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Christopher R Erwin

Publications and source records attributed to Christopher R Erwin.

At least 19 recordsLinked to original sources
PubMed2006

Absent STAT-1 expression perturbs adaptation and apoptosis after massive intestinal resection.

BACKGROUND: We have previously established the significance of epidermal growth factor receptor (EGFR) activity and the cyclin-dependent kinase inhibitor p21waf1/cip1 (p21) for the adaptive response of the intestine to massive small bowel resection (SBR). In this study, we tested the role of the signal transducer and activator of transcription 1 (STAT-1) as this transcription factor is activated by the EGFR and known to induce p21 expression. METHODS: Control (n = 40; C57/Bl6) and STAT-1-null mice (n = 40) underwent 50% proximal SBR or sham operation. After 3 days, the remnant ileum was harvested and the villus and crypt morphology was measured along with changes in rates of enterocyte proliferation and apoptosis. RESULTS: The magnitude of resection-induced adaptation was greater in STAT-1-null animals as verified by taller villi and deeper crypts. The expected increase in enterocyte apoptosis did not occur after SBR in the background of STAT-1 deficiency. Western blotting revealed elevated expression of p21 protein in both STAT-1-null and controls after SBR. CONCLUSION: Increased p21 expression after SBR in the absence of STAT-1 suggests an alternate mechanism for resection-induced regulation of p21. Enhanced adaptation in STAT-1-null animals suggests that this transcription factor serves an inhibitor to the process of adaptation, perhaps via regulation of enterocyte apoptosis.

Adaptation, Physiological↗
PubMed2006

Combined pharmacotherapy that increases proliferation and decreases apoptosis optimally enhances intestinal adaptation.

BACKGROUND: Adaptation after massive small bowel resection (SBR) is associated with increased rates of enterocyte proliferation (P) and apoptosis (A). In the present study, we sought to determine the effect of dual therapy designed to increase P and simultaneously reduce A. METHODS: C57Bl/6 mice underwent a 50% small bowel resection (SBR) or sham operation, and then received an inhibitor of apoptosis (pan-caspase inhibitor), a stimulus for proliferation (epidermal growth factor; EGF), a combination, or vehicle control. After 3 days, adaptive morphology (villus height, crypt depth) and rates of enterocyte turnover (proliferation and apoptosis) were measured in the remnant ileum. RESULTS: Adaptation in controls and treated with the inhibitor was similar. EGF-treated mice demonstrated an even greater adaptive response. Combined therapy with the inhibitor and EGF resulted in maximal adaptation as gauged by the greatest increases in villus height and crypt depth and ratio of rates of P to A. CONCLUSION: The capacity for adaptation following massive SBR is maintained via tight regulation of cell production and death. Pharmacologic intervention directed at increasing enterocyte proliferation while simultaneously decreasing apoptosis augments adaptation greater than either intervention alone and may provide a useful strategy to clinically amplify adaptation.

Adaptation, Physiological↗
PubMed2006

Epidermal growth factor receptor signaling regulates Bax and Bcl-w expression and apoptotic responses during intestinal adaptation in mice.

BACKGROUND & AIMS: Normal intestinal adaptation to massive small-bowel resection requires intact epidermal growth factor receptor signaling and consists of increased enterocyte proliferation and apoptosis. Although emphasis has been placed on understanding the regulation of proliferation, few studies have evaluated the mechanism and contribution of apoptosis to the adaptation response. We sought to test the hypothesis that epidermal growth factor receptor signaling regulates specific Bcl-2 family members (Bax and Bcl-w) to direct apoptosis and adaptation after massive small-bowel resection. METHODS: Laser capture microdissection microscopy permitted measurement of Bax and Bcl-w messenger RNA expression in crypt and villus enterocytes in control conditions and under epidermal growth factor receptor-inhibited (waved-2 mice) or stimulated (epidermal growth factor transgenic mice) conditions after a 50% small-bowel resection or sham operation. Resection-induced adaptation was then studied in Bax-null and Bcl-w-null mice under control circumstances and after epidermal growth factor receptor stimulation. RESULTS: When compared with Bcl-w, the most significant expression changes were observed with Bax and took place within crypt enterocytes. Epidermal growth factor receptor stimulation resulted in a decreased ratio of Bax to Bcl-w expression and decreased rates of apoptosis. Bax-null mice had no apoptosis response to small-bowel resection and displayed an amplified adaptation response to the administration of epidermal growth factor. Bcl-w-null mice had poor survival and impaired adaptation to small-bowel resection, an effect that was rescued by crossbreeding these mice with epidermal growth factor transgenic mice. CONCLUSIONS: The crypt expression of Bax and Bcl-w is influenced by epidermal growth factor receptor signaling and is key for the regulation of apoptosis. Epidermal growth factor receptor stimulation, coupled with apoptosis inhibition, may provide a novel strategy to amplify adaptation responses in patients after massive intestinal loss.

