Age-related matrix stiffening epigenetically regulates α-Klotho expression and compromises chondrocyte integrity

Abstract

Extracellular matrix stiffening is a quintessential feature of cartilage aging, a leading cause of knee osteoarthritis. Yet, the downstream molecular and cellular consequences of age-related biophysical alterations are poorly understood. Here, we show that epigenetic regulation of α-Klotho represents a novel mechanosensitive mechanism by which the aged extracellular matrix influences chondrocyte physiology. Using mass spectrometry proteomics followed by a series of genetic and pharmacological manipulations, we discovered that increased matrix stiffness drove Klotho promoter methylation, downregulated Klotho gene expression, and accelerated chondrocyte senescence in vitro. In contrast, exposing aged chondrocytes to a soft matrix restored a more youthful phenotype in vitro and enhanced cartilage integrity in vivo. Our findings demonstrate that age-related alterations in extracellular matrix biophysical properties initiate pathogenic mechanotransductive signaling that promotes Klotho promoter methylation and compromises cellular health. These findings are likely to have broad implications even beyond cartilage for the field of aging research.

A network medicine approach to elucidate mechanisms underlying menopause-induced knee osteoarthritis

“…We first performed an unbiased Kyoto Encyclopedia of Genes and Genomes (KEGG) Pathway Analysis using ROnToTools. ( 49 ) In the non-menopause group, the only pathway changing across time was Complement and coagulation cascades ( Figure 4B, S4A ), consistent with a previous report( 35 ). Conversely, in the menopause group, changes were progressive.…”

“…These findings suggest that menopausal aging induces progressive cartilage degeneration, while non-menopausal aging does not and are in line with previous work. ( 35 ) Additionally, the OARSI scores in the menopause, but not the non-menopause, group are in line with radiographic tracking of cartilage degeneration in women( 36–39 ), suggesting the menopause group presents with a representative phenotype of KOA in women.…”

Network-based cytokine inference implicates Oncostatin M as a driver for inflammation phenotype of knee osteoarthritis

“…ECM remodeling is a widely-recognized cause of ECM stiffening 98 . In turn, ECM stiffening is a known driver of chondrocyte dysfunction and disrupted cartilage integrity via mechanotransductive pathways, both in the post-traumatic KOA in young mice 37 as well as naturally occurring KOA in aged mice 99 . Studies have shown that traumatic injury in young murine knee joints display altered transcripts associated with ECM remodeling and induced ECM stiffening via LOX-mediated increased collagen crosslinking 30,37 .…”

“…For this reason, matrix alterations have recently been proposed to be a hallmark of aging 40 . It is well established that increased ECM stiffness disrupts chondrocyte functionality via mechanotransductive signals 37,[41][42][43] . We therefore sought to dissect biophysical from biochemical effects of the ECM.…”

“…Young, middle-aged, and aged mice were defined as 2-7, 9-15, and 18-24 months old, respectively, and correspond to ages 20-30, 38-47, and 56-69 years in humans, respectively 128 . Since middle-aged and aged mice display similar proteomic signatures 99 , this study combined middle-aged and aged mice and defined them as the "aged" group. No restrictions were set according to mouse strain or article publication year.…”