Molecular and anatomical roadmap of stroke pathology in immunodeficient mice

BackgroundStroke remains a leading cause of disability and death worldwide. It has become apparent that inflammation and immune mediators have a pre-dominant role in initial tissue damage and long-term recovery following the injury. Still, different immunosuppressed mouse models are necessary in stroke research e.g., to evaluate therapies using human cell grafts. Despite mounting evidence delineating the importance of inflammation in the stroke pathology, it is poorly described to what extent partial immune deficiency influences the overall stroke outcome. MethodsHere, we assessed the stroke pathology of popular genetic immunodeficient mouse models, i.e., NOD scid gamma (NSG) and recombination activating gene 2 (Rag2-/-) mice as well as pharmacologically immunosuppressed mice and compared them to immune competent, wildtype (WT) C57BL/6J mice up to three weeks after injury. We performed histology, gene expression profiling, serum analysis and functional behavioural tests to identify the impact of immunosuppression on the stroke progression. ResultsWe detected distinct changes in microglia infiltration, scar-forming and vascular repair in immune-suppressed mice three weeks after injury. Gene expression analysis of stroked tissue revealed the strongest deviation from immune competent mice was observed in NSG mice, for instance, affecting immunological and angiogenic pathways. Pharmacological immunosuppression resulted in the least variation in gene expression compared with the WT. Major differences have been further identified in the systemic inflammatory response following stroke acutely and three weeks following injury. These anatomical, genetic, and systemic changes did not affect functional deficits and recovery in a time course of three weeks. To determine whether the timing of immunosuppression after stroke is critical, we compared mice with acute and delayed pharmacological immunosuppression after stroke. Mice with a delayed immunosuppression (7d) after stroke showed increased inflammatory and scarring responses compared to animals acutely treated with tacrolimus, thus more closely resembling WT pathology. Transplantation of human cells in the brains of immunosuppressed mouse models led to prolonged cell survival in all immunosuppressed mouse models, which was most consistent in NSG and Rag2-/- mice. ConclusionsIn sum, we detected distinct anatomical and molecular changes in the stroke pathology between the individual immunosuppressed mouse models that should be carefully considered when selecting an appropriate mouse model for stroke research.