Collagen production by human smooth muscle cells isolated during intestinal organogenesis

Idiopathic Megacolon-Short Review

INTRODUCTION

Idiopathic megacolon (IM) is a rare condition with a more or less known etiology, which involves management challenges, especially therapeutic, and both gastroenterology and surgery services. With insufficiently drawn out protocols, but with occasionally formidable complications, the condition management can be difficult for any general surgery team, either as a failure of drug therapy (in the context of a known case, initially managed by a gastroenterologist) or as a surgical emergency (in which the diagnostic surprise leads additional difficulties to the tactical decision), when the speed imposed by the severity of the case can lead to inadequate strategies, with possibly critical consequences.

METHOD

With such a motivation, and having available experience limited by the small number of cases (described by all medical teams concerned with this pathology), the revision of the literature with the update of management landmarks from the surgical perspective of the pathology appears as justified by this article.

RESULTS

If the diagnosis of megacolon is made relatively easily by imaging the colorectal dilation (which is associated with initial and/or consecutive clinical aspects), the establishing of the diagnosis of idiopathic megacolon is based in practice almost exclusively on a principle of exclusion, and after evaluating the absence of some known causes that can lead to the occurrence of these anatomic and clinical changes, mimetically, clinically, and paraclinically, with IM (intramural aganglionosis, distal obstructions, intoxications, etc.). If the etiopathogenic theories, based on an increase in the performance of the arsenal of investigations of the disease, have registered a continuous improvement and an increase of objectivity, unfortunately, the curative surgical treatment options still revolve around the same resection techniques. Moreover, the possibility of developing a form of etiopathogenic treatment seems as remote as ever.

A neural crest cell isotropic-to-nematic phase transition in the developing mammalian gut

While the colonization of the embryonic gut by neural crest cells has been the subject of intense scrutiny over the past decades, we are only starting to grasp the morphogenetic transformations of the enteric nervous system happening in the fetal stage. Here, we show that enteric neural crest cell transit during fetal development from an isotropic cell network to a square grid comprised of circumferentially-oriented cell bodies and longitudinally-extending interganglionic fibers. We present ex-vivo dynamic time-lapse imaging of this isotropic-to-nematic phase transition and show that it occurs concomitantly with circular smooth muscle differentiation in all regions of the gastrointestinal tract. Using conditional mutant embryos with enteric neural crest cells depleted of β1-integrins, we show that cell-extracellular matrix anchorage is necessary for ganglia to properly reorient. We demonstrate by whole mount second harmonic generation imaging that fibrous, circularly-spun collagen I fibers are in direct contact with neural crest cells during the orientation transition, providing an ideal orientation template. We conclude that smooth-muscle associated extracellular matrix drives a critical reorientation transition of the enteric nervous system in the mammalian fetus.

Association Analysis of SLC6A20 Polymorphisms With Hirschsprung Disease

PURPOSE

Hirschsprung disease (HSCR) is a congenital and heterogeneous disorder, which is caused by no neuronal ganglion cells in part or all of distal gastrointestinal tract. Recently, our genome-wide association study has identified solute carrier family 6, proline IMINO transporter, member 20 (SLC6A20) as one of the potential risk factors for HSCR development. This study performed a replication study for the association of SLC6A20 polymorphisms with HSCR and an extended analysis to investigate further associations for subgroups and haplotypes.

METHODS

For the replication study, a total of 40 single nucleotide polymorphisms (SNPs) of SLC6A20 were genotyped in 187 HSCR subjects composed of 121 short-segment HSCR, 45 long-segment HSCR (L-HSCR), 21 total colonic aganglionosis, and 283 unaffected controls. Imputation was performed using genotype data from our genome-wide association study and this replication study.

RESULTS

Imputed meta-analysis revealed that 13 SLC6A20 SNPs (minimum P = 0.0002 at rs6770261) were significantly associated with HSCR even after correction for multiple comparisons using false discovery rate (FDR) (minimum PFDR =  .005). In further subgroup analysis, SLC6A20 polymorphisms appeared to have increased associations with L-HSCR. Moreover, haplotype analysis also showed significant associations between 2 haplotypes (BL3_ht2 and BL4_ht2) and HSCR susceptibility (PFDR <  .05).

