Multiple connexins localized to individual gap-junctional plaques in human myometrial smooth muscle

Isobaric tags for relative and absolute quantification-based proteomic analysis that reveals the roles of progesterone receptor, inflammation, and fibrosis for slow-transit constipation

BACKGROUND AND AIM

Progesterone receptor, inflammation, neurotransmitter expression, and fibrosis are involved in slow-transit constipation. The aim of the present study was to examine whether patients with slow-transit constipation have an overexpression of progesterone receptor and serotonin, which may impair the fibrosis of muscularis propria in colorectal wall.

METHODS

High-resolution colon manometry was used to record the colorectal peristaltic contractions of the proximal ascending and sigmoid colon in patients. Protein samples prepared from frozen sigmoid colon tissue and the proximal margin of the ascending colon of four female patients were compared using isobaric tags for relative and absolute quantification labeling technique coupled to 2D liquid chromatography-tandem mass spectrometry analysis. Immunohistochemical staining of progesterone receptor, serotonin, and fibronectin was performed in paraffin-embedded sigmoid colon tissues and the proximal margin of the ascending colon or ileum from 43 patients with slow-transit constipation.

RESULTS

Among these differentially regulated proteins based on isobaric tags for relative and absolute quantification and liquid chromatography-tandem mass spectrometry analysis, 56 proteins involved in the response to progesterone, inflammation, matrix remodeling, fibrosis, and muscle metabolism. Immunohistochemical staining confirmed that there was significantly higher expression of progesterone receptor (t = 19.19, P = 0.000) and serotonin (t = 13.52, P = 0.004) in sigmoid colon than in the proximal margin of the ascending colon and ileum. Progesterone receptor and fibronectin expression in the outer layer of muscularis propria were higher than in the middle layer.

CONCLUSIONS

These results demonstrate that progesterone receptor, along with inflammation and fibrosis, may take part in slow-transit constipation development.

Physiological roles of connexins in labour and lactation

The connexin family of proteins are best known as oligomerizing to form intercellular membrane channels (gap junctions) that metabolically and ionically couple cells to allow for coordinated cellular function. Nowhere in the body is this role better illustrated than in the uterine smooth muscle during parturition, where gap junctions conduct the contraction wave throughout the tissue to deliver the baby. Parturition is followed by the onset of lactation with connexins contributing to both the dramatic reorganization of mammary gland tissue leading up to lactation and the smooth muscle contraction of the myoepithelial cells which extrudes the milk. This review summarizes what is known about the expression and roles of individual connexin family members in the uterus during labour and in the mammary glands during development and lactation. Connexin loss or malfunction in mammary glands and the uterus can have serious implications for the health of both the mother and the newborn baby.

Changes in expression of P2X1 receptors and connexin 43 in the rat myometrium during pregnancy

OBJECTIVE

To investigate the expression of P2X(1) receptors and connexin 43 in gap junctions between smooth muscle cells. Contraction mediated by P2X receptors is known to occur in the bladder and male reproductive tract, and cell-cell coupling of smooth muscle via gap junctions is essential for synchronized rhythmic activity of these tissues.

DESIGN

We selected for this study rat myometrial smooth muscle during pregnancy and at postpartum day l.

SETTING

University medical school.

ANIMAL(S)

Laboratory rats.

INTERVENTION(S)

Rats were mated and became pregnant.

MAIN OUTCOME MEASURE(S)

Immunostaining and fluorescence and confocal microscopy.

RESULT(S)

The level of P2X(1) receptor expression remained low throughout pregnancy (days 4 to 20) but was greatly up-regulated at day 22 (postpartum day 1). Connexin 43 expression showed a pattern of up-regulation, with progression through pregnancy and peaking near labor, but exhibited a rapid down-regulation after parturition.

CONCLUSION(S)

The functional significance of the changes in connexin 43 and P2X(1) receptor expression that have been observed is discussed in relation to triggering and modulation of uterine contractility during and after pregnancy.

Preterm labour. Myometrial function in prematurity

The primary function of the uterus during gestation is to harbour the growing conceptus in a largely quiescent environment. Upon maturation of the fetus to a point sufficient for extrauterine survival, the uterus must remodel itself sufficiently to generate forceful contractions during labour. During preterm delivery, the process of remodelling of the myometrium occurs early due to a number of different causes, although the underlying basis for myometrial contraction remains the same. This review summarises the anatomical, physiological and molecular basis for contraction. We describe the fibre structure of the human uterus and how this relates to the spread of electrical excitation during a contraction. The process of excitation within a single myometrial cell is described, as well as how this relates to contraction. We then focus on how excitation-contraction coupling is modulated by intercellular communication, pharmacomechanical-coupling and hormonal milieu. Lastly, we consider the actions of the commonly accepted uterine agonists oxytocin, prostaglandin F(2alpha), and prostaglandin E(2), and the tocolytic ritodrine.

