A TNBS-Induced Rodent Model to Study the Pathogenic Role of Mechanical Stress in Crohn's Disease

Ramasatyaveni Geesala; You-Min Lin; Ke Zhang; Suimin Qiu; Xuan-Zheng Shi

doi:10.3791/63499

JoVE Journal > Immunology and Infection

Immunologie et infection

A TNBS-Induced Rodent Model to Study the Pathogenic Role of Mechanical Stress in Crohn’s Disease

Published: March 01, 2022

doi:

10.3791/63499

Ramasatyaveni Geesala*¹, You-Min Lin*¹, Ke Zhang*¹, Suimin Qiu², Xuan-Zheng Shi¹

¹Department of Internal Medicine,the University of Texas Medical Branch, ²Department of Pathology,the University of Texas Medical Branch

Summary

The present protocol describes the development of a Crohn’s-like colitis model in rodents. Transmural inflammation leads to stenosis at the TNBS instillation site, and mechanical enlargement is observed in the segment proximal to the stenosis. These changes allow studying mechanical stress in colitis.

Abstract

Inflammatory bowel diseases (IBD) such as Crohn's disease (CD) are chronic inflammatory disorders of the gastrointestinal tract affecting approximately 20 per 1,000,000 in Europe and USA. CD is characterized by transmural inflammation, intestinal fibrosis, and luminal stenosis. Although anti-inflammatory therapies may help control inflammation, they have no efficacy on fibrosis and stenosis in CD. The pathogenesis of CD is not well understood. Current studies focus mainly on delineating dysregulated gut immune response mechanisms. While CD-associated transmural inflammation, intestinal fibrosis, and luminal stenosis all represent mechanical stress to the gut wall, the role of mechanical stress in CD is not well defined. To determine if mechanical stress plays an independent pathogenic role in CD, a protocol of TNBS-induced CD-like colitis model in rodents has been developed. This TNBS-induced transmural inflammation and fibrosis model resembles pathological hallmarks of CD in the colon. It is induced by intracolonic instillation of TNBS into the distal colon of adult Sprague-Dawley rats. In this model, transmural inflammation leads to stenosis at the TNBS instillation site (Site I). Mechanical distention is observed in the portion proximal to the instillation site (Site P), representing mechanical stress but not visible inflammation. Colonic portion distal to inflammation (Site D) presents neither inflammation nor mechanical stress. Distinctive changes of gene expression, immune response, fibrosis, and smooth muscle growth at different sites (P, I, and D) were observed, highlighting a profound impact of mechanical stress. Therefore, this model of CD-like colitis will help us better understand CD's pathogenic mechanisms, particularly the role of mechanical stress and mechanical stress-induced gene expression in immune dysregulation, intestinal fibrosis, and tissue remodeling in CD.

Introduction

Inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), is characterized by chronic inflammation in the gastrointestinal (GI) tract. It affects ~1-2 million Americans¹. The estimated annual costs for IBD care in the US are $11.8 billion. Unlike UC, the CD is characterized by transmural inflammation and stricture formation²^,³. Stricture formation (stenosis) occurs in up to 70% of CD patients³ and may be caused by transmural inflammation (inflammatory stenosis) or intestinal fibrosis (fibrotic stenosis)⁴^,⁵. Intestinal fibrosis is characterized by excessive collagen deposition and other extracellular matrices (ECM) with smooth muscle cells (SMC) as one of the main mesenchymal cell types involved in the process³^,⁴. Smooth muscle hyperplasia associated with hypertrophy is another significant histological change in fibrotic stenosis in CD⁶. Although stricture formation in CD is associated with chronic inflammation, no anti-inflammatory treatment is effective, except surgical treatment²^,⁶. However, post-surgery recurrences are almost 100%, given sufficient time²^,⁷. As an inflammatory response, fibrosis and SMC hyperplasia may also develop in non-inflammatory conditions (i.e., bowel obstruction) in the gut⁸^,⁹; it is believed that both inflammation-dependent and independent mechanisms are involved in stricture formation³^,⁴. Given that extensive research into the inflammation-dependent mechanisms has not translated into any effective therapy for stricture formation, studies into the possible role of inflammation-independent mechanisms in intestinal fibrosis are needed.

