocular Barrier and the Blood-Brain Barrier, reached brain cells, passed the optical nerves, and transcribed mRNA-Tph2-FLAG in different brain areas. The recombinant Tph2-FLAG was observed in amygdala and brainstem, mainly in raphe dorsal and medial. Relative Tph2 expression of threefold over basal level was recorded three days after Op-Ad. These results demonstrated that pIRES-hrGFP-Tph2-FLAG, administrated through the eyes was capable of reaching the brain, transcribing, and translating Tph2. In conclusion, this study showed the feasibility of delivering therapeutic genes, such as the Tph2, the first enzyme, rate-limiting step in the 5-HT biosynthesis.

Influence of Echeveria gibbiflora DC aqueous crude extract on mouse sperm energy metabolism and calcium-dependent channels

ETHNOPHARMACOLOGY RELEVANCE

In traditional Mexican medicine, Echeveria gibbiflora DC has been used as a vaginal post-coital rinse to prevent pregnancy. The aqueous crude extract (OBACE) induces sperm immobilization/agglutination and a hypotonic-like effect, likely attributed to the high concentration of calcium bis-(hydrogen-1-malate) hexahydrate [Ca²⁺ (C₄H₅O₅)₂•6H₂O]. Likewise, OBACE impedes the increase of [Ca²⁺]i during capacitation.

AIM OF THE STUDY

Evaluate the effect of OBACE on sperm energy metabolism and the underlying mechanism of action on sperm-specific channel.

MATERIAL AND METHODS

In vitro, we quantified the mouse sperm immobilization effect and the antifertility potential of OBACE. The energetic metabolism status was also evaluated by assessing the ATP levels, general mitochondrial activity, mitochondrial membrane potential, and enzymatic activity of three key enzymes of energy metabolism. Furthermore, the effect of the ion efflux of Cl^- and K⁺, as well as the pHi, were investigated in order to elucidate which channel is suitable to perform an in silico study.

RESULTS

Total and progressive motility notably decreased, as did fertility rates. ATP levels, mitochondrial activity and membrane potential were reduced. Furthermore, the activities of the three enzymes decreased. Neither Cl^- or K⁺ channels activities were affected at low concentrations of OBACE; nevertheless, pHi did not alkalinize. Finally, an in silico analysis was performed between the Catsper channel and calcium bis-(hydrogen-1-malate) hexahydrate, which showed a possible blockade of this sperm cation channel.

CONCLUSION

The results were useful to elucidate the effect of OBACE and to propose it as a future male contraceptive.

Domains two and three of Escherichia coli ribosomal S1 protein confers 30S subunits a high affinity for downstream A/U-rich mRNAs

S1, a multi-domain ribosomal protein associated with the 30S subunit, is essential for translation initiation. S1 binds with high affinity to single-stranded mRNA containing A/U-rich patches upstream of the start codon. It was previously reported that domains 1-3 of S1 protein play a role in the docking and unfolding of structured mRNAs to the ribosome. Moreover, S1-deficient 30S subunits are still able to bind to low structured mRNAs. However, mRNAs containing A/U-rich patches in the early base positions after start codon enhance protein synthesis and mRNA binding to the ribosome, which suggests that S1 is also able to interact with these A/U-rich regions. To evaluate the essentiality of S1 domains in the binding to low structured mRNAs containing A/U/G nucleotides after the start codon as well as their role in translation and cell viability, S1 protein deletion variants were generated. We show that S1 domain 3 is necessary to discriminate these mRNAs according to the nucleotide nature since its absence abrogated S1 binding to A/U-rich mRNAs and allowed binding to G-rich mRNAs. Interestingly, domains 2 and 3 were required for the binding of mRNAs containing A/U-rich sequences after the start codon to 30S, in vitro translation and cell viability.

