The immune system plays a prominent role in the initiation and maintenance of hypertension. The innate immune system, via toll‐like receptors (TLRs), identifies distinct signatures of invading microbes and damage‐associated molecular patterns and triggers a chain of downstream signalling cascades, leading to secretion of pro‐inflammatory cytokines and shaping the adaptive immune response. Over the past decade, a dysfunctional TLR‐mediated response, particularly via TLR4, has been suggested to support a chronic inflammatory state in hypertension, inducing deleterious local and systemic effects in host cells and tissues and contributing to disease progression. While the underlying mechanisms triggering TLR4 need further research, evidence suggests that sustained elevations in BP disrupt homeostasis, releasing endogenous TLR4 ligands in hypertension. In this review, we discuss the emerging role of TLR4 in the pathogenesis of hypertension and whether targeting this receptor and its signalling pathways could offer a therapeutic strategy for management of this multifaceted disease.Linked Articles: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc

Introduction: While increased toll-like receptor (TLR)4 activity may contribute to the pathophysiology of vascular diseases, the molecular mechanisms disrupted by this receptor in the vasculature are still poorly understood. Additionally, it is unknown if TLR4 mediates erectile dysfunction (ED) during diabetes. Aim: To investigate whether pharmacological blockade of TLR4 affects erectile function in a murine model of diabetes. Methods: Sprague Dawley rats (Charles River Laboratory, Wilmington, MA, USA) received a single streptozotocin injection (65 mg/kg, 28 days) and were treated with an anti-TLR4 antibody (1 μg/d, intraperitoneally) for the last 14 days of the treatment. Additionally, cavernosal strips were acutely incubated for 30 minutes with CLI-095 (10−5 mol/L), a TLR4 inhibitor. Functional studies, Western blotting, erectile function, immunohistochemistry, and biochemical analyses were performed. Main Outcome Measures: Oxidative stress, cyclic guanosine monophosphate (cGMP) levels, and functional studies were evaluated in treated and nontreated cavernosal strips from control and diabetic animals. Additionally, in vivo erectile function was assessed. Results: Enhanced TLR4 expression was observed in corpus cavernosum from diabetic rats compared with control animals. Long-term blockade of TLR4 slightly improved diabetes–induced ED in rats due to attenuation of oxidative stress and increased cGMP levels in penile tissue, which ameliorated cavernosal relaxation. Functional experiments revealed that acute or chronic inhibition of TLR4 decreased hypercontractility in response to phenylephrine and improved nitrergic relaxation in corpus cavernosum from diabetic rats. Clinical Implications: TLR4 blockade may be a novel therapeutic strategy to assist in ED management. Strengths & Limitations: The strength of this article stems from the fact that we showed that TLR4 blockade partly improves erectile function in vivo in diabetic rats. Its limitations mainly include that messenger RNA analysis for the nitric oxide/cGMP pathway were not performed. Conclusion: In summary, TLR4 participates in the mechanisms of diabetes-associated ED and blockade of this receptor positively affects penile vascular function.

Toll-Like Receptor 4 and Blood Pressure: Lessons From Animal Studies

While precise mechanisms underlying cardiovascular diseases (CVDs) are still not fully understood, previous studies suggest that the innate immune system, through Toll-like receptor 4 (TLR4), plays a crucial part in the pathways leading to these diseases, mainly because of its interplay with endogenous molecules. The Heat-shock protein 70 family (HSP70-70kDa) is of particular interest in cardiovascular tissues as it may have dual effects when interacting with TLR4 pathways. Although the hypothesis of the HSP70 family members acting as TLR4 ligands is becoming widely accepted, to date no co-crystal structure of this complex is available and it is still unknown whether this process requires the co-adaptor MD2. In this study, we aimed at investigating the interplay between the TLR4/MD2 complex and HSP70 family members in the human cardiovascular system through transcriptomic data analysis and at proposing a putative interaction model between these proteins. We report compelling evidence of correlated expression levels between TLR4 and MD2 with HSP70 cognate family members, especially in heart tissue. In our molecular docking simulations, we found that HSP70 in the ATP-bound state presents a better docking score towards the TLR4/MD2 complex compared to the ADP-bound state (−22.60 vs. −10.29 kcal/mol, respectively). Additionally, we show via a proximity ligation assay for HSP70 and TLR4, that cells stimulated with ATP have higher formation of fluorescent spots and that MD2 might be required for the complexation of these proteins. The insights provided by our computational approach are potential scaffolds for future in vivo studies investigating the interplay between the TLR4/MD2 complex and HSP70 family members in the cardiovascular system.