Sustainable Grape Antioxidant Dietary Fiber Preserves Proximal Colonic Homeostasis via Hsp27 and AMPK Signaling

The colonic epithelium renews rapidly and must balance proliferation with apoptosis to preserve barrier integrity. We investigated whether grape antioxidant dietary fiber (GADF), a grape pomace-derived dietary fiber matrix naturally rich in high molecular weight non-extractable polyphenols, modulates barrier integrity, through proliferation/cell cycle and apoptosis. To gain mechanistic insight, we examined the role of heat-shock proteins (Hsps), and AMP-activated protein kinase (AMPK)-mTOR-lipid-metabolism signaling in healthy proximal colon. Male Wistar rats received either a cellulose-based control diet or an isoenergetic diet where cellulose was replaced with 5% GADF for four weeks. Morphometric analysis, immunohistochemistry, Western blotting, TUNEL, and caspase activity assays quantified cell cycle, apoptotic, Hsps, and metabolic pathways. GADF strengthened the epithelial barrier, increasing goblet cells, occludin, and ZO-1, while reducing crypt depth. Proliferation was suppressed, as indicated by reduced PCNA, cyclins E and D1, and higher p-p53^Ser392, p21^Cip1/Waf1, and p27^Kip1 levels, consistent with G1 arrest. Apoptosis was attenuated, with increased mitochondrial Bcl-2/Bax and Bcl-xL/Bax ratios, lower cytosolic cytochrome c and apoptosis-inducing factor (AIF), and reduced caspase-9 and caspase-3 activities. Hsp27, but not Hsp70, was selectively induced. GADF activated AMPK and p-Raptor, enhanced ACC1 phosphorylation and CPT1, and supported a shift toward fatty acid β-oxidation. Correlation analysis revealed a strong association between Hsp27 and p-p53^Ser392, suggesting potential links between barrier proteins and metabolic pathways. In conclusion, GADF preserves barrier integrity and redirects metabolism via AMPK-Hsp27 signaling, thereby promoting colonic homeostasis. These findings highlight grape pomace as a sustainable source of functional ingredients for nutritional strategies to reinforce epithelial defenses and reduce disease risk.