Xavier Guillonneau

Alzheimer’s disease (AD) is one of the most common neurodegenerative disorders, yet the environmental drivers that accelerate its progression remain poorly defined. Traffic-related air pollution is emerging as a modifiable AD risk factor, but how inhaled particles perturb microglial clearance of amyloid beta (Aβ) is unknown. Microglia are the principal Aβ-clearing phagocytes of the brain. Here, we showed that exposure of primary mouse microglia and human induced pluripotent stem cell-derived microglia (iMGLs) to 3–100 µg/mL diesel exhaust particles (DEP) disrupted microglial homeostasis, induced morphological abnormalities, increased reactive oxygen species, impaired lysosomal degradation, and led to a concentration-dependent loss of phagocytic capacity. Importantly, DEP markedly reduces Aβ uptake in both species. Transcriptomic profiling revealed a DEP-induced, non-canonical state characterized by metabolic reprogramming, broad suppression of inflammatory pathways, antigen-presentation, chemokine, and species-specific remodeling during subsequent Aβ challenge, including defective chemotaxis, cell cycle, and cytoskeletal signatures. These data show that DEP profoundly alters microglial transcriptional and metabolic states, leading to impaired Aβ clearance, which could, thereby, further contribute to AD progression.

Neovascular age-related macular degeneration (nAMD) remains a major cause of visual impairment and puts considerable burden on patients and health care systems. L-DOPA-treated Parkinson Disease (PD) patients have been shown to be partially protected from nAMD, but the mechanism remains unknown. Using murine models, combining 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD and laser-induced nAMD, standard PD treatment of L-DOPA/DOPA-decarboxylase inhibitor, or specific dopamine receptor inhibitors, we here demonstrate that L-DOPA treatment-induced increase of dopamine mediated dopamine receptor D2 (DRD2) signaling inhibits choroidal neovascularization independently of MPTP-associated nigrostriatal pathway lesion. Analyzing a retrospective cohort of more than two hundred thousand nAMD patients receiving anti-VEGF treatment from the French nationwide insurance database, we show that DRD2-agonist treated (PD) patients have a significantly delayed age of onset for nAMD (81.4 (±7.0) vs 79.4 (±8.1) years old, respectively, p<0.0001) and reduced need for anti-VEGF therapies (-0.6 injections per 100 mg/day daily dose of DRD2 agonists the second year of treatment), similar to the L-DOPA treatment. While providing a mechanistic explanation for an intriguing epidemiological observation, our findings suggest that systemic DRD2 agonists might constitute an adjuvant therapy to delay and reduce the need for anti-VEGF therapy in nAMD patients.

Type 2 diabetes mellitus (T2DM), characterized by hyperglycemia and dyslipidemia, leads to nonproliferative diabetic retinopathy (NPDR). NPDR is associated with blood-retina barrier disruption, plasma exudates, microvascular degeneration, elevated inflammatory cytokine levels, and monocyte (Mo) infiltration. Whether and how the diabetes-associated changes in plasma lipid and carbohydrate levels modify Mo differentiation remains unknown. Here, we show that mononuclear phagocytes (MPs) in areas of vascular leakage in DR donor retinas expressed perilipin 2 (PLIN2), a marker of intracellular lipid load. Strong upregulation of PLIN2 was also observed when healthy donor Mos were treated with plasma from patients with T2DM or with palmitate concentrations typical of those found in T2DM plasma, but not under high-glucose conditions. PLIN2 expression correlated with the expression of other key genes involved in lipid metabolism (ACADVL, PDK4) and the DR biomarkers ANGPTL4 and CXCL8. Mechanistically, we show that lipid-exposed MPs induced capillary degeneration in ex vivo explants that was inhibited by pharmaceutical inhibition of PPARγ signaling. Our study reveals a mechanism linking dyslipidemia-induced MP polarization to the increased inflammatory cytokine levels and microvascular degeneration that characterize NPDR. This study provides comprehensive insights into the glycemia-independent activation of Mos in T2DM and identifies MP PPARγ as a target for inhibition of lipid-activated MPs in DR.

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by impaired episodic memory and two pathological lesions: amyloid plaques and neurofibrillary tangles. In AD, damaged neurons and the accumulation of amyloid β (Aβ) peptides cause a significant release of high amounts of extracellular ATP, which acts as a danger signal. The purinergic receptor P2X7 is the main sensor of high concentrations of ATP, and P2X7 has been shown to be upregulated in the brains of AD patients, contributing to the disease’s pathological processes. Further, there are many polymorphisms of the P2X7 gene that impact the risk of developing AD. P2X7 can directly modulate Aβ plaques and Tau protein lesions as well as the inflammatory response by regulating NLRP3 inflammasome and the expression of several chemokines. The significant role of microglial P2X7 in AD has been well established, although other cell types may also be important in P2X7-mediated mechanisms. In this review, we will discuss the different P2X7-dependent pathways involved in the development of AD.

