Regional differences in signalling transduction pathways among smooth muscle cells from rabbit colon

Tissue engineering of the gastrointestinal tract: the historic path to translation

The gastrointestinal (GI) tract is imperative for multiple functions including digestion, nutrient absorption, and timely waste disposal. The central feature of the gut is peristalsis, intestinal motility, which facilitates all of its functions. Disruptions in GI motility lead to sub-optimal GI function, resulting in a lower quality of life in many functional GI disorders. Over the last two decades, tissue engineering research directed towards the intestine has progressed rapidly due to advances in cell and stem-cell biology, integrative physiology, bioengineering and biomaterials. Newer biomedical tools (including optical tools, machine learning, and nuanced regenerative engineering approaches) have expanded our understanding of the complex cellular communication within the GI tract that lead to its orchestrated physiological function. Bioengineering therefore can be utilized towards several translational aspects: (i) regenerative medicine to remedy/restore GI physiological function; (ii) in vitro model building to mimic the complex physiology for drug and pharmacology testing; (iii) tool development to continue to unravel multi-cell communication networks to integrate cell and organ-level physiology. Despite the significant strides made historically in GI tissue engineering, fundamental challenges remain including the quest for identifying autologous human cell sources, enhanced scaffolding biomaterials to increase biocompatibility while matching viscoelastic properties of the underlying tissue, and overall biomanufacturing. This review provides historic perspectives for how bioengineering has advanced over time, highlights newer advances in bioengineering strategies, and provides a realistic perspective on the path to translation.

Mechanisms of Meconium Passage: Cholinergic Stimulation of Electromechanical Coordination in the Fetal Colon

OBJECTIVE

Fetal gastrointestinal function develops in utero, with evidence of enhanced motility near-term. Although colonic passage of meconium in utero may be associated with fetal maturation or stress, little is known of the mechanisms potentiating motility. We assessed the effect of bethanechol, a cholinergic prokinetic agent, on colonic muscle muscular contractile and electromyogram (EMG) activity in the near-term ovine fetus.

METHODS

Near-term (130 days, n = 8) singleton ovine fetuses were chronically prepared with vascular catheters and three sets of miniature strain gauges and bipolar EMGs on the serosal surface of the transverse colon, left colic flexure, and distal colon. Following a 60-minute control period, fetuses received intravenous bethanechol (60 microg/kg, Low-Beth; 120 microg/kg, High-Beth) at 60 and 180 minutes. Colonic activity was recorded digitally and analyzed for short-duration (2<SHORT<15 seconds) and long-duration (15<LONG<120 seconds) strain gauge and EMG contractions. Data were expressed as means +/- SEM and analyzed using one-way analysis of variance (ANOVA) and paired t test.

RESULTS

During the control period, there was significantly greater SHORT versus LONG strain gauge contractions in all segments (P <.05). As compared to control values, Low-Beth and High-Beth significantly increased SHORT strain gauge contractions in the transverse colon (160 +/- 13 to 201 +/- 36 and 307 +/- 74 spikes/30 min, respectively, P <.05), although not in left colic flexure or distal colon. Bethanecol did not affect LONG strain gauge contractions. SHORT-EMG and LONG-EMG spike bursts did not change in response to bethanecol (280 +/- 20, 59 +/- 2 spikes/30 min, respectively).

CONCLUSION

Cholinergic stimulation of fetal sheep colonic activity at 0.9 gestation occurs in the transverse colon, but not the more distal left colic flexure or distal colon. The increased strain gauge, but not EMG activity, suggests that cholinergic stimulation improves electromechanical coordination in the fetal colon. We speculate that cholinergic-induced delivery of gastrointestinal contents to the distal colon evokes local contractile/expulsive mechanisms resulting in meconium passage.

Myogenic regional responsiveness to cholinergic and vipergic stimulation in human colon

BACKGROUND

Differences in the actions of enteric neurotransmitters on colonic circular and longitudinal muscle layers have not been clearly determined, nor the possible existence of intrinsic myogenic phenotypes that might contribute to regional differences in human colon motor activity. The aim of this study was to analyze the direct pharmaco-mechanical coupling of carbachol (CCh) and vasoactive intestinal polypeptide (VIP) on human colonic smooth muscle strips and cells.

METHODS

Circular and longitudinal muscle strips and cells were obtained from 15 human specimens of ascending and sigmoid colon. Both isometric tension on muscle strips and contraction and relaxation on cells were measured in response to increasing CCh and VIP concentrations.

KEY RESULTS

Circular muscle strips of ascending colon were more sensitive to the effect of CCh than that of sigmoid colon, EC(50) values being, respectively, 4.15μmolL(-1) and 8.47μmolL(-1) (P<0.05), although there were no differences in maximal responses. No regional differences were observed in longitudinal muscle strips or in smooth muscle cells. Maximal responses to CCh were higher on circular than longitudinal muscle strips and cells throughout the colon. A greater sensitivity to VIP was observed in ascending colon compared with sigmoid colon, both in circular (EC(50:) 0.041 and 0.15μmolL(-1) , respectively, P<0.01) and longitudinal (EC(50:) 0.043 and 0.09μmolL(-1) , respectively, P<0.05) strips, and similar differences were observed in longitudinal smooth muscle cells (EC(50:) 44.85 and 75.24nmolL(-1) , respectively, P<0.05).

CONCLUSIONS & INFERENCES

Regional myogenic differences in pharmaco-mechanical coupling between the enteric neurotransmitters and smooth muscle contribute to the complex regional motor patterns of human colon.

Optimisation of isolation of richly pure and homogeneous primary human colonic smooth muscle cells

BACKGROUND

Inherent properties of gastrointestinal smooth muscle can be assessed using isolated cell suspensions. Currently available isolation techniques, based on short 2-h enzymatic digestion, however, present the disadvantage of low cellular yield with brief viability. These features are an important limiting factor especially in studies in humans in which tissue may not be available daily and mixing of samples is not recommended.

AIMS

To optimise the isolation procedure of cells from human colon to obtain a richly pure primary smooth muscle cell preparation.

METHODS

Slices of circular muscle layer, obtained from surgical specimens of human colon, were incubated overnight in Dulbecco's modified eagle's medium supplemented with antibiotics, foetal bovine serum, an ATP-regenerating system and collagenase. On the following day, digested muscle strips were suspended in HEPES buffer, and spontaneously dissociated smooth muscle cells were harvested and used either immediately or maintained in suspension for up to 72 h. Cell yield, purity, viability, contractile responses, associated intracellular calcium signals and RNA and protein extraction were evaluated and compared to cell suspensions obtained with the current short digestion protocol.

RESULTS AND CONCLUSION

The overnight isolation protocol offers the advantage of obtaining a pure, homogeneous, long-life viable cell suspension that maintains a fully differentiated smooth muscle phenotype unchanged for at least 72 h and that allows multiple functional/biochemical studies and efficient RNA extraction from a single human specimen.