Publication Highlight: Sirt6 Loss Promotes Disc Degeneration
Authors
Ramteke P, Watson B, Toci M, Tran VA, Johnston S, Tsingas M, Barve RA, Mitra R, Loeser RF, Collins JA, Risbud MV.
Overview:
This study investigates the critical role of the SIRT6 protein in maintaining the health of the intervertebral disc during aging and identifies it as a potential therapeutic target for disc degeneration.
Purpose:
The study aimed to explore the role of SIRT6, a mammalian sirtuin and histone deacetylase, in intervertebral disc health and age-associated degeneration. Researchers sought to determine if the loss of SIRT6 would accelerate degenerative phenotypes and to understand the underlying molecular mechanisms, such as changes in chromatin accessibility, DNA damage, and cell senescence.
Methods:
- Disc-specific Sirt6 knockout mice were generated using a conditional model targeting aggrecan-expressing cells (i.e., nucleus pulposus (NP)). Disc degeneration was assessed at 12 and 24 months.Â
- In a separate set of experiments, primary NP cells were isolated from rat and treated with lentiviral ShRNAs to knockdown SIRT6, which permitted additional mechanistic studies.Â
- RNA sequencing was performed on disc tissues and cells.Â
- Senescence and DNA damage were evaluated using p21 and p19 as markers, while autophagy was measured via LC3 levels using an ELISA.Â
Key Findings:
- SIRT6 deficiency significantly accelerated disc degeneration in an age-dependent manner, characterized by NP fibrosis and altered disc height.
- Sirt6-deficient cells showed a higher cell senescence and increased levels of p21, p19, IL-6, IL-1β, and TGF-β.
- The authors reported an increase in DNA damage and a decrease in autophagy in SIRT6-deficient tissues.
Conclusions & Implications:
These data established SIRT6 as a master regulator of disc health, which maintains tissue integrity by inhibiting senescence and DNA damage while promoting autophagy. Because SIRT6 activity is tied to NAD+ levels, which naturally decline with age, the findings suggest that pharmacological activation of SIRT6 or restoring NAD+ could offer a non-invasive therapeutic strategy to treat or prevent age-related intervertebral disc degeneration.
Product Highlight:
The InVivO2 400 hypoxia workstation by Baker Ruskinn was used to culture primary rat NP cells during the in vitro experiments. This was critical to replicate physiologically relevant conditions for this cell population, which naturally reside in a low-oxygen (i.e., hypoxic) environment. Thus, to mimic physiological hypoxia (termed “physioxia), the InVivO2 chamber was set to a mixture of 1% O2, 5% CO2, and 94% N2. These conditions allowed for the accurate evaluation of SIRT6 knockdown and downstream cellular responses, ensuring the outcomes were representative of the actual biological environment of the disc.
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