Animals↗
PubMed2006

Developmental characteristics of adapting mouse small intestine crypt cells.

BACKGROUND & AIMS: Following massive small bowel resection (SBR), the remnant intestine undergoes an adaptive process characterized by increases in a number of physiologic and morphologic parameters. These changes are the result of a stimulus that increases crypt cell mitosis and augments cellular progression along the villus axis. To better define this process, we identified patterns of gene expression specifically within adapting intestinal crypt cells following SBR. METHODS: Laser capture microdissection was used to isolate mouse intestinal crypt cells following SBR or sham operation. Multiple biological and technical complementary DNA microarray replicates allowed rigorous statistical analyses for identification of important expression profiles. Major groups of genes were classified as to site of action, functional pathway, and possible regulatory groups. RESULTS: A total of 300 genes differentially expressed at significant levels within adapting crypt enterocytes were analyzed. Comparison of this list of differentially expressed adapting crypt cell genes with a generalized mouse gene expression database (from 82 developing and adult mouse tissues) showed the greatest overlap with developing and immature intestinal tissues. We identified prominent groups of genes involved with cell growth, signal transduction, and nucleic acid binding. Genes not previously shown to be involved with adaptation or development and maturation were identified. CONCLUSIONS: Identification of similar genes coordinately regulated during both adaptation and development, processes that share key morphologic features, provides a basis for new mechanistic insights into these shared characteristics.

Adaptation, Physiological↗
PubMed2006

Critical roles for EGF receptor signaling during resection-induced intestinal adaptation.

The adaptation response of the remnant gut to massive intestinal resection represents a mitogenic signal involving all bowel wall layers. In the mucosa, this response results in taller villi, deeper crypts, and enhanced enterocyte turnover as gauged by greater rates of both proliferation and apoptosis. Although the exact mechanisms and mediators of this important compensatory response remain incompletely understood, work from this laboratory over the past decade has illuminated a crucial role for intact receptor signaling for a robust response. Using a murine model for intestinal resection, transgenic, null and mutant mouse strains have provided unique experimental paradigms to dissect molecular mechanisms for epidermal growth factor (EGF) receptor-directed influence on adaptation. Stimulation of this receptor is linked with a magnified adaptation response, whereas attenuation of the activity of this receptor is associated with impaired adaptation. EGF receptor activation and expression are both elevated in enterocytes after resection, and salivary levels of EGF-the major ligand for the EGF receptor-are increased. In addition to stimulation of enterocyte proliferation, EGF receptor signaling prevents the typical increase in rates of enterocyte apoptosis, probably by affecting the ratio of expression of both pro- and anti-apoptotic Bcl-2 family members. The key to optimizing care for patients with short gut syndrome will necessarily follow a thorough understanding of intestinal adaptation responses.

Adaptation, Physiological↗
PubMed2005

Roles for p21waf1/cip1 and p27kip1 during the adaptation response to massive intestinal resection.

