Astrocytic DLL4-NOTCH1 signaling pathway promotes neuroinflammation via the IL-6-STAT3 axis.

Under neuroinflammatory conditions, astrocytes acquire a reactive phenotype that drives acute inflammatory injury as well as chronic neurodegeneration. We hypothesized that astrocytic Delta-like 4 (DLL4) may interact with its receptor NOTCH1 on neighboring astrocytes to regulate astrocyte reactivity via downstream juxtacrine signaling pathways. Here we investigated the role of astrocytic DLL4 on neurovascular unit homeostasis under neuroinflammatory conditions. We probed for downstream effectors of the DLL4-NOTCH1 axis and targeted these for therapy in two models of CNS inflammatory disease. We first demonstrated that astrocytic DLL4 is upregulated during neuroinflammation, both in mice and humans, driving astrocyte reactivity and subsequent blood-brain barrier permeability and inflammatory infiltration. We then showed that the DLL4-mediated NOTCH1 signaling in astrocytes directly drives IL-6 levels, induces STAT3 phosphorylation promoting upregulation of astrocyte reactivity markers, pro-permeability factor secretion and consequent blood-brain barrier destabilization. Finally we revealed that blocking DLL4 with antibodies improves experimental autoimmune encephalomyelitis symptoms in mice, identifying a potential novel therapeutic strategy for CNS autoimmune demyelinating disease. As a general conclusion, this study demonstrates that DLL4-NOTCH1 signaling is not only a key pathway in vascular development and angiogenesis, but also in the control of astrocyte reactivity during neuroinflammation.

Endothelial DLL4 Is an Adipose Depot-Specific Fasting Sensor Regulating Fatty Acid Fluxes.

BACKGROUND: Adaptation of fat depots to change in fuel availability is critical for metabolic flexibility and cardiometabolic health. The mechanisms responsible for fat depot-specific lipid sensing and shuttling remain elusive. Adipose tissue microvascular endothelial cells (AT-EC) regulates bidirectional fatty acid fluxes depending on fed or fasted state. How AT-EC sense and adapt to metabolic changes according to AT location remains to be established. METHODS: We combined transcriptional analysis of native human AT-EC together with in vitro approaches in primary human AT-EC and in vivo and ex vivo studies of mice under fed and fasted conditions. RESULTS: Transcriptional large-scale analysis of human AT-EC isolated from gluteofemoral and abdominal subcutaneous AT revealed that the endothelium exhibits a fat depot-specific signature associated with lipid handling and Notch signaling enrichment. We uncovered a functional link between metabolic status and endothelial DLL4 (delta-like canonical notch ligand 4), which decreases with fasting. DLL4 regulates fatty acid uptake through nontranscriptional modulation of macropinocytosis-dependent long chain fatty acid uptake. Importantly, the changes in DLL4 expression, in response to energy transition state, is impaired under obesogenic conditions, an early alteration coinciding with a defect in systemic fatty acid fluxes adaptation and a resistance to weight loss. CONCLUSIONS: DLL4 is a major actor in the adaptive mechanisms of AT-EC to regulate lipid fluxes. It likely contributes to fat depot-dependent metabolism in response to energy transition states. AT-EC alteration with obesity may favor metabolic inflexibility and the development of cardiometabolic disorders.

OP2113, a new drug for chronic hypoxia-induced pulmonary hypertension treatment in rat.

BACKGROUND AND PURPOSE: Pulmonary hypertension (PH) is a cardiovascular disease characterised by an increase in pulmonary arterial (PA) resistance leading to right ventricular (RV) failure. Reactive oxygen species (ROS) play a major role in PH. OP2113 is a drug with beneficial effects on cardiac injuries that targets mitochondrial ROS. The aim of the study was to address the in vivo therapeutic effect of OP2113 in PH. EXPERIMENTAL APPROACH: PH was induced by 3 weeks of chronic hypoxia (CH-PH) in rats treated with OP2113 or its vehicle via subcutaneous osmotic mini-pumps. Haemodynamic parameters and both PA and heart remodelling were assessed. Reactivity was quantified in PA rings and in RV or left ventricular (LV) cardiomyocytes. Oxidative stress was detected by electron paramagnetic resonance and western blotting. Mitochondrial mass and respiration were measured by western blotting and oxygraphy, respectively. KEY RESULTS: In CH-PH rats, OP2113 reduced the mean PA pressure, PA remodelling, PA hyperreactivity in response to 5-HT, the contraction slowdown in RV and LV and increased the mitochondrial mass in RV. Interestingly, OP2113 had no effect on haemodynamic parameters, both PA and RV wall thickness and PA reactivity, in control rats. Whereas oxidative stress was evidenced by an increase in protein carbonylation in CH-PH, this was not affected by OP2113. CONCLUSION AND IMPLICATIONS: Our study provides evidence for a selective protective effect of OP2113 in vivo on alterations in both PA and RV from CH-PH rats without side effects in control rats.