Hypothesis

Oral NMN supplementation increases SIRT6 activity specifically in human subcutaneous adipose tissue, leading to enhanced deacetylation of the autophagy adaptor p62/SQSTM1, increased autophagic flux, and improved metabolic health markers.

Mechanistic Rationale

SIRT6 is an NAD+-dependent deacetylase that promotes DNA repair, suppresses NF‑κB signaling, and stimulates de novo NAD+ biosynthesis by upregulating NAMPT and NMNAT15. NMN serves as a direct precursor for NAD+ biosynthesis, raising intracellular NAD+ pools and thereby providing the co‑factor required for SIRT6 catalysis. In adipose tissue, SIRT6 deacetylates p62 at lysine residues that regulate its ubiquitin‑binding capacity and interaction with LC3, a modification that has been shown to promote selective autophagy of damaged mitochondria and lipid droplets2. Increased SIRT6 activity would therefore shift p62 toward a conformation that favors autophagosome formation, amplifying autophagy flux without altering total p62 protein levels.

Furthermore, SIRT6 modulates hydrogen sulfide (H2S) production by regulating CSE expression5. H2S can act as a signaling molecule that stimulates autophagy through phosphorylation of AMPK and inhibition of mTORC1. By elevating SIRT6 activity, NMN‑induced NAD+ may augment this H2S‑mediated autophagy branch, creating a synergistic loop where NAD+ fuels SIRT6, SIRT6 boosts H2S, and H2S further sustains autophagic activity.

Testable Predictions

1. Biochemical readout – After 12 weeks of daily NMN (500 mg), subcutaneous adipose biopsies will show a significant increase in SIRT6‑dependent deacetylation of histone H3K9ac and of p62 (measured by immunoprecipitation followed by acetyl‑lysine Western blot) compared with placebo.1
2. Flux assay – The same biopsies will exhibit elevated LC3‑II/I ratio and reduced p62 accumulation after ex vivo treatment with bafilomycin A1, indicating heightened autophagic flux.2
3. Metabolic outcome – Participants in the NMN arm will display improved insulin sensitivity (HOMA‑IR reduction) and decreased adipose inflammation (lower CSF‑1R and IL‑6 mRNA) that correlate with the magnitude of p62 deacetylation and autophagic flux changes.
4. Mechanistic link – Pharmacological inhibition of SIRT6 (using a selective inhibitor such as MC1568) in isolated adipocytes from NMN‑treated donors will abolish the NMN‑induced increase in p62 deacetylation and autophagic flux, confirming SIRT6 dependence.

Potential Outcomes and Falsifiability

• Confirmation: If NMN raises adipose SIRT6 activity, p62 deacetylation, and autophagic flux, and these changes correlate with metabolic improvements, the hypothesis is supported.
• Refutation: If NMN fails to alter SIRT6‑specific acetylation marks or autophagic flux in adipose tissue despite raising systemic NAD+ levels, or if SIRT6 inhibition does not block the observed effects, the hypothesis is falsified.

This framework directly addresses the current gap in human evidence linking NMN to SIRT6 activity4 and provides a clear, measurable pathway through which NAD+ supplementation could exert longevity‑related benefits via adipose‑specific autophagy regulation.36