Regulatory T Cells Contribute to Sexual Dimorphism in Neonatal Hypoxic-Ischemic Brain Injury

Abstract

Background and Purpose: Neonatal encephalopathy caused by hypoxia-ischemia (HI) is a major cause of death and disability in newborns. Clinical and experimental studies suggest a sexual dimorphism in HI-induced brain injury and therapy responses. A major hallmark of HI pathophysiology is the infiltration of peripheral immune cells into the injured brain. However, the specific role of regulatory T cells (Tregs) in neonatal HI is still unknown. Methods: Nine-day-old mice were exposed to HI by ligation of the right common carotid artery followed by 1 hour hypoxia (10% oxygen). Using immunohistochemistry, flow cytometry, and microarray analyses, Tregs were investigated in the brain, spleen, and blood 24 hours post HI. The functional role of Tregs was evaluated by acute Treg depletion in depletion of regulatory T cells transgenic mice. Brain injury, neuroinflammatory responses, and vascular injury were analyzed via immunohistochemistry and Western blot 48 hours and 7 days after HI. Functional outcome was assessed 3 days and 5 weeks after HI. Results: Female mice revealed an increased cerebral Treg infiltration, coinciding with elevated chemokine receptor expression. Treg depletion in females aggravated HI-induced brain tissue injury, short-term motor deficits, and long-term deficits in exploratory activity, paralleled by an increased microglia and endothelial activation and leukocyte infiltration. Treg depletion in male mice reduced HI-induced brain injury, short-term motor, and long-term cognitive deficits, associated with reduced vascular injury. Ex vivo isolated female Tregs displayed an increased immunosuppressive activity on effector T cell proliferation and an increased gene enrichment in pathways related to enhanced Treg activity. Conclusions: Tregs from neonatal female mice provide endogenous neuroprotection, whereas Tregs from male mice increase secondary neurodegeneration. As potential mechanisms, we identified intrinsic transcriptional differences associated with enhanced anti-inflammatory activity of female Tregs. Our study emphasizes the urgent need for sex-stratified clinical and preclinical analyses.

Implications of regulatory T cells in non-lymphoid tissue physiology and pathophysiology

“…Systemic depletion of Treg cells in female mice followed by intrathecal CSF-1 injection resulted in microglia adopting a transcriptional landscape similar to the state observed in male mice, together with the induction of pain in such female mice, highlighting a sex-specific protective function of CNS Treg cells in female animals (110). Another example of sexual dimorphism of brain Treg cells was observed in the setting of hypoxia-induced encephalopathy in neonates (111). Brain Treg cells were more numerous in the brains of female mice 24 hours post induction of hypoxia, expressing the chemokine receptors CCR4 and CXCR4.…”

“…Strikingly, Treg depletion in male neonatal mice mitigated neuronal injury and motor and cognitive deficits. Mechanistically, Treg cells from female mice exhibited greater suppressive capacity of effector T cells, and their depletion resulted in enhanced microglial and endothelial cell activation in female but not male mice (111).…”

“…Brain Treg cells were more numerous in the brains of female mice 24 hours post induction of hypoxia, expressing the chemokine receptors CCR4 and CXCR4. Depletion of Treg cells in female mice exacerbated neuropathology as well as motor and behavioral impairments (111). Strikingly, Treg depletion in male neonatal mice mitigated neuronal injury and motor and cognitive deficits.…”

“…Recently, sex discrepancies have been described for tissues such as VAT (38), CNS (110,111), or the kidneys (133, 143) revealing a knowledge gap that needs to be addressed in future investigations. This is particularly evident from the findings in VAT where sex hormones actually influence Treg cell differentiation and phenotype.…”

Biomarker und Neuromonitoring zur Entwicklungsprognose nach perinataler Hirnschädigung

“…Die Ausprägung des Schadens hängt maßgeblich vom Grad der Hirnreife, der Schadensursache und dem genetischen Hintergrund ab [ 52 ]. Einige Arbeiten konnten zeigen, dass die individuelle Immunantwort und das Geschlecht wesentliche Einflussfaktoren sind [ 6 , 44 , 52 ]. Auch Reifungsprozesse der weißen Substanz unterscheiden sich signifikant zwischen den Geschlechtern [ 81 ].…”