Age-dependent changes in protein incorporation into collagen-rich tissues of mice by in vivo pulsed SILAC labelling

Abstract

Collagen-rich tissues have poor reparative capacity that predisposes to common age-related disorders such as osteoporosis and osteoarthritis. We used in vivo pulsed SILAC labelling to quantify new protein incorporation into cartilage, bone, and skin of mice across the healthy life course. We report dynamic turnover of the matrisome, the proteins of the extracellular matrix, in bone and cartilage during skeletal maturation, which was markedly reduced after skeletal maturity. Comparing young adult with older adult mice, new protein incorporation was reduced in all tissues. STRING clustering revealed changes in epigenetic modulators across all tissues, a decline in chondroprotective growth factors such as FGF2 and TGFβ in cartilage, and clusters indicating mitochondrial dysregulation and reduced collagen synthesis in bone. Several pathways were implicated in age-related disease. Fewer changes were observed for skin. This methodology provides dynamic protein data at a tissue level, uncovering age-related molecular changes that may predispose to disease.

Age-associated changes in knee osteoarthritis, pain-related behaviors, and dorsal root ganglia immunophenotyping of male and female mice

“…Here, we saw increased signs of OA, including cartilage degeneration, osteophytes, and synovitis in aged male and female mice, with worse OA in males than in females. This supports previous reports that have evaluated naturally occurring mouse OA joint degeneration predominantly in male mice (44, 49–55). McNulty et al reported that older male mice (16-month, 17-month, and 23-month old) had significantly thinner articular cartilage compared to 4.5-month old mice (44).…”

“…Another study showed significant cartilage degeneration in 18- and 25-month old male mice (by safranin-O stain) in the temporomandibular joint (TMJ) (50). In addition, collagen-rich tissues are pre-disposed to common age-related disorders, such as OA, and studies reported age-associated changes in cartilage matrix protein content, such as reduced protein incorporation in all tissues (cartilage, bone, skin), dynamic turnover of matrisome, and reduced collagen synthesis in bone of older mice, compared to younger mice (49, 56). Here, we found mild synovitis and osteophyte presence in both male and female 20-month old mice.…”

Scleraxis-lineage cells are required for tendon homeostasis and their depletion induces an accelerated extracellular matrix aging phenotype

“…Indeed, the combination of transcriptomic and proteomic analyses in these models has facilitated identification of the key alterations in ECM composition that are associated with initiation and progression of tendon degeneration. Consistent with declines in highturnover rate proteoglycans and glycoproteins with aging in other tissues [10,[59][60][61], these classes of proteins were decreased in both aged and young depleted tendons, demonstrating that Scx Lin cells are required to directly regulate the synthesis and maintenance of multiple GPs and PGs, which are crucial to maintain tendon structure-function, since their decrease results in significantly impaired collagen fibril organization and biomechanical properties. While other studies have shown through genetic KO models, that high turnover rate GPs and PGs are required to maintain tissue (tendon, bone, cartilage, skin) homeostasis during adulthood [57,58,[62][63][64][65][66][67][68][69][70][71][72][73], they have been primarily descriptive.…”

The Extracellular Matrix of Articular Cartilage Controls the Bioavailability of Pericellular Matrix-Bound Growth Factors to Drive Tissue Homeostasis and Repair

“…The ECM of cartilage is made up of two main components: type II collagen and the sulfated proteoglycan, aggrecan. In addition, there are many other less abundant collagens, proteoglycans, and glycoproteins that collectively constitute the matrisome [ 2 , 3 ].…”

“…The result was almost identical in individuals whose joints were being removed at the time of arthroplasty surgery for OA, indicating that even when the cartilage is damaged, new type II collagen is not being replaced [ 25 ]. Low integration of type II collagen into post-natal articular cartilage is also demonstrated in mice using pulse SILAC labeling, in which stable isotope-labeled amino acids are delivered in the diet and their incorporation into tissues measured by proteomic analysis [ 3 ]. Using this technique, the incorporation of collagens and other matrisomal proteins was examined during healthy aging.…”