Huang, Xiao-Zhong*; Li, Zhong-Rong*; Zhu, Li-Bin*; Huang, Hui-Ya†; Hou, Long-Long*; Lin, Jing‡
Normal abdominal action depends on the enactment and aliment of a mucosal barrier that is lined by a monolayer of abdominal epithelial cells. The abdominal epithelium undergoes apparent structural and anatomic changes during development, characterized by continuous, well-organized, genetic, and endocrine-controlled corpuscle proliferation, differentiation, and apoptosis (1,2). The accession of the assorted apparatus of the abdominal barrier is accomplished during fetal development and continues during aboriginal postnatal life. It is able-bodied accustomed that abortion of the postnatal development of the abdominal barrier in the adolescent civil may accord to the pathogenesis of neonatal necrotizing enterocolitis (NEC), a ache apparent mainly in breed with an adolescent abdominal film (3,4).
Short-chain blubbery acids (SCFAs), mainly acerb acid, butyric acid, and propionic acid, are the articles of the bacterial beverage of undigested carbohydrates and proteins in the intestine. With the addition of enteral agriculture and the enactment of gut bacterial colonization, SCFAs are produced in the civil of abortive breed (5,6). Normally, SCFAs are rapidly captivated and comedy an important role in abdominal mucosal assay and adjustment of abdominal barrier integrity. An aberrant accompaniment of SCFA overproduction or accession may appear during periods of cogent carbohydrate malabsorption and/or bacterial overgrowth, beyond the buffering and absorptive accommodation of the intestine, and arch to an added absorption of SCFAs in the bowel. Overproduction/accumulation of SCFAs in the bowel and disability to bright the intraluminal SCFAs as a aftereffect of poor gastrointestinal activity in abortive breed may account abdominal mucosal abrasion (7), which has been accepted to comedy a role in the pathogenesis of NEC (8).
By application a Caco-2 corpuscle monolayer archetypal of abdominal barrier, we accept ahead approved that the aftereffect of butyrate on the abdominal barrier is paradoxical, that is, although low concentrations of butyrate may be benign in announcement abdominal barrier function, boundless butyrate may abet astringent abdominal epithelial corpuscle apoptosis and agitate abdominal barrier (9). Although butyrate is able-bodied accepted to abet apoptosis in altered kinds of cells, the atomic mechanisms with which butyrate mediates this aftereffect are not able-bodied understood. p38 is a affiliate of the mitogen-activated protein kinase (MAPK) superfamily that regulates corpuscle proliferation, differentiation, apoptosis, and corpuscle responses to accent (10–12). Cho et al (13) begin that the p38 MAPK alleyway has analytical roles in butyrate-induced apoptosis in prostate blight cells. We accepted that p38 MAPK signaling pathways are complex in butyrate-induced apoptosis and abdominal barrier impairment. The present abstraction was advised to added appraise the furnishings of butyrate and SB203580, a specific p38 inhibitor, on the abdominal barrier action in a absolute Caco-2 abdominal epithelial model. We present beginning affirmation advertence that the adverse aftereffect of butyrate on the abdominal barrier action is accompanying to butyrate-induced apoptosis and the p38 MAPK signaling alleyway plays an important role in this process.
Caco-2 cells, a animal colonic epithelial corpuscle band (Shanghai Chinese Academy of Sciences, Shanghai), were maintained commonly in a 25-cm2 corpuscle ability canteen at 37°C with a 5% CO2−95% air atmosphere and >95% humidity. The corpuscle monolayers were developed in minimum capital average (Gibco, Grand Island, NY) supplemented with 20% fetal bovine serum (Gibco), 1.5 g/L sodium bicarbonate, and 0.11 g/L sodium pyruvate. All abstracts were performed in the aforementioned average afterwards fetal bovine serum, that is, in the serum-free medium.
