The NADase CD38 is a central regulator in gouty inflammation and a novel druggable therapeutic target

OBJECTIVES

Cellular NAD+ declines in inflammatory states associated with increased activity of the leukocyte-expressed NADase CD38. In this study, we tested the potential role of therapeutically targeting CD38 and NAD+ in gout.

METHODS

We studied cultured mouse wild type and CD38 knockout (KO) murine bone marrow derived macrophages (BMDMs) stimulated by monosodium urate (MSU) crystals and used the air pouch gouty inflammation model.

RESULTS

MSU crystals induced CD38 in BMDMs in vitro, associated with NAD+ depletion, and IL-1β and CXCL1 release, effects reversed by pharmacologic CD38 inhibitors (apigenin, 78c). Mouse air pouch inflammatory responses to MSU crystals were blunted by CD38 KO and apigenin. Pharmacologic CD38 inhibition suppressed MSU crystal-induced NLRP3 inflammasome activation and increased anti-inflammatory SIRT3-SOD2 activity in macrophages. BMDM RNA-seq analysis of differentially expressed genes (DEGs) revealed CD38 to control multiple MSU crystal-modulated inflammation pathways. Top DEGs included the circadian rhythm modulator GRP176, and the metalloreductase STEAP4 that mediates iron homeostasis, and promotes oxidative stress and NF-κB activation when it is overexpressed.

CONCLUSIONS

CD38 and NAD+ depletion are druggable targets controlling the MSU crystal- induced inflammation program. Targeting CD38 and NAD+ are potentially novel selective molecular approaches to limit gouty arthritis.

Targeting CD38 to Suppress Osteoarthritis Development and Associated Pain After Joint Injury in Mice

OBJECTIVE

This study was undertaken to determine the role of CD38, which can function as an enzyme to degrade NAD⁺ , in osteoarthritis (OA) development.

METHODS

Human knee cartilage from normal donors and OA donors were examined for CD38 expression. "Gain-of-function," through overexpression of CD38 via transient transfection, and "loss-of-function," through pharmacologic inhibition of CD38, approaches were used to assess the effects of CD38 on intracellular NAD⁺ :NADH ratio and catabolic activity in chondrocytes. We also initiated joint injury-induced OA by surgical destabilization of the medial meniscus (DMM) in CD38 knockout mice and wild-type (WT; C57BL/6) mice and in WT male mice in the presence or absence of apigenin treatment. Cartilage degradation, synovial inflammation, subchondral bone changes, and pain behavior were evaluated after DMM surgery. We also examined expression of CD38 and the neuropeptide calcitonin gene-related peptide (CGRP) in knee sections from these mice.

RESULTS

CD38 expression was up-regulated in human knee OA cartilage and in chondrocytes stimulated with the proinflammatory cytokine interleukin-1β (IL-1β). Overexpression of CD38 in chondrocytes resulted in reduced cellular NAD⁺ :NADH ratio and augmented catabolic responses to IL-1β. These effects were reversed by pharmacologic inhibition of CD38. Cartilage degradation and synovial inflammation, associated with increased CD38 expression in cartilage and synovium, osteophyte formation and subchondral bone sclerosis, and pain-like behavior linked to increased CGRP expression in the synovium were observed in WT mice after joint injury. Such effects were significantly reduced in mice deficient in CD38 through either genetic knockout or pharmacologic inhibition.

CONCLUSION

CD38 deficiency exerts OA disease-modifying effects. Inhibition of CD38 has the potential to be a novel therapeutic approach for OA treatment.