β-Arrestin2 is increased in liver fibrosis in humans and rodents

β-arrestin2 promotes angiogenesis of liver sinusoidal endothelial cells through the VEGF/VEGFR2 pathway to aggravate cirrhosis

Excessive extracellular matrix deposition and increased intrahepatic angiogenesis are prominent features of cirrhosis. β-arrestin2 is thought to be involved in the pathological processes of various fibrotic diseases. This study aimed to investigate the role and possible mechanism of β-arrestin2 in the angiogenesis of cirrhosis. Firstly, β-arrestin2 expression in liver tissues of cirrhotic patients was detected, and the correlation between β-arrestin2 and α-SMA, CD-31, PDGF, and VEGF indexes was analyzed. Then, after liver cirrhosis induced by CCL4 in Arrb2-KO mice (β-arrestin2 coding gene), liver histopathological changes were observed, and the expressions of α-SMA, CD-31, PDGF, VEGF, and VEGFR2 were detected. Finally, VEGF-A was used to treat human liver sinusoidal endothelial cells (LSECs) to simulate pathological conditions. After transfection with si-ARRB2, the cell activity, MDA and GSH-PX activities, cell invasion, angiogenesis, and the expressions of α-SMA, CD-31, and VEGF/VEGFR2 pathway were detected. Results showed that β-arrestin2 expression in the liver increased significantly during cirrhosis and was positively correlated with angiogenesis. In vivo, Arrb2-KO significantly inhibited fibrosis and angiogenesis in cirrhotic mice, and decreased the expressions of α-SMA, CD31, PDGF, VEGF, and VEGFR2. Studies using LSECs in vitro showed that after intervention of ARRB2, the activity of LSECs and the number of invasions and tubule formations were significantly reduced. Similarly, after transfection with si-ARRB2, the expressions of α-SMA, CD31, PDGF, VEGF, and VEGFR2 in LSECs were significantly decreased. Collectively, β-arrestin2 aggravated cirrhosis by promoting the angiogenesis of LSECs. Blocking β-arrestin2 may be an important target against angiogenesis and fibrosis in cirrhosis.

β-Arrestin pathway activation by selective ATR1 agonism promotes calcium influx in podocytes, leading to glomerular damage

Angiotensin receptor blockers (ARBs) are the first-line treatment for hypertension; they act by inhibiting signaling through the angiotensin 1 receptor (AT1R). Recently, a novel biased AT1R agonist, TRV120027 (TRV), which selectively activates the β-arrestin cascade and blocks the G-protein-coupled receptor pathway has been proposed as a potential blood pressure medication. Here, we explored the effects of TRV and associated β-arrestin signaling in podocytes, essential cells of the kidney filter. We used human podocyte cell lines to determine β-arrestin's involvement in calcium signaling and cytoskeletal reorganization and Dahl SS rats to investigate the chronic effects of TRV administration on glomerular health. Our experiments indicate that the TRV-activated β-arrestin pathway promotes the rapid elevation of intracellular Ca2+ in a dose-dependent manner. Interestingly, the amplitude of β-arrestin-mediated Ca2+ influx was significantly higher than the response to similar Ang II concentrations. Single-channel analyses show rapid activation of transient receptor potential canonical (TRPC) channels following acute TRV application. Furthermore, the pharmacological blockade of TRPC6 significantly attenuated the β-arrestin-mediated Ca2+ influx. Additionally, prolonged activation of the β-arrestin pathway in podocytes resulted in pathological actin cytoskeleton rearrangements, higher apoptotic cell markers, and augmented glomerular damage. TRV-activated β-arrestin signaling in podocytes may promote TRPC6 channel-mediated Ca2+ influx, foot process effacement, and apoptosis, possibly leading to severe defects in glomerular filtration barrier integrity and kidney health. Under these circumstances, the potential therapeutic application of TRV for hypertension treatment requires further investigation to assess the balance of the benefits versus possible deleterious effects and off-target damage.

Hepatic β-arrestins: potential roles in liver health and disease

Β-arrestins are intracellular scaffolding proteins that have multifaceted roles in different types of disorders. In this review article, we gave a summary about the discovery, characterization and classification of these proteins and their intracellular functions. Moreover, this review article focused on the hepatic expression of β-arrestins and their hepatocellular distribution and function in each liver cell type. Also, we showed that β-arrestins are key regulators of distinct types of hepatic disorders. On the other hand, we addressed some important points that have never been studied before regarding the role of β-arrestins in certain types of hepatic disorders which needs more research efforts to cover.

Vincamine as an agonist of G protein-coupled receptor 40 effectively ameliorates pulmonary fibrosis in mice

BACKGROUND

Pulmonary fibrosis (PF) is an irreversible and fatal lung disease with limited therapeutic options. G protein-coupled receptor 40 (GPR40) has been developed as a promising therapeutic target for metabolic disorders and functions potently in varied pathological and physiological processes. Vincamine (Vin) is a monoterpenoid indole alkaloid originated from Madagascar periwinkle and was reported as a GPR40 agonist in our previous work.

