Targeting monocyte derived macrophage for stroke treatment

Veterans Health Administration, Decatur PA

Investigators

Abstract

Crosstalk between the central nervous system and the immune system is known to steer the progression of ischemic brain injury. However, there are no clinical treatments that can harness the power of the immune system to temper inflammation-induced secondary injuries or promote brain repair. The reasons for this gap are multifactorial, including preclinical emphases on young animals of the male sex and a lack of understanding of cellular and molecular mechanisms underlying stroke outcomes. We have discovered that monocyte-derived macrophages (MDMø) partly drive sex-dependent stroke outcomes. Further mechanistic elucidation of sex and age distinctions in MDMø responses and their significance in stroke outcomes may identify viable targets for brain protection and repair in patients of both sexes. We performed single-cell RNA sequencing analyses of brain cells collected from young male and female mice at 5d after transient (60 min) middle cerebral artery occlusion (tMCAO) and found sex-specific clustering of MDMø, with high galectin 3 (Gal3) expression in male MDMø. Gal3 is a carbohydrate-binding molecule and a modulator of inflammation. Higher blood levels of Gal3 in the acute stage after stroke are associated with worse outcomes in patients. Previous animal studies document diverse roles of Gal3 in cerebral ischemiadepending on the stage of stroke evolution. However, the cell-specific functions of Gal3 in MDMø after stroke remain elusive. Our pilot data suggest that Gal3 is an age and sex-dependent modulator of damaged lysosome-mediated inflammation in MDMø. 1) Gal3 expression in MDMø is much higher in young male mice and aged mice of both sexes vs. young females early after tMCAO. 2) Gal3 deficiency reduces lysosomal accumulation and inflammasome activation in MDMø and alleviates ischemic brain injury 3d after tMCAO. 3) Exposure to dead ischemic neurons results in higher lysosomal accumulation of Gal3, lysosome leakage, inflammasome activation, and inflammatory cytokine production in male vs. female Mø; and these deleterious effects are mitigated by a selective Gal3 inhibitor, TD139. 4) Transient post-stroke TD139 treatment inhibits neuroinflammation, reduces brain infarct, and improves long-term neurological functions in young and aged male mice. The proposed work will elucidate the significance of Gal3 in MDMø responses in young and aged mice of both sexes and will develop TD139 as a novel strategy to improve stroke outcomes. The central hypothesis is that high Gal3 expression in MDMø after stroke increases accumulation of damaged lysosomes, leading to inflammasome activation in MDMø and worse outcomes. Transient Gal3 inhibition early after stroke ameliorates brain injury and improves long term outcomes in young and aged mice of both sexes. Aim 1: Test if Gal3 expression in MDMø plays a role in acute brain injury after stroke. Aim 2: Test if high Gal3 expression leads to lysosomal accumulation and enhances NLRP3 inflammasome-dependent pro-inflammatory/neurotoxic responses in MDMø. Aim 3: Test the effects of TD139 in young and aged mice of both sexes after stroke.