Terminalia Arjuna bark extract impedes foam cell formation and promotes apoptosis in ox-LDL-stimulated macrophages by enhancing UPR-CHOP pathway

Abstract

BackgroundIncreased macrophage and foam cell apoptosis during early atherogenesis retards plaque progression by impeding foam cell formation, suppressing inflammation and limiting lesion cellularity. Our previous in vitro study in THP1 macrophages demonstrated that Terminalia Arjuna (TA) attenuates dual-specificity phosphatase1 (DUSP1), a key negative regulator of JNK/P38MAPK signaling cascade, the branch also implicated in the UPR (unfolded protein response)-CHOP-mediated apoptotic pathway; however this pathway has not been explored so far in the presence of TA. Therefore, we aimed to elucidate the pro-apoptotic effect of aqueous bark extract of TA (aqTAE) on macrophage and foam cells and the underlying mechanism associated with it.MethodsTHP1 cells were initially differentiated into macrophages with phorbol-12-myristate-13-acetate (PMA) (100 ng/ml) for 24 h, followed by ox-LDL (100 μg/ml) treatment for another 24 h to induce foam cell formation. Thereafter, macrophages and ox-LDL- treated cells were incubated with aqTAE (100 μg/ml) for the next 24 h. Further, Oil Red O (ORO) staining, CD36 expression profiling, apoptotic assay and transcriptional and translational expression of ER-stress markers i.e., X-box binding protein 1 (XBP1) and C/EBP homologous protein (CHOP) were performed for elucidating the potential mechanism underlying TA-induced macrophage and foam cell apoptosis.ResultsWe demonstrated that ox-LDL treatment significantly increased lipid accumulation and upregulated CD36 expression, indicating foam cell formation; while the addition of aqTAE resulted in a significant decline in ORO positive cells, and suppression of CD36 expression in ox-LDL-stimulated macrophages, suggestive of reduced formation of lipid-laden foam cells. Further, aqTAE treatment alone and in combination with oxidized low-density lipoprotein (ox-LDL) stimulus, significantly attenuated CD36 expression; increased apoptosis; and augmented the expression of UPR regulatory proteins including XBP1 and CHOP, and similar observations were noted when cells were treated with ox-LDL alone. These findings indicate that TA promotes macrophage and foam cell apoptosis via enhancing UPR-mediated activation of JNK/p38MAPK-CHOP pathway in a DUSP1-dependent manner, implying a possible interplay between ox-LDL-induced ER stress- and TA-mediated MAPK signaling.ConclusionOur data shows that aqTAE inhibits foam cell formation, as well as promotes macrophage and foam cell apoptosis by augmenting UPR- JNK/p38MAPK-CHOP signaling cascade via inhibiting DUSP1. These findings provide novel mechanistic insight into the anti-atherogenic potential of TA, which may prove beneficial against early-stage atherosclerotic lesions.

Quercetin Suppresses the Progression of Atherosclerosis by Regulating MST1-Mediated Autophagy in ox-LDL-Induced RAW264.7 Macrophage Foam Cells

“…Therefore, we used 100 μg/mL ox-LDL to induce the formation of foam cells in subsequent experiments. The same concentration of ox-LDL (100 μg/mL) has been reported in other studies [23]. Next, we assessed the effect of QUE on RAW264.7 cell viability.…”

Theranostic nanoplatform to target macrophages enables the inhibition of atherosclerosis progression and fluorescence imaging of plaque in ApoE(−/−) mice

“…Additionally, such cytoplasmic fluorescence signal was significantly stronger for ox-LDL-stimulated RAW264.7 cells (Fig. 3 b: *** P < 0.001 vs. unstimulated cells), which might benefit from the upregulated expression of CD36 on macrophages after ox-LDL treatment [ 20 ]. The western blot result further showed that the expression of CD36 was increased in ox-LDL-treated RAW264.7 cells ( P < 0.05 ox-LDL stimulation group vs. control group) (Additional file 1 : Fig.…”

“…Studies have shown that CD36, which is expressed on the surface of macrophage, is a key regulatory point for the formation and development of AS. It can mediate the conversion of macrophage into foam cell after phagocytosis of ox-LDL [ 19 , 20 ]. AntiCD36 can specifically bind to CD36 and inhibit macrophage phagocytosis of ox-LDL [ 21 ].…”

Role of various imbalances centered on alveolar epithelial cell/fibroblast apoptosis imbalance in the pathogenesis of idiopathic pulmonary fibrosis

“…[ 82 ] However, when stress is overloaded or prolonged, the UPR becomes maladaptive and triggers apoptotic cell death through activating cell death pathways such as caspase-4, c-Jun NH2 terminal kinase, and C/EBP homologous protein. [ 83 – 85 ] ER stress may cause fibrosis through AEC apoptosis, EMT, myofibroblast differentiation, and M2 macrophage polarization. [ 14 – 16 ]…”