The magnitude of gut adaptation is a decisive factor in determining whether patients are able to live independent of parenteral nutrition after massive small bowel loss. We previously established that the cyclin-dependent kinase inhibitor (CDKI) p21(waf1/cip1) is necessary for enterocyte proliferation and a normal adaptation response. In the present study, we have further elucidated the role of this CDKI in the context of p27(kip1), another member of the Cip/Kip CDKI family. Small bowel resections (SBRs) or sham operations were performed in control (C57/BL6), p21(waf1/cip1)-null, p27(kip1)-null, and p21(waf1/cip1)/p27(kip1) double-null mice. Morphological (villus height/crypt depth) alterations in the mucosa, the kinetics of enterocyte turnover (rates of enterocyte proliferation and apoptosis), and the protein expression of various cell cycle-regulatory proteins were recorded at various postoperative times. Enterocyte compartment-specific mRNA expression was investigated using laser capture microdissection. Resection-induced adaptation in control mice coincided with increased protein expression of p21(waf1/cip1) and decreased p27(kip1) within 3 days postoperatively. Identical changes in mRNA expression were detected in crypt but not in villus enterocytes. Adaptation occurred normally in control and p27(kip1)-null mice; however, mice deficient in both p21(waf1/cip1) and p27(kip1) failed to increase baseline rates of enterocyte proliferation and adaptation. The expression of p21(waf1/cip1) protein and mRNA in the proliferative crypt compartment is necessary for resection-induced enterocyte proliferation and adaptation. The finding that deficient expression of p27(kip1) does not affect adaptation suggests that these similar CDKI family members display distinctive cellular functions during the complex process of intestinal adaptation.

Adaptation, Physiological↗
PubMed2005

Haploinsufficiency of Atp2a2, encoding the sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2 Ca2+ pump, predisposes mice to squamous cell tumors via a novel mode of cancer susceptibility.

A null mutation in one copy of the Atp2a2 or ATP2A2 gene, encoding sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2 (SERCA2), leads to squamous cell tumors in mice and to Darier disease in humans, a skin disorder that also involves keratinocytes. Here, we examined the time course and genetic mechanisms of tumor development in the mutant animals. Atp2a2+/- mice overexpressed keratins associated with keratinocyte hyperactivation in normal forestomachs as early as 2 months of age. By the age of 5 to 7 months, 22% of mutants had developed papillomas of the forestomach, and 89% of mutants older than 14 months had developed squamous cell papillomas and/or carcinomas, with a preponderance of the latter. Tumors occurred in regions that had keratinized epithelium and were subjected to repeated mechanical irritation. The genetic mechanism of tumorigenesis did not involve loss of heterozygosity, as tumor cells analyzed by laser capture microdissection contained the wild-type Atp2a2 allele. Furthermore, immunoblot and immunohistochemical analysis showed that tumor keratinocytes expressed the SERCA2 protein. Mutations were not observed in the ras proto-oncogenes; however, expression of wild-type ras was up-regulated, with particularly high levels of K-ras. Loss of the p53 tumor suppressor gene occurred in a single massive tumor, whereas other tumors had increased levels of p53 protein but no mutations in the p53 gene. These findings show that SERCA2 haploinsufficiency predisposes mice to tumor development via a novel mode of cancer susceptibility involving a global change in the tumorigenic potential of keratinized epithelium in Atp2a2+/- mice.

Alleles↗
PubMed2005

Epidermal growth factor receptor signaling regulates goblet cell production after small bowel resection.

BACKGROUND/PURPOSE: Intestinal adaptation is a compensatory response to massive small bowel loss in which there are increased numbers of absorptive enterocytes. However, the generation of secretory epithelial cell subtypes in this process has not been investigated. The purpose of this study was to examine the adaptive changes of several small intestinal cell lineage changes in response to massive small bowel resection (SBR). METHODS: A 75% SBR or sham operation was performed on male Sprague-Dawley rats. On postoperative day 7, the remnant ileum was harvested and immunohistochemical staining for goblet, Paneth, and enteroendocrine cells was performed. Cell subtypes were evaluated as cells per micrometer of villus/crypt length and compared among operations. RESULTS: A significant increase in goblet cell density occurred after SBR. Intestinal resection did not alter the number of Paneth and enteroendocrine cells. In additional experiments, inhibition of epidermal growth factor receptor signaling was associated with a diminished goblet cell density. CONCLUSIONS: The adaptive response of the intestine to massive bowel loss results in an expansion of the goblet cell population in addition to greater numbers of absorptive enterocytes. Although the mechanism and purpose for selective expansion of these stem cell-derived lineages are not presently known, epidermal growth factor receptor signaling appears to be a common pathway.