Cor interacts with outer membrane proteins to exclude FhuA-dependent phages

Superinfection exclusion (Sie) of FhuA-dependent phages is carried out by Cor in the Escherichia coli mEp167 prophage lysogenic strain. In this work, we present evidence that Cor is an outer membrane (OM) lipoprotein that requires the participation of additional outer membrane proteins (OMPs) to exclude FhuA-dependent phages. Two Cor species of ~13 and ~8.5 kDa, corresponding to the preprolipoprotein/prolipoprotein and lipoprotein, were observed by Western blot. Cell mutants for CorC17F, CorA18D and CorA57E lost the Sie phenotype for FhuA-dependent phages. A copurification affinity binding assay combined with LC_ESI_MS/MS showed that Cor bound to OMPs: OmpA, OmpC, OmpF, OmpW, LamB, and Slp. Interestingly, Sie for FhuA-dependent phages was reduced on Cor overexpressing FhuA+ mutant strains, where ompA, ompC, ompF, ompW, lamB, fhuE, genes were knocked out. The exclusion was restored when these strains were supplemented with plasmids expressing these genes. Sie was not lost in other Cor overexpressing FhuA+ null mutant strains JW3938(btuB-), JW5100(tolB-), JW3474(slp-). These results indicate that Cor interacts and requires some OMPs to exclude FhuA-dependent phages.

Intranasal Administration of a Naked Plasmid Reached Brain Cells and Expressed Green Fluorescent Protein, a Candidate for Future Gene Therapy Studies

BACKGROUND

Intranasal administration (Int adm) has been well-studied and offers the possibility to deliver larger molecular weight biologics, such as proteins, viral vectors, nanoparticles, and naked plasmids to the brain and treat a variety of diseases in the central nervous system. The predominant challenge in this field is finding efficient vectors that are capable of crossing the blood-brain barrier (BBB).

OBJECTIVES

Here, we investigated whether a naked plasmid (pIRES-hrGFP-1a), could cross the BBB, reach brain cells and express green fluorescent protein (GFP) after int-adm and propose it as candidate for future gene therapy studies.

MATERIAL AND METHODS

Thirty-six mice were divided into 2 groups. Eighteen animals were assigned to each cluster. Mice from experimental groups received 25 μg of pIRES-hrGFP-1a. The control groups received 25 μl of PBS. Plasmids were given intranasally by applying little drops in both nostrils. Twenty-four hours later, the mice were sacrificed, and their brains were removed. Later, PCR, RT-PCR, and immunohistochemical techniques were performed.

RESULTS

pIRES-hrGFP-1a crossed the BBB and was mainly detected in the olfactory nerves (20%) and hypothalamus (16%). In contrast, GFP/18S-expressing mRNAs were detected mostly in the olfactory bulbs (95%), frontal cortex (71%) and amygdala (60%). GFP was detected in the olfactory bulb, hippocampus, frontal cortex and brainstem at 24 h.

CONCLUSIONS

pIRES-hrGFP-1a could be considered a good candidate for gene therapy studies. In the future could be cloned some therapeutic genes in the pIRES-hrGFP-1a and could transcribe and translates deficient proteins that are required to restore a function.

Novel insight into streptozotocin-induced diabetic rats from the protein misfolding perspective

Protein folding is a process of self-assembly defined by the sequence of the amino acids of the protein involved. Additionally, proteins tend to unfold, misfold and aggregate due to both intrinsic and extrinsic causes. Human islet amyloid polypeptide (hIAPP) aggregation is an early step in diabetes mellitus. However, the aggregation of rat IAPP (rIAPP) remains an open question. Adult female Sprague-Dawley rats weighing 150-250 g were divided into two groups. The experimental group (streptozotocin [STZ]) (n = 21) received an intraperitoneal injection of a single dose of 40 mg/kg STZ. We used the mouse anti-IAPP antibody and the anti-amyloid oligomer antibody to study the temporal course of rIAPP oligomerization during STZ-induced diabetes using a wide array of methods, strategies and ideas derived from biochemistry, cell biology, and proteomic medicine. Here, we demonstrated the tendency of rIAPP to aggregate and trigger cooperative processes of self-association or hetero-assembly that lead to the formation of amyloid oligomers (trimers and hexamers). Our results are the first to demonstrate the role of rIAPP amyloid oligomers in the development of STZ-induced diabetes in rats. The IAPP amyloid oligomers are biomarkers of the onset and progression of diabetes and could play a role as therapeutic targets.

