Lihua Sun

The protective effect of enteric glial cells on intestinal epithelial barrier function is enhanced by inhibiting inducible nitric oxide synthase activity under lipopolysaccharide stimulation

Enteric glial cells (EGC) play an essential role in maintaining the integrity of intestinal epithelial barrier (IEB). However, the mechanism of EGCs in the regulation of IEB functions under lipopolysaccharide (LPS) stimulation is unknown. To investigate the barrier-related role of EGCs in response to the LPS challenge, the coculture model of EGCs and intestinal epithelial cells (IEC) IEC-6 was established in vitro. Transepithelial resistance (TER) measurements showed that, LPS treatment significantly increased barrier permeability of IEC monolayer from the basolateral side (35.4±6.3 Ω/cm(2), p<0.05) but not the apical side (69.7±6.3 Ω/cm(2)) when compared with the control group (81.8±10.9 Ω/cm(2)). The assessment of intestinal epithelial integrity by TER reading and by measuring expression of tight junction protein revealed that, incubation with EGCs or EGC conditioned media significantly increased the TER of IEC monolayers under normal condition as well as the LPS stimulation, accompanied with upregulating zonula occludens-1 and occludin expression at mRNA and protein levels. Real-time quantitative polymerase chain reaction and nitric production assay demonstrated that LPS exposure elicited a maximally 13-fold increase of inducible nitric oxide synthase (iNOS) mRNA expression and 10-fold increase of nitric oxide production of EGCs. After being pretreated with the selective iNOS inhibitor 1400 W, EGCs significantly increased the TER of IEC monolayers against the disruption effect of LPS (p<0.05). These findings suggest that EGCs play an important role in maintaining the IEB function in response to the LPS stimulation. The protective effect of EGCs on IEB functions could be enhanced by inhibiting the increase of iNOS activity induced by LPS.

Angiotensin II induces apoptosis in intestinal epithelial cells through the AT2 receptor, GATA-6 and the Bax pathway

Angiotensin II (Ang II) has been shown to play an important role in cell apoptosis. However, the mechanisms of Ang-II-induced apoptosis in intestinal epithelial cells are not fully understood. GATA-6 is a zinc finger transcription factor expressed in the colorectal epithelium, which directs cell proliferation, differentiation and apoptosis. In the present study we investigated the underlying mechanism of which GATA-6 affects Ang-II induced apoptosis in intestinal epithelial cells. The in vitro intestinal epithelial cell apoptosis model was established by co-culturing Caco-2 cells with Ang II. Pretreatment with Angiotensin type 2 (AT2) receptor antagonist, PD123319, significantly reduced the expression of Bax and prevented the Caco-2 cells apoptosis induced by Ang II. In addition, Ang II up-regulated the expression of GATA-6. Interestingly, GATA-6 short hairpin RNA prevented Ang II-induced intestinal epithelial cells apoptosis and reduced the expression of Bax, but not Bcl-2. Taken together, the present study suggests that Angiotensin II promotes apoptosis in intestinal epithelial cells through GATA-6 and the Bax pathway in an AT2 receptor-dependent manner.

Keratinocyte Growth Factor Improves Epithelial Structure and Function in a Mouse Model of Intestinal Ischemia/Reperfusion

Background Intestinal ischemia/reperfusion (I/R) induces the desquamation of the intestinal epithelium, increases the intestinal permeability, and in patients often causes fatal conditions including sepsis and multiple organ failure. Keratinocyte growth factor (KGF) increases intestinal growth, although little is known about KGF activity on intestinal function after intestinal I/R. We hypothesized that KGF administration would improve the intestinal function in a mouse model of intestinal I/R. Methods Adult C57BL/6J mice were randomized to three groups: Sham, I/R group and I/R+KGF group. Mice were killed on day 5, and the small bowel was harvested for histology, wet weight, RNA and protein content analysis. Epithelial cell (EC) proliferation was detected by immunohistochemistry for PCNA, and apoptosis was determined by TUNEL staining. The expressions of Claudin-1 and ZO-1 were detected by immunohistochemistry. Epithelial barrier function was assessed with transepithelial resistance (TER). Results KGF significantly increased the intestinal wet weight, contents of intestinal protein and RNA, villus height, crypt depth and crypt cell proliferation, while KGF resulted in the decrease of epithelial apoptosis. KGF also stimulated the recovery of mucosal structures and attenuated the disrupted distribution of TJ proteins. Moreover, KGF attenuated the intestinal I/R-induced decrease in TER and maintained the intestinal barrier function. Conclusion KGF administration improves the epithelial structure and barrier function in a mouse model of intestinal I/R. This suggests that KGF may have clinical applicability.

