Differential expression of inositol 1,4,5-trisphosphate receptor types 1, 2, and 3 in rat myometrium and endometrium during gestation

Assessing the Potency of the Novel Tocolytics 2-APB, Glycyl-H-1152, and HC-067047 in Pregnant Human Myometrium

The intracellular signaling pathways that regulate myometrial contractions can be targeted by drugs for tocolysis. The agents, 2-APB, glycyl-H-1152, and HC-067047, have been identified as inhibitors of uterine contractility and may have tocolytic potential. However, the contraction-blocking potency of these novel tocolytics was yet to be comprehensively assessed and compared to agents that have seen greater scrutiny, such as the phosphodiesterase inhibitors, aminophylline and rolipram, or the clinically used tocolytics, nifedipine and indomethacin. We determined the IC₅₀ concentrations (inhibit 50% of baseline contractility) for 2-APB, glycyl-H-1152, HC-067047, aminophylline, rolipram, nifedipine, and indomethacin against spontaneous ex vivo contractions in pregnant human myometrium, and then compared their tocolytic potency. Myometrial strips obtained from term, not-in-labor women, were treated with cumulative concentrations of the contraction-blocking agents. Comprehensive dose-response curves were generated. The IC₅₀ concentrations were 53 µM for 2-APB, 18.2 µM for glycyl-H-1152, 48 µM for HC-067047, 318.5 µM for aminophylline, 4.3 µM for rolipram, 10 nM for nifedipine, and 59.5 µM for indomethacin. A single treatment with each drug at the determined IC₅₀ concentration was confirmed to reduce contraction performance (AUC) by approximately 50%. Of the three novel tocolytics examined, glycyl-H-1152 was the most potent inhibitor. However, of all the drugs examined, the overall order of contraction-blocking potency in decreasing order was nifedipine > rolipram > glycyl-H-1152 > HC-067047 > 2-APB > indomethacin > aminophylline. These data provide greater insight into the contraction-blocking properties of some novel tocolytics, with glycyl-H-1152, in particular, emerging as a potential novel tocolytic for preventing preterm birth.

Effect of alpha-lipoic acid and myoinositol on endometrial inflammasome from recurrent pregnancy loss women

PROBLEM

A significant increased expression/activation of one of the most well-characterized inflammasomes, the NAcht leucine-rich-repeat protein-3 (NALP-3), in the endometrium from idiopathic recurrent pregnancy loss women (RPL) has been previously found by our research group. We therefore, suggested this event as being one of the molecular mechanisms altering endometrial inflammatory status during early pregnancy. In the present research, we attempt to investigate whether molecules with anti-inflammatory activity, alpha-lipoic acid (ALA), and/or myoinositol affect the endometrial NALP-3 expression and activation.

METHOD OF STUDY

Women with a history of idiopathic RPL (n = 30) were included in the study and compared to a control group (n = 15). Endometrial tissues were collected by hysteroscopy during the mid-luteal phase. RPL women underwent a three-month prescription of tablets containing ALA plus myoinositol (Sinopol^® ). After treatment, hysteroscopic biopsies were repeated in RPL patients. Inflammasome expression was evaluated by immunohistochemical and Western blot analysis. NALP-3 activation was studied by quantifying the secretion of both caspase-1 and interleukin (IL)-1ß and IL-18 through ELISA. In ex vivo experiments, the effects of each molecule on endometrial inflammasome were studied.

RESULTS

Sinopol^® significantly reduced the RPL endometrial inflammasome expression and activation. ALA, but not myoinositol, significantly reduced the endometrial inflammasome expression and activity.

CONCLUSION

Our data suggest a role for ALA on RPL inflammasome. Understanding the mechanisms involved in RPL and the observation that specific molecules are able to interfere with such complex at the endometrium might provide new rational design approaches to a personalized evaluation of endometrial status and, ultimately, a targeted medicine.

