How Is NAD+ Metabolism Studied in Cartilage and Osteoarthritis Research?

NAD+ Depletion and Metabolic Changes in Osteoarthritic Cartilage

A study examined NAD+ metabolism in human cartilage and in murine and rat OA models. NAD+ levels were decreased in human and murine OA cartilage. The investigators also measured enzymes involved in NAD+ metabolism and found increased expression of both NAMPT and PARP14. These findings established an altered NAD+ metabolic state in the OA tissues examined.

The study also examined NAD+ changes alongside metabolic and extracellular matrix measurements. This approach allowed researchers to determine whether altered NAD+ availability occurred together with other OA-associated cellular changes. The study therefore used NAD+ concentration as one measurement within a broader metabolic profile rather than as a standalone marker.

NAD+ Consumption Through PARP14 and Related Pathways

PARP14 was examined separately as a potential source of increased NAD+ consumption. In the 2025 study PARP14 expression was increased in OA cartilage. Researchers then used siRNA knockdown in chondrocytes under inflammatory conditions to test the effect of reducing PARP14 expression.

PARP14 knockdown increased NAD+ levels and was associated with changes in OA-related metabolic and matrix-degrading measurements. The experimental design is important because it moved beyond an association between OA and reduced NAD+. It allowed researchers to manipulate one NAD+-consuming enzyme and then measure the resulting cellular changes.

NAMPT, Sirtuin Signaling, and Chondrocyte Function

NAMPT has been examined in human and experimental chondrocytes as part of NAD+ metabolism. In human OA chondrocytes, changing NAMPT activity altered cellular NAD levels, SIRT activity, and cartilage-specific gene expression. The same study found that SIRT1 interacted with SOX9 and influenced transcription from the collagen II promoter.

Other work has shown that the NAMPT-NAD+-SIRT pathway can behave differently under OA-associated signaling conditions. In mouse articular chondrocytes, HIF-2α increased NAMPT expression and stimulated NAD+ synthesis. SIRT2 and SIRT4 were then linked with HIF-2α stability and transcriptional activity. The pathway was associated with expression of MMP3, MMP12, and MMP13 in experimental OA.

SIRT7 has been studied as a separate NAD+-dependent signaling factor. In a mouse OA model, Sirt7 deficiency altered OA development, while attenuation of Sirt7 in ATDC5 chondrogenic cells increased glycosaminoglycan-rich extracellular matrix deposition and expression of Col2a1 and Acan. The study also identified SOX9 transcriptional activity as a SIRT7-related mechanism.

NAD+ Metabolism and Cartilage Matrix Remodeling

Cartilage matrix research focuses on measurable changes in extracellular matrix composition and degradation. Studies have examined collagen II, aggrecan, glycosaminoglycans and matrix-degrading enzymes. These measurements help determine whether molecular changes in chondrocytes are accompanied by changes in cartilage-related gene expression or matrix production.

The SIRT1 study in human OA chondrocytes measured cartilage-specific genes and found that increased SIRT1 activity enhanced expression through a SOX9-dependent mechanism involving the collagen II promoter. The SIRT7 study measured Col2a1, Acan, and glycosaminoglycan-rich matrix deposition after altering SIRT7 activity.

The newer NAD+ metabolism study added extracellular matrix gene profiling and cartilage assessment in animal OA models. This creates a separate tissue level endpoint: researchers can compare changes in NAD+ metabolism with measurable alterations in cartilage structure and matrix-related outcomes.

NAD+ and the Cellular Microenvironment of the Joint

Research has also expanded beyond isolated chondrocytes. A 2025 study investigated an NAD-loaded hydrogel system in an experimental OA model and examined chondrocyte senescence together with synovial changes. The investigators used transcriptomic and metabolomic approaches to characterize cellular responses within the joint environment.

This broader approach is distinct from studies focused only on cartilage cells. It allows researchers to examine whether NAD+-related experimental systems are associated with changes in other joint compartments and cell populations. However, the studies reviewed here do not provide sufficient evidence to describe a defined NAD+ metabolic pathway in subchondral bone. That tissue should therefore not be presented as an established NAD+ mechanism in this article.

NAD+ Restoration and Tissue-Targeted Experimental Systems

Researchers have used different approaches to alter NAD+ availability in experimental OA. A 2025 study examined NMN and NR and tested NMNAT1 overexpression in aging related and surgical OA models. NAD+ metabolism and cartilage related outcomes were then assessed.

Separate studies have examined engineered NAD+-related delivery systems. One used NAD-loaded hydrogel microspheres and measured release behavior, chondrocyte senescenc and synovial macrophage metabolism. Another developed a cartilage-targeted hydrogel containing mitochondria-directed nanoparticles and an NAD+ precursor with measurements of the NAD+/NADH ratio, antioxidant enzymes, senescence-associated factors, and cartilage matrix integrity.

Research Evidence, Experimental Endpoints, and Remaining Gaps

The current research uses several experimental levels. Human cartilage provides direct tissue measurements. Cultured chondrocytes allow researchers to manipulate individual pathways such as NAMPT, SIRT1, SIRT7 and PARP14. Animal OA models add cartilage-level and tissue-level measurements that cannot be obtained from isolated cells.

The endpoints also differ between studies. Researchers have measured NAD+ levels, SIRT activity, NAD+/NADH ratios, gene expression, matrix-related markers, glycosaminoglycan deposition, mitochondrial-related measurements, senescence-associated factors and cartilage structure. The 2025 NAD+ study also combined human tissue analysis with cell and animal experiments, providing several levels of evidence within one investigation.

The evidence remains largely experimental. Human tissue studies can identify associations, while cell and animal experiments allow more direct pathway manipulation. These approaches do not provide equivalent evidence and findings from one model cannot automatically be transferred to another. An important remaining question is how altered NAD+ metabolism relates causally to OA associated changes across different cell types and joint tissues.

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References

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