Evidence that angiotensin II does not directly stimulate the MD2-TLR4 innate inflammatory pathway

Evidence for Interplay Between the Renin-Angiotensin System and Toll-Like Receptor 4 Signaling Pathways in the Induction of Virus-Induced Acute Lung Injury

Dedication: This article is dedicated to Howard Young, an exceptional scientist who has provided outstanding mentorship to many postbaccalaureates, graduate students, and postdoctoral fellows during his career. Howard has been a colleague to many and was never tired of learning new things. He has brought "thinking out of the box" to the level of an art form and has always provided thoughtful and constructive suggestions to those who have sought his counsel. I am personally greatly indebted to Howard for his guidance in molecular biology over the past 30 years, and hope that we will continue to share a passion for learning and mentoring others for years to come. Thank you, Howard! -Stephanie N. Vogel The SARS-CoV-2 pandemic has led to an unprecedented explosion in studies that have sought to identify key mechanisms that underlie the ravaging aspects of this disease on individuals. SARS-CoV-2 virus gains access to cells by (1) binding of the viral spike (S) protein to cell-associated angiotensin-converting enzyme 2 (ACE2), a key receptor in the renin-angiotensin system (RAS), followed by (2) cleavage of S protein by a cellular serine protease ("S protein priming") to facilitate viral entry. Dysregulation of the RAS system has been implicated in the spectrum of clinical symptoms associated with SARS-CoV-2, including hypercytokinemia, elevated markers of endothelial injury and thrombosis, and both localized and systemic inflammation. However, the underlying mechanisms have yet to be fully delineated.

μ-Opioid Receptor-Mediated AT1R-TLR4 Crosstalk Promotes Microglial Activation to Modulate Blood Pressure Control in the Central Nervous System

Opioids, a kind of peptide hormone involved in the development of hypertension, cause systemic and cerebral inflammation, and affects regions of the brain that are important for blood pressure (BP) control. A cause-and-effect relationship exists between hypertension and inflammation; however, the role of blood pressure in cerebral inflammation is not clear. Evidence showed that AT1R and μOR heterodimers’ formation in the NTS might lead to the progression of hypertension. In this study, we investigated the formation of the μOR/AT1R heterodimer, determined its correlation with μORs level in the NTS, and explored the role of TLR4-dependent inflammation in the development of hypertension. Results showed that Ang II increased superoxide and Iba-1 (microgliosis marker: ionized calcium-binding adaptor molecule (1) levels in the NTS of spontaneously hypertensive rats (SHRs). The AT1R II inhibitor, losartan, significantly decreased BP and abolished superoxide, Iba-1, TLR4 expression induced by Ang II. Furthermore, losartan significantly increased nNsOS^S1416 phosphorylation. Administration of a μOR agonist or antagonist in the NTS of WKY and SHRs increased endogenous μ-opioids, triggered the formation of μOR/AT1R heterodimers and the TLR4-dependent inflammatory pathway, and attenuated the effect of depressor nitric oxide (NO). These results imply an important link between neurotoxicity and superoxides wherein abnormal increases in NTS endogenous μ-opioids promote the interaction between Ang II and μOR, the binding of Ang II to AT1R, and the activation of microglia. In addition, the interaction between Ang II and μOR enhanced the formation of the AT1R and μOR heterodimers, and inactivated nNOS-derived NO, leading to the development of progressive hypertension.

Toll-Like Receptors in Acute Kidney Injury

Acute kidney injury (AKI) is an important health problem, affecting 13.3 million individuals/year. It is associated with increased mortality, mainly in low- and middle-income countries, where renal replacement therapy is limited. Moreover, survivors show adverse long-term outcomes, including increased risk of developing recurrent AKI bouts, cardiovascular events, and chronic kidney disease. However, there are no specific treatments to decrease the adverse consequences of AKI. Epidemiological and preclinical studies show the pathological role of inflammation in AKI, not only at the acute phase but also in the progression to chronic kidney disease. Toll-like receptors (TLRs) are key regulators of the inflammatory response and have been associated to many cellular processes activated during AKI. For that reason, a number of anti-inflammatory agents targeting TLRs have been analyzed in preclinical studies to decrease renal damage during AKI. In this review, we updated recent knowledge about the role of TLRs, mainly TLR4, in the initiation and development of AKI as well as novel compounds targeting these molecules to diminish kidney injury associated to this pathological condition.