GDNF is Involved in the Barrier-Inducing Effect of Enteric Glial Cells on Intestinal Epithelial Cells Under Acute Ischemia Reperfusion Stimulation

Acute intestinal ischemia reperfusion (IR) injury is often associated with intestinal epithelial barrier (IEB) dysfunction. Enteric glial cells (EGCs) play an essential role in maintaining the integrity of IEB functions. However, the precise mechanism of EGCs under IR stimulation remains unclear. Here, we report that EGCs are closely involved in the modulation of IEB functions in response to IR challenge. The intestinal IR treatment led to the significant upregulation of the EGC activation marker, glial fibrillary acidic protein, accompanied by the increasing abundance of glial-derived neurotrophic factor (GDNF) and inducible nitric oxidase (iNOS) proteins, which was also confirmed in in vitro hypoxia reoxygenation (HR) tests. Co-culturing with EGCs attenuated the tight junctional abnormalities, blocked the downregulation of ZO-1 and occludin protein expression, and relieved the decrease of permeability of intestinal epithelial cell (IEC) monolayers under HR treatment. Furthermore, exogenous GDNF administration displays the barrier-protective effects similar to EGCs against HR stimulation, while RNA interference-mediated knockdown of GDNF significantly inhibited the protective capability of EGCs. The expression of both GDNF and iNOS proteins of EGCs was significantly upregulated by co-culturing with IECs, which was further increased by HR treatment. Interestingly, through inhibiting iNOS activity, the barrier-protective effect of EGCs was influenced in normal condition but enhanced in HR condition. These results suggest that GDNF plays an important role in the barrier-protective mechanism of activated EGCs under IR stimulation, whereas EGCs (via iNOS release) are also involved in intestinal inflammation response, which may contribute to IEB damage induced by IR injury.

Aryl Hydrocarbon Receptor Activation in Intestinal Obstruction Ameliorates Intestinal Barrier Dysfunction Via Suppression of MLCK-MLC Phosphorylation Pathway.

Background: Accumulating evidence suggests that the aryl hydrocarbon receptor (AhR) plays an important role in the maintenance of the function of the intestinal barrier in patients with inflammatory bowel disease and in mouse models. Intestinal obstruction (IO) is a clinical emergency consisting of severe dysfunction of intestinal barrier function, and whether AhR plays a role in the pathogenesis of IO remains unknown but would be highly significant. Methods: Male C57BL/6 mice were subjected to IO and either treated with AhR endogenous agonist 6-formylindolo [3, 2-b] carbazole (FICZ) or left untreated. Intestinal tissue was harvested after 24 h. Correspondingly, Caco-2 monolayers were treated with FICZ in the absence or presence of hypoxia in vitro or left untreated. The cells were used after 12 h. Results: Damage to the intestinal mucosa was anabatic and intestinal permeability was significantly higher in murine IO and hypoxia-induced Caco-2 models than in controls. Under these conditions the activity of AhR was lower and the fluorescence of zonula occludens-1 (ZO-1) was absent. The increased expression of myosin light chain kinase (MLCK) and phosphorylated MLC (pMLC) indicated that this pathway was open. However, treatment with FICZ caused retention of the tight junction protein ZO-1, alleviated the increase of intestinal permeability, and mitigated epithelial injury. Depletion of AhR by AhR small interfering RNA facilitated the unblocking of the MLCK-pMLC signaling pathway and repressed the protein expression of ZO-1 in vitro. Conclusion: AhR activation can ameliorate epithelial barrier dysfunction induced by IO through the suppression of MLCK-pMLC signaling, suggesting that AhR agonist may be a suitable means of addressing this condition.

