Peripherally misfolded proteins exacerbate ischemic stroke-induced neuroinflammation and brain injury

BACKGROUND: Protein aggregates can be found in peripheral organs, such as the heart, kidney, and pancreas, but little is known about the impact of peripherally misfolded proteins on neuroinflammation and brain functional recovery following ischemic stroke. METHODS: Here, we studied the ischemia/reperfusion (I/R) induced brain injury in mice with cardiomyocyte-restricted overexpression of a missense (R120G) mutant small heat shock protein, αB-crystallin (CryAB(R120G)), by examining neuroinflammation and brain functional recovery following I/R in comparison to their non-transgenic (Ntg) littermates. To understand how peripherally misfolded proteins influence brain functionality, exosomes were isolated from CryAB(R120G) and Ntg mouse blood and were used to treat wild-type (WT) mice and primary cortical neuron-glia mix cultures. Additionally, isolated protein aggregates from the brain following I/R were isolated and subjected to mass-spectrometric analysis to assess whether the aggregates contained the mutant protein, CryAB(R120G). To determine whether the CryAB(R120G) misfolding can self-propagate, a misfolded protein seeding assay was performed in cell cultures. RESULTS: Our results showed that CryAB(R120G) mice exhibited dramatically increased infarct volume, delayed brain functional recovery, and enhanced neuroinflammation and protein aggregation in the brain following I/R when compared to the Ntg mice. Intriguingly, mass-spectrometric analysis of the protein aggregates isolated from CryAB(R120G) mouse brains confirmed presence of the mutant CryAB(R120G) protein in the brain. Importantly, intravenous administration of WT mice with the exosomes isolated from CryAB(R120G) mouse blood exacerbated I/R-induced cerebral injury in WT mice. Moreover, incubation of the CryAB(R120G) mouse exosomes with primary neuronal cultures induced pronounced protein aggregation. Transduction of CryAB(R120G) aggregate seeds into cell cultures caused normal CryAB proteins to undergo dramatic aggregation and form large aggregates, suggesting self-propagation of CryAB(R120G) misfolding in cells. CONCLUSIONS: These results suggest that peripherally misfolded proteins in the heart remotely enhance neuroinflammation and exacerbate brain injury following I/R likely through exosomes, which may represent an underappreciated mechanism underlying heart-brain crosstalk. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12974-021-02081-7.