Adaptation, Physiological↗
PubMed2005

Evidence for active Wnt signaling during postresection intestinal adaptation.

BACKGROUND: In the intestine, Wnt proteins are powerful regulators of cell proliferation, differentiation, and adhesion. Mutations of the adenomatous polyposis coli (APC) gene elevate nuclear beta-catenin and provoke intestinal tumor formation. We sought to determine whether Wnt signaling is involved in adaptive response to massive small bowel resection (SBR). METHODS: Male Min mice with a mutation of the APC gene and wild-type controls underwent a 50% proximal SBR or sham operation. After 3 days, villus height, crypt depth, and rates of proliferation and apoptosis were recorded in the remnant ileum. RESULTS: After SBR, villus height and enterocyte proliferation were significantly greater in the Min mice. Western blotting demonstrated resection-induced increases in beta-catenin, c-Myc, and E-cadherin after SBR, which was more pronounced in Min mice. CONCLUSIONS: Mutation of the APC gene and augmented Wnt signaling in the intestine results in an enhanced adaptive response to massive SBR. These data, for the first time, implicate an important role for Wnt signaling during the pathogenesis of resection-induced intestinal adaptation.

Animals↗
PubMed2005

Opposing roles for p21(waf1/cip1) and p27(kip1) in enterocyte differentiation, proliferation, and migration.

BACKGROUND: Originating from proliferating stem cells of the intestinal crypt, enterocytes differentiate as they migrate up the crypt-villus axis. A regulatory role of the cyclin-dependent kinase inhibitors p21(waf1/cip1) and p27(kip1) in these processes has been suggested by in vitro models. We sought to determine the effect of p21(waf1/cip1) and p27(kip1) deficiency on enterocyte differentiation, proliferation and migration. METHODS: Three strains of mice including control (C57Bl/6), p27(kip1)-null, and p21(waf1/cip1)-null were studied. Enterocyte differentiation was evaluated by immunostaining for intestinal alkaline phosphatase, by colorimetric assaying for intestinal alkaline phosphatase and sucrase enzyme activity, and by polymerase chain reaction for intestinal fatty acid-binding protein and villin-messenger RNA in enterocytes extracted by laser capture microdissection. Rates of enterocyte proliferation and migration were determined by 5-bromo 2-deoxyuridine immunostaining after a 50% small-bowel resection (SBR). RESULTS: Compared with controls, p27(kip1)-null mice demonstrated minimal differentiation but maintained a normal proliferative response to SBR. Contrarily, p21(waf1/cip1)-null mice demonstrated greater enterocyte differentiation without significant increases in enterocyte proliferation after SBR. CONCLUSIONS: These findings suggest that p21(waf1/cip1) and p27(kip1) have distinctive and opposing roles in the pathogenesis of enterocyte differentiation, proliferation, and migration.

Animals↗
PubMed2004

Smooth muscle overexpression of IGF-I induces a novel adaptive response to small bowel resection.

Prior studies of intestinal adaptation after massive small bowel resection (SBR) have focused on growth factors and their effects on amplification of the gut mucosa. Because adaptive changes have also been described in intestinal smooth muscle, we sought to determine the effect of targeted smooth muscle growth factor overexpression on resection-induced intestinal adaptation. Male transgenic mice with smooth muscle cell overexpression of insulin-like growth factor I (IGF-I) by virtue of an alpha-smooth muscle actin promoter were obtained. SMP8 IGF-I transgenic (IGF-I TG) and nontransgenic (NT) littermates underwent 50% proximal SBR or sham operation and were then killed after 3 or 28 days. NT mice showed the expected alterations in mucosal adaptive parameters after SBR, such as increased wet weight and villus height. The IGF-I TG mice had inherently taller villi, which did not increase significantly after SBR. In addition, IGF-I TG mice had a 50% postresection persistent increase in remnant intestinal length, which was associated with an early decline and later increase in relative mucosal surface area. These results indicate that growth factor overexpression within the muscularis layer of the bowel wall induces significant postresection adaptive intestinal lengthening and a unique mucosal response. IGF-I signaling within the muscle wall may play an important role in the pathogenesis of resection-induced adaptation.