PURPOSE

Here, we aimed to clarify the role of GPR40 in PF pathogenesis by using the determined GPR40 agonist Vin as a probe and explore the potential of Vin in ameliorating PF in mice.

METHODS

Pulmonary GPR40 expression alterations were assessed in both PF patients and bleomycin-induced PF mice (PF mice). Vin was used to evaluate the therapeutic potential of GPR40 activation for PF and the underlying mechanism was intensively investigated by assays against GPR40 knockout (Ffar1^-/-) mice and the cells transfected with si-GPR40 in vitro.

RESULTS

Pulmonary GPR40 expression level was highly downregulated in PF patients and PF mice. Pulmonary GPR40 deletion (Ffar1^-/-) exacerbated pulmonary fibrosis as evidenced by the increases in mortality, dysfunctional lung index, activated myofibroblasts and extracellular matrix (ECM) deposition in PF mice. Vin-mediated pulmonary GPR40 activation ameliorated PF-like pathology in mice. Mechanistically, Vin suppressed ECM deposition by GPR40/β-arrestin2/SMAD3 pathway, repressed inflammatory response by GPR40/NF-κB/NLRP3 pathway and inhibited angiogenesis by decreasing GPR40-mediated vascular endothelial growth factor (VEGF) expression in the region of interface to normal parenchyma in pulmonary fibrotic tissues of mice.

CONCLUSION

Pulmonary GPR40 activation shows promise as a therapeutic strategy for PF and Vin exhibits high potential in treating this disease.

Beta-blockers in patients with liver cirrhosis: Pragmatism or perfection?

With increasing decompensation, hyperdynamic circulatory disturbance occurs in liver cirrhosis despite activation of vasoconstrictors. Here, the concept of a therapy with non-selective beta-blockers was established decades ago. They lower elevated portal pressure, protect against variceal hemorrhage, and may also have pleiotropic immunomodulatory effects. Recently, the beneficial effect of carvedilol, which blocks alpha and beta receptors, has been highlighted. Carvedilol leads to "biased-signaling" via recruitment of beta-arrestin. This effect and its consequences have not been sufficiently investigated in patients with liver cirrhosis. Also, a number of questions remain open regarding the expression of beta-receptors and its intracellular signaling and the respective consequences in the intra- and extrahepatic tissue compartments. Despite the undisputed role of non-selective beta-blockers in the treatment of liver cirrhosis, we still can improve the knowledge as to when and how beta-blockers should be used in which patients.

Liver Fibrosis-From Mechanisms of Injury to Modulation of Disease

The Transregional Collaborative Research Center "Organ Fibrosis: From Mechanisms of Injury to Modulation of Disease" (referred to as SFB/TRR57) was funded for 13 years (2009-2021) by the German Research Council (DFG). This consortium was hosted by the Medical Schools of the RWTH Aachen University and Bonn University in Germany. The SFB/TRR57 implemented combined basic and clinical research to achieve detailed knowledge in three selected key questions: (i) What are the relevant mechanisms and signal pathways required for initiating organ fibrosis? (ii) Which immunological mechanisms and molecules contribute to organ fibrosis? and (iii) How can organ fibrosis be modulated, e.g., by interventional strategies including imaging and pharmacological approaches? In this review we will summarize the liver-related key findings of this consortium gained within the last 12 years on these three aspects of liver fibrogenesis. We will highlight the role of cell death and cell cycle pathways as well as nutritional and iron-related mechanisms for liver fibrosis initiation. Moreover, we will define and characterize the major immune cell compartments relevant for liver fibrogenesis, and finally point to potential signaling pathways and pharmacological targets that turned out to be suitable to develop novel approaches for improved therapy and diagnosis of liver fibrosis. In summary, this review will provide a comprehensive overview about the knowledge on liver fibrogenesis and its potential therapy gained by the SFB/TRR57 consortium within the last decade. The kidney-related research results obtained by the same consortium are highlighted in an article published back-to-back in Frontiers in Medicine.

Portal hypertension in cirrhosis: Pathophysiological mechanisms and therapy

Portal hypertension, defined as increased pressure in the portal vein, develops as a consequence of increased intrahepatic vascular resistance due to the dysregulation of liver sinusoidal endothelial cells (LSECs) and hepatic stellate cells (HSCs), frequently arising from chronic liver diseases. Extrahepatic haemodynamic changes contribute to the aggravation of portal hypertension. The pathogenic complexity of portal hypertension and the unsuccessful translation of preclinical studies have impeded the development of effective therapeutics for patients with cirrhosis, while counteracting hepatic and extrahepatic mechanisms also pose a major obstacle to effective treatment. In this review article, we will discuss the following topics: i) cellular and molecular mechanisms of portal hypertension, focusing on dysregulation of LSECs, HSCs and hepatic microvascular thrombosis, as well as changes in the extrahepatic vasculature, since these are the major contributors to portal hypertension; ii) translational/clinical advances in our knowledge of portal hypertension; and iii) future directions.