Protective effects of GPR120 agonist-programmed macrophages on renal interstitial fibrosis in unilateral ureteral obstruction (UUO) rats

Epithelial-mesenchymal plasticity in kidney fibrosis

Epithelial-mesenchymal transition (EMT) is an important biological process contributing to kidney fibrosis and chronic kidney disease. This process is characterized by decreased epithelial phenotypes/markers and increased mesenchymal phenotypes/markers. Tubular epithelial cells (TECs) are commonly susceptible to EMT by various stimuli, for example, transforming growth factor-β (TGF-β), cellular communication network factor 2, angiotensin-II, fibroblast growth factor-2, oncostatin M, matrix metalloproteinase-2, tissue plasminogen activator (t-PA), plasmin, interleukin-1β, and reactive oxygen species. Similarly, glomerular podocytes can undergo EMT via these stimuli and by high glucose condition in diabetic kidney disease. EMT of TECs and podocytes leads to tubulointerstitial fibrosis and glomerulosclerosis, respectively. Signaling pathways involved in EMT-mediated kidney fibrosis are diverse and complex. TGF-β1/Smad and Wnt/β-catenin pathways are the major venues triggering EMT in TECs and podocytes. These two pathways thus serve as the major therapeutic targets against EMT-mediated kidney fibrosis. To date, a number of EMT inhibitors have been identified and characterized. As expected, the majority of these EMT inhibitors affect TGF-β1/Smad and Wnt/β-catenin pathways. In addition to kidney fibrosis, these EMT-targeted antifibrotic inhibitors are expected to be effective for treatment against fibrosis in other organs/tissues.

Huangqin Decoction ameliorates ulcerative colitis by regulating fatty acid metabolism to mediate macrophage polarization via activating FFAR4-AMPK-PPARα pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Huangqin Decoction (HQD), a traditional Chinese medicine (TCM) formula chronicled in Shang Han Lun, is safe and effective for treatment of ulcerative colitis (UC).

AIM OF THE STUDY

To investigate the effect of HQD against dextran sulfate sodium (DSS)-induced UC mice by regulating gut microbiota and metabolites, and further explore the mechanism of fatty acid metabolism on macrophage polarization.

MATERIALS AND METHODS

Based on 3% dextran sulfate sodium (DSS)-induced UC mice model, clinical symptoms observation (body weight, DAI, and colon length) and histological inspection were used to evaluate the efficacy of HQD and fecal microbiota transplantation (FMT) from HQD-treated mice. The gut microbiota and metabolites were detected by 16S rRNA sequencing and metabolomics analysis. The parameters of fatty acid metabolism, macrophage polarization, and FFAR1/FFAR4-AMPK-PPARα pathway were analyzed by immunofluorescence analysis, western blotting, and real-time PCR. Then, the effects of FFAR1 and FFAR4 on macrophage polarization were examined by agonists based on LPS-induced RAW264.7 cell model.

RESULTS

The results showed that FMT, like HQD, ameliorated UC by improving weight loss, restoring colon length, and reducing DAI scores and histopathological scores. Besides, HQD and FMT both enhanced the richness of gut microbiota, and modulated intestinal bacteria and metabolites to achieve a new balance. Untargeted metabolomics analysis revealed that fatty acids, especially long-chain fatty acids (LCFAs), dominated in HQD against DSS-induced UC by regulating the gut microenvironment. Further, FMT and HQD recovered the expression of fatty acid metabolism-related enzymes, and simultaneously activated FFAR1/FFAR4-AMPK-PPARα pathway but suppressed NF-κB pathway. Combined with cell experiment, HQD and FMT promoted macrophage polarization from M1 toward M2, which were well associated with anti-inflammatory cytokines and combined with the activated FFAR4.

CONCLUSIONS

The mechanism of HQD against UC was related to regulating fatty acid metabolism to mediate M2 macrophage polarization by activating the FFAR4-AMPK-PPARα pathway.

Verbascoside alleviates renal fibrosis in unilateral ureteral obstruction rats by inhibiting macrophage infiltration

Objective(s):

To explore the effect of verbascoside on renal fibrosis in unilateral ureteral obstruction (UUO) rats.

Materials and Methods:

Twenty Sprague-Dawley rats were randomly distributed into sham-operated, UUO, and UUO+Verbascoside groups. After two weeks of rat model construction, urine and blood samples were collected for biochemical analysis while kidney tissues were harvested for hematoxylin and eosin (H&E), Masson’s Trichrome, and immunohistochemistry staining. Pearson coefficient was used to analyze the correlation between the two proteins.