As a non-inflammatory factor, mechanical stress (MS) associated with edema, inflammatory cell infiltration, tissue deformation, fibrosis, and stenosis¹⁰^,¹¹^,¹²^,¹³ is commonly encountered in IBD, especially CD, which is characterized by transmural inflammation. Mechanical stress is most remarkable in stenotic CD, where stenosis (inflammatory or fibrotic) in the inflammation site presents mechanical stress in the local tissue and leads to lumen distention in the segment proximal to the obstruction site¹⁰^,¹⁴. Previous in vitro studies have demonstrated that mechanical stress alters gene expression of specific inflammatory mediators (i.e., COX-2, IL-6)⁸^,¹⁴^,¹⁵ and growth factors (i.e., TGF-β) in the gastrointestinal tissues, especially gut smooth muscle cells (SMC)¹⁶. Recent studies also found that the expression of specific pro-fibrotic mediators such as connective tissue growth factor (CTGF) is highly sensitive to mechanical stress¹⁷^,¹⁸. It was hypothesized that mechanical stress might play an independent pathogenic role in CD-associated inflammation, fibrosis, and tissue remodeling. However, the pathogenic significance of mechanical stress in gut inflammation, fibrosis, and smooth muscle hyperplasia in CD remains largely unexplored. This may be partly because inflammation is a more visible and better-studied process than mechanical stress. More importantly, there has been no well-defined animal model of IBD to distinguish the effect of mechanical stress from that of inflammation.

The current work describes a rodent model of Crohn's-like colitis induced by intracolonic injection of hapten reagent 2,4,6-trinitrobenzene sulfonic acid (TNBS)¹⁹^,²⁰, which may serve the purpose to study the role of mechanical stress in CD. It was found that TNBS instillation induced a localized (~2 cm in length) transmural inflammation with lumen narrowing (stenosis) in the distal colon. The stenosis leads to marked bowel distention (mechanical stress)¹⁴^,¹⁵ but not visible inflammation in the colonic segment proximal to the instillation site. On the contrary, the colon segment distal to the stenosis site presents neither inflammation nor mechanical stress. Significant site-specific changes in gene expression, inflammation, fibrosis, and SMC hyperplasia were observed in the three different sites. The results suggest that mechanical stress, particularly mechanical stress-induced gene expression, may play a critical role in developing fibrosis and hyperplasia in Crohn's colitis.

Protocol

All animal experiments were conducted according to the institutional animal care and use committee of the University of Texas Medical Branch (#0907051C). Male or female Sprague-Dawley rats, ~8-9 weeks old, were used for the study.

1. Animal preparation

Fast rats for 24 h and treat them with laxative (bowel cleanser, see Table of Materials) overnight.
The next day, anesthetize rats using an anesthesia system (see Table of Materials) by exposing them to 2% isoflurane along with 1 L/min of oxygen during TNBS administration. Check for reflexes or pinch toes to confirm anesthetization.
Prepare fresh TNBS solution according to body weights.
NOTE: TNBS – 65 mg/kg of body weight in 250 µL of 40% ethanol/saline was used.
Put rats in a supine position on the anesthesia table. To induce colitis, insert through the anus a medical-grade open-end polyurethane catheter for ~7-8 cm from the anal verge and gently instill TNBS (prepared in step 1.3) into the colon¹⁹. Administer the sham control rats with 250 µL of saline only.
After instilling TNBS or saline, keep rats in supine and slightly head-down position (~30°), with the anus closed for 2 min to help TNBS distribution and avoid spills.
Provide rats with food and water ad libitum for 7 days and observe the rats daily for body weight, food uptakes, feces, and general health condition.

