Atasoy‐Zeybek, Aysegul

Aging is a major risk factor for osteoarthritis (OA), but the specific mechanisms connecting aging and OA remain unclear. Although chondrocytes rarely divide in adult articular cartilage, they undergo replicative senescence in vitro, offering a model to study aging-related changes under controlled conditions. OA cartilage was obtained from an 80-year-old male and a 72-year-old female, while normal cartilage was sourced from a 26-year-old male. Chondrocyte cultures were established and sub-cultured to their Hayflick limit. Bulk RNA sequencing on early- and late-passage human articular chondrocytes identified transcriptomic changes associated with cellular aging. Early-passage OA chondrocytes already showed senescent phenotypes, unlike normal chondrocytes. All three cultures underwent 30 population doublings before replicative exhaustion, at which point all cells displayed senescence. During this process, cells lost their ability to form cartilaginous pellets. Differential gene expression analysis revealed distinct transcriptomic profiles between early- and late-passage chondrocytes and between normal and OA-derived cells. Genes related to matrix synthesis, degradation, inflammation, and the senescence-associated secretory phenotype (SASP) showed significant expression changes. Despite being a small pilot study, these findings suggest that further research into the molecular and metabolic changes during chondrocyte senescence could provide valuable insights into OA pathobiology.

Abstract Objective Aging is a major risk factor for OA, but the specific mechanisms underlying this connection remain unclear. Although chondrocytes rarely divide in adult articular cartilage, they undergo replicative senescence in vitro which provides an opportunity to study changes related to aging under controlled laboratory conditions. Methods Cartilage was recovered from two knees with OA and one normal knee. Chondrocyte cultures were established and sub-cultured until their Hayflick limit. Bulk RNA sequencing on early- and late-passage human articular chondrocytes allowed identification of transcriptomic changes associated with cellular aging. Results One male (80 years old) and one female (72 years old) patient provided OA cartilage. The donor of normal chondrocytes was a 26-year old male. Early passage chondrocytes from the two OA samples already had the phenotype of senescing cells, unlike normal chondrocytes. Nevertheless, all three chondrocyte cultures underwent 30 population doublings before replicative exhaustion, by which point all cells displayed a senescent phenotype. During this process, the cells lost their ability to form cartilaginous pellets. Differentially expressed genes (DEGs) analysis confirmed distinct transcriptomic profiles between early- and late-passage chondrocytes, as well as between cells isolated from normal and OA cartilage. Various changes in expression of genes related to cartilage matrix synthesis, degradation, inflammation and the senescence-associated secretory phenotype (SASP) were noted. Conclusions Although only a small pilot study, its data suggest that a larger and deeper study of the molecular and metabolic events accompanying the senescence of chondrocytes could provide important insights into the pathobiology of OA.

AbstractThis study defined and compared the course of native, impaired and growth factor‐stimulated bone regeneration in a rat femoral defect model. A mid‐diaphyseal defect with rigid internal fixation was surgically created in the right femur of male Fischer rats and serially analyzed over 36 weeks. Native bone regeneration was modeled using a sub‐critical, 1 mm size defect, which healed uneventfully. Critical size defects of 5 mm were used to analyze impaired bone regeneration. In a third group, the 5 mm defects were filled with 11 µg of recombinant human bone morphogenetic protein 2 (rhBMP2) impregnated onto an absorbable collagen sponge, modeling its clinical use. Native bone regeneration was characterized by endochondral ossification with progressive remodeling to ultimately resemble intact femora. An endochondral response was also observed under conditions of impaired bone regeneration, but by week 8 medullary capping occurred with fibrofatty consolidation of the tissue within the defect, resembling an atrophic non‐union. rhBMP2 treatment was associated with prolonged inflammatory cytokine expression and rapid intramembranous bone formation occurring with reduced expression of cartilage‐associated collagens. Between weeks 4 and 36, rhBMP2‐treated bones demonstrated decreased trabecular number and increased trabecular separation, which resulted in inferior mechanical properties compared with bones that healed naturally. Clinical Significance: Recombinant human bone morphogenetic protein 2 (rhBMP2) is used clinically to promote healing of long bones. Our data suggest that it drives intramembraneous ossification producing an inferior regenerate that deteriorates with time. Clinical outcomes would be improved by technologies favoring endochondral regenerative ossification.