A absolute of 24-well transwell arrangement plates with collagen-coated film inserts (Corning, Ithaca, NY) were acclimated for this assay, as declared in detail ahead (9,14). Briefly, 8 × 104 Caco-2 beef in 0.2 mL average were seeded in the aciculate alcove that bathed in the basal alcove with 0.8 mL of medium, and the changes in transepithelial electrical attrition (TER) were abstinent with an epithelial volt ohmmeter (WPI, Sarasota, FL). Already developed to assemblage back TER accomplished abiding condition, the beef were rinsed with phosphate-buffered acrid (PBS) and incubated in serum-free average abandoned or with added reagents as indicated. Values were adapted for accomplishments attrition because of the film admit and the collagen layer. Values were affected as follows: TER = (R1 − R0) × A Ω cm2, breadth R1 is the accomplishments resistance, R0 the attrition of the film admit and the collagen layer, and A the film area.
The action was performed as declared in detail previously, with some modification (9,14). Briefly, Caco-2 beef were argent in 24-well transwell clarify inserts for the assay. At 72 hours afterward evolution with altered reagents, 100 μL of fluorescein isothiocyanate-conjugated inulin (inulin-FITC) (1 mg/mL; Sigma-Aldrich, St Louis, MO) was added into the aciculate chamber, and 3 alongside aliquots were taken from the basal alcove afterwards 60 minutes’ evolution at 37°C. The fluorescence discharge at 535 nm was abstinent afterwards action at 480 nm by application a microplate fluorescence clairvoyant (Tecan, Männedorf, Switzerland). Values were affected as cm/h permeability = [ΔC/ΔT × V]/(A × CO), breadth ΔC/ΔT is the alteration bulk of inulin-FITC in assemblage time, V the absolute aggregate of basal chamber, A the film area, and CO the aboriginal absorption of inulin-FITC added into the aciculate chamber.
At 72 hours afterward evolution with altered reagents, Caco-2 corpuscle monolayers argent in the 24-well transwell clarify inserts were rinsed alert in PBS, and afresh anchored with 3% glutaraldehyde at 4°C overnight. Afterwards abrasion with PBS, the monolayers were afresh dehydrated in graded booze series, exhaustion dried, and advised with a scanning electron microscope (Hitachi S-3000N, Tokyo, Japan) afterwards they had been gold sputtered.
An annexin V–FITC apoptosis appraisal kit (KeyGEN Biological Technology, Nanjing, China) was acclimated to quantify the apoptosis. Afterwards assay in assorted conditions, beef able in 6-well plates were harvested, done with PBS at 4°C, and afresh resuspended in 500 μL bounden absorber absolute 5 μL annexin V–FITC and 5 μL of propidium iodide. Afterwards 15 account of evolution at allowance temperature while adequate from light, decrepit beef were analyzed by breeze cytometry (Becton Dickinson, Franklin Lakes, NJ).
Caco-2 beef were developed to abounding assemblage and afresh incubated with altered reagents for altered time periods. The beef were rinsed with PBS and afresh lysed in radioimmunoprecipitation appraisal absorber with protease/phosphatase inhibitor cocktail (Cell Signaling Technology, Danvers, MA) at 4°C. Absolute corpuscle lysate was afar with 10% sodium dodecyl sulfate–polyacrylamide gel electrophoresis, and transferred to polyvinylidene difluoride membrane. The ambition protein was probed application a aerial anti-p38 MAPK polyclonal antibiotic (Cell Signaling Technology), a aerial anti-phospho-p38 MAPK monoclonal antibiotic (Cell Signaling Technology), and a aerial anti-β-tubulin monoclonal antibiotic (Cell Signaling Technology), in aggregate with horseradish peroxidase–conjugated anti-rabbit IgG (Santa Cruz Biotech, Santa Cruz, CA). Blots were developed application electrochemiluminescence Western blotting apprehension reagent kit (Beyotime Institute of Biotechnology, Shanghai, China).
Most of the abstracts were afresh at atomic 3 times. Accession abstracts from all of the abstracts are presented as beggarly ± accepted absurdity except breadth noted, and the numbers in anniversary accession acclimated for statistical assay are mentioned in the amount legends. Assay of about-face was acclimated for statistical analysis. The aberration amid anniversary accession was compared with the Tukey test. A P amount <0.05 was advised statistically cogent in all of the patients. All of the statistical analyses were performed application SPSS 16.0 software (SPSS, Chicago, IL).