2. Tissue preparations

On the day of euthanasia, euthanize the rats using CO₂ inhalation and confirm euthanasia with cervical dislocation.
Open the rat abdomen using surgical-grade scissors and forceps.
Carefully remove the entire colon (above the anal canal) and transfer the colon immediately to ice-cold 1x HBSS buffer.
Straighten the colon in the buffer and measure the colon length using a ruler. Take nylon thread and circle around the colon to measure the external circumference of the colon segments in control and TNBS-treated rats. Take full-thickness tissues for histology.
Cut open the colon along the mesenteric board and clean the colon well with HBSS buffer. Assess the colon for macroscopic inflammation score based on the criteria as previously described¹⁹ with minimal modifications.
NOTE: 0 = normal mucosa; 1 = localized hyperemia but no erosions or ulcers; 2 = ulcer and stenosis (affected area < 5 mm); 3 = severe ulcer, scar, and stenosis (affected area > 5 mm).
Collect colonic tissue samples from site P (portion 2-3 cm before the oral margin of inflammation site), site I (inflammation site, typically 4-6 cm from the end of the colon, where TNBS is instilled to), and site D (portion 1-2 cm distal to the aboral margin of inflammation site), respectively from TNBS-treated rats.
NOTE: Colon tissue of ~1-2 cm-long was taken from each segment. In addition, the colon tissues of 2 cm long (~4-6 cm from the end of the colon) of the saline-treated rats were taken as sham control (S) (Figure 1).
Take tissue samples from each site for full-thickness preparation, and if desired, mucosa/submucosa and muscularis externa layers, respectively, as well²¹^,²².
Freeze tissue samples in liquid nitrogen first before storing them at -80 °C for storage up to one year and for future purposes (i.e., RNA preparations).

3. Histopathologic assessment of gut inflammation and fibrosis

Fix the full-thickness colon tissues in 10% formalin for 48 h, then transfer to 70% ethanol for 24-48 h.
Use a microtome to cut paraffin sections of 5 µm thickness for Hematoxylin and eosin (H&E) and Masson's Trichrome stains⁶^,¹⁹^,²³ (see Table of Materials), respectively.
Acquire and view images with an upright microscope equipped with a high-resolution camera with compatible software (see Table of Materials).
Grade inflammation and fibrosis indexes by two independent investigators, including a gastrointestinal surgical pathologist according to criteria described previously⁶^,²³ with modifications. See Supplementary File 1 for the scores.
Measure the thickness and cell numbers of the circular and longitudinal muscle layers per cross-section in four views of each H&E stained specimen and take the mean of the four measurements for each specimen.

4. RNA extraction and quantitative RT-PCR

Homogenize excised colon tissues obtained from the sham control and three sites (P, I, D) of TNBS colitis rats in the extraction reagent of an RNA extraction kit (see Table of Materials).
Isolate RNA from each sample utilizing the kit. Elute the RNA pellet in 30 µL of RNase-free water.
Quantify RNA concentration and check for purity using a microvolume UV-Vis spectrophotometer (see Table of Materials).
Use 1 µg of total RNA to synthesize cDNA²¹^,²² using the RNA synthesis kit (see Table of Materials).
Analyze and quantify gene expression levels by performing real-time PCR with 50 ng of cDNA as a template, probes of IL-6, and CTGF using a commercial PCR kit for real-time PCR system (see Table of Materials).
Use control gene 18S rRNA to normalize the samples and quantify relative gene expression utilizing the Cq values obtained.

5. Statistical analysis

Utilize statistical analysis software (see Table of Materials) to compare sham control and TNBS colitis rats.
Consider p value < 0.05 to be statistically significant¹⁵^,¹⁹.
To test the differences between two groups, use Student's t-test analysis and perform an ANOVA test if comparisons are more than two groups¹⁵^,¹⁹.