CONCLUSIONS

Although further replications and functional evaluations are required, our results suggest that SLC6A20 may have roles in HSCR development and in the extent of aganglionic segment during enteric nervous system development.

The pathogenesis of idiopathic megacolon

BACKGROUND

Even today, the pathogenesis of idiopathic megacolon is still a subject of controversy. Anomalies of the gastrointestinal autonomous nervous system or of the smooth muscle of the muscularis propria are being considered.

METHODS

Sixty-three idiopathic megacolon resections between 1997 and June 2004 were investigated. The native specimens were coiled caudo-cranially and cryostat-cut. Connective tissue was stained with picric acid/Sirius red after Delauney fixation. Immunohistochemistry was performed for collagen types I, II, III and IV, as well as smooth muscle actin, vimentin, desmin fibronectin and CD117 for interstitial cells of Cajal. The enteric nervous system was examined by enzyme histochemistry for acetylcholine-esterase, lactate dehydrogenase, succinic dehydrogenase and nitroxide synthase.

RESULTS

Histologically, idiopathic megacolon was characterized by a total atrophy of the collagenous tendinous connective tissue membrane of the myenteric plexus and the tendinous collagen fibre net of the muscularis propria. Immunohistochemically, mainly collagen type III was missing in the muscularis propria. Interestingly, the incidence of idiopathic megacolon in those of the female sex was seven times more frequent than in the male sex. The myenteric plexus was normal in the majority of patients. Interstitial cells of Cajal, collagen II and IV, as well as smooth muscle actin, desmin and fibronectin showed no consistent alteration.

CONCLUSION

A normally structured tendinous fibre net of muscularis propria is an essential prerequisite for effective gut peristalsis. Atrophy of the tendinous fibre net abolishes peristalsis and allows for unlimited distension of the colon. A diagnosis of idiopathic megacolon can reliably be made on a collagen stain. The normal findings of myenteric plexus support the hypothesis that a primary metabolic defect of muscularis propria may be the underlying cause of idiopathic megacolon.

Vesicle-associated protein-A is differentially expressed during intestinal smooth muscle cell differentiation

Gastrointestinal (GI) smooth muscle diseases represent a major health concern affecting in excess of 2 million people each year. Little is currently known regarding the molecular mechanisms controlling either normal or pathogenic GI smooth muscle development. In an effort to identify the specific gene products responsible for modulating GI smooth muscle cell (SMC) differentiation, we performed differential display on distinct intestinal SMC (ISMC) phenotypes. This analysis identified over 40 unique transcripts that appeared to be differentially expressed in distinct SMC phenotypes. One such transcript that appeared to be preferentially expressed in immature smooth muscle myocytes was identified as vesicle-associated membrane protein, associated protein A (VAP-A). Northern blot analysis confirmed that VAP-A was expressed threefold higher in immature smooth muscle myocytes when compared with both smooth muscle myoblasts and mature smooth muscle myocytes. VAP-A mRNA was differentially expressed during normal rat development and showed peak levels of expression in the intestine during late embryogenesis and early neonatal development. These observations provide the first evidence that VAP-A-mediated membrane trafficking may play an important role in modulating ISMC differentiation.

Differential binding of an SRF/NK-2/MEF2 transcription factor complex in normal versus neoplastic smooth muscle tissues

The malignant potential of smooth muscle tumors correlates strongly with the disappearance of gamma-smooth muscle isoactin, a lineage-specific marker of smooth muscle development. In this paper, we identify a 36-base pair regulatory motif containing an AT-rich domain, CArG box, and a non-canonical NK-2 homeodomain-binding site that has the capacity to regulate smooth muscle-specific gene expression in cultured intestinal smooth muscle cells. Serum-response factor associates with an NK-2 transcription factor via protein-protein interactions and binds to the core CArG box element. Our studies suggest that the NK-2 transcription factor that associates with serum-response factor during smooth muscle differentiation is Nkx2-3. Myocyte-specific enhancer factor 2 binding to this regulatory complex was also observed but limited to uterine smooth muscle tissues. Smooth muscle neoplasms displayed altered transcription factor binding when compared with normal myometrium. Differential nuclear accessibility of serum-response factor protein during smooth muscle differentiation and neoplastic transformation was also observed. Thus, we have identified a unique regulatory complex whose differential binding properties and nuclear accessibility are associated with modulating gamma-smooth muscle isoactin-specific gene expression in both normal and neoplastic tissues.

