Trained immunity induced by high‐salt diet impedes stroke recovery

Abstract A high‐salt diet (HSD) elicits sustained sterile inflammation and worsens tissue injury. However, how this occurs after stroke, a leading cause of morbidity and mortality, remains unknown. Here, we report that HSD impairs long‐term brain recovery after intracerebral hemorrhage, a severe form of stroke, despite salt withdrawal prior to the injury. Mechanistically, HSD induces innate immune priming and training in hematopoietic stem and progenitor cells (HSPCs) by downregulation of NR4a family and mitochondrial oxidative phosphorylation. This training compromises alternative activation of monocyte‐derived macrophages (MDMs) without altering the initial inflammatory responses of the stroke brain. Healthy mice transplanted with bone marrow from HSD‐fed mice retain signatures of reduced MDM reparative functions, further confirming a persistent form of innate immune memory that originates in the bone marrow. Loss of NR4a1 in macrophages recapitulates HSD‐induced negative impacts on stroke outcomes while gain of NR4a1 enables stroke recovery in HSD animals. Together, we provide the first evidence that links HSD‐induced innate immune memory to the acquisition of persistent dysregulated inflammatory responses and unveils NR4a1 as a potential therapeutic target.

A Graphs depicting body weight, food intake, water intake, and sodium intake in ND (n = 22-33) and HSD (n = 24-35) mice over 8 weeks of diet manipulation.Two- way ANOVA and Bonferroni test.n: biological replicates.B Graphs depicting heart rate, mean arterial pressure, systolic blood pressure, and diastolic blood pressure in ND and HSD animals over 8 weeks of diet manipulation.n = 7-11/group, two-way ANOVA and Bonferroni test.n: biological replicates.
Data information: All data are mean AE SEM; *P < 0.05, n.s., not significant.Source data are available online for this figure.

EMBO reports
Tze-Yen Lin et al  A Schematic of the 4-week diet regimen.Six-week-old mice were fed with ND or HSD for 4 weeks before being subjected to ICH surgery.Behavioral tests and flow cytometry were performed 1 week after blood ICH induction.B Cylinder test results of mice after 4-week ND and HSD on days 1, 3, and 7 after ICH.n = 9 ND, 11 HSD, two-way ANOVA and Bonferroni test.n: biological replicates.C Percentages of CD36 + , CD206 + , and CD36 + CD206 + MDMs in 4-week ND and HSD mice after ICH.n = 5/group, Student's t-test.n: biological replicates.D Percentages of CD36 + or CD206 + microglia (MG) after 4-week ND and HSD.n = 5/group, Student's t-test.n: biological replicates.E Survival rates of ND and HSD chimeras that were subjected to a collagenase ICH model.F Cylinder test and forelimb placement test results of ND➔ND and HSD➔ND chimeras.n = 6 ND chimeras and 3 HSD chimeras on day 3, n = 4 ND chimeras and 2 HSD chimeras on day 10.G Schematic of experimental design.ND and HSD BM were transplanted into HSD recipients.Tze-Yen Lin et al EMBO reports

Figure EV1 .
Figure EV1.Physiological measurements of ND and HSD mice.
Figure EV2.HSD reduces alternative activation of peritoneal macrophages in a thioglycollate-elicited peritoneal model.A Schematic of experimental design.B Bar graphs depicting the percentages of CD36 + and CD206 + peritoneal macrophages from ND and HSD mice on days 0, 3, and 7 following thioglycollate injection.n= 4/group on day 0, n = 3 ND, 4 HSD on day 3, and n = 8/group on day 7, two-way ANOVA and Bonferroni test.n: biological replicates.All data are mean AE SEM, each symbol represents one mouse or one biological replicate, *P < 0.05, **P < 0.01, ***P < 0.001, and # P < 0.001, n.s., not significant.Source data are available online for this figure.Figure EV3.HSD impairs mitochondrial oxidative phosphorylation and promotes glycolysis in bone marrow (BM) cells.A OCR traces and maximum respiratory capacity of BM cells after 4-week ND and HSD.n = 9 ND, 6 HSD, Student's t-test.n: biological replicates.B OCR traces and maximum respiratory capacity of BM cells after 8-week ND and HSD.n = 9 ND, 6 HSD, Student's t-test.n: biological replicates.