Mark Kidd

The guanylate cyclase-C signaling pathway is down-regulated in inflammatory bowel disease

Abstract Objective. Activation of membrane receptor guanylate cyclase-C (GC-C) is implicated in gastrointestinal fluid and electrolyte balance, preservation of intestinal barrier integrity, anti-trophic effects and inhibition of pain sensation. To evaluate GC-C signaling, we examined the regulation of GC-C (GUCY2C/Gucy2c) and its endogenous ligands guanylin (GN/GUCA2A/Guca2a) and uroguanylin (UGN/GUCA2B/Guca2b) in colonic Crohn’s disease (CD), ulcerative colitis (UC) and in rats with 2,4,6-Trinitrobenzene sulphonic acid (TNBS) colitis. Correlation analyses between expression of GUCA2A and GUCY2C and expression of inflammatory cytokines (IL1A, IL1B, TNFA and IFNG) were conducted. Additionally, expression of transcription factors for GUCA2A and GUCY2C, and the GC-C signaling pathway, were examined. Material and methods. Biopsies from active UC/CD, un-inflamed UC/CD and healthy controls, and inflamed and healthy rat colon were investigated with gene expression microarray, immunohistochemistry (IHC) and in situ hybridization (ISH). Results. GUCA2A/Guca2a, GUCA2B, GUCY2C/Gucy2c, transcription factors, as well as several cyclic guanosine-3′,5′-monophosphate downstream mediators were all significantly down-regulated in both inflamed colonic inflammatory bowel disease (IBD) mucosa and TNBS colitis. Expression of GUCA2A and GUCY2C negatively correlated to expression of inflammatory cytokines. IHC and ISH confirmed microarray results for GUCA2A/Guca2a and GUCY2C/Gucy2c in inflamed samples. We identified a highly significant positive correlation between the expression of the transcription factor caudal type homeobox 2 (CDX2) and the expression of the downstream target gene GUCY2C. Conclusions. GUCA2A, GUCA2B and GUCY2C as well as several steps of the GC-C signaling pathway are down-regulated in IBD. This may have implications in IBD pathogenesis.

Cellular localization of guanylin and uroguanylin mRNAs in human and rat duodenal and colonic mucosa.

Guanylin (GUCA2A/Guca2a/GN) and uroguanylin (GUCA2B/Guca2b/UGN) are expressed in the gastrointestinal tract and have been implicated in ion and fluid homeostasis, satiety, abdominal pain, growth and intestinal barrier integrity. Their cellular sources are debated and include goblet cells, entero-/colonocytes, enteroendocrine (EE) cells and tuft cells. We therefore investigated the cellular sources of GN and UGN mRNAs in human and rat duodenal and colonic epithelium with in situ hybridization (ISH) to determine co-expression with Chromogranin A (CHGA/Chga/CgA; enterochromaffin [EC] cells), defensin alpha 6 (DEFA6/Defa6; Paneth cells), mucin 2 (MUC2/Muc2; goblet cells) and selected tuft cell markers. GUCA2A/Guca2a expression was localized to goblet cells and colonocytes in human and rat colon. In human duodenum, GUCA2A was expressed in Paneth cells and was scarce in villous epithelial cells. In rat duodenum, Guca2a was only localized to goblet cells. Guca2b was focally expressed in rat colon. In human and rat duodenum and in human colon, GUCA2B/Guca2b was expressed in dispersed solitary epithelial cells, some with a tuft cell-like appearance. Neither GUCA2A nor GUCA2B were co-expressed with CHGA in human duodenal cells. Consequently, EC cells are probably not the major source of human GN or UGN but other EE cells as a source of GN or UGN are not entirely excluded. No convincing overlap with tuft cell markers was found. For the first time, we demonstrate the cellular expression of GUCA2B in human duodenum. The specific cellular distribution of both GN and UGN differs between duodenum and colon and between human and rat intestines.

The Molecular Biology of NET: Current Status and Evaluation of Biomarkers for Prediction and Prognosis

Neuroendocrine neoplasms (NEN) represent a heterogeneous neoplasia that are ubiquitous in location, exhibit protean symptomatology, and have ill-defined pathobiology. Clinical challenges include but are not limited to the general inability to establish an early diagnosis as well as the lack of a predictably effective management strategy. While clinical guidelines are useful and serve as a template for consensus-based thought, there is a paucity of scientific and mechanistic data necessary to accurately guide optimal management.

Neuroendocrine Gene Transcripts: The Role of Molecular Biomarkers in Diagnosis and Management

Biomarkers as an entity broadly describe tools and technologies that can facilitate the prediction, cause, diagnosis, progression, regression, or outcome of treatment of disease. Their identification and measurement are used to evaluate and examine a number of processes including normal biological functions, pathological events, or pharmacologic responses to a therapeutic intervention. In general, biological markers (biomarkers) are considered “cellular, biochemical or molecular alterations that are measurable in biological media such as human tissues, cells, or fluids” [1]. Although the majority of previous biomarkers have assessed cell surface or secreted proteins, the current focus has been on the identification of “candidate” biomarkers expressed in the nucleus or cytoplasm. At present, there is limited data on this group, and not all of the putative markers are clinical accessible.

Neoplastic lesions of endocrine cells in the gastrointestinal tract: ten evolving principles as a basis for clinical understanding

Timely and appropriate diagnosis and treatment of patients with gastroentero- pancreatic neuroendocrine neoplasms is a difficult clinical endeavor. The field is particularly dynamic, not only in terms of expanding therapeutic options, but in the classifications and bio - logical principles that underpin good decision-making. Acknowledging the confusion created by past changes and the inevitability of future development, we combine our clinical experience with a review of the literature to frame the current understanding of gastroenteropancreatic neuroendocrine neoplasms in terms of a set of principles that have stabilized in the midst of this change. Firstly, we present five principles that guide classification of neuroendocrine neoplasms; specifically principles of prognostic classification, mechanisms of tumorigenesis, undiagnosed disease burden, clues regarding genetic etiology, and typical clinical presentation. Secondly, we offer five clinical principles upon which to build a therapeutic strategy. Specifically, these treatment principles include the separation of options by tumor cell differentiation, and the site of the primary lesion in well differentiated tumors. Chromogranin A is a moderately useful biomarker. Treatment should only be considered by clinicians in a multidisciplinary team, and in the face of multiple potential therapeutic options without a supporting evidence base, clinical trial enrolment remains imperative. Therefore, we provide a current synopsis of classification of gastroenteropancreatic neuroendocrine neoplasms, and their etiology, clinical presentation, and management in a novel framework of ten relatively stable principles.