Functional inositol 1,4,5-trisphosphate receptors assembled from concatenated homo- and heteromeric subunits

Vertebrate genomes code for three subtypes of inositol 1,4,5-trisphosphate (IP3) receptors (IP3R1, -2, and -3). Individual IP3R monomers are assembled to form homo- and heterotetrameric channels that mediate Ca(2+) release from intracellular stores. IP3R subtypes are regulated differentially by IP3, Ca(2+), ATP, and various other cellular factors and events. IP3R subtypes are seldom expressed in isolation in individual cell types, and cells often express different complements of IP3R subtypes. When multiple subtypes of IP3R are co-expressed, the subunit composition of channels cannot be specifically defined. Thus, how the subunit composition of heterotetrameric IP3R channels contributes to shaping the spatio-temporal properties of IP3-mediated Ca(2+) signals has been difficult to evaluate. To address this question, we created concatenated IP3R linked by short flexible linkers. Dimeric constructs were expressed in DT40-3KO cells, an IP3R null cell line. The dimeric proteins were localized to membranes, ran as intact dimeric proteins on SDS-PAGE, and migrated as an ∼1100-kDa band on blue native gels exactly as wild type IP3R. Importantly, IP3R channels formed from concatenated dimers were fully functional as indicated by agonist-induced Ca(2+) release. Using single channel "on-nucleus" patch clamp, the channels assembled from homodimers were essentially indistinguishable from those formed by the wild type receptor. However, the activity of channels formed from concatenated IP3R1 and IP3R2 heterodimers was dominated by IP3R2 in terms of the characteristics of regulation by ATP. These studies provide the first insight into the regulation of heterotetrameric IP3R of defined composition. Importantly, the results indicate that the properties of these channels are not simply a blend of those of the constituent IP3R monomers.

Inositol 1,4,5-trisphosphate-induced Ca2+ signalling is involved in estradiol-induced breast cancer epithelial cell growth

Background

Ca²⁺ is a ubiquitous messenger that has been shown to be responsible for controlling numerous cellular processes including cell growth and cell death. Whereas the involvement of IP₃-induced Ca²⁺ signalling (IICS) in the physiological activity of numerous cell types is well documented, the role of IICS in cancer cells is still largely unknown. Our purpose was to characterize the role of IICS in the control of growth of the estrogen-dependent human breast cancer epithelial cell line MCF-7 and its potential regulation by 17β-estradiol (E₂).

Results

Our results show that the IP₃ receptor (IP₃R) inhibitors caffeine, 2-APB and xestospongin C (XeC) inhibited the growth of MCF-7 stimulated by 5% foetal calf serum or 10 nM E₂. Furthermore, Ca²⁺ imaging experiments showed that serum and E₂ were able to trigger, in a Ca²⁺-free medium, an elevation of internal Ca²⁺ in a 2-APB and XeC-sensitive manner. Moreover, the phospholipase C (PLC) inhibitor U-73122 was able to prevent intracellular Ca²⁺ elevation in response to serum, whereas the inactive analogue U-73343 was ineffective. Western-blotting experiments revealed that the 3 types of IP₃Rs are expressed in MCF-7 cells and that a 48 hours treatment with 10 nM E₂ elevated IP₃R3 protein expression level in an ICI-182,780 (a specific estrogen receptor antagonist)-dependent manner. Furthermore, IP₃R3 silencing by the use of specific small interfering RNA was responsible for a drastic modification of the temporal feature of IICS, independently of a modification of the sensitivity of the Ca²⁺ release process and acted to counteract the proliferative effect of 10 nM E₂.

Conclusions

Altogether, our results are in favour of a role of IICS in MCF-7 cell growth, and we hypothesize that the regulation of IP₃R3 expression by E₂ is involved in this effect.

Hormonal signaling and signal pathway crosstalk in the control of myometrial calcium dynamics

Understanding the basis for the control of myometrial contractant and relaxant signaling pathways is important to understanding how to manage myometrial contractions. Signaling pathways are influenced by the level of expression of the signals and signal pathway components, the location of these components in the appropriate subcellular environment, and covalent modification. Crosstalk between these pathways regulates the effectiveness of signal transduction and represents an important way by which hormones can regulate phenotype. This review deals primarily with signaling pathways that control Ca2+ entry and intracellular release, as well as the interplay between these pathways.

Differential expression of glucose transporter GLUT8 during mouse spermatogenesis

GLUT8 is a facilitative glucose transporter expressed at high levels in the testis. In this study, we analyzed the GLUT8 expression in mouse testis during spermatogenesis by RT–PCR, Western blot and immunohistochemistry methods. Our results show that GLUT8 expression is limited to spermatids and spermatozoa in the testis. Expression begins when round spermatids are formed at postnatal day 24. The expression persists throughout spermiogenesis, and it is also detected in spermatozoa, but it is absent in more immature germ cells, Sertoli cells and interstitial tissue. GLUT8 immunoreactivity is always restricted to the acrosomic system in a manner that matches the acrosome system formation. The GLUT8 expression is mainly associated with the acrosomic membrane in the acrosome, although significant immunoreactivity is also found inside the acrosomic lumen. The specific GLUT8 location suggests that this transporter plays a pivotal role in the fuel supply of spermatozoa, and in the traffic of sugars during the capacitation and fertilization processes.