Results:

Verbascoside improved UUO-induced renal dysfunction as detected by decreased serum creatinine, urea nitrogen, and urinary protein excretion rate. In UUO rats, H&E staining result revealed increased total nucleated cell number, and Masson’s Trichrome staining results showed tubular interstitial fibrosis with the deposition of collagen fibrils. Besides, expressions of fibrosis-related proteins including collagen type I (COL-I), α-smooth muscle actin (a-SMA), and tissue inhibitor of metalloproteinase 2 (TIMP2) expressed higher in the UUO group. Moreover, macrophage infiltration-related factors such as CD68+, F4/80+ cells, and suppressor of cytokine signaling-3 (SOCS3) were significantly higher in the UUO group than in sham-operated rats. However, after administration with verbascoside, the accumulation of collagen fibrils and total nucleated cell numbers were mitigated. Likewise, macrophage infiltration was extenuated and fibrosis-related proteins were down-regulated in the UUO+Verbascoside rats. Correlation analysis indicated that macrophage infiltration-related markers were related to fibrosis-related factors.

Conclusion:

Verbascoside could alleviate renal fibrosis in UUO rats probably through ameliorating macrophage infiltration.

The Anti-Atherosclerotic Action of FFAR4 Agonist TUG-891 in ApoE-Knockout Mice Is Associated with Increased Macrophage Polarization towards M2 Phenotype

Background: Over the past few years, a better understanding of the biology of G-protein coupled receptors (GPRs) has led to the identification of several receptors as novel targets for free fatty acids (FFAs). FFAR4 has received special attention in the context of chronic inflammatory diseases, including atherosclerosis, obesity and NAFLD, through to its anti-inflammatory effect. Methods: The present study investigates the influence of prolonged treatment with TUG-891-FFAR4 agonist on the development of atherosclerosis plaque in apoE-knockout mice, using morphometric and molecular methods. Results: TUG-891 administration has led to the reduction of atherosclerotic plaque size and necrotic cores in an apoE-knockout mice model. TUG-891-treated mice were administered subcutaneously at a dose of 20 mg/kg three times a week for 4 months. The FFAR4 agonist reduced the content of pro-inflammatory M1-like macrophages content in atherosclerotic plaques, as evidenced by immunohistochemical phenotyping and molecular methods. In atherosclerotic plaque, the population of smooth muscle cells increased as evidenced by α-SMA staining. We observed changes in G-CSF and eotaxin markers in the plasma of mice; changes in the levels of these markers in the blood may be related to macrophage differentiation. Importantly, we observed a significant increase in M2-like macrophage cells in atherosclerotic plaque and peritoneum. Conclusions: Prolonged administration of TUG-891 resulted in significant amelioration of atherogenesis, providing evidence that the strategy based on macrophage phenotype switching toward an M2-like activation state via stimulation of FFAR4 receptor holds promise for a new approach in the prevention or treatment of atherosclerosis.

Long Chain Fatty Acids as Modulators of Immune Cells Function: Contribution of FFA1 and FFA4 Receptors

Long-chain fatty acids are molecules that act as metabolic intermediates and constituents of membranes; however, their novel role as signaling molecules in immune function has also been demonstrated. The presence of free fatty acid (FFA) receptors on immune cells has contributed to the understanding of this new role of long-chain fatty acids (LCFAs) in immune function, showing their role as anti-inflammatory or pro-inflammatory molecules and elucidating their intracellular mechanisms. The FFA1 and FFA4 receptors, also known as GPR40 and GPR120, respectively, have been described in macrophages and neutrophils, two key cells mediating innate immune response. Ligands of the FFA1 and FFA4 receptors induce the release of a myriad of cytokines through well-defined intracellular signaling pathways. In this review, we discuss the cellular responses and intracellular mechanisms activated by LCFAs, such as oleic acid, linoleic acid, palmitic acid, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), in T-cells, macrophages, and neutrophils, as well as the role of the FFA1 and FFA4 receptors in immune cells.