Adaptation, Physiological↗
PubMed2004

Preventing enterocyte apoptosis after massive small bowel resection does not enhance adaptation of the intestinal mucosa.

BACKGROUND: After massive small bowel resection (SBR), increased rates of enterocyte apoptosis are observed in the remnant bowel via a mechanism requiring bax gene expression. This study tested the hypothesis that adaptive mucosal growth could be enhanced by the novel strategy of preventing postresection enterocyte apoptosis. METHODS: Male bax-null and corresponding wild-type (WT) mice underwent a 50% proximal SBR or sham operation (bowel transaction with reanastomosis alone). Mice were killed after a full adaptation interval of 1 month. Adaptation was measured in the remnant ileum as alterations in villus height, crypt depth, and wet weight. Rates of enterocyte proliferation were derived by immunostaining of crypt enterocytes for Ki-67 and apoptosis by the presence of apoptosis bodies. RESULTS: The expected increase in enterocyte apoptosis after SBR occurred in the WT mice but was unchanged in the bax-null mice. Despite the prevention of postresection apoptosis in the bax-null mice, all parameters of adaptation and proliferation increased equally after SBR in both groups of mice. CONCLUSIONS: Bax deficiency prevents the increase in enterocyte apoptosis that occurs after massive SBR throughout the entire adaptation period. Attenuation of postresection enterocyte apoptosis does not augment mucosal adaptation to massive intestinal loss.

Adaptation, Physiological↗
PubMed2004

Bax deficiency rescues resection-induced enterocyte apoptosis in mice with perturbed EGF receptor function.

BACKGROUND: Adaptation after massive smallbowel resection (SBR) is associated with increased cell turnover, increased rates of enterocyte proliferation, and apoptosis. Epidermal growth factor receptor (EGFR) inhibition attenuates adaptation and increases apoptosis. Intestinal levels of bax appear to correlate with EGFR signaling. This study tested the hypothesis that bax is required for the exaggerated postresection apoptosis induced by perturbed EGFR signaling. METHODS: Waved-2 mice with impaired EGFR signaling were crossbred with bax-null mice. Offspring were subjected to either 50% proximal SBR or sham operation (bowel transection and reanastomosis). After 7 days, parameters of adaptation (villus height, wet weight), proliferation (% Ki-67 immunostaining of crypt cells), and apoptosis (# apoptotic bodies per crypt) were recorded in the remnant ileum. RESULTS: Enterocyte apoptosis was increased in waved-2 mice and prevented in bax-null mice after SBR. The accelerated apoptosis in the waved-2 mice was rescued in the context of deficient bax expression. Other parameters of adaptation were restored in the bax-null/waved-2 mice. CONCLUSION: Bax is required for the induction of postresection enterocyte apoptosis. Defective EGFR signaling augments resection-induced enterocyte apoptosis via a mechanism that also requires bax expression. These data implicate a link between EGFR signaling and bax in the genesis of postresection apoptosis and adaptation.

Adaptation, Physiological↗
PubMed2003

Enterocyte apoptosis after enterectomy in mice is activated independent of the extrinsic death receptor pathway.

Intestinal adaptation following small bowel resection (SBR) is associated with greater rates of enterocyte apoptosis by unknown mechanism(s). Because postresection adaptation is associated with increased translocation of luminal bacteria, we sought to characterize the role for the extrinsic, death receptor pathway for the activation of enterocyte apoptosis after massive SBR. We first performed SBR or sham operations in mice, and the temporal expression of caspases 8, 9, and 3, death receptors tumor necrosis factor receptor-1 (TNFR1) and Fas and corresponding ligands (TNF and Fas ligand) was determined in the remnant intestine at various postoperative time points. Ileal TNFR1 and Fas expression were then measured after SBR in the setting of increased (waved-2 mice) or decreased (exogenous EGF administration) apoptosis. Finally, intestinal adaptation and apoptosis were recorded in the remnant ileum after SBR in TNFR1-null and Fas-null mice. The expression of death receptor family proteins and caspases demonstrated only modest changes after SBR and did not correlate with the histological appearance of apoptosis. In the setting of accelerated apoptosis, TNFR1 and Fas expression were paradoxically decreased. Apoptotic and adaptive responses were preserved in both TNFR1-null and Fas-null mice. These results suggest that the mechanism for increased enterocyte apoptosis following massive SBR does not appear to involve the extrinsic, death receptor-mediated pathway.