Estrogen increases CD38 gene expression and leads to differential regulation of adenosine diphosphate (ADP)-ribosyl cyclase and cyclic ADP-ribose hydrolase activities in rat myometrium

Hormones influence uterine contractility through their effects on intracellular calcium. The regulation of intracellular calcium in uterine smooth muscle is achieved by several mechanisms and includes mobilization from intracellular stores by inositol 1,4,5-trisphosphate and ryanodine-sensitive channels. Cyclic ADP-ribose (cADPR), a metabolite of NAD(+), is known to mediate calcium release through ryanodine receptor channels. A cell surface glycoprotein, CD38, catalyzes the synthesis and breakdown of cADPR and thus possesses bifunctional enzymatic activity. The regulation of cADPR synthesis by ADP-ribosyl cyclase (cyclase) or degradation by cADP-ribose hydrolase (hydrolase) by hormones in the myometrium is poorly understood. We investigated the effects of estradiol-17 beta on CD38 expression and the synthesis and degradation of cADPR in myometrial smooth muscle obtained from ovariectomized rats. CD38 expression was studied by reverse transcription polymerase chain reaction and Western blot analyses. In uterine microsomal fractions, cyclase and hydrolase activities were measured using nicotinamide guanine dinucleotide and [(32)P]cADPR as substrates, respectively. Microsomal proteins subfractionated by SDS-PAGE and gel filtration were used to determine the fractions containing cyclase and hydrolase activities. The results demonstrate that cyclase and hydrolase activities are associated with a single protein fraction, similar to CD38 in uteri from both ovariectomized and estradiol-treated rats, and estradiol-17 beta causes 1) increased CD38 mRNA and protein expression and 2) significantly enhanced cyclase but not hydrolase activity. The differential regulation of CD38 by estradiol-17 beta, resulting in increased cADPR synthesis, would have profound effects on calcium regulation and myometrial contractility.

Tissue-specific regulation of Ca(2+) channel protein expression by sex hormones

The L-type Ca(2+) channel pore-forming alpha subunit, alpha(1C) can be detected in brain and heart as two proteins with molecular masses of approximately 240 kDa and approximately 190 kDa known as alpha(1C-long) and alpha(1C-short), respectively. In brain, the alpha(1C-short) is thought to be the product of a approximately 50 kDa C-terminus calpain-mediated proteolytic deletion. We now show that uterine smooth muscle also possesses alpha(1C-long) and alpha(1C-short) isoforms, and that the relative expression of these two forms is regulated by sex hormones in a tissue-specific manner. Protein expression of alpha(1C) L-type Ca(2+) channels was examined in uterine smooth muscle, brain and heart, comparing non-pregnant (NP) estrus vs. late-pregnant (21 days) rats. The two forms of alpha(1C) were detected in all studied tissues. In late-pregnant uterus, alpha(1C-long) doubled the expression of alpha(1C-short); in NP uterus the opposite occurred. However, these changes were restricted to the uterine muscle, with no changes in brain and heart. To investigate the mechanism of such regulation, ovariectomized rats were treated with sex hormones, progesterone (P4) and/or 17beta-estradiol (estrogen, E2). P4 treatment, which yielded P4 plasma levels of 5 +/- 1 ng/ml and a high P4/E2 ratio (3 +/- 1.5 x 10(3)) similar to the ratio in late-pregnant uterus (1.5 +/- 0.3 x10(3)), facilitated alpha(1C-long) expression. In contrast, E2 or E2+P4 treatment that increased E2 plasma levels to 60 +/- 8 pg/ml and 75 +/- 24 pg/ml, produced low P4/E2 ratios of 0.03 +/- 0.006 and 0.2 +/- 0.1, respectively. These low P4/E2 ratios also found in NP rats at estrus (0.3 +/- 0.1) favored the expression of alpha(1C-short) form in myometrium. Neither hormone treatment altered alpha(1C) expression in brain or heart. Our results indicate that expression of alpha(1C) isoforms depends on P4/E2 ratios. Plasma P4/E2 ratios <1 x 10(3) favor the expression of the alpha(1C-short); whereas ratios >1 x 10(3) facilitate the expression of the alpha(1C-long) form. This regulation is tissue-specific for myometrium since it did not occur in heart and brain tissues.