ABSTRACT Over half of pediatric stroke survivors have permanent neurologic and cognitive deficits, and some children develop new or worsening cognitive impairment late after stroke. Their cognitive symptoms are associated with chronic alterations of brain structure in regions distant from the infarct, including in the uninjured hemisphere. However, the mechanisms that cause children’s late cognitive symptoms and disrupted brain growth outside the infarcted tissue remain unknown. We therefore developed and validated a mouse model of pediatric ischemic stroke that causes infarct-induced, delayed cognitive decline accompanied by chronic innate and adaptive neuroinflammation in the infarct and in uninjured subcortical regions that are connected to the infarct. Methods Male and female C57BL/6J mice were randomized to stroke or sham surgery at p28 to model stroke in late childhood and compared to adult 6-month-old mice. We used permanent distal MCAO followed by 60 minutes of hypoxia, an established model for focal ischemia that generates a purely cortical stroke. Mice underwent behavioral testing at 1- and 7-weeks post stroke Barnes Maze protocol adapted for reversal learning. We performed immunostaining to quantify stroke size, atrophy, and innate and adaptive neuroinflammation at 3 days and 7 weeks after surgery. Results At 7 weeks post-stroke, juvenile stroke mice performed significantly worse on reversal learning on Barnes Maze testing than sham mice (n = 7 stroke, 7 sham, p = 0.0265 2-way ANOVA with repeated measures). At 3 days after stroke, juvenile mice had greater innate immune cell activation at subcortical sites of secondary neurodegeneration; however, by 7 weeks after surgery, this relationship was reversed, and adults had greater chronic innate immune cell activation at these uninjured subcortical sites (corpus callosum, corticospinal tract, thalamus). Like adult mice, pediatric mice exhibited chronic innate and adaptive neuroimmunity in the infarct scar; the inflammation in the stroke scar did not differ by age. Conclusions In a model of pediatric ischemic stroke, juvenile mice develop a delayed cognitive deficit that is associated with chronic innate and adaptive neuroinflammation in uninjured subcortical structures that undergo secondary neurodegeneration. Our results suggest that infarct-induced neurodegeneration occurs after stroke in juvenile mice and that juvenile and adult mice have divergent trajectories in the innate immune response to stroke.

Acquired resistance to PARP inhibitors (PARPi) remains a treatment challenge for BRCA1/2-mutant breast cancer that drastically shortens patient survival. Although several resistance mechanisms have been identified, none have been successfully targeted in the clinic. Using new PARPi-resistance models of Brca1- and Bard1-mutant breast cancer generated in-vivo, we identified FLT1 (VEGFR1) as a driver of resistance. Unlike the known role of VEGF signaling in angiogenesis, we demonstrate a novel, non-canonical role for FLT1 signaling that protects cancer cells from PARPi in-vivo through a combination of cell-intrinsic and cell-extrinsic pathways. We demonstrate that FLT1 blockade suppresses AKT activation, increases tumor infiltration of CD8+ T cells, and causes dramatic regression of PARPi-resistant breast tumors in a T-cell-dependent manner. Moreover, PARPi-resistant tumor cells can be readily re-sensitized to PARPi by targeting Flt1 either genetically (Flt1-suppression) or pharmacologically (axitinib). Importantly, a retrospective series of breast cancer patients treated with PARPi demonstrated shorter progression-free survival in cases with FLT1 activation at pre-treatment. Our study therefore identifies FLT1 as a potential therapeutic target in PARPi-resistant, BRCA1/2-mutant breast cancer.
© 2024. The Author(s).

Stroke is a pervasive and debilitating global health concern, necessitating innovative therapeutic strategies, especially during recovery. While existing literature often focuses on acute interventions, our study addresses the uniqueness of brain tissue during wound healing, emphasizing the chronic phase following the commonly used middle cerebral artery (MCA) occlusion model. Using clinically relevant endpoints in male and female mice such as magnetic resonance imaging (MRI) and plasma neurofilament light (NFL) measurement, along with immunohistochemistry, we describe injury evolution. Our findings document significant alterations in edema, tissue remodeling, and gadolinium leakage through MRI. Plasma NFL concentration remained elevated at 30 days poststroke. Microglia responses are confined to the region adjacent to the injury, rather than continued widespread activation, and boron-dipyrromethene (BODIPY) staining demonstrated the persistent presence of foam cells within the infarct. Additional immunohistochemistry highlighted sustained B and T lymphocyte presence in the poststroke brain. These observations underscore potentially pivotal roles played by chronic inflammation brought on by the lipid-rich brain environment, and chronic blood-brain barrier dysfunction, in the development of secondary neurodegeneration. This study sheds light on the enduring consequences of ischemic stroke in the most used rodent stroke model and provides valuable insights for future research, clinical strategies, and therapeutic development.© 2024 The Author(s). Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.

Neurovascular impairments and neuroimmune deregulation contribute to injury progression after ischemic stroke. Dickkopf-1 (DKK1) elevated levels correlates with poor stroke outcomes. DKK1 antagonizes the canonical Wnt pathway that plays a critical role in regulating neurovascular and neuroimmune functions. Herein, we report that DKK1 expression in the normal adult brain is absent, but is de novo expressed at the lesion site after experimental ischemic stroke. Using genetic tools to conditionally induce DKK1 expression in a tissue-specific manner, we reveal that its early induction aggravates neurological deficits and injury severity after stroke, associated with altered neuronal and vascular functions. DKK1 post-stroke induction hinders lesion containment by disorganizing the astroglial scar, leading to a chronic neuroinflammation and increased anxiety-like behaviors. Using chimeric mice, we unravel thatDKK1 is released by bone marrow-derived cells (BMDCs) expressing myeloid markers that infiltrate the lesion site. DKK1 restricted induction in BMDCs is sufficient to mediate astroglial scar disorganization. Notably, neutralization of DKK1 limits injury progression and improves neurological recovery after stroke. Our findings indicate that BMDCs-derived DKK1 promotes injury progression after stroke and suggest that neutralizing its biological activity represent a promising therapeutic avenue for ischemic stroke.

Theiler's murine encephalomyelitis virus (TMEV) induces an acute polioencephalomyelitis and a chronic demyelinating leukomyelitis in SJL mice. C57BL/6 (B6) mice generally do not develop TMEV-induced demyelinating disease (TMEV-IDD) due to virus elimination. However, TMEV can persist in specific immunodeficient B6 mice such as IFNβ-/- mice and induce a demyelinating process. The proinflammatory cytokines IL-1β and IL-18 are activated by the inflammasome pathway, which consists of a pattern recognition receptor molecule sensing microbial pathogens, the adaptor molecule Apoptosis-associated speck-like protein containing a CARD (ASC), and the executioner caspase-1. To analyze the contribution of the inflammasome pathway to the resistance of B6 mice to TMEV-IDD, ASC- and caspase-1-deficient mice and wild type littermates were infected with TMEV and investigated using histology, immunohistochemistry, RT-qPCR, and Western Blot. Despite the antiviral activity of the inflammasome pathway, ASC- and caspase-1-deficient mice eliminated the virus and did not develop TMEV-IDD. Moreover, a similar IFNβ and cytokine gene expression was found in the brain of immunodeficient mice and their wild type littermates. Most importantly, Western Blot showed cleavage of IL-1β and IL-18 in all investigated mice. Consequently, inflammasome-dependent activation of IL-1β and IL-18 does not play a major role in the resistance of B6 mice to TMEV-IDD.
© 2023. The Author(s).