No abstract

Transient receptor ion channels have emerged as immensely important channels/receptors in diverse physiological and pathological responses. Of particular interest is the transient receptor potential channel subfamily V member 4 (TRPV4), which is a polymodal, nonselective, calciumpermeant cation channel, and is activated by both endogenous and exogenous stimuli. Both neuronal and nonneuronal cells express functional TRPV4, which is responsive to a variety of biochemical and biomechanical stimuli. Emerging discoveries have advanced our understanding of the role of macrophage TRPV4 in numerous inflammatory diseases. In lung injury, TRPV4 mediates macrophage phagocytosis, secretion of pro-resolution cytokines, and generation of reactive oxygen species. TRPV4 regulates lipid-laden macrophage foam cell formation, the hallmark of atheroinflammatory conditions, in response to matrix stiffness and lipopolysaccharide stimulation. Accumulating data also point to a role of macrophage TRPV4 in the pathogenesis of the foreign body response, a chronic inflammatory condition, through the formation of foreign body giant cells. Deletion of TRPV4 in macrophages suppresses the allergic and nonallergic itch in a mouse model, suggesting a role of TRPV4 in skin disease. Here, we discuss the current understanding of the role of macrophage TRPV4 in various inflammatory conditions.

Porphyromonas gingivalis (P.g), a major causative agent of periodontitis, has been linked to atherosclerosis, a chronic inflammatory vascular disease. Recent studies have suggested a link between periodontitis and arterial stiffness, a risk factor for atherosclerosis. However, the mechanisms by which P.g infection contributes to atherogenesis remain elusive. The formation of lipid‐laden macrophage “foam cells” is critically important to development and progression of atherosclerosis. We have obtained evidence that TRPV 4 (transient receptor potential channel of the vanilloid subfamily 4), a mechanosensitive channel, is a regulator of macrophage foam cell formation both in response to P.g‐derived lipopolysaccharide (Pg LPS ) or to an increase in matrix stiffness. Importantly, we found that TRPV 4 activity (Ca 2+ influx) was increased in response to Pg LPS . Genetic deletion or chemical antagonism of TRPV 4 channels blocked Pg LPS ‐triggered exacerbation of oxidized LDL (ox LDL )‐mediated foam cell formation. Mechanistically, we found that (1) T RPV 4 regulated ox LDL uptake but not its cell surface binding in macrophages; (2) reduced foam cell formation in TRPV 4 null cells was independent of expression of CD 36, a predominant receptor for ox LDL , and (3) co‐localization of TRPV 4 and CD 36 on the macrophage plasma membrane was sensitive to the increased level of matrix stiffness occurring in the presence of Pg LPS . Altogether, our results suggest that TRPV 4 channels play an essential role in P.g‐induced exacerbation of macrophage foam cell generation through a mechanism that modulates uptake of ox LDL .

Atherosclerosis, a chronic inflammatory disease of large arteries, is the major contributor to the growing burden of cardiovascular disease-related mortality and morbidity. During early atherogenesis, as a result of inflammation and endothelial dysfunction, monocytes transmigrate into the aortic intimal areas, and differentiate into lipid-laden foam cells, a critical process in atherosclerosis. Numerous natural compounds such as flavonoids and polyphenols are known to have anti-inflammatory and anti-atherogenic properties. Herein, using a fluorometric imaging plate reader-supported Ca2+ influx assay, we report semi high-throughput screening-based identification of ginkgetin, a biflavone, as a novel inhibitor of transient receptor potential vanilloid 4 (TRPV4)-dependent proatherogenic and inflammatory processes in macrophages. We found that ginkgetin (1) blocks TRPV4-elicited Ca2+ influx into macrophages, (2) inhibits oxidized low-density lipoprotein (oxLDL)-induced foam cell formation by suppressing the uptake but not the binding of oxLDL in macrophages, and (3) attenuates oxLDL-induced phosphorylation of JNK2, expression of TRPV4 proteins, and induction of inflammatory mRNAs. Considered all together, the results of this study show that ginkgetin inhibits proatherogenic/inflammatory macrophage function in a TRPV4-dependent manner, thus strengthening the rationale for the use of natural compounds for developing therapeutic and/or chemopreventive molecules.

Atherosclerosis, a chronic inflammatory disease, is the major cause of mortality and morbidity in the United States. Studies suggest that arterial stiffness is a marker and a risk factor for atherosclerosis. Recent reports from our laboratory showed that TRPV4 (transient receptor potential channel of the vanilloid subfamily 4), a mechanosensitive ion channel, plays a role in oxidized LDL (oxLDL)‐induced macrophage foam cell formation, a critical process in atherogenesis. We performed a high‐throughput screening for antagonists of TRPV4 from a library of 2000 natural compounds using a fluorometric imaging plate reader (FLIPR)‐based Ca2+ influx assay. We identified ginkgetin, a biflavone, as a novel small molecule chemical inhibitor of TRPV4. Primary and secondary screening was performed with mouse bone marrow derived macrophages (BMDMs) to assess the ability of ginkgetin and other candidates to inhibit TRPV4‐dependent Ca2+ influx. In our hand’s, ginkgetin demonstrated an IC50 of 0.5 μM for inhibition of TRPV4‐dependent Ca2+ influx. Furthermore, we found that antagonism of TRPV4 by ginkgetin blocks oxLDL‐induced macrophage foam cell formation. Moreover, we found that ginkgetin treatment 1) attenuated oxLDL uptake but not its cell surface binding in BMDMs, 2) inhibited lipopolysaccharide‐induced phosphorylation of JNK, and 3) inhibited oxLDL‐induced expression of proinflammatory cytokines. Taken together, our results show that ginkgetin is a novel inhibitor of TRPV4‐mediated proatherogenic processes in macrophages. Support or Funding Information This work was supported by NIH (1R01EB024556‐01) and NSF (CMMI‐1662776) grants to Shaik O. Rahaman.