Estrogen-regulated expression of SK3 channel in rat colonic smooth muscle contraction

Estrogen inhibits colonic smooth muscle contractions by regulating BKβ1 signaling

The estrogen inhibits colonic smooth muscle contractions, which may lead to constipation. However, the mechanisms of inhibition are poorly understood. Therefore, the present study examined the effect of estrogen on rat colonic smooth muscle contractions and its potential association with the large-conductance Ca2+-activated K+ channels β1 (BKβ1) subunit. Twenty-four female Sprague Dawley rats were randomly assigned to 4 groups. After 2 weeks of intervention, the contraction activity of isolated colonic smooth muscle and the expression of BKβ1 in colonic smooth muscle of rats were detected. Additionally, in order to investigate the effects of estrogen on BKβ1 expression and calcium mobilization, in vitro experiments were conducted using rat and human colonic smooth muscle cells (SMCs). BKβ1 shRNA was used to investigate whether calcium mobilization is affected by BKβ1 in colonic SMCs. To explore the relationship between ERβ and BKβ1, serial deletions, site-directed mutagenesis, a dual-luciferase reporter assay, and chromatin immunoprecipitation assays were employed. In response to E2, colonic smooth muscle strips showed a decrease in tension, while IBTX exposure transiently increased tension. Furthermore, in these muscle tissues, BKβ1 and α-SMA were found to be co-expressed. The E2 group showed significantly higher BKβ1 expression. In cultured colonic SMCs, the expression of BKβ1 was found to increase in the presence of E2 or DPN. E2 treatment reduced Ca2+ concentrations, while BKβ1 shRNA treatment increased Ca2+ concentrations relative to the control. ERβ-initiated BKβ1 expression appears to occur via binding to the BKβ1 promoter. These results indicated that E2 may upregulate BKβ1 expression via ERβ and inhibit colonic smooth muscle contraction through ERβ by directly targeting BKβ1.

Estrogen increases the expression of BKCa and impairs the contraction of colon smooth muscle via upregulation of sphingosine kinase 1

Estrogen (E2) may impair the contraction of colonic smooth muscle (SM) leading to constipation. Large conductance Ca2+ -activated K+ channels (BKCa ) are widely expressed in the smooth muscle cells (SMCs) contributing to hyperpolarization and relaxation of SMCs. Sphingosine kinase 1 (SphK1) is known to influence the expression of BKCa . We aimed to elucidate the potential underlying molecular mechanism of BKCa and SphK1 that may influence E2-induced colonic dysmotility. In ovariectomized rats, SM contraction and expression of BKCa , SphK1, sphingosine-1-phosphate receptor (S1PR) were analyzed after the treatment with vehicle, BSA-E2, E2, and E2 receptor antagonist. The role of BKCa , SphK1, and S1PR in E2-induced SM dysmotility was investigated in rat colonic SMCs. The effect of SphK1 on SM contraction as well as on the expression of BKCa and S1PR was analyzed in SphK1 knock-out mutant mice and wild-type (WT) mice treated with or without E2. The E2-treated group exhibited a weak contraction of colonic SM and a delayed colonic transit. The treatment with E2 significantly upregulated the expression of BKCa , SphK1, S1PR1, and S1PR2, but not S1PR3, in colon SM and SMCs. Inhibition of BKCa , SphK1, S1PR1, and S1PR2 expression attenuated the effect of E2 on Ca2+ mobilization in rat colon SMCs. WT mice treated with E2 showed impaired gastrointestinal motility and enhanced expression of BKCa , S1PR1, and S1PR2 compared with those without E2 treatment. Conversely, in SphK1 knock-out mice treated with E2, these effects were partially reversed. E2 increased the release of S1P which in turn could have activated S1PR1 and S1PR2. Loss of SphK1 attenuated the effect of E2 on the upregulation of S1PR1 and S1PR2 expression. These findings indicated that E2 impaired the contraction of colon SM through activation of BKCa via the upregulation of SphK1 and the release of S1P. In the E2-induced BKCa upregulation, S1PR1 and S1PR2 might also be involved. These results may provide further insights into a therapeutic target and optional treatment approaches for patients with constipation.

Ca2+-Activated K+ Channels and the Regulation of the Uteroplacental Circulation

Adequate uteroplacental blood supply is essential for the development and growth of the placenta and fetus during pregnancy. Aberrant uteroplacental perfusion is associated with pregnancy complications such as preeclampsia, fetal growth restriction (FGR), and gestational diabetes. The regulation of uteroplacental blood flow is thus vital to the well-being of the mother and fetus. Ca²⁺-activated K⁺ (K_Ca) channels of small, intermediate, and large conductance participate in setting and regulating the resting membrane potential of vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) and play a critical role in controlling vascular tone and blood pressure. K_Ca channels are important mediators of estrogen/pregnancy-induced adaptive changes in the uteroplacental circulation. Activation of the channels hyperpolarizes uteroplacental VSMCs/ECs, leading to attenuated vascular tone, blunted vasopressor responses, and increased uteroplacental blood flow. However, the regulation of uteroplacental vascular function by K_Ca channels is compromised in pregnancy complications. This review intends to provide a comprehensive overview of roles of K_Ca channels in the regulation of the uteroplacental circulation under physiological and pathophysiological conditions.