Regulation of Free Fatty Acid Receptor 4 on Inflammatory Gene Induced by LPS in Large Yellow Croaker (Larimichthys crocea)

Free fatty acid receptor 4 (FFAR4) plays a key role in regulating the inflammatory response in mammals. The present study aimed to investigate the function of large yellow croaker FFAR4 on inflammation. In the present study, ffar4 was widely expressed in 10 tissues of large yellow croaker including gill, head kidney and spleen. Further studies showed that treatment of head kidney macrophages with agonists (TUG891 or GSK137647A) or overexpression of ffar4 reduced the mRNA expression of pro-inflammatory genes induced by LPS, and increased the expression of pparγ. Treatment of macrophages with antagonist AH7614 increased the mRNA expression of pro-inflammatory genes induced by LPS, and decreased the mRNA expression of pparγ. In order to verify the immunomodulatory effect of PPARγ, PPARγ was overexpressed in macrophages which significantly reduced the mRNA expression of pro-inflammatory genes il6, il1β, il8, tnfα and cox2. Moreover, results of dual-luciferase assays showed that PPARγ downregulated the transcriptional activity of il6 and il1β promoters. In conclusion, FFAR4 showed anti-inflammatory effects on LPS-induced inflammation in large yellow croaker.

DHA attenuated Japanese Encephalitis virus infection-induced neuroinflammation and neuronal cell death in cultured rat Neuron/glia

Japanese Encephalitis Virus (JEV) is a neurotropic virus and its Central Nervous System (CNS) infection causes fatal encephalitis with high mortality and morbidity. Microglial activation and consequences of bystander damage appear to be the dominant mechanisms for Japanese Encephalitis and complications. Docosahexaenoic acid (DHA), an essential fatty acid and a major component of brain cell membranes, possesses additional biological activities, including anti-apoptosis, anti-inflammation, and neuroprotection. Through this study, we have provided experimental evidence showing the anti-inflammatory, neuroprotective, and anti-viral effects of DHA against JEV infection in rat Neuron/glia cultures. By Neuron/glia and Neuron cultures, DHA protected against neuronal cell death upon JEV infection and reduced JEV amplification. In Neuron/glia and Microglia cultures, the effects of DHA were accompanied by the downregulation of pro-inflammatory M1 microglia, upregulation of anti-inflammatory M2 microglia, and reduction of neurotoxic cytokine expression, which could be attributed to its interference in the Toll-Like Receptor (TLR), Mitogen-Activated Protein Kinase (MAPK), and Interferon/Janus Kinase/Signal Transducers and Activators of Transcription (Stat), along with the NF-κB, AP-1, and c-AMP Response Element Binding Protein (CREB) controlled transcriptional programs. Parallel anti-inflammatory effects against JEV infection were duplicated by G Protein-Coupled Receptor (GPR120) and GPR40 agonists and a reversal of DHA-mediated anti-inflammation was seen in the presence of GPR120 antagonist, while the GPR40 was less effectiveness. Since increasing evidence indicates its neuroprotection against neurodegenerative diseases, DHA is a proposed anti-inflammatory and neuroprotective candidate for the treatment of neuroinflammation-accompanied viral pathogenesis such as Japanese Encephalitis.

TGF-β1 Signaling: Immune Dynamics of Chronic Kidney Diseases

Chronic kidney disease (CKD) is a major cause of morbidity and mortality worldwide, imposing a great burden on the healthcare system. Regrettably, effective CKD therapeutic strategies are yet available due to their elusive pathogenic mechanisms. CKD is featured by progressive inflammation and fibrosis associated with immune cell dysfunction, leading to the formation of an inflammatory microenvironment, which ultimately exacerbating renal fibrosis. Transforming growth factor β1 (TGF-β1) is an indispensable immunoregulator promoting CKD progression by controlling the activation, proliferation, and apoptosis of immunocytes via both canonical and non-canonical pathways. More importantly, recent studies have uncovered a new mechanism of TGF-β1 for de novo generation of myofibroblast via macrophage-myofibroblast transition (MMT). This review will update the versatile roles of TGF-β signaling in the dynamics of renal immunity, a better understanding may facilitate the discovery of novel therapeutic strategies against CKD.