Keratinocyte growth factor pretreatment prevents radiation-induced intestinal damage in a mouse model

Abstract Background. Radiation-induced gastrointestinal syndrome is usually severe in clinical practice. Keratinocyte growth factor (KGF) plays an important role in the intestinal mucosal growth and repair of intestinal injury. This study was to investigate the effects of KGF on radiation-induced intestinal damage, especially the barrier dysfunction, in a mouse model. Methods. Adult C57BL/6J mice were randomized into three groups: normal control, irradiation group, and KGF-treated group. Mice in the later two groups received irradiation with a dose of 6 Gy from Co-60 source. In the KGF-treated group, KGF was intraperitoneally given once daily (5 mg/kg/day) for 5 consecutive days before irradiation. Mice were killed at 3 days after irradiation and the small bowel was collected for histology. Epithelial cell proliferation was studied by immunohistochemistry for proliferating cell nuclear antigen. Claudin-1 and ZO-1 expressions were determined by western blot assay and immunohistochemistry. Epithelial barrier function was assessed with transepithelial resistance. Results. KGF significantly promoted the recovery of mucosa from radiation-induced injury demonstrated by mucosal histology, villus height, crypt depth, and crypt cell proliferation. KGF also improved the disrupted distribution of tight junction proteins and the epithelial barrier dysfunction after irradiation. Conclusion. KGF pretreatment could improve radiation-induced intestinal injury including the epithelial structure and function in a mouse model.

The Jagged-2/Notch-1/Hes-1 Pathway Is Involved in Intestinal Epithelium Regeneration after Intestinal Ischemia-Reperfusion Injury

Background Notch signaling plays a critical role in the maintenance of intestinal crypt epithelial cell proliferation. The aim of this study was to investigate the role of Notch signaling in the proliferation and regeneration of intestinal epithelium after intestinal ischemia reperfusion (I/R) injury. Methods Male Sprague-Dawley rats were subjected to sham operation or I/R by occlusion of the superior mesenteric artery (SMA) for 20 min. Intestinal tissue samples were collected at 0, 1, 2, 4, and 6 h after reperfusion. Proliferation of the intestinal epithelium was evaluated by immunohistochemical staining of proliferating nuclear antigen (PCNA). The mRNA and protein expression levels of Notch signaling components were examined using Real-time PCR and Western blot analyses. Immunofluorescence was also performed to detect the expression and location of Jagged-2, cleaved Notch-1, and Hes-1 in the intestine. Finally, the γ-secretase inhibitor DAPT and the siRNA for Jagged-2 and Hes-1 were applied to investigate the functional role of Notch signaling in the proliferation of intestinal epithelial cells in an in vitro IEC-6 culture system. Results I/R injury caused increased intestinal crypt epithelial cell proliferation and increased mRNA and protein expression of Jagged-2, Notch-1, and Hes-1. The immunofluorescence results further confirmed increased protein expression of Jagged-2, cleaved Notch-1, and Hes-1 in the intestinal crypts. The inhibition of Notch signaling with DAPT and the suppression of Jagged-2 and Hes-1 expression using siRNA both significantly inhibited the proliferation of IEC-6 cells. Conclusion The Jagged-2/Notch-1/Hes-1 signaling pathway is involved in intestinal epithelium regeneration early after I/R injury by increasing crypt epithelial cell proliferation.

The Canonical Notch Signaling Was Involved in the Regulation of Intestinal Epithelial Cells Apoptosis after Intestinal Ischemia/Reperfusion Injury

Notch signaling plays a critical role in the maintenance of intestinal homeostasis. The aim of the present study was to investigate the role of Notch signaling in the apoptosis of intestinal epithelial cells after intestinal ischemia reperfusion (I/R) injury. Male C57BL/6 mice were subjected to sham operation or I/R injury. Intestinal tissue samples were collected at 12 h after reperfusion. TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling) staining showed that intestinal I/R injury induced significantly increased apoptosis of intestinal epithelial cells. Meanwhile, the mRNA expression of Jagged1, DLL1, Notch2, and Hes5, and protein expression of NICD2 and Hes5 were increased significantly after I/R injury in intestinal epithelial cells. In an in vitro IEC-6 culture model, flow cytometry analyses showed that inhibition of Notch signaling by γ-secretase inhibitor DAPT and the suppression of Hes5 expression using siRNA both significantly increased the apoptosis of IEC-6 cells under the condition of hypoxia/reoxygenation (H/R). In conclusion, the Notch2/Hes5 signaling pathway was activated and involved in the regulation of intestinal epithelial cells apoptosis in intestinal I/R injury.

