Systemic clearance of p16^INK4a‐positive senescent cells mitigates age‐associated intervertebral disc degeneration

Abstract

Rationale Age‐related changes in the intervertebral discs are the predominant contributors to back pain, a common physical and functional impairment experienced by older persons. Cellular senescence, a process wherein cells undergo growth arrest and chronically secrete numerous inflammatory molecules and proteases, has been reported to cause decline in the health and function of multiple tissues with age. Although senescent cells have been reported to increase in intervertebral degeneration (IDD), it is not known whether they are causative in age‐related IDD. Objective The study aimed to elucidate whether a causal relationship exists between cellular senescence and age‐related IDD. Methods and Results To examine the impact of senescent cells on age‐associated IDD, we used p16‐3MR transgenic mice, which enables the selective removal of p16Ink4a‐positive senescent cells by the drug ganciclovir. Disc cellularity, aggrecan content and fragmentation alongside expression of inflammatory cytokine (IL‐6) and matrix proteases (ADAMTS4 and MMP13) in discs of p16‐3MR mice treated with GCV and untreated controls were assessed. In aged mice, reducing the per cent of senescent cells decreased disc aggrecan proteolytic degradation and increased overall proteoglycan matrix content along with improved histological disc features. Additionally, reduction of senescent cells lowered the levels of MMP13, which is purported to promote disc degenerative changes during aging. Conclusions The findings of this study suggest that systemic reduction in the number of senescent cells ameliorates multiple age‐associated changes within the disc tissue. Cellular senescence could therefore serve as a therapeutic target to restore the health of disc tissue that deteriorates with age.

Comparison of inbred mouse strains shows diverse phenotypic outcomes of intervertebral disc aging

“…Alterations in genes that are associated with inflammatory processes, response to stress, cell differentiation, cell metabolism and cell division were shared. Recent aging studies supports the importance of inflammation and metalloproteases secretion (Novais et al, 2019; Tessier et al, 2019), cell differentiation (Mohanty, Pinelli, Pricop, Albert, & Dahia, 2019) and cell cycle (Novais et al, 2019; Patil et al, 2019) in disc health. Moreover, comparison of altered pathways in LG/J aging with changes seen between old LG/J versus BL6, suggested that 23M LG/J mice evidence similar changes in cell differentiation/ossification, inflammation, cell death, phosphate metabolism along with altered DNA repair and immune response‐related processes.…”

Pathomechanism of intervertebral disc degeneration

“…These markers were positively correlated with the expression of matrix metalloproteases including matrix metalloproteinase 13 (MMP13) and a disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS5) . Recently, Patil et al demonstrated the causal relationship between cellular senescence and age‐related IDD using the p16‐3MR transgenic mouse model in which p16‐positive senescent cells can be selectively eliminated by treatment with ganciclovir . The aging mice (age: 1 year) treated with ganciclovir showed decreased levels of catabolic factors along with improved histological features of IDD at age 2 years compared with control mice, indicating that cellular senescence has a direct impact on IDD development.…”

Development of an in vitro senescent hepatic cell model for metabolic studies in aging

“…Moreover, the mRNA expression of senescence marker genes, P53, P21 and P16 were increased in the senescent AML12 cells compared to control AML12 cells (Figure 1d). Similarly, the expression of these genes also was increased in livers from old mice (100-108 week age) compared to those from young mice (12)(13)(14)(15)(16)(17)(18)(19)(20) week age) (Figure 1e). Furthermore, multiple H2O2 treatments increased senescence since there was increased activated -Gal (SA -Gal)-positive cells (Figure 2a,b) and H2A.X-positive cells containing condensed chromatin in larger nuclei (Figure 2c,d).…”

“…Under pathological stress conditions, excessive accumulation of senescence cells in affected tissues adversely affects the tissue's regenerative ability and creates a proinflammatory environment that can resemble various age-related disorders such as Alzheimer's disease, cancer, arthritis, cataracts, osteoporosis, atherosclerosis, hypertension, cardiovascular disease, Type 2 diabetes, and chronic liver disorders [3,5,7,[9][10][11][12]. Targeting senescent cells has the potential to delay age-associated disorders and/or reverse pathological metabolic phenotypes [3,[13][14][15][16]. Recent studies in the liver show that inducing hepatocyte senescence promotes fat accumulation and hepatic steatosis in vitro and in vivo [17].…”