Crosstalk between the Gut Microbiome and Colonic Motility in Chronic Constipation: Potential Mechanisms and Microbiota Modulation

Chronic constipation (CC) is a highly prevalent and burdensome gastrointestinal disorder. Accumulating evidence highlights the link between imbalances in the gut microbiome and constipation. However, the mechanisms by which the microbiome and microbial metabolites affect gut movement remain poorly understood. In this review, we discuss recent studies on the alteration in the gut microbiota in patients with CC and the effectiveness of probiotics in treating gut motility disorder. We highlight the mechanisms that explain how the gut microbiome and its metabolism are linked to gut movement and how intestinal microecological interventions may counteract these changes based on the enteric nervous system, the central nervous system, the immune function, and the ability to modify intestinal secretion and the hormonal milieu. In particular, microbiota-based approaches that modulate the levels of short-chain fatty acids and tryptophan catabolites or that target the 5-hydroxytryptamine and Toll-like receptor pathways may hold therapeutic promise. Finally, we discuss the existing limitations of microecological management in treating constipation and suggest feasible directions for future research.

Tamoxifen administration alters gastrointestinal motility in mice

BACKGROUND

Tamoxifen is widely used for Cre-estrogen receptor-mediated genomic recombination in transgenic mouse models to mark cells for lineage tracing and to study gene function. However, recent studies have highlighted off-target effects of tamoxifen in various tissues and cell types when used for induction of Cre recombination. Despite the widespread use of these transgenic Cre models to assess gastrointestinal (GI) function, the effect of tamoxifen exposure on GI motility has not been described.

METHODS

We examined the effects of tamoxifen on GI motility by measuring total GI transit, gastric emptying, small intestinal transit, and colonic contractility in wild-type adult mice.

KEY RESULTS

We observed a significant delay in total GI transit in tamoxifen-treated mice, with unaltered gastric emptying, accelerated small intestinal transit, and abnormal colonic motility.

CONCLUSION

Our findings highlight the importance of considering GI motility alterations induced by tamoxifen when designing protocols that utilize tamoxifen as a Cre-driver for studying GI function.

The role of SK3 in progesterone-induced inhibition of human fallopian tubal contraction

BACKGROUND

Normal motor activity of the fallopian tube is critical for human reproduction, and abnormal tubal activity may lead to ectopic pregnancy (EP) or infertility. Progesterone has an inhibitory effect on tubal contraction; however, the underlying mechanisms remain unclear. Small-conductance calcium-activated K⁺ channel 3 (SK3) is abundantly expressed in platelet-derived growth factor receptor α positive (PDGFRα+) cells and was reported to be important for the relaxation of smooth muscle. The present study aims to explore the expression of SK3 in the human fallopian tube and its role in progesterone-induced inhibition of tubal contraction.

METHODS

We collected specimens of fallopian tubes from patients treated by salpingectomy for EP (EP group) and other benign gynecological diseases (Non-EP group). The expression of SK3 was detected by quantitative real-time polymerase chain reaction, western blot, immunocytochemistry, and immunohistochemistry analyses. Isometric tension experiments were performed to investigate the role of SK3 in progesterone-induced inhibition of tubal contraction.

RESULTS

The baseline amplitude and frequency of human fallopian tube contraction were both statistically lower in the EP group compared with the non-EP group. The expression levels of SK3 in different portions of fallopian tubes from the non-EP group were significantly higher than in those from the EP group. Progesterone had an inhibitory effect on tubal contraction, mainly on the amplitude, in both groups, and SK3 as well as other calcium-activated K⁺ channels may be involved. SK3-expressing PDGFRα (+) cells were detected in the human fallopian tube.

CONCLUSIONS

The expression of SK3 is lower in the EP group, and SK3 is involved in the progesterone-induced inhibition of human fallopian tube contraction.

Arsenic suppresses GDF1 expression via ROS-dependent downregulation of specificity protein 1

Inorganic arsenic, an environmental contaminant, has adverse health outcomes. Our previous studies showed that arsenic causes abnormal cardiac development in zebrafish embryos by downregulating Dvr1/GDF1 expression and that folic acid protects against these effects. However, the mechanism by which arsenic represses Dvr1/GDF1 expression remains unknown. Herein, we demonstrate that specificity protein 1 (Sp1) acts as a transcriptional activator of GDF1. Arsenic treatment downregulated Sp1 at both the mRNA and protein level and its downstream targets GDF1 and SIRT1. Chromatin immunoprecipitation analysis showed that the occupancy of Sp1 on the GDF1 or SIRT1 promoter was significantly reduced in response to arsenite. Further investigation showed that Sp1 overexpression inhibited the arsenic-mediated decrease in GDF1 and SIRT1, while Sp1 knockdown had the opposite effect. We found that expression of the oxidative adaptor p66shc was inversely related to that of SIRT1 and that the binding of SIRT1 to the p66shc promoter was sharply attenuated by arsenite treatment. SIRT1 overexpression attenuated p66shc expression but enhanced GDF1 protein expression, while SIRT1 depletion exerted the opposite effect. Both the antioxidants N-acetylcysteine and folic acid reversed the arsenic-mediated repression of Sp1, GDF1 and SIRT1. Moreover, wild-type p66shc overexpression enhanced the arsenic-mediated repression of Sp1, GDF1 and SIRT1, which was accompanied by an increase in intracellular reactive oxygen species (ROS) levels, while both overexpression of a dominant negative p66shcSer36Ala mutant and deficiency in p66shc reversed these effects. Taken together, our results revealed that arsenic suppresses GDF1 expression via the ROS-dependent downregulation of the Sp1/SIRT1 axis, which forms a negative feedback loop with p66shc to regulate oxidative stress. Our findings reveal a novel molecular mechanism underlying arsenic toxicity and provide new insight into the protective effect of folic acid in arsenic-mediated toxicity.