[Genetic and neuroendocrine aspects in autism spectrum disorder]

The autism spectrum disorder (ASD) was described in 1943 and is defined as a developmental disorder that affects social interaction and communication. It is usually identified in early stages of development from 18 months of age. Currently, autism is considered a neurological disorder with a spectrum covering cases of different degrees, which is associated with genetic factors, not genetic and environmental. Among the genetic factors, various syndromes have been described that are associated with this disorder. Also, the neurobiology of autism has been studied at the genetic, neurophysiological, neurochemical and neuropathological levels. Neuroimaging techniques have shown multiple structural abnormalities in these patients. There have also been changes in the serotonergic, GABAergic, catecholaminergic and cholinergic systems related to this disorder. This paper presents an update of the information presented in the genetic and neuroendocrine aspects of autism spectrum disorder.

Pituitary-testicular axis function, biological to immunological ratio and charge isoform distribution of pituitary LH in male rats with experimental diabetes

Men with insulinopenic diabetes mellitus frequently present hypogonadism and exhibit circulating luteinizing hormone (LH) molecules with increased biological activity. To further study this latter issue, we analyzed the pattern of isoform distribution and the impact of changes in terminal glycosylation of pituitary LH on the bioactivity of this gonadotropin in experimental diabetes. Adult male rats were treated with streptozotocin or vehicle and euthanized on days 30, 60, or 90 posttreatment. All diabetic groups exhibited a significant decrease in serum insulin and testosterone levels as well as in sperm count; serum gonadotropins and 17beta-estradiol decreased only after 90 days of insulinopenia. Both the immunoreactive concentrations and the biological to immunological ratio of intrapituitary LH significantly increased in all experimental groups, as assessed by an in vitro homologous bioassay in HEK-293 cells expressing a recombinant LH receptor. Chromatofocusing of pituitary extracts revealed the presence of multiple LH charge isoforms; the pH distribution profile of LH in diabetic and control rats was indistinguishable on days 30 and 60 posttreatment. By contrast, the abundance of more basic isoforms (pH 9.99-9.0) decreased and that of isoforms with pH values 8.99-8.0 increased in rats with long-standing diabetes compared to controls. It is concluded that experimental diabetes alters the function of the pituitary-testicular axis, resulting in reduced sex steroids levels and hypogonadotropism. Long-standing insulinopenia leads to a paradoxical accumulation of intrapituitary LH molecules enriched in bioactivity with altered terminal glycosylation, which are apparently subserved by distinct mechanisms involving altered hypothalamic and/or gonadal inputs on the gonadotrope.

Proteolytic cleavage of the voltage-gated Ca2+ channel alpha2delta subunit: structural and functional features

By mediating depolarization-induced Ca(2+) influx, high-voltage-activated Ca(2+) channels control a variety of cellular events. These heteromultimeric proteins are composed of an ion-conducting (alpha(1)) and three auxiliary (alpha(2)delta, beta and gamma) subunits. The alpha(2)delta subunit enhances the trafficking of the channel complex to the cell surface and increases channel open probability. To exert these effects, alpha(2)delta must undergo important post-translational modifications, including a proteolytic cleavage that separates the extracellular alpha(2) from its transmembrane delta domain. After this proteolysis both domains remain linked by disulfide bonds. In spite of its central role in determining the final conformation of the fully mature alpha(2)delta, almost nothing is known about the physiological implications of this structural modification. In the current report, by using site-directed mutagenesis, the proteolytic site of alpha(2)delta was mapped to amino acid residues Arg-941 and Val-946. Substitution of these residues renders the protein insensitive to proteolytic cleavage as evidenced by the lack of molecular weight shift upon treatment with a disulfide-reducing agent. Interestingly, these mutations significantly decreased whole-cell patch-clamp currents without affecting the voltage dependence or kinetics of the channels, suggesting a reduction in the number of channels targeted to the plasma membrane.

