Expression of p16^INK4a is a biomarker of chondrocyte aging but does not cause osteoarthritis

Abstract

SummaryCellular senescence drives a functional decline of numerous tissues with aging by limiting regenerative proliferation and/or by producing pro‐inflammatory molecules known as the senescence‐associated secretory phenotype (SASP). The senescence biomarker p16 INK 4a is a potent inhibitor of the cell cycle but is not essential for SASP production. Thus, it is unclear whether p16 INK 4a identifies senescence in hyporeplicative cells such as articular chondrocytes and whether p16 INK 4a contributes to pathologic characteristics of cartilage aging. To address these questions, we examined the role of p16 INK 4a in murine and human models of chondrocyte aging. We observed that p16 INK 4a mRNA expression was significantly upregulated with chronological aging in murine cartilage (~50‐fold from 4 to 18 months of age) and in primary human chondrocytes from 57 cadaveric donors (r 2 = .27, p < .0001). Human chondrocytes exhibited substantial replicative potential in vitro that depended on the activity of cyclin‐dependent kinases 4 or 6 (CDK4/6), and proliferation was reduced in cells from older donors with increased p16 INK 4a expression. Moreover, increased chondrocyte p16 INK 4a expression correlated with several SASP transcripts. Despite the relationship between p16 INK 4a expression and these features of senescence, somatic inactivation of p16 INK 4a in chondrocytes of adult mice did not mitigate SASP expression and did not alter the rate of osteoarthritis (OA) with physiological aging or after destabilization of the medial meniscus. These results establish that p16 INK 4a expression is a biomarker of dysfunctional chondrocytes, but that the effects of chondrocyte senescence on OA are more likely driven by production of SASP molecules than by loss of chondrocyte replicative function.

Targetable mechanisms driving immunoevasion of persistent senescent cells link chemotherapy-resistant cancer to aging

“…Box plot length: 25% and 75% of data; centerline: median; whiskers: 25% -(or 75% +) 1.5 × IQR, dots: outliers. relevant in adult organisms, where retaining arrested yet functional cells may help maintain tissue homeostasis (1,3,63,64). This also raises the possibility that p16 can prevent tumor formation not only by triggering senescence arrest as an early sensor of cellular stress (65), but also by precluding the induction of immune signals that may become detrimental over time if unresolved or unwarranted.…”

The Role of Chondrocyte Hypertrophy and Senescence in Osteoarthritis Initiation and Progression

“…In chondrocytes isolated from cadaveric donors without evidence of OA between 17 to 72 years old, age was found to be responsible for 27% of the variation in p16 levels. However, loss of p16 was not critical enough to prevent the development of age-induced or injury-induced traumatic OA [72]. Collagen type II expression is negatively correlated with p21 expression [73].…”

Controlled induction and targeted elimination of p16INK4a‐expressing chondrocytes in cartilage explant culture

“…Reverse transcription was performed using qScript XLT cDNA SuperMix (VWR International) according to the manufacturer's instructions. Quantitative PCR was performed with TaqMan Universal Master Mix on a QuantStudio 6 Flex Machine (Thermo Fisher Scientific) as recently described in Diekman et al (22). SASP gene expression was analyzed using TaqMan primer probes for IL-6 (Mm00446190_m1), IGF binding protein 3 (Mm01187817_m1), matrix metallopeptidase 13 (Mm00439491), and chemokine (C-C motif) ligand 2 (Mm00441242_m1).…”