Systemic drugs can treat various retinal pathologies such as retinal cancers; however, their ocular diffusion may be limited by the blood–retina barrier (BRB). Sonication corresponds to the use of ultrasound (US) to increase the permeability of cell barriers including in the BRB. The objective was to study the efficacy and safety of sonication using microbubble-assisted low-intensity pulsed US in inducing a transient opening of the BRB. The eyes of C57/BL6J mice were sonicated at different acoustic pressures (0.10 to 0.50 MPa). Efficacy analyses consisted of fluorescein angiography (FA) performed at different timepoints and the size of the leaked molecules was assessed using FITC-marked dextrans. Tolerance was assessed by fundus photographs, optical coherence tomography, immunohistochemistry, RT-qPCR, and electroretinograms. Sonication at 0.15 MPa was the most suitable pressure for transient BRB permeabilization without altering the morphology or function of the retina. It did not increase the expression of inflammation or apoptosis markers in the retina, retinal pigment epithelium, or choroid. The dextran assay suggested that drugs up to 150 kDa in size can cross the BRB. Microbubble-assisted sonication at an optimized acoustic pressure of 0.15 MPa provides a non-invasive method to transiently open the BRB, increasing the retinal diffusion of systemic drugs without inducing any noticeable side-effect.

Hypoxia is potentially one of the essential triggers in the pathogenesis of wet age-related macular degeneration (wetAMD), characterized by choroidal neovascularization (CNV) which is driven by the accumulation of subretinal mononuclear phagocytes (MP) that include monocyte-derived cells. Here we show that systemic hypoxia (10% O₂) increased subretinal MP infiltration and inhibited inflammation resolution after laser-induced subretinal injury in vivo. Accordingly, hypoxic (2% O₂) human monocytes (Mo) resisted elimination by RPE cells in co-culture. In Mos from hypoxic mice, Thrombospondin 1 mRNA (Thbs1) was most downregulated compared to normoxic animals and hypoxia repressed Thbs-1 expression in human monocytes in vitro. Hypoxic ambient air inhibited MP clearance during the resolution phase of laser-injury in wildtype animals, but had no effect on the exaggerated subretinal MP infiltration observed in normoxic Thbs1^−/−-mice. Recombinant Thrombospondin 1 protein (TSP-1) completely reversed the pathogenic effect of hypoxia in Thbs1^−/−-mice, and accelerated inflammation resolution and inhibited CNV in wildtype mice. Together, our results demonstrate that systemic hypoxia disturbs TSP-1-dependent subretinal immune suppression and promotes pathogenic subretinal inflammation and can be therapeutically countered by local recombinant TSP-1.

Muller glial cells (MGCs) are responsible for the homeostatic and metabolic support of the retina. Despite the importance of MGCs in retinal disorders, reliable and accessible human cell sources to be used to model MGC‐associated diseases are lacking. Although primary human MGCs (pMGCs) can be purified from post‐mortem retinal tissues, the donor scarcity limits their use. To overcome this problem, we developed a protocol to generate and bank human induced pluripotent stem cell‐derived MGCs (hiMGCs). Using a transcriptome analysis, we showed that the three genetically independent hiMGCs generated were homogeneous and showed phenotypic characteristics and transcriptomic profile of pMGCs. These cells expressed key MGC markers, including Vimentin, CLU, DKK3, SOX9, SOX2, S100A16, ITGB1, and CD44 and could be cultured up to passage 8. Under our culture conditions, hiMGCs and pMGCs expressed low transcript levels of RLPB1, AQP4, KCNJ1, KCJN10, and SLC1A3. Using a disease modeling approach, we showed that hiMGCs could be used to model the features of diabetic retinopathy (DR)‐associated dyslipidemia. Indeed, palmitate, a major free fatty acid with elevated plasma levels in diabetic patients, induced the expression of inflammatory cytokines found in the ocular fluid of DR patients such as CXCL8 (IL‐8) and ANGPTL4. Moreover, the analysis of palmitate‐treated hiMGC secretome showed an upregulation of proangiogenic factors strongly related to DR, including ANG2, Endoglin, IL‐1β, CXCL8, MMP‐9, PDGF‐AA, and VEGF. Thus, hiMGCs could be an alternative to pMGCs and an extremely valuable tool to help to understand and model glial cell involvement in retinal disorders, including DR.