Title: TrkB-mediated sustained neuroprotection is sex-specific and estrogen receptor alpha (ERa)-dependent in adult mice following neonatal hypoxia ischemia (HI)
Legend: 7,8 DHF therapy rescues recognition and location memory only in females in an ERa-dependent way. Mice were subjected to NOR testing P60 + post-HI. Novel object recognition (NOR) testing in males (A) and females (A’) is shown for ERa+/+sham+VC, ERa+/+HI+VC, ERa+/+HI+DHF, ERa−/−sham+VC, ERa−/−HI+ VC, and ERa−/−HI+DHF groups. Data are mean ± SEM. *p < 0.05 compared to corresponding sham. #p < 0.05 compared to corresponding male ERa+/+HI+DHF. Mice were subjected to NOL testing P60 + post-HI. Novel object location (NOL) testing in males (B) and females (B’) is shown for ERa+/+sham+VC, ERa+/+HI+VC, ERa+/+HI+DHF, ERa−/−sham+VC, ERa−/−HI+ VC, and ERa−/−HI+DHF groups. Dotted line at 0.5 indicates no preference for the novel object. Data are mean ± SEM. *p< 0.05 compared to corresponding sham. #p< 0.05 compared to corresponding male ERa+/+HI+DHF.
Citation: Chanana, V., Hackett, M., Deveci, N., Aycan, N., Ozaydin, B., Cagatay, N. S., Hanalioglu, D., Kintner, D. B., Corcoran, K., Yapici, S., Camci, F., Eickhoff, J., Frick, K. M., Ferrazano, P., Levine, J. E., & Cengiz, P. (2023). TrkB-mediated sustained neuroprotection is sex-specific and ERα dependent in adult mice following neonatal hypoxia ischemia. Research square, rs.3.rs-3325405. https://doi.org/10.21203/rs.3.rs-3325405/v1
Abstract: Background – Neonatal hypoxia ischemia (HI) related brain injury is one of the major causes of life-long neurological morbidities that result in learning and memory impairments. Evidence suggests that male neonates are more susceptible to the detrimental effects of HI, yet the mechanisms mediating these sex-specific responses to neural injury in neonates remain poorly understood. We previously tested the effects of treatment with a small molecule agonist of the tyrosine kinase B receptor (TrkB), 7,8-dihydroxyflavone (DHF) following neonatal HI and determined that females, but not males exhibit increased phosphorylation of TrkB and reduced apoptosis in their hippocampi. Moreover, these female-specific effects of the TrkB agonist were found to be dependent upon the expression of ERa. These findings demonstrated that TrkB activation in the presence of ERa comprises one pathway by which neuroprotection may be conferred in a female-specific manner. The goal of this study was to determine the role of ERa dependent TrkB-mediated neuroprotection in memory and anxiety in young adult mice exposed to HI during the neonatal period. Methods – In this study, we used a unilateral hypoxic ischemic (HI) mouse model. ERa+/+ or ERa -/- mice were subjected to HI on postnatal day (P) 9 and mice were treated with either vehicle control or the TrkB agonist, DHF, for 7 days following HI. When mice reached young adulthood, we used the novel object recognition, novel object location and open field tests to assess long-term memory and anxiety-like behavior. The brains were then assessed for tissue damage using immunohistochemistry. Results – Neonatal DHF treatment prevented HI-induced decrements in recognition and location memory in adulthood in females, but not in males. This protective effect was absent in female mice lacking ERa. The female-specific improved recognition and location memory outcomes in adulthood conferred by DHF therapy after neonatal HI tended to be or were ERa dependent, respectively. Interestingly, DHF triggered anxiety-like behavior in both sexes only in the mice that lacked ERa. When we assessed the severity of injury, we found that DHF therapy did not decrease the percent tissue loss in proportion to functional recovery. We additionally observed that the presence of ERa significantly reduced overall HI-associated mortality in both sexes. Conclusions – These observations provide evidence for a therapeutic role for DHF in which TrkB-mediated sustained recovery of recognition and location memories in females are ERa associated and dependent, respectively. However, the beneficial effects of DHF therapy did not include reduction of gross tissue loss but may be derived from the enhanced functioning of residual tissues in a cell-specific manner. Keywords –7,8-Dihydroxyflavone; Brain injury; DHF; Estrogen receptor; Hypoxia; Hypoxic ischemic encephalopathy; Ischemia; Neonate; Sex differences; TrkB; Tyrosine kinase B
Investigator: Pelin Cengiz, MD
About the Lab: Dr. Pelin Cengiz’s research focuses on finding a novel therapy for neonatal encephalopathy after hypoxia ischemia (HI). She uses the experimental (Vannucci-Rice) mouse model of hypoxia ischemia (HI) to study the sexually differentiated role of neurotrophin signaling in the neonatal hippocampus post-HI. The neurotrophin receptor, tyrosine kinase B (TrkB), plays an important role in neuroprotection and improving the long-term functional recovery following cerebral ischemia by increasing neuronal survival. She has shown that administration of 7,8 dihydroxyflavone (7,8-DHF; potent and selective TrkB agonist) increases TrkB phosphorylation and hippocampal neuronal survival following HI in female, but not in male newborn mice. This female-specific responsiveness to TrkB agonist therapy mimics improved outcomes observed clinically in female newborn humans post-HI. Her studies focus on the cellular mechanisms of the female-specific responsiveness to TrkB agonist and their roles in improving long-term neurological and functional outcome post-HI. An improved understanding of the cellular mechanisms that underlie sex-specific neurotrophin responses will identify new avenues for developing novel therapeutics for neonates and children suffering from brain injury.