Senescent mesenchymal cells accumulate in human fibrosis by a telomere‐independent mechanism and ameliorate fibrosis through matrix metalloproteinases

Abstract

Fibrosis can occur in many organs, where it is a debilitating and preneoplastic condition. The senescence of activated fibroblasts has been proposed to ameliorate fibrosis via the innate immune system but its role in humans has not been investigated. The availability of oral submucous fibrosis (OSMF) biopsies at different stages of disease progression allowed us to test the hypothesis that senescent fibroblasts accumulate with the progression of human fibrosis in vivo, and also to examine the mechanism of senescence. We tested the hypothesis that senescent cells may ameliorate fibrosis by increasing the secretion of matrix metalloproteinases (MMPs). We have used a combination of in situ immunodetection techniques, drug treatments, fluorescence-activated cell sorting and enzyme-linked absorbance assays on tissue samples and fibroblast cultures. We report a novel panning technique, based on fibronectin adhesion rates, to enrich and deplete senescent cells from fibroblast populations. Senescent fibroblasts, as determined by the presence of senescence-associated heterochromatic foci, accumulated with OSMF progression (R(2) = 0.98) and possessed a reduced replicative lifespan in vitro. Unlike wounds, however, OSMF fibroblasts were quiescent in vivo and consistent with this observation, possessed functional telomeres of normal length. Senescence was associated in vivo and in vitro with oxidative damage, DNA damage foci and p16(INK4A) accumulation and required the production of reactive oxygen species (ROS), perhaps from damaged mitochondria, but not the continuous presence of the disease stimulus (areca nut and tobacco), the tissue environment or other cell types. Depletion of OSMF fibroblasts of senescent cells showed that these cells accounted for 25-83 times more MMP-1 and -2 than their pre-senescent counterparts. The results show that the accumulation of senescent fibroblasts in human fibrosis occurs by a telomere-independent mechanism involving ROS and may locally ameliorate the condition by the increased expression of MMPs prior to clearance by the immune system.

Replicatively senescent human fibroblasts reveal a distinct intracellular metabolic profile with alterations in NAD+ and nicotinamide metabolism

“…We also reported previously that the intracellular metabolic profile surprisingly showed a shift of energy metabolism away from the tri-carboxylic acid (TCA) cycle and towards glycolysis and the pentose phosphate pathway23 and more recent evidence suggests that the shift to glycolysis may dependent on mitochondrial dysfunction24. In addition, we reported evidence of a strong redox homeostasis response that is consistent with relatively low levels of cells positive for nuclear 8-hydroxy-2-deoxyguanosine compared to DNA damage foci in established PEsen cells2325.…”

Oral Submucous Fibrosis: Review on Mechanisms of Pathogenesis and Malignant Transformation

“…Furthermore it was observed that the senescent fibroblasts produce 25-83 times more MMP-1 and -2 than their pre-senescent counterparts. Therefore, senescent cells may locally ameliorate the fibrosis by increased expression of MMPs prior to their clearance by the innate immune system [75]. Although, our two studies show slightly different findings in relation to senescence and arecoline, increase amount of senescent cells appeared to be common.…”

Oral submucous fibrosis: a historical perspective and a review on etiology and pathogenesis

“…Significance of ROS in the pathogenesis and malignant transformation of OSF. 55 has been highlighted.…”