Similar to our antecedent address (9), TER of Caco-2 monolayers advised with a aerial absorption (5 mM or higher) of butyrate decreased decidedly by 72 hours as compared with that of the ascendancy cells. Changes in permeability abstinent as the alteration of inulin-FITC from aciculate accommodation to basal accommodation through Caco-2 monolayer afterwards butyrate assay were constant with the changes of TER. Butyrate at 5 or 8 mM absorption broken the barrier action and acquired a cogent access in inulin-FITC permeability. These adverse furnishings of butyrate on the barrier functions of Caco-2 monolayers were attenuated by the assay of SB203580, a specific p38 MAPK inhibitor (Table 1, Fig. 1). This indicates that p38 MAPK alleyway is complex in the action of butyrate-induced crime of abdominal barrier functions.
As apparent in Amount 2, butyrate assay induced a decidedly college amount of apoptosis in Caco-2 cells. The amount of apoptosis was 44.9 ± 3.8% in the Caco-2 beef advised with 5 mM of butyrate as compared with 13.8% ± 4.9% in the ascendancy beef (P < 0.001). This aftereffect was attenuated by the cotreatment of 20 μM of SB203580, which bargain the amount of apoptosis to 30.2% ± 3.3% (P = 0.007 vs 5 mM butyrate group). SB203580 assay abandoned had no aftereffect on the all-embracing apoptosis amount as compared with the ascendancy cells.
Scanning electron microscopy appear that the Caco-2 corpuscle monolayers advised with 2 mM of butyrate were agnate to those of the average controls (Fig. 3A and B). Caco-2 corpuscle monolayers advised with 5 mM of butyrate appeared to accept added beef address from the monolayers. Possibly this was attenuated by the cotreatment of 20 μM of SB203580 (Fig. 3C and D).
These after-effects announce that sodium butyrate at 5 mM induces cytotoxicity and corpuscle afterlife in the Caco-2 corpuscle monolayers best acceptable accompanying to apoptosis. The p38 MAPK adversary SB203580 can arrest butyrate-induced Caco-2 corpuscle apoptosis.
The phosphorylation of p38 was bent by Western blotting analysis. We abstinent the announcement of p38 MAPK, p-p38 MAPK, and β-tubulin in Caco-2 beef afterwards actuality advised with butyrate at altered concentrations and altered duration. As apparent in Amount 4, butyrate activates p38 MAPK in a dose- and time-dependent manner. As expected, cotreatment of SB203580 inhibited the activation of p38 MAPK induced by assay of butyrate (Fig. 5). These after-effects authenticate that butyrate-induced apoptosis in Caco-2 beef may be advised via p38 MAPK-dependent pathway.
SCFAs, of which butyrate is one of the capital blubbery acids, are important end articles of bacterial beverage in the abdominal lumen and are complex in the adjustment of abdominal barrier function. In the present study, by application an in vitro archetypal of the abdominal barrier, we authenticate that butyrate in abstinent doses abet apoptosis via activation of p38 MAPK, arch to disruption of the mucosal barrier. Inhibition of p38 MAPK activation can decidedly abate butyrate-induced apoptosis and ameliorates apoptosis-related abdominal barrier dysfunction. Our after-effects advance that the MAPK-dependent apoptosis alleyway is complex in butyrate-induced abdominal barrier impairment.
In humans, the accession of SCFAs as a aftereffect of bacterial beverage of undigested carbohydrates occurs commonly already enteral agriculture is alien and accustomed bacterial colonization is established. In physiological conditions, the accession of SCFAs in the bowel is important for activity deliver and acute for gastrointestinal adjustment and maturation. SCFAs may additionally be the important molecules that arbitrate the authoritative aftereffect of accustomed abdominal microflora on abdominal barrier action (15). It has been speculated that adjustment of the bound alliance proteins may be one of the mechanisms basal the role of SCFAs on the abdominal barrier function. Butyrate adjustment of the barrier action in the Caco-2 corpuscle monolayer archetypal is absurd to be explained by the changes in the levels of announcement of some above bound alliance proteins. Instead, butyrate enhances the abdominal barrier function, at atomic partly, by facilitating the accession of bound junctions (14).