Mechanical stretch modulates TGF-beta1 and alpha1(I) collagen expression in fetal human intestinal smooth muscle cells

Intestinal muscle undergoes stretch intermittently during peristalsis and persistently proximal to obstruction. The influence of this pervasive biomechanical force on developing smooth muscle cell function remains unknown. We adapted a novel in vitro system to study whether stretch modulates transforming growth factor-beta1 (TGF-beta1) and type I collagen protein and component alpha1 chain [alpha1(I) collagen] expression in fetal human intestinal smooth muscle cells. Primary confluent cells at 20-wk gestation, cultured on flexible silicone membranes, were subjected to two brief stretches or to 18 h tonic stretch. Nonstretched cultures served as controls. TGF-beta1 protein was measured by ELISA and type I collagen protein was assayed by Western blot. TGF-beta1 and alpha1(I) collagen mRNA abundance was determined by Northern blot analysis, quantitated by phosphorimaging, and normalized to 18S rRNA. Transcription was examined by nuclear run-on assay. Tonic stretch increased TGF-beta1 protein 40%, type I collagen protein 100%, TGF-beta1 mRNA content 2.16-fold, and alpha1(I) collagen mRNA 3.80-fold and enhanced transcription of TGF-beta1 and alpha1(I) collagen by 3.1- and 4.25-fold, respectively. Brief stretch stimulated a 50% increase in TGF-beta1 mRNA content but no change in alpha1(I) collagen. Neutralizing anti-TGF-beta1 ablated stretch-mediated effects on alpha1(I) collagen. Therefore, stretch upregulates transcription for TGF-beta1, which stimulates alpha1(I) collagen gene expression in smooth muscle from developing gut.

cFKBP/SMAP; a novel molecule involved in the regulation of smooth muscle differentiation

During embryogenesis, smooth muscle cells of the gut differentiate from mesenchymal cells derived from splanchnic mesoderm. We have isolated a gene involved in the differentiation of smooth muscle cells in the gut using differential display between the chicken proventriculus in which the smooth muscle layer develops poorly and the gizzard in which smooth muscles develop abundantly. The protein encoded by this gene showed highest similarity to mouse FK506 binding protein, FKBP65, and from the function of this protein it was designated chicken FKBP/smooth muscle activating protein (cFKBP/SMAP). cFKBP/SMAP was first expressed in smooth muscle precursor cells of the gut and, after smooth muscles differentiate, expression was restricted to smooth muscle cells. In organ culture of the gizzard, the differentiation of smooth muscle cells was inhibited by the addition of FK506, the inhibitor of FKBPs. Moreover, overexpression of cFKBP/SMAP in lung and gizzard mesenchymal cells induced smooth muscle differentiation. In addition, cFKBP/SMAP-induced smooth muscle differentiation was inhibited by FK506. We postulate therefore that cFKBP/SMAP plays a crucial role in smooth muscle differentiation in the gut and provides a powerful tool to study smooth muscle differentiation mechanisms, which have been poorly analyzed so far.

Identification of distinct molecular phenotypes in cultured gastrointestinal smooth muscle cells

BACKGROUND & AIMS

Cultured gastrointestinal smooth muscle cells have been shown to dedifferentiate and reinitiate their myogenic program in vitro. The aim of this study was to determine whether the cellular phenotypes observed in vitro were similar to those previously characterized in vivo.

