Objective: Heart failure with preserved ejection fraction is a major health care issue which has been difficult to manage to date, due to its complex and not well understood pathophysiology. Specifically, if a wealth of literature focuses on heart failure with preserved ejection fraction cardiac component, very little information can be found on its vascular component. Our goal is to unravel the critical role of cardiac small vessel disease in the pathophysiology of diastolic dysfunction. Approach and Results: To do so, we used leptin receptor deficient (Lepr db/db ) female mice, a recognized model of diastolic dysfunction. In these mice, the increased end-diastolic pressure signing diastolic dysfunction is associated with vascular leakage, endothelial cell activation, and leucocyte infiltration. Strikingly, a RNA sequencing analysis of the cardiac vascular fraction of both Lepr db/db and control mice confirmed endothelial dysfunction and systemic inflammation, but above all, revealed a strong increase in several mast cell markers (notably FceR1a [high affinity immunoglobulin epsilon receptor subunit α], tryptase, and chymase). We then confirmed this accumulation of activated mast cells in the heart of Lepr db/db mice via histology. Importantly, we found that both mast cell degranulation inhibition and specific histamine blockade reduced vascular leakage, leucocyte infiltration, and subsequently end-diastolic pressure in Lepr db/db mice. This demonstrated, for the first time, that mast cells, via histamine release, participate in the development of cardiac small vessel disease leading to diastolic dysfunction. Conclusions: Cardiac small vessel disease is a key mechanism of heart failure with preserved ejection fraction pathophysiology that can be targeted to prevent the occurrence of diastolic dysfunction, by using both mast cell stabilizers and antihistaminic drugs.

Inflammation of the central nervous system (CNS) induces endothelial blood–brain barrier (BBB) opening as well as the formation of a tight junction barrier between reactive astrocytes at the Glia Limitans. We hypothesized that the CNS parenchyma may acquire protection from the reactive astrocytic Glia Limitans not only during neuroinflammation but also when BBB integrity is compromised in the resting state. Previous studies found that astrocyte-derived Sonic hedgehog (SHH) stabilizes the BBB during CNS inflammatory disease, while endothelial-derived desert hedgehog (DHH) is expressed at the BBB under resting conditions. Here, we investigated the effects of endothelial Dhh on the integrity of the BBB and Glia Limitans. We first characterized DHH expression within endothelial cells at the BBB, then demonstrated that DHH is down-regulated during experimental autoimmune encephalomyelitis (EAE). Using a mouse model in which endothelial Dhh is inducibly deleted, we found that endothelial Dhh both opens the BBB via the modulation of forkhead box O1 (FoxO1) transcriptional activity and induces a tight junctional barrier at the Glia Limitans. We confirmed the relevance of this glial barrier system in human multiple sclerosis active lesions. These results provide evidence for the novel concept of “chronic neuroinflammatory tolerance” in which BBB opening in the resting state is sufficient to stimulate a protective barrier at the Glia Limitans that limits the severity of subsequent neuroinflammatory disease. In summary, genetic disruption of the BBB generates endothelial signals that drive the formation under resting conditions of a secondary barrier at the Glia Limitans with protective effects against subsequent CNS inflammation. The concept of a reciprocally regulated CNS double barrier system has implications for treatment strategies in both the acute and chronic phases of multiple sclerosis pathophysiology.