Hongmei Yang

BACKGROUND: In people living with HIV (PLWH), persistent systemic inflammation drives comorbidities, including cardiovascular and cerebrovascular diseases. Monocyte-mediated inflammation, rather than T-cell activation, is a major contributor to chronic inflammation. However, the underlying mechanisms remain elusive. Here, we investigated the role of Dll4 (delta-like 4)-Notch signaling in monocyte-mediated inflammation. METHODS: In clinical specimens, we quantified monocyte mDll4 (membrane-bound Dll4) expression and plasma levels of exDll4 (extracellular Dll4). We also analyzed the association between circulating exDll4 and monocyte subsets in PLWH. In vitro, human primary monocytes, endothelial cells, and T cells were stimulated with lipopolysaccharide or TNF-α (tumor necrosis factor-α) to assess Dll4 mRNA and protein expression and exDll4 secretion. RNA sequencing was performed after Dll4 silencing to determine downstream signaling pathways. In addition, molecular and functional studies examined the effects of Dll4-Notch1 signaling on interferon-related gene expression, monocyte adhesion, and transmigration. RESULTS: Both male and female PLWH exhibited significantly increased mDll4 expression, activation of Dll4-Notch1 signaling, and increased Notch-targeted inflammatory factors. Although monocyte mDll4 did not differ by sex in PLWH, plasma exDll4 was significantly elevated in males, but not females, compared with HIV-uninfected individuals. In male PLWH, plasma exDll4 levels paralleled monocyte mDll4 expression. Circulating exDll4 was positively associated with proinflammatory monocytes and negatively associated with classical monocytes in male PLWH. Mechanistically, lipopolysaccharide or TNF-α robustly increased Dll4 mRNA and protein expression in human primary monocytes, along with exDll4 secretion from monocytes, but not from endothelial cells or T cells. RNA sequencing after Dll4 silencing showed that Dll4-Notch signaling suppresses a broad anti-pathogen program regulated by interferon and NF-κB, as well as cell-mobility-related genes. At the molecular level, Dll4 activated Notch1, which upregulated Hes1, forming a heterotrimer with STATs (signal transducers and activators of transcription), and repressed interferon pathway-related gene expression. Functionally, loss of Dll4 significantly reduced monocyte adhesion and transmigration. CONCLUSIONS: Proinflammatory cues upregulate Dll4 in monocytes and activate Dll4-Notch signaling, thereby suppressing antiviral responses and enhancing monocyte transmigration. Together, these effects sustain systemic inflammation in PLWH of both sexes. Our data identify monocyte-derived Dll4 as a promising biomarker and therapeutic target for systemic inflammation.

Background: Despite the success of combination antiretroviral therapy (cART), vascular comorbidities, including cerebrovascular disease, are more prominent in people living with HIV (PLWH) compared to people without HIV (PWOH). However, quantitative assessments of cerebrovascular morphometry and their associations with cognitive outcomes in the context of HIV are still limited. In this study, we explore this missing link. Methods: Magnetic Resonance Angiography (MRA) data, blood markers, and neurocognitive assessments were collected from 73 PWOH subjects ( male : 57, female : 16; age : 53 ± 16) and 99 PLWH subjects ( male : 66, female : 30, age : 53 ± 11). Vessel morphometric features were quantified using intraCranial Artery Feature Extraction (iCafe) to investigate associations between vessel morphometry, markers of monocytes, endothelial cell activation, and cognitive performance. Results: HIV status predicted a lower total number of branches ( β = − 0.224, p = 0.001, d = − 0.517) and shorter total distal length ( β = − 0.173, p = 0.021, d = –0.370) with a moderate effect size. Total branch number was found to be negatively associated with plasma levels of monocyte markers (sCD14: r = –0.167, p = 0.033; sCD163: r = –0.157, p = 0.045) and positively correlated with white matter cerebral blood flow ( r = 0.550; p ≤ 0.05). HIV status was the strongest predictor of overall cognitive performance in ANCOVA model ( β = –0.219, p = 0.006, d = –0.453). Conclusions: Our results suggest that cognitive impairment in PLWH is associated with vessel morphology metrics. Monocyte immune activation may contribute to changes in vessel morphology.