In dissection conditions, boundless accession and accession of SCFAs acquired by malabsorption or poor abdominal activity may account exceptionable adverse effects. We accept ahead approved that aerial concentrations of SCFAs can abet concentration- and maturation-dependent abdominal mucosal abrasion in bairn rats and proposed that SCFAs may comedy a role in the pathogenesis of NEC, a adverse abdominal emergency in abortive breed characterized by the abdominal mucosal abrasion (16,17). Almost all SCFAs are cytotoxic and can abet apoptosis in able abdominal epithelial beef (18). Normally, apoptosis and address action at the tips of mucosal villi as allotment of the physiological face-lifting of the abdominal epithelium (19). With added apoptosis, abdominal epithelial barrier crime may action (20). This apparatus may be complex in the pathogenesis of NEC.
Several atomic mechanisms by which butyrate induces apoptosis accept been proposed and elucidated. Above pathways in butyrate-induced apoptosis accommodate caspase-, proteasome-, and autophagic-induced corpuscle death, which frequently action in alongside or in cross-talk (21–23). One key endpoint represents caspase-3, a affiliate of a cysteine protease family, accurately complex in the admission and beheading of the apoptotic affairs (21,22). Schwab et al (24) approved that PPARγ is a key ambition in the butyrate-induced signaling avalanche arch to apoptosis via caspase-3 in Caco-2 cells. In the present study, we appearance that butyrate activates p38 MAPK and that assay with a specific p38 MAPK inhibitor prevents the activation of p38 MAPK and attenuates the barrier crime induced by butyrate, acerb suggesting that p38 MAPK signaling pathways are complex in the butyrate-induced apoptosis and accompanying abdominal barrier impairment. This, therefore, may represent a abeyant ambition for intervention.
As a affiliate of the MAPK superfamily, p38 is a accepted signaling alleyway from a array of alien stimuli such as lipopolysaccharides and cytokines. On activation by absolute site-specific Ser/Thr phosphorylation, the p38 MAPK can advance to abundant biological changes in the cell, including activation of after protein kinases and archetype factors, and adjustment of chromatin remodeling. These changes ultimately aftereffect in announcement of ambition genes and accompanying biological responses (12). It is accepted that p38 MAPK is activated mainly by cytotoxic insult and stress, and plays important roles in the adjustment of corpuscle adaptation and adverse (12,25). Here we present affirmation that butyrate activates p38 MAPK in a dose- and time-dependent manner. Others accept additionally apparent that activation of p38 MAPK seems to be a analytical upstream accident in butyrate-induced caspase-3 activation (26). Fung et al (27) begin that butyrate acceptable induces a cellular accent acknowledgment in HCT116 beef characterized by p38 MAPK activation and an endoplasmic cloth accent response, consistent in caspase 3/7 activation and corpuscle death. The atomic apparatus basal the butyrate activation of p38 MAPK and consecutive apoptosis charcoal to be added elucidated.
Whether this is additionally accurate in in vivo altitude charcoal to be answered. Until now, there accept been no abstracts accessible apropos the accustomed SCFA absorption in the civil of abortive infants. Back compared with the butyrate concentrations begin in the developed animal ample civil or in the stools of formula-fed appellation infants, the butyrate concentrations acclimated in the present study, in fact, may be physiological (28,29). Therefore, the after-effects acquired from the corpuscle ability archetypal may not be anon translatable to the in vivo situation. Added studies are bare to added actuate whether p38 MAPK alleyway is absolutely complex in the adjustment of SCFAs on the abdominal barrier in vivo.
In summary, by application a Caco-2 corpuscle monolayer archetypal of the abdominal barrier, we acquisition that p38 MAPK can be activated by butyrate and the p38 MAPK alleyway is complex in the butyrate-induced apoptosis and crime of abdominal barrier function. Inhibition of p38 MAPK can decidedly abate butyrate-induced abdominal barrier dysfunction. It, therefore, may be a abeyant ambition for intervention. Added studies are bare to annotate the atomic apparatus basal the butyrate activation of p38 MAPK and consecutive apoptosis. Whether this award is additionally accurate in in vivo altitude and the accessible role of SCFAs in the pathogenesis of NEC abide to be determined.
The authors acknowledge Drs Ian R. Holzman and Hui Cai for comments and afterlight of the manuscript.
barrier function; butyrate; abdominal mucosa; p38 MAPK; short-chain blubbery acid
Journal of Pediatric Gastroenterology and Nutrition59(2):264-269, August 2014.
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