Developmental changes of TGF-β1 and Smads signaling pathway in intestinal adaption of weaned pigs

Abstract

Weaning stress caused marked changes in intestinal structure and function. Transforming growth factor-β1 (TGF-β1) and canonical Smads signaling pathway are suspected to play an important regulatory role in post-weaning adaptation of the small intestine. In the present study, the intestinal morphology and permeability, developmental expressions of tight junction proteins and TGF-β1 in the intestine of piglets during the 2 weeks after weaning were assessed. The expressions of TGF-β receptor I/II (TβRI, TβRII), smad2/3, smad4 and smad7 were determined to investigate whether canonical smads signaling pathways were involved in early weaning adaption process. The results showed that a shorter villus and deeper crypt were observed on d 3 and d 7 postweaning and intestinal morphology recovered to preweaning values on d 14 postweaning. Early weaning increased (P<0.05) plasma level of diamine oxidase (DAO) and decreased DAO activities (P<0.05) in intestinal mucosa on d 3 and d 7 post-weaning. Compared with the pre-weaning stage (d 0), tight junction proteins level of occludin and claudin-1 were reduced (P<0.05) on d 3, 7 and 14 post-weaning, and ZO-1 protein was reduced (P<0.05) on d 3 and d 7 post-weaning. An increase (P<0.05) of TGF-β1 in intestinal mucosa was observed on d 3 and d 7 and then level down on d 14 post-weaning. Although there was an increase (P<0.05) of TβR II protein expression in the intestinal mucosa on d3 and d 7, no significant increase of mRNA of TβRI, TβRII, smad2/3, smad4 and smad7 was observed during postweaning. The results indicated that TGF-β1 was associated with the restoration of intestinal morphology and barrier function following weaning stress. The increased intestinal endogenous TGF-β1 didn't activate the canonical Smads signaling pathway.

Figure 1. Tight junction protein levels of occludin, claudin-1 and zonula occludens-1 (ZO-1).

(A) shows representative blots of occludin, claudin, zonula occludens-1 (ZO-1), and β-actin on 0, 3, 7 and 14 post-weaning, respectively. (B) shows relative tight junction proteins expression. Data are means ± SD. ^a,bMeans with different letters differ significantly (P<0.05). The control sample on day 0 post-weaning was used as the reference sample. The protein expression of all samples was expressed as fold changes, calculated relative to the control group on day 0 post-weaning.

Figure 2. The change of TGF-β1 level in jejunal mucosa of weaned piglets during the 2 weeks.

(A) shows representative blots of TGF-β1 expression and β-actin on 0, 3, 7 and 14 post-weaning, respectively. (B) shows relative TGF-β1 protein expression in jejunal mucosa of piglets after weaning. ^a,b,c Mean values with unlike letters were significantly different (P<0.05). Values are means and standard deviations represented by vertical bars. The control sample on day 0 post-weaning was used as the reference sample. The protein expression of all samples was expressed as fold changes, calculated relative to the control group on day 0 post-weaning.

Figure 3. The protein levels of TβRI and TβRII in jejunal mucosa during the 2 weeks after weaning.

(A) shows representative blots of TβR I, TβR II proteins expression and β-actin on 0, 3, 7 and 14 post-weaning, respectively. (B) shows relative TβR I and TβR II proteins expression. ^a,b,Mean values with unlike letters were significantly different (P<0.05). Values are means and standard deviations represented by vertical bars. The value of protein expression was the ratio of the densitometry units of TβR I, TβR II protein and β-actin. The control sample on day 0 post-weaning was used as the reference sample. The protein expression of all samples was expressed as fold changes, calculated relative to the control group on day 0 post-weaning.