Representative Results

Macroscopic view of Crohn's-like colitis induced by intra-colonic instillation of TNBS
As shown in Figure 1, intracolonic instillation of TNBS in rats induced a localized transmural inflammation (~2 cm in length) with thickened bowel wall and narrowed lumen (stenosis) in the site of instillation in the distal colon (Figure 1A). The site of TNBS instillation is referred to as site I. As a result of transmural inflammation and stenosis, both inflammation and mechanical stress are present in site I. The stenosis in site I led to marked lumen distention in the segment proximal to the site of TNBS instillation (site P) (Figure 1). The colon circumference was significantly increased in sites P and I, compared to sham control colon (p < 0.05 vs. control) (Figure 1B). While mechanically distended, site P did not show visible inflammation. On the contrary, the colonic segment distal to the TNBS instillation site is site D and presents neither inflammation nor mechanical distention (Figure 1A,B).

To help distinguish the effect of mechanical stress from inflammation, we followed a unique design in collecting tissue samples from the colon in the model described in step 2.6. Site P is the primary focus of the study, as this part is mechanically distended in the CD model. Site D is self-control, as it does not present mechanical stress. Sites P and D do not demonstrate any visible inflammation (Figure 1). However, the site I experience inflammation and mechanical stress (Figure 1).

Site-specific changes of inflammation score in sites P, I, and D in colitis rats
Criteria were developed in grading inflammation based on the macroscopic score of live tissue (0-3)¹⁹ and the microscopic score of H&E stained specimens (0-3)²³ as described with modifications. The results showed that the macroscopic score of inflammation in site I was 2.70 ± 0.20 in the TNBS treated rats (7 days after induction of inflammation), dramatically increased compared to that of sham controls (0.30 ± 0.22, p < 0.05) and that of sites P (0.80 ± 0.26) and D (0.50 ± 0.22) of colitis rats (Figure 1C). The inflammation scores in sites P and D are not significantly increased compared to sham (Figure 1C). Microscopic imaging showed TNBS treatment-induced transmural inflammation in rats (Figure 2A). The microscopic score of inflammation in site I was 2.80 ± 0.27 in the TNBS treated rats, again significantly (p < 0.05, n = 5 each group) increased compared to that in sham controls (0.3 ± 0.2) and in sites P (1.0 ± 0.31) and D (0.80 ± 0.38) of colitis rats. The inflammation scores in sites P and D were not significantly increased compared to sham (Figure 2C).

Site-specific changes of fibrosis and smooth muscle hyperplasia and hypertrophy in sites P, I, and D in colitis rats
The fibrosis score was determined based on Mason's trichrome stain (Figure 2B) in different sites (P, I, D) (Figure 2A). The grading system for fibrosis is described in Supplementary File 1. It was found that fibrosis score is significantly increased not only in site I (2.60 ± 0.25) but also in site P (1.60 ± 0.24) of the colitis rats, compared to sham control (0.40 ± 0.25. p < 0.05) (Figure 2D). The thickness and cell numbers of circular and longitudinal smooth muscle layers were measured in different sites in H&E stained specimens (4 views per specimen). The thickness and cell numbers of both circular and longitudinal smooth muscle layers were significantly increased in sites I and P (Figure 2E,F). The site D in the colitis rats does not show any significant increase in fibrosis score, smooth muscle cell numbers, or muscle thickness (Figure 2).

Site-specific expression of mechano-sensitive genes in sites P, I, and D in colitis rats
IL-6 plays a critical role in gut inflammation, as it promotes T cell differentiation, damages barrier function, and affects neuromuscular function⁸^,²⁴. CTGF is a well-recognized pro-fibrotic mediator, as its inhibition can reverse the process of fibrosis¹⁷. More importantly, recent studies found that gene expression of IL-6 and CTGF is highly responsive to mechanical stress⁸^,¹⁴^,¹⁸. The site-specific expression of IL-6 and CTGF mRNAs were determined in the full thickness tissue of sham control and TNBS colitis rats. The mRNA expression levels of IL-6 and CTGF were significantly increased in the inflammation site (site I) compared to sham controls. In site P, where there is mechanical distention but no visible inflammation, the mRNA expression of IL-6 and CTGF was also dramatically increased compared to control rats (Figure 3A,B). However, IL-6 and CTGF mRNA levels in site D of colitis rats were not significantly different from that in sham controls (Figure 3).

