Abnormal expression and distribution of nidogen in Hirschsprung's disease

Persistent bowel dysfunction after surgery for Hirschsprung’s disease: A neuropathological perspective

Hirschsprung’s disease (HD) is a congenital disorder, characterized by aganglionosis in the distal part of the gastrointestinal tract. Despite complete surgical resection of the aganglionic segment, both constipation and fecal incontinence persist in a considerable number of patients with limited treatment options. There is growing evidence for structural abnormalities in the ganglionic bowel proximal to the aganglionosis in both humans and animals with HD, which may play a role in persistent bowel dysfunction. These abnormalities include: (1) Histopathological abnormalities of enteric neural cells; (2) Imbalanced expression of neurotransmitters and neuroproteins; (3) Abnormal expression of enteric pacemaker cells; (4) Abnormalities of smooth muscle cells; and (5) Abnormalities within the extracellular matrix. Hence, a better understanding of these previously unrecognized neuropathological abnormalities may improve follow-up and treatment in patients with HD suffering from persistent bowel dysfunction following surgical correction. In the long term, further combination of clinical and neuropathological data will hopefully enable a translational step towards more individual treatment for HD.

The corneal epithelial basement membrane: structure, function, and disease

The corneal epithelial basement membrane (BM) is positioned between basal epithelial cells and the stroma. This highly specialized extracellular matrix functions not only to anchor epithelial cells to the stroma and provide scaffolding during embryonic development but also during migration, differentiation, and maintenance of the differentiated epithelial phenotype. Basement membranes are composed of a diverse assemblage of extracellular molecules, some of which are likely specific to the tissue where they function; but in general they are composed of four primary components--collagens, laminins, heparan sulfate proteoglycans, and nidogens--in addition to other components such as thrombospondin-1, matrilin-2, and matrilin-4 and even fibronectin in some BM. Many studies have focused on characterizing BM due to their potential roles in normal tissue function and disease, and these structures have been well characterized in many tissues. Comparatively few studies, however, have focused on the function of the epithelial BM in corneal physiology. Since the normal corneal stroma is avascular and has relatively low keratocyte density, it is expected that the corneal BM would be different from the BM in other tissues. One function that appears critical in homeostasis and wound healing is the barrier function to penetration of cytokines from the epithelium to stroma (such as transforming growth factor β-1), and possibly from stroma to epithelium (such as keratinocyte growth factor). The corneal epithelial BM is also involved in many inherited and acquired corneal diseases. This review examines this structure in detail and discusses the importance of corneal epithelial BM in homeostasis, wound healing, and disease.

Neuroglial differentiation of adult enteric neuronal progenitor cells as a function of extracellular matrix composition

Enteric neuronal progenitor cells are neural crest-derived stem cells that can be isolated from fetal, post-natal and adult gut. Neural stem cell transplantation is an emerging therapeutic paradigm to replace dysfunctional or lost enteric neurons in several aganglionic disorders of the GI tract. The impetus to identify an appropriate microenvironment for enteric neuronal progenitor cells derives from the need to improve survival and phenotypic stability following implantation. Extracellular matrix composition can modulate stem cell fate and direct differentiation. Adult mammalian myenteric ganglia in vivo are surrounded by a matrix composed primarily of Collagen IV, Laminin and a Heparan sulfate proteoglycan. In these studies, adult mammalian enteric neuronal progenitor cells isolated from full thickness rabbit intestines were induced to differentiate when cultured on various combinations of neural ECM substrates. Neuronal and glial differentiation was studied as a function of ECM composition on coated glass coverslips. Poly-lysine coated coverslips (control) supported extensive glial differentiation but very minimal neuronal differentiation. Individual culture substrata (Laminin, Collagen I and Collagen IV) were conducive for both neuronal and glial differentiation. The addition of laminin or heparan sulfate to collagen substrates improved neuronal differentiation, significantly increased neurite lengths, branching and initiation of neuronal network formation. Glial differentiation was extensive on control poly lysine coated coverslips. Addition of laminin or heparan sulfate to composite collagen substrates significantly reduced glial immunofluorescence. Various neural ECM components were evaluated individually and in combination to study their effect of neuroglial differentiation of adult enteric neuronal progenitor cells. Our results indicate that specific ECM substrates that include type IV Collagen, laminin and heparan sulfate support and maintain neuronal and glial differentiation to different extents. Here, we identify a matrix composition optimized to tissue engineer transplantable innervated GI smooth muscle constructs to remedy aganglionic disorders.