Müllerian anomalies, hearing loss, and connexin 26 mutations

In a study of the possible inter-relationship among müllerian anomalies, hearing loss, and connexin 26 mutations, we evaluated all women in whom müllerian anomalies were diagnosed on hysterosalpingography during a 6-year period (n = 24/519). Audiometric testing revealed five (22.7%) with unrecognized sensorineural hearing loss; however, on genetic evaluation, none harbored a connexin 26 mutation.

Ablation of connexin43 in uterine smooth muscle cells of the mouse causes delayed parturition

Gap junctions are characteristically increased in the myometrium during term and preterm delivery and are thought to be essential for the development of uterine contractions during labour. Expression of connexin43 (Cx43), the major myometrial gap junction protein, is increased during delivery. We have generated a mouse mutant (Cx43fl/fl:SM-CreERT2), in which the coding region of Cx43 can be specifically deleted in smooth muscle cells at any given time point by application of tamoxifen. By this approach, we were able to study long-term effects on myometrial functions that are necessary for parturition as well as gap junction intercellular communication in primary myometrial cell cultures. We found a prolongation of the pregnancy in 82% of tamoxifen-treated Cx43fl/fl:SM-CreERT2 mice as well as decreased dye coupling in cultured primary myocytes of these animals. Other parturition-specific parameters such as the regulation of oxytocin receptor, prostaglandin F receptor or progesterone remained unchanged. Our results indicate the important function of Cx43 during parturition in the living animal and suggest further strategies to investigate the role of connexins in uterine contractility in transgenic mice.

Plasma membrane channels formed by connexins: their regulation and functions

Members of the connexin gene family are integral membrane proteins that form hexamers called connexons. Most cells express two or more connexins. Open connexons found at the nonjunctional plasma membrane connect the cell interior with the extracellular milieu. They have been implicated in physiological functions including paracrine intercellular signaling and in induction of cell death under pathological conditions. Gap junction channels are formed by docking of two connexons and are found at cell-cell appositions. Gap junction channels are responsible for direct intercellular transfer of ions and small molecules including propagation of inositol trisphosphate-dependent calcium waves. They are involved in coordinating the electrical and metabolic responses of heterogeneous cells. New approaches have expanded our knowledge of channel structure and connexin biochemistry (e.g., protein trafficking/assembly, phosphorylation, and interactions with other connexins or other proteins). The physiological role of gap junctions in several tissues has been elucidated by the discovery of mutant connexins associated with genetic diseases and by the generation of mice with targeted ablation of specific connexin genes. The observed phenotypes range from specific tissue dysfunction to embryonic lethality.

Impedance measurements and connexin expression in human detrusor muscle from stable and unstable bladders

Three of this month's Scientific Discovery papers highlight the importance of collaboration in delivering high quality scientific research. As scientific technology increases in power and cost, and specific areas of interest become more specialized, it is becoming more difficult to cover all aspects of a completeresearch story. Collaborating with other experts in the field or other fields, including industry, allows strong scientific proof to be generated for the hypothesis and aims. Building strong collaborative,inter-disciplinary, multi-institutional, international groups with academic and industrial partners is the way forward for all discovery. We look forward to publishing more of these collaborative papersin future issues of the BJU International.

OBJECTIVES

To test the hypothesis that intercellular electrical coupling is altered in human detrusor smooth muscle from patients with unstable bladders.

MATERIALS AND METHODS

Human detrusor biopsy samples were obtained from patients with stable and unstable bladders. Intracellular electrical impedance was measured with alternating current (20 Hz-300 kHz) across the ends of detrusor strips in an oil-gap, after correcting for extracellular space resistance. Gap junctions were identified by localization of connexins (Cx), specifically Cx45, Cx43 and Cx40 transcripts, using immunoconfocal microscopy.

RESULTS

Total intracellular resistivity was greater in strips from unstable than from stable bladders (median 1246 vs 817 Omega.cm). The increase was attributed to an increase in junctional resistance; cytoplasmic resistance was unchanged. Cx43 was localized to a submucosal layer and to connective tissue; Cx40 label was confined to endothelial cells of blood vessels. Cx45 labelling was localized to detrusor bundles and appeared to be less marked in samples from unstable bladders. Semi-quantitative analysis of Northern blots showed that Cx45 expression in unstable was less than that in stable bladders.

CONCLUSIONS

These data suggest that intercellular coupling is reduced in detrusor from unstable bladders. Cx45 was localized to the detrusor layer, with Cx 43 more evident in the suburothelial mucosa. Cx45 labelling was less intense in detrusor samples from unstable bladders. These results are consistent with reduced gap junction coupling in detrusor from unstable bladders.