Figure 1: Rodent model of TNBS-induced CD-like colitis (7 day). (A) Outlook view of sham control and TNBS-treated colon (top) and macroscopic view of the mucosal surface of the distal colon (bottom). The yellow boxes indicate different sites of colon tissue. S, sham control; I, inflammation site; P, distended colon site proximal to inflammation site; D, non-distended site distal to inflammation. (B) Colon circumference in sham control and different sites (P, I, D) of TNBS-treated colon. (C) Macroscopic inflammation score of sham control colon and different sites of TNBS-treated colon. n = 5, *p < 0.05 vs. sham rats of the group. Bars represent SEM. Please click here to view a larger version of this figure.

Figure 2: Histopathologic assessment. Microscopic views in H&E (A) and Masson's trichrome stains (B) showing collagen distribution in sham and different sites of colitis rats. Quantitative analysis shows increased microscopic inflammation index (C), fibrosis (D) and muscular thickness (hypertrophy) (E), and smooth muscle cell number (hyperplasia) (F) in sites I and P, but not D, in TNBS treated rats. In (E) and (F), the open bars are for the circular smooth muscle layer, and streaked bars are for the longitudinal smooth muscle layer. n = 5 in each group, *p < 0.05 vs. sham rats of the group. Bars in graphs represent SEM. Bars in (A) and (B) = 100 µm. Please click here to view a larger version of this figure.

Figure 3: Site-specific expression of mechanosensitive genes (IL-6 and CTGF) in CD-like colitis. (A) Expression of IL-6 mRNA in sham control colon and different sites (P, I, and D) of TNBS-treated colitis colon. (B) Expression of CTGF mRNA in sham control colon and different sites (P, I, and D) of TNBS-treated colitis colon. n = 4 or 5, *p < 0.05 vs. S (sham control). Bars represent SEM. Please click here to view a larger version of this figure.

Supplementary File 1: Score of inflammation and fibrosis. Please click here to download this File.

Discussion

TNBS-induced colitis was introduced in 1989 and has been used as an experimental model of Crohn's disease since then¹⁹^,²⁰^,²³. Significant features of this model in rodents include the development of a transmural inflammation that closely resembles the histopathological lesions developed in human Crohn's disease¹⁹^,²⁰. Previous studies on the model have focused mainly on aberrant immune response in the mucosa layer in the site of visible inflammation (the site I)¹⁹^,²⁰^,²³. Little attention has been paid to the bowel portions proximal and distal to inflammation. The present study on the inflammation site, as well as the distended proximal segment and the non-distended distal segment, reveals apparent site-specific changes in gene expression, inflammatory response, and histopathological features. The model has been revisited to address the potential pathogenic role of mechanical stress in fibrosis and tissue remodeling in Crohn's disease.

