TGF-β-Dependent α11 Integrin Expression Is Reduced in Aging Gingival Wounds

TGF-β regulates the expression of the α11 integrin, a crucial collagen receptor in wound healing. As healing is impaired in older mammals, we examined the influence of aging on the regulation of TGF-β-mediated α11 integrin expression in gingival repair. Primary cultures of human gingival fibroblasts from young and aged donors were examined by RT-qPCR and Western blot to assess the expression of α2 and α11 integrins, TGF-β (isoforms 1, 2, 3), and TGF-β receptors 1 and 2. TGF-β1 and TGF-β2 were quantified by ELISA. TGF-β activity was evaluated using a gene reporter assay. In gingival wounds created in young and aged mice, collagen deposition and organisation, and expression levels of α11 integrin, TGF-β1 and TGF-β2 were quantified. Data were analysed using unpaired t-test, Mann-Whitney or ANOVA. There were reduced expression levels of α11 integrin (76% mRNA/33% protein) and TGF-β1 (34% mRNA/40% protein), and reduced TGF-β activity (38%) in cultured fibroblasts from older compared with younger donors. Treatment with TGF-β1 induced a 3.6-fold increase of α11 integrin mRNA and a 45% increase of α11 integrin protein in fibroblasts from younger donors, but there was no change in treated cells obtained from older donors. Compared with younger mice, gingival wounds in older mice demonstrated lower levels of collagen deposition (61%), collagen alignment (48%), α11 integrin (77%) and TGF-β1 (86%). Aging is associated with reduced TGF-β1 expression and signalling in gingival fibroblasts, which leads to diminished α11 integrin expression. This disruption of TGF-β1-dependent α11 integrin signalling underpins one potential mechanism for impaired gingival connective tissue repair seen during aging.