Activation of GPR120 in podocytes ameliorates kidney fibrosis and inflammation in diabetic nephropathy

Diabetic nephropathy (DN) is one of the most common causes of end-stage renal disease worldwide. ω3-Fatty acids (ω3FAs) were found to attenuate kidney inflammation, glomerulosclerosis, and albuminuria in experimental and clinical studies of DN. As G protein-coupled receptor 120 (GPR120) was firstly identified as the receptor of ω3FAs, we here investigated the function of GPR120 in DN. We first examined the renal biopsies of DN patients, and found that GPR120 expression was negatively correlated with the progression of DN. Immunofluorescence staining analysis revealed that GPR120 protein was mainly located in the podocytes of the glomerulus. A potent and selective GPR120 agonist TUG-891 (35 mg · kg^-1 · d^-1, ig) was administered to db/db mice for 4 weeks. We showed that TUG-891 administration significantly improved urinary albumin excretion, protected against podocyte injury, and reduced collagen deposition in the glomerulus. In db/db mice, TUG-891 administration significantly inhibited the mRNA and protein expression of fibronectin, collagen IV, α-SMA, TGF-β1, and IL-6, and downregulated the phosphorylation of Smad3 and STAT3 to alleviate glomerulosclerosis. Similar results were observed in high-glucose-treated MPC5 podocytes in the presence of TUG-891 (10 μM). Furthermore, we showed that TUG-891 effectively upregulated GPR120 expression, and suppressed TAK1-binding protein-1 expression as well as the phosphorylation of TAK1, IKKβ, NF-κB p65, JNK, and p38 MAPK in db/db mice and high-glucose-treated MPC5 podocytes. Knockdown of GPR120 in MPC5 podocytes caused the opposite effects of TUG-891. In summary, our results highlight that activation of GPR120 in podocytes ameliorates renal inflammation and fibrosis to protect against DN.

GPR120 Ameliorates Apoptosis and Inhibits the Production of Inflammatory Cytokines in Renal Tubular Epithelial Cells

Acute kidney injury (AKI) is the most common complication of sepsis with a high mortality rate. In this study, we focus on the renal injury caused by the immune response of renal tubular epithelial cells and inflammation-induced renal tubular epithelial cell apoptosis. We studied the role of GRP120 in the inflammation and apoptosis of human renal cell line HK-2 and mouse primary renal tubular epithelial cells. GPR120 agonist GW9508 activated the GPR120 pathway. Inflammatory factors were detected using quantitative real-time PCR and enzyme-linked immunosorbent assay. Cell apoptosis experiments included the annexin V and PI double-staining method combined with flow cytometry, TUNEL method, and Western blot. The level of cytokines including TNF-α, IL-6, IL-1β, and iNOS was significantly decreased (P < 0.05) in HK-2 and TECs after the activation of the GPR120 pathway. Besides, the cell apoptosis of both cells increased. Overexpressed GPR120 and shGPR120 were established. Treatment with lipopolysaccharide (LPS) increased the level of cytokines including TNF-α, IL-6, IL-1β, and iNOS in HK-2 cell and TECs. Compared with control-LPS and negative control (NC)-LPS, the overexpression of GPR120 and shGPR120 could decrease and increase the level of secreted cytokines significantly (P < 0.05), respectively, after LPS-induced apoptosis. After H₂O₂- and LPS-induced apoptosis, respectively, compared with the control and NC groups, overexpressed GPR120 and shGPR120 could reduce and increase the expression of caspase-3, respectively. GPR120 could suppress the cellular immune response and apoptosis in renal tubular epithelial cells, thereby possibly protecting the kidney and relieving sepsis-induced AKI.

Activation of GPR120 by TUG891 ameliorated cisplatin-induced acute kidney injury via repressing ER stress and apoptosis

Activation of G protein-coupled receptor 120 (GPR120) could inhibit apoptosis and inflammation in cerebral ischemic injury and liver ischemia-reperfusion injury. However, whether GPR120 agonism exerted potential for cisplatin-induced acute kidney injury and the involved mechanisms remained unknown. In our study, pharmacological activation of GPR120 by TUG891 treatment remarkably reduced the elevated serum creatinine level and attenuated tubular injury. Cisplatin triggered ATF6, PERK and IRE1 pathways of unfolded protein response (UPR) of ER stress in the injured kidney tissue, as well as the downstream molecules eIF2α, ATF4 and XBP1. Protein of ER stress-mediated apoptosis, CHOP, was overexpressed in the cisplatin group. Oral application of TUG891 displayed effective inhibition of ER stress and apoptosis. TUG891 treatment significantly decreased the TUNEL positive cells and the flow cytometry of HK-2 cells delineated the similar results that the apoptosis rates were considerably reduced in the TUG891 group compared to cisplatin group. Collectively, activation of GPR120 by TUG891 exhibited renal protection against cisplatin-induced AKI via suppressing ER-associated apoptosis in tubular epithelial cells.