It was found that acute inflammation is immediately developed after mucosal exposure of TNBS in ethanol and is peaked at day 3¹⁹. Transmural inflammation and inflammatory stenosis are present, which is associated with lumen distention in site P in every rat treated with TNBS. By day 7, chronic transmural inflammation is well developed in site I, as found in the current study and reported elsewhere²⁰. Meanwhile, fibrotic changes are apparent in the site, characterized by excessive collagen deposition, as seen in the present study and elsewhere²⁰. TNBS instillation in ethanol in the distal colon injures the local mucosa tissue²³ and leads to transmural inflammation in a localized area in the colon. The transmural inflammation with inflammatory infiltration, edema, and tissue deformation¹⁰^,¹²^,¹³ in the instillation site present inflammation and mechanical stress¹⁴ to the localized area (Site I). Moreover, transmural inflammation also causes luminal stenosis in site I¹⁰. It was found that stenosis, a partial bowel obstruction, causes mechanical distention in the proximal segment (site P). However, the part distal to the instillation site is not distended (site D). As found in the macroscopic and histological scoring systems, while site I presents both inflammation and mechanical stress, sites P and D do not present inflammation. Furthermore, site P shows significantly increased circumference (and thus mechanical stress, according to the law of Laplace¹⁴), but site D does not. Therefore, a study on the site-specific changes, especially the site P, will explore the pathogenic importance of mechanical stress in the inflammation model in the gut.

It was observed that the expression of mechano-sensitive genes IL-6 and CTGF was increased in site I and in mechanically stretched site P, but not in neighboring site D, where there is no mechanical distention. To examine the hypothesis that mechanical stress may contribute to the development of fibrosis and smooth muscle hyperplasia, fibrosis scores and measured smooth muscle cell numbers and muscle thickness in sites P, I, and D were determined separately. It was found that fibrosis and SMC hyperplasia are present in sites I and P. However, fibrosis and smooth muscle hyperplasia are not detected in site D. These findings indicate that mechanical stress may play an independent pathogenic role in collagen synthesis and cell proliferation in gut inflammation. Further studies are warranted to determine if this effect may be mediated by mechanical stress-induced expression of pro-fibrotic and growth factors such as CTGF in the sites P and I.

Although the described animal model itself can be used to address mechanical stress in stenotic CD-like colitis, it has limitations in the long-term goal to fully define the pathogenic role of mechanical stress in inflammation. For example, the effects of mechanical stress and inflammation in site I of the described model cannot be differentiated. Although it is assumed that mechanical stress is present in site I because of inflammatory infiltration, tissue deformation, stenosis, and distention, how much mechanical stress contributes to the pathological changes there cannot be determined. Further comprehensive studies using in vitro, in vivo, and ex vivo approaches may be needed. For example, preventing mechanical distention by feeding the colitis animals exclusively with a clear liquid diet²⁵ may help create a loss-of-mechanical distention status in the colitis model. On the other hand, induction of pure mechanical distention by obstruction band¹⁵ may help create a gain-of-mechanical stress model. Moreover, the in vitro mechanical stretch model in cultured cells¹⁴^,¹⁵ assists in the quantitative determination of the effects of mechanical stress on gene expression and function, as the mode and extent of mechanical stress can be finely controlled in the in vitro setting.

To prepare a reproducible model of transmural and stenotic inflammation in CD-like colitis as described in the study, TNBS at 65 mg/kg in 250 µL of 40% ethanol must be used. The model was tested mainly in rats, male or female, 8-9 weeks old. After instillation of TNBS at the dose, transmural inflammation is consistently developed at the local instillation site. The inflammation is associated with inflammatory cells infiltration, edema, and bowel wall thickening, leading to lumen narrowing at the instillation site, resembling pathological characteristics of Crohn's disease²⁰. Pilot studies in the lab showed that TNBS at doses lower than 50 mg/kg in the same volume of 40% ethanol might cause gut inflammation but not reliable stenosis in site I. Thus, there would be no apparent mechanical distention in site P. On the other hand, TNBS at doses greater than 80 mg/kg may cause severe inflammation and fatalities. The current protocol using TNBS at 65 mg/kg in 250 µL of 40% ethanol hardly causes fatalities (1 in 16 rats of TNBS colitis).

It was found that bowel cleansing the day before instillation of TNBS is an important step to ensure a relatively clean colon for a reliable model of stenotic colitis. For that, rats need to fast for 24 h and give bowel cleanser overnight before TNBS treatment. It is also important to keep rats in a supine and slightly head-down position with the anus closed for 2 min after instillation of TNBS. This helps to ensure a good distribution of TNBS inside the distal colon.

