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AbstractINTRODUCTIONRecent studies have identified important species‐dependent differences in the response of microglia to β‐amyloid (Aβ) pathology. Yet, whether human microglia also interact differently with the pathognomonic combination of amyloid and tau pathologies that occur in Alzheimer's disease (AD) remains unclear.METHODSWe generated a xenotolerant mouse model of AD that develops both plaque and tangle pathologies, transplanted stem cell‐derived microglial progenitors and examined the interactions between human microglia and AD pathologies with scRNA sequencing, immunohistochemistry, and in vitro modeling.RESULTSThe combined amyloid and tau pathologies induced robust type‐I interferon and proinflammatory cytokine responses, as well as an increased adoption of a distinct “rod” morphology in human microglia. The rod morphology could be induced with type‐I interferon treatment in vitro.DISCUSSIONWe provide new insights into human microglial responses to combined AD pathologies and a novel platform to investigate and manipulate human microglia in vivo.Highlights Amyloid pathology promotes the rapid development of neurofibrillary tangles and neuronal loss in a novel chimeric model of AD.Combined Alzheimer's disease pathologies lead to an expansion of disease‐associated microglia (DAM) and exacerbate Interferon‐responsive and cytokine/chemokine‐enriched states in xenotransplanted human microglia.The combination of amyloid and tau promotes the development of a distinctive rod microglial phenotype that closely correlates with tau pathology and neurodegeneration.Rod morphology and transcriptional changes can be modeled in vitro by treatment of induced pluripotent stem cells (iPSC) ‐microglia with type‐I interferons.

Age-related macular degeneration (AMD) is a leading cause of blindness worldwide, with a clinical presentation that varies between sexes. In late-stage AMD, choroidal neovascularization (CNV) triggers retinal inflammation and degeneration, processes that are exacerbated by an overactive response of retinal microglial cells. Short-chain fatty acids (SCFAs) have emerged as potential treatments for AMD due to their anti-inflammatory properties. In this study, we investigate the effects of SCFA treatment in a laser-induced CNV mouse model, focusing on sex-dependent differences in disease progression and microglial response. Our findings demonstrate distinct sex-specific patterns in the development of CNV and associated pathological hallmarks. SCFA treatment resulted in a slight increase in density of Iba1 + microglial cells in females at 3 days post-laser (3dpl), while it prevented an increase in males at 7 dpl, with both sexes showing enhanced microglial ramification. The dynamics of microglial density were likely linked to protective effects on CNV lesion, leakage size, and inflammation, which occurred earlier in females and later in males. At transcriptional level, SCFA showed mixed effects, mainly targeting inflammation resolution, mitochondrial support, and neuronal repair in a sex-dependent manner. In vitro, SCFAs reduced microglial phagocytosis of retinal debris, suggesting a potential anti-inflammatory action. This study underscores the importance of considering sex-specific responses in the development of AMD treatments, such as SCFAs, and highlights the need for personalized therapeutic strategies. The online version contains supplementary material available at 10.1186/s12974-025-03508-1.

Microvesicles (MV) isolated from septic individuals were observed to impact systemic hemodynamics and cardiac function. The aim of this in vitro study was to analyze the effects of TNFα-induced endothelial MV (TMV) and MV from septic patients (SMV) on beating frequency and Ca2+ transient kinetics of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM). MV were isolated from supernatants of TNFα-stimulated primary human pulmonary microvascular endothelial cells (HPMEC) and plasma from 20 sepsis patients by ultracentrifugation and quantified using flow cytometry. Spontaneous Ca2+ transients were measured in hiPSC-CM using the Ca2+-sensitive ratiometric indicator fura-2 at different time points of incubation with different MV concentrations. At 16 h of incubation, higher MV concentrations showed significant differences, especially regarding decay and beating frequency. Despite high variability, at 10 × 106 MV/mL and 16 h of incubation, TMV significantly decreased frequency compared to control MV (CMV). SMV from septic patients did not reveal any significant effects on Ca2+ transients under these experimental settings. MV isolated from control or TNFα-treated HPMEC affected Ca2+ handling and spontaneous activity of hiPSC-CM, however, the measured effects were not consistent throughout the different conditions. Further refinement of the experiment conditions is needed to specify the exact conditions for crosstalk between endothelium-derived MV and cardiomyocytes.