Two PEST-like motifs regulate Ca2+/calpain-mediated cleavage of the CaVbeta3 subunit and provide important determinants for neuronal Ca2+ channel activity

An increase in intracellular Ca2+ due to voltage-gated Ca2+ (CaV) channel opening represents an important trigger for a number of second-messenger-mediated effects ranging from neurotransmitter release to gene activation. Ca2+ entry occurs through the principal pore-forming protein but several ancillary subunits are known to more precisely tune ion influx. Among them, the CaVbeta subunits are perhaps the most important, given that they largely influence the biophysical and pharmacological properties of the channel. Notably, several functional features may be associated with specific structural regions of the CaVbeta subunits emphasizing the relevance of intramolecular domains in the physiology of these proteins. In the current report, we show that CaVbeta3 contains two PEST motifs and undergoes Ca2+ -dependent degradation which can be prevented by the specific calpain inhibitor calpeptin. Using mutant constructs lacking the PEST motifs, we present evidence that they are necessary for the cleavage of CaVbeta3 by calpain. Furthermore, the deletion of the PEST sequences did not affect the binding of CaVbeta3 to the ion-conducting CaV2.2 subunit and, when expressed in human embryonic kidney-293 cells, the PEST motif-deleted CaVbeta3 significantly increased whole-cell current density and retarded channel inactivation. Consistent with this observation, calpeptin treatment of human embryonic kidney-293 cells expressing wild-type CaVbeta3 resulted in an increase in current amplitude. Together, these findings suggest that calpain-mediated CaVbeta3 proteolysis may be an essential process for Ca2+ channel functional regulation.

Microbial starch-binding domain

Glucosidic bonds from different non-soluble polysaccharides such as starch, cellulose and xylan are hydrolyzed by amylases, cellulases and xylanases, respectively. These enzymes are produced by microorganisms. They have a modular structure that is composed of a catalytic domain and at least one non-catalytic domain that is involved in polysaccharide binding. Starch-binding modules are present in microbial enzymes that are involved in starch metabolism; these are classified into several different families on the basis of their amino acid sequence similarities. Such binding domains promote attachment to the substrate and increase its concentration at the active site of the enzyme, which allows microorganisms to degrade non-soluble starch. Fold similarities are better conserved than sequences; nevertheless, it is possible to notice two evolutionary clusters of microbial starch-binding domains. These domains have enormous potential as tags for protein immobilization, as well as for the tailoring of enzymes that play a part in polysaccharide metabolism.

Glycosylation of asparagines 136 and 184 is necessary for the α2δ subunit-mediated regulation of voltage-gated Ca2+channels

The CaValpha2delta auxiliary subunit is a glycosylated protein that regulates the trafficking and function of voltage-gated Ca2+ channels. One of the most prominent roles of CaValpha2delta is to increase whole-cell Ca2+ current amplitude. Using N-glycosidase F and truncated forms of CaValpha2delta, earlier studies suggested an important role for N-linked glycosylation in current stimulation. Here, we used site-directed mutagenesis and heterologous expression in HEK-293 cells to examine the impact of individual glycosylation sites within the CaValpha2delta subunit on the regulation of Ba2+ currents through recombinant Ca2+ channels. We found two N-glycosylation consensus sites (NX(S/T)) in the extracellular alpha2 domain of the protein that are functional. Substitution of asparagines for glutamines at amino acid positions 136 and 184 rendered these sites non-functional as shown by patch-clamp experiments. These results corroborate that N-glycosylation is required for the CaValpha2delta subunit-induced current stimulation and suggest that sites N136 and N184 are directly involved in this action. Likewise, N136Q and N184Q mutations prevented whole-cell current stimulation without altering its kinetic properties, suggesting a regulation on the number of functional channels at the plasma membrane.