This goal of this project is to better understand the connection between aging and osteoarthritis (OA). OA is a painful disease of the joints that affects an estimated 27 million people in the United States. While it is well established that the risk for OA increases with age, the reason for this is not fully known. One potential explanation is that chondrocytes, the cells that make up cartilage tissue, exhibit a particular form of dysfunction associated with aging known as cellular senescence. Senescent cells are characterized by the inability to divide, the excessive production of inflammatory molecules, and the expression of a gene known as p16Ink4a. This project will explore the hypothesis that cellular senescence increases in joints during the development or OA associated with aging or injury, and that chondrocyte senescence functionally contributes to OA development. The scientific approach is to utilize mice that have been genetically engineered to have distinct functions in place of the normal expression of p16Ink4a.
The first aim will track the development of senescence at the single cell level by analyzing mice that express the fluorescent protein tdTomato instead of p16Ink4a. This will allow precise identification of the frequency of senescence during the development of OA with aging and after joint injury. Furthermore, cells will be sorted with flow cytometry based on tdTomato expression and the transcriptional profile of senescent cells will be compared to non-senescent cells using RNA-sequencing.
The second aim will assess the progression of OA in mice that have a chondrocyte-specific deletion of p16Ink4a upon administration of tamoxifen in adulthood. Because these mice are expected to exhibit less chondrocyte senescence, observations that OA is reduced in the context of aging or joint injury would support the hypothesis that maintaining a senescent state is functionally important to the development of OA. The long-term objective of this work is to identify new strategies for preventing or slowing the progression of OA, including the clearance of senescent cells from the joint. This fellowship grant will also train the principle investigator in technique of murine genetics and cartilage aging in order to establish a research career in the field.

Public Health Relevance

Osteoarthritis (OA) is a common cause of joint pain and disability in the elderly, and a form of age- associated cellular dysfunction known as senescence may be involved. This project will use genetically engineered mice to track the development of cellular senescence with aging and joint injury, and will also assess the effect of preventing chondrocyte senescence on the development of OA. The long-term goal of this training fellowship is to generate novel strategies for treating or preventing OA, and to provide extensive training in the techniques required for the principle investigator to continue research in the area of cartilage aging.

National Institute of Health (NIH)
National Institute on Aging (NIA)
Postdoctoral Individual National Research Service Award (F32)
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Special Emphasis Panel (ZRG1)
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Williams, John
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University of North Carolina Chapel Hill
Schools of Medicine
Chapel Hill
United States
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Diekman, Brian O; Sessions, Garrett A; Collins, John A et al. (2018) Expression of p16INK4a is a biomarker of chondrocyte aging but does not cause osteoarthritis. Aging Cell :e12771
Collins, John A; Diekman, Brian O; Loeser, Richard F (2018) Targeting aging for disease modification in osteoarthritis. Curr Opin Rheumatol 30:101-107
Loeser, Richard F; Collins, John A; Diekman, Brian O (2016) Ageing and the pathogenesis of osteoarthritis. Nat Rev Rheumatol 12:412-20