Aging Bone May Be an Inflammation Problem
Bone loss with age may be driven partly by marrow fat signaling to immune cells, not just weak osteoblasts or low hormones. In aging mice, blocking STING, an innate immune pathway, helped preserve bone structure.
Why it matters: Osteoporosis is usually framed as a mineral or hormone problem. This study points to a different lever: inflammaging inside bone marrow. If marrow fat activates immune cells, and those immune cells drain the NAD⁺ metabolism of bone-forming cells, bone aging becomes a systems problem.
The evidence:
- A 2026 study by Li et al. in Advanced Science found that aging mouse bone marrow showed rising cGAS-STING activation, including more cytoplasmic DNA, more cGAMP, and more activated STING signaling proteins.
- Macrophages had the highest baseline Sting expression among marrow cells. Silencing Sting specifically in macrophages from 12 to 18 months preserved bone density and structure, increased new bone deposition, and reduced marrow fat-cell numbers.
- Old marrow fat cells secreted more inflammatory factors, including DPP4. DPP4 appeared to amplify STING activation through TLR4, especially in the presence of old marrow fluid and mitochondrial DNA stress.
- Activated STING increased CD38, an enzyme that degrades NAD⁺ and related precursors. This may limit NAD⁺ availability to nearby bone marrow mesenchymal stem cells, impairing their mitochondrial function and osteoblast formation.
- Combining the STING inhibitor H-151 with NMN from 12 to 18 months preserved bone density, reduced inflammatory markers, and improved NAD⁺ and mitochondrial metrics in bone-forming cells. Effects were broadly similar to alendronate in several structural measures.
- This fits broader aging biology. Gulen et al. reported in Nature in 2023 that cGAS-STING drives aging-related inflammation and functional decline, linking misplaced DNA sensing to inflammaging.
What to do: Do not treat this as a reason to seek STING inhibitors. Treat it as a reason to protect bone through proven inputs: progressive resistance training, impact or power work when safe, adequate protein, vitamin D sufficiency, calcium adequacy, fall-risk reduction, and DXA screening when indicated.
The counterpoint: This is mouse data, the intervention combined STING inhibition with NMN, and human bone aging may not respond the same way.