Up-Regulation of Intestinal Epithelial Cell Derived IL-7 Expression by Keratinocyte Growth Factor through STAT1/IRF-1, IRF-2 Pathway

Background Epithelial cells(EC)-derived interleukin-7 (IL-7) plays a crucial role in control of development and homeostasis of neighboring intraepithelial lymphocytes (IEL), and keratinocyte growth factor (KGF) exerts protective effects on intestinal epithelial cells and up-regulates EC-derived IL-7 expression through KGFR pathway. This study was to further investigate the molecular mechanism involved in the regulation of IL-7 expression by KGF in the intestine. Methods Intestinal epithelial cells (LoVo cells) and adult C57BL/6J mice were treated with KGF. Epithelial cell proliferation was studied by flow cytometry for BrdU-incorporation and by immunohistochemistry for PCNA staining. Western blot was used to detect the changes of expression of P-Tyr-STAT1, STAT1, and IL-7 by inhibiting STAT1. Alterations of nuclear extracts and total proteins of IRF-1, IRF-2 and IL-7 following IRF-1 and IRF-2 RNA interference with KGF treatment were also measured with western blot. Moreover, IL-7 mRNA expressions were also detected by Real-time PCR and IL-7 protein level in culture supernatants was measured by enzyme linked immunosorbent assay(ELISA). Results KGF administration significantly increased LoVo cell proliferation and also increased intestinal wet weight, villus height, crypt depth and crypt cell proliferation in mice. KGF treatment led to increased levels of P-Tyr-STAT1, RAPA and AG490 both blocked P-Tyr-STAT1 and IL-7 expression in LoVo cells. IRF-1 and IRF-2 expression in vivo and in vitro were also up-regulated by KGF, and IL-7 expression was decreased after IRF-1 and IRF-2 expression was silenced by interfering RNA, respectively. Conclusion KGF could up-regulate IL-7 expression through the STAT1/IRF-1, IRF-2 signaling pathway, which is a new insight in potential effects of KGF on the intestinal mucosal immune system.

Aryl hydrocarbon receptor activation modulates CD8αα(+)TCRαβ(+) IELs and suppression of colitis manifestations in mice.

BACKGROUND This research is dedicated to investigating the effects and potential mechanism of action of the aryl hydrocarbon receptor on the intestinal mucosal immune system in dextran sulfate sodium (DSS)-induced colitis. METHODS Colitis was induced by the administration of 3% DSS to wild-type C57BL/6J mice for 7days. 6-formylindolo(3, 2-b)carbazole (FICZ), an endogenous agonist of the aryl hydrocarbon receptor (AhR), was given intraperitoneally on a daily basis beginning 2days after the start of DSS administration. The mice were weighed and assessed, and colon tissues were measured. Intraepithelial lymphocytes (IELs) were isolated from the colon and examined by flow cytometry and quantitative real-time PCR. RESULTS FICZ ameliorated DSS-induced colitis, resulting in a reduced disease activity index and improvement in the histology and length of the colon. Colitis reduced the percentage and number of CD8αα+TCRαβ+ IELs. FICZ prevented the reduction in the numbers of CD8αα+TCRαβ+ IELs by upregulating the expression of the IL-15 receptor and the aryl hydrocarbon receptor (AhR), and attenuating the apoptotic rate of CD8αα+TCRαβ+ IELs. Finally, IL-10 was increased and IFN-γ was decreased in CD8αα+TCRαβ+ IELs by FICZ administration in DSS-induced colitis. CONCLUSIONS The results suggest that AhR activation ameliorated DSS-induced acute colitis, in a manner that is associated with the local expansion and functions of CD8αα+TCRαβ+ IELs in acute colitis. The findings indicate that AhR-related ligands might be targeted as novel drug targets for IBD.