In summary, it was found that intracolonic instillation of TNBS at 65 mg/kg in 250 µL of 40% ethanol consistently induced CD-like colitis in rats. Transmural inflammation in the model is associated with stenosis at the TNBS instillation site. Mechanical distention, but not inflammation, is observed in the segment proximal to the stenosis. Neither inflammation nor mechanical stress is present in the segment distal to the stenosis. With these changes in different colon sites in a colitis rat, mechanical stress from inflammation in CD-like colitis can be distinguished.

Divulgations

The authors have nothing to disclose.

Acknowledgements

This work is supported in part by grants from NIH (R01 DK124611 to XZS) and the US Department of Defense (W81XWH-20-1-0681 to XZS). The histology work was done with the help of the UTMB Surgical Pathology Lab.

Materials

ACT-1 Control Software Ver2.63	Nikon	DXM1200F
C1000 Touch Thermal Cycler with 96-Well Fast Reaction Module	BIO-RAD	1851196
CFX96 Optical Reaction Module for Real-Time PCR Systems	BIO-RAD	1845097
Dako Agilent Artisan Link Pro Special stainer	Dako	AR310
Dako-Agilent Masson's Trichrome Kit ref# AR173	Dako	AR173
DXM1200 Digital Color HR Camera	Nikon	DXM1200
Eukaryotic 18S rRNA Endogenous Control	ThermoFisher Scientific	4352930E
E-Z Anesthesia	E-Z Systems Inc.	EZ-155
GraphPad Prism 9	GraphPad	9.0.2 (161)
Hard-Shell 96-Well PCR Plates, low profile, thin wall, skirted, white/clear	BIO-RAD	HSP9601
HBSS (Corning Hank's Balanced Salt Solution, 1x without calcium and magnesium)	CORNING	21-021-CV
HM 325 Microtome	Thermo Scientific	23-900-667
Isoflurane	Piramal	NDC 66794-017-10
LI-COR Odyssey Digital Imaging System	LI-COR	9120
Mastercycler epGradient Thermal Cycler with Control Panel 5340 Thermal Cycler	Eppendorf	5341
Medical grade open end polyurethane catheter	Covidien	8890703013
NanoDrop 2000/2000c Spectrophotometers	Thermo Fisher Scientific	ND2000CLAPTOP
Nikon Eclipse E800 Upright Microscope	Nikon	E800
Nitrocellulose/Filter Paper Sandwiches Pkg of 50, 0.45 μm, 7 x 8.5 cm	BIO-RAD	1620215
Polyethylene Glycol 3350, Osmotic Laxative	Miralax	C8175	Dose: 17g in 226 mL of water
RNeasy Mini Kit (250) 250 RNeasy Mini Spin Columns, Collection Tubes (1.5 mL and 2 mL), RNase-free Reagents and Buffers	QIAGEN	74106
SuperScript III First-Strand Synthesis System	ThermoFisher Scientific	18080051
TaqMan Gene Expression Assays Rn00573960_g1 CTGF Probe	ThermoFisher Scientific	4331182
TaqMan Gene Expression Assays Rn99999011_m1 IL6 Probe	ThermoFisher Scientific	4331182
TaqMan Fast Advanced Master Mix	ThermoFisher Scientific	4444557
Tissue-Tek Prisma H&E Stain Kit #1	Sakura	6190
Tissue-Tek Prisma Plus Automated Slide Stainer	Sakura	6171
TNBS (Picrylsulfonic acid solution)	SIGMA-ALDRICH	92822

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Geesala, R., Lin, Y., Zhang, K., Qiu, S., Shi, X. A TNBS-Induced Rodent Model to Study the Pathogenic Role of Mechanical Stress in Crohn’s Disease. J. Vis. Exp. (181), e63499, doi:10.3791/63499 (2022).