METHODS

Differential isoactin expression was examined in primary cultures of intestinal smooth muscle cells (ISMCs) by Northern blot and immunohistochemical analysis. Cellular phenotype was determined for cultured ISMCs grown at high density, at low density, in the presence and absence of serum supplementation, and on several distinct substrates including collagen type IV, laminin, fibronectin, and plastic.

RESULTS

The unique patterns of isoactin protein and gene expression observed in cultured ISMCs indicate that distinct cellular phenotypes were present in vitro. The production and maintenance of these distinct smooth muscle cell phenotypes was dependent on cell density, serum supplementation, and substrate used.

CONCLUSIONS

Cultured ISMCs appear to recapitulate a portion of their in vivo myogenic program in vitro, providing a unique opportunity for the molecular mechanisms controlling gastrointestinal smooth muscle myogenesis and pathogenesis to begin to be identified.

Microtubule disruption stimulates system A transport in cultured vascular smooth muscle cells

This study has focused on the possible influence of microtubules for the regulation of Na(+)-dependent system A neutral amino acid transport in A10 cells, a cultured cell line derived from rat aortic vascular smooth muscle. When microtubules were disrupted by incubating cells for 5 h in serum-free medium containing colchicine, nocodazole, or vinblastine, there was a twofold increase in system A transport (Vmax change). The dose for the disruption of microtubules by colchicine was similar to the dose required for the stimulation of system A. The time course showed that system A stimulation did not occur until widespread disruption of microtubules was established. The stimulation was specific for system A; there were no changes in glucose transport and Na(+)-dependent transport of phosphate and glutamate. Serum refeeding of quiescent cells from 2 days of serum starvation led to stimulation of system A, glucose, and phosphate transport. However, only system A was activated when colchicine was added to the serum-free medium. Addition of colchicine during serum refeeding had no additive effect for the stimulation of system A. The stimulation by both colchicine and serum was blocked by cycloheximide and actinomycin D. These findings suggest that microtubule disruption may activate system A gene expression.

Etiology of intestinal damage in gastroschisis. III: Morphometric analysis of the smooth muscle and submucosa

The response of intestinal smooth muscle to injury may explain some of the motility derangement observed in infants with gastroschisis. An experimental model of gastroschisis was created and a detailed analysis of the intestinal muscle layer was undertaken to study this response. An abdominal wall defect and evisceration of the bowel were carried out in fetal lambs at 80 days' gestation (full term, 145 days), with delivery at 100 days or 135 days. Smooth muscle cell size and number were determined by detailed morphometric analysis, proliferative rate was determined using proliferating cell nuclear antigen staining, and collagen content was determined by morphometry after Verhoeff van Gieson staining. Compared with controls, there was a significant increase in cell number (hyperplasia) in the gastroschisis animals at 100 days and an increase in size (hypertrophy) at 135 days. The proliferation rate of smooth muscle was significantly lower and the submucosal collagen thickness was significantly greater in the gastroschisis animals during both periods. These data suggest that gastroschisis is characterised by initial hyperplasia, with subsequent diminution in smooth muscle proliferation. The hypertrophy may reflect a response to injury in which cell growth instead of proliferation occurs. The persistent elevation in collagen throughout gestation in animals with gastroschisis may be a reflection of this hyperplastic response in the smooth muscle cells and an important factor in the bowel-wall thickening. This deranged pattern of growth may lead to the clinical problems observed in human infants with this disease.

Scar formation in the fetal alimentary tract

The aim of this study was to determine whether the fetal alimentary tract shares the unique scarless healing properties of fetal skin. Full-thickness incisional gastric wounds were created and sutured closed in fetal lambs at 60, 75, and 120 days' gestation (full term, 145 days), and in adult control sheep. At the time of harvest, 14 days postwounding, dense fibrous adhesions were found intraperitoneally in all fetal and adult animals. Histologically, all fetal and adult gastric wounds healed with pronounced scar formation. In contrast to the adult wound, there was no significant inflammatory response in the fetal wounds. Because scar formed in the absence of inflammation in fetal gastric wounds, there is no obvious relation between scarring and the inflammatory response at this location. This study shows that not all fetal tissues exhibit scarless repair properties.