Animals↗
PubMed2003

A serum factor(s) after small bowel resection induces intestinal epithelial cell proliferation: effects of timing, site, and extent of resection.

BACKGROUND/PURPOSE: After small bowel resection (SBR), serum induces proliferation in rat intestinal epithelial cells (RIEC-6). This study was designed to elucidate the effects of postoperative time interval, site, and magnitude of SBR on RIEC-6 proliferation. METHODS: Serum was collected from rats at various times after a 75% mid-SBR or sham operation and added to RIEC-6 cells and growth determined over 5 days. In other experiments, cell growth was recorded in the presence of serum from rats after 25%, 50%, or 75% SBR, or after jejunal or ileal SBR. RESULTS: SBR serum enhanced RIEC-6 cell proliferation as early as 12 hours after resection. The extent of SBR directly correlated with the level of adaptation; however, the effects on cell growth by the serum were similar. SBR serum induced proliferation equally after either proximal or distal resection. CONCLUSIONS: Serum contains a factor that stimulates intestinal cell proliferation soon after SBR but independent of the degree or site of intestinal resection. Although humoral factor(s) play a role in the early induction of enterocyte proliferation after SBR, further modulation of adaptation to varied lengths or sites of intestinal resection are probably governed by mechanisms independent of factors that circulate in the serum.

Adaptation, Physiological↗
PubMed2003

EGF receptor signaling affects bcl-2 family gene expression and apoptosis after massive small bowel resection.

BACKGROUND: After massive small bowel resection (SBR), enterocyte apoptosis is elevated and inversely correlates with epidermal growth factor receptor (EGFR) signaling. The purpose of the current study was to determine whether EGFR manipulation affects the expression of specific bcl-2 family members. METHODS: A 50% proximal SBR or sham operation was performed in 3 groups of mice control, after exogenous EGF, or mutant mice with defective EGFR signaling (waved-2). Apoptotic index (no. of apoptotic bodies per crypt), and bax (pro-apoptosis) and bcl-w (anti-apoptosis) protein expression was measured in the remnant ileum after 12, 24, and 72 hours. RESULTS: Waved-2 mice with defective EGFR showed the greatest increase in apoptosis and altered the ratio of bax to bcl-w in favor of apoptosis after SBR. Conversely, EGF prevented the expected increase in apoptosis after SBR by shifting the ratio of bax to bcl-w in favor of cell survival. CONCLUSIONS: After massive small bowel resection, inhibition of the EGFR accelerates the rate of apoptosis and modifies the expression of specific bcl-2 family members to favor apoptosis. These results further support a specific mechanistic pathway for the regulation of enterocyte apoptosis after SBR via EGFR signaling.

Animals↗
PubMed2003

Characterization of small bowel resection and intestinal adaptation in germ-free rats.

BACKGROUND: After massive small bowel resection (SBR), the remnant bowel adapts by increasing enterocyte proliferation and apoptosis. The purpose of this study was to investigate the relevance of luminal bacteria on postresection intestinal cell turnover. METHODS: Male germ-free (GF) and normally colonized control rats underwent either a 75% mid-SBR or sham operation. In other experiments, normally colonized control rats were given antibiotics in the drinking water. After 7 days, the remnant ileum was harvested and adaptation verified by alterations in wet weight, crypt depth, and villus height. Proliferation and apoptosis were measured in crypts as the percent of crypt cells staining for Ki-67 or the number of apoptotic bodies per crypt. RESULTS: Both GF and control rats demonstrated significant increases in all adaptive parameters. Proliferation was increased after SBR in both groups, but significantly greater in the GF animals over control. This response could not be recapitulated after antibiotic treatment. Apoptosis increased equally after SBR in all groups. CONCLUSION: Resection-induced intestinal adaptation occurs normally in GF animals. Epithelial-microbial interactions are probably not involved in the activation of enterocyte apoptosis. The germ-free studies offer the possibility that luminal bacteria may attenuate the proliferative response of the enterocyte to massive small bowel resection.

Adaptation, Physiological↗