Acetylcholinesterase in Hirschsprung's disease

The association between the congenital absence of colonic ganglion cells and an increased acetylcholinesterase (AChE) expression in the affected tissue is of diagnostic importance in Hirschsprung's disease (HSCR). Investigation of AChE's function in development may also help unravel some of the complex pathophysiology in HSCR. Normal nerves do not stain for AChE, but increased AChE expression is associated with the hypertrophied extrinsic nerve fibres of the aganglionic segment in HSCR. Although a high degree of histochemical diagnostic accuracy exists, results are not always uniform, and false positives and false negatives are reported. False negative results are primarily related to age, and an absence of AChE reaction does not exclude HSCR in neonates within the first 3 weeks after birth. AChE staining results may lack uniformity, resulting in a number of technical modifications that have been made to improve standardization of AChE staining. At least two distinct histological patterns are described, types A and B. The interpretation of increased AChE staining patterns in ganglionated bowel at the time of surgical pull-through remains a problem in patients with HSCR. The development of rapid staining techniques has helped to identify normal ganglionated bowel with greater certainty. The presence of fine AChE neurofibrils in the ganglionated segment has contributed to the debate surrounding intestinal neuronal dysplasia. Quantitative assay of cholinesterase activity confirms the pattern of histochemical staining. AChE is particularly increased in relation to butrylcholinesterase, with one molecular form, the G4 tetrameric form, predominating. It is likely that the raised levels of AChE in aganglionic tissue are the transcriptional consequence of the abnormalities in signalling molecules that characterize HSCR. Evidence suggests that this AChE is functioning in a nonenzymatic capacity to promote cell adhesion and differentiation and that the hypertrophied nerves and neurofibrils may be the result of this increased AChE expression.

Development of the enteric nervous system, smooth muscle and interstitial cells of Cajal in the human gastrointestinal tract

The generation of functional neuromuscular activity within the pre-natal gastrointestinal tract requires the coordinated development of enteric neurons and glial cells, concentric layers of smooth muscle and interstitial cells of Cajal (ICC). We investigated the genesis of these different cell types in human embryonic and fetal gut material ranging from weeks 4-14. Neural crest cells (NCC), labelled with antibodies against the neurotrophin receptor p75NTR, entered the foregut at week 4, and migrated rostrocaudally to reach the terminal hindgut by week 7. Initially, these cells were loosely distributed throughout the gut mesenchyme but later coalesced to form ganglia along a rostrocaudal gradient of maturation; the myenteric plexus developed primarily in the foregut, then in the midgut, and finally in the hindgut. The submucosal plexus formed approximately 2-3 weeks after the myenteric plexus, arising from cells that migrated centripetally through the circular muscle layer from the myenteric region. Smooth muscle differentiation, as evidenced by the expression of alpha-smooth muscle actin, followed NCC colonization of the gut within a few weeks. Gut smooth muscle also matured in a rostrocaudal direction, with a large band of alpha-smooth muscle actin being present in the oesophagus at week 8 and in the hindgut by week 11. Circular muscle developed prior to longitudinal muscle in the intestine and colon. ICC emerged from the developing gut mesenchyme at week 9 to surround and closely appose the myenteric ganglia by week 11. By week 14, the intestine was invested with neural cells, longitudinal, circular and muscularis mucosae muscle layers, and an ICC network, giving the fetal gut a mature appearance.