TrkB-mediated neuroprotection in female hippocampal neurons is autonomous, estrogen receptor alpha-dependent, and eliminated by testosterone: a proposed model for sex differences in neonatal hippocampal neuronal injury

• Published in: Biology of sex differences 2024-04, Vol.15 (1), p.30-30, Article 30
• Main Authors: Chanana, Vishal, Zafer, Dila, Kintner, Douglas B, Chandrashekhar, Jayadevi H, Eickhoff, Jens, Ferrazzano, Peter A, Levine, Jon E, Cengiz, Pelin
• Format: Article
• Language: English
• Subjects: 7,8-dihydroxyflavone; Apoptosis; Bioavailability; Blood flow; Brain; Brain injury; Cell survival; Estrogen; Estrogen receptor alpha; Estrogen receptors; Estrogens; Ethylenediaminetetraacetic acid; Experiments; Females; Gender differences; Growth factors; Hippocampus; Hypoxia; Hypoxia ischemia; Infants (Newborn); Ischemia; Kinases; Males; Morphology; Neonatal; Neonates; Nerve growth factor; Neurons; Neuroprotection; Neurotrophin receptor; Penicillin; Phenols; Phosphorylation; Sex differences; Testosterone; TrkB receptors; Tyrosine kinase B receptor
• ISSN: 2042-6410; 2042-6410
• DOI: 10.1186/s13293-024-00596-1

Neonatal hypoxia ischemia (HI) related brain injury is one of the major causes of learning disabilities and memory deficits in children. In both human and animal studies, female neonate brains are less susceptible to HI than male brains. Phosphorylation of the nerve growth factor receptor TrkB has been shown to provide sex-specific neuroprotection following in vivo HI in female mice in an estrogen receptor alpha (ERα)-dependent manner. However, the molecular and cellular mechanisms conferring sex-specific neonatal neuroprotection remain incompletely understood. Here, we test whether female neonatal hippocampal neurons express autonomous neuroprotective properties and assess the ability of testosterone (T) to alter this phenotype. We cultured sexed hippocampal neurons from ERα and ERα mice and subjected them to 4 h oxygen glucose deprivation and 24 h reoxygenation (4-OGD/24-REOX). Sexed hippocampal neurons were treated either with vehicle control (VC) or the TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) following in vitro ischemia. End points at 24 h REOX were TrkB phosphorylation (p-TrkB) and neuronal survival assessed by immunohistochemistry. In addition, in vitro ischemia-mediated ERα gene expression in hippocampal neurons were investigated following testosterone (T) pre-treatment and TrkB antagonist therapy via q-RTPCR. Multifactorial analysis of variance was conducted to test for significant differences between experimental conditions. Under normoxic conditions, administration of 3 µM 7,8-DHF resulted an ERα-dependent increase in p-TrkB immunoexpression that was higher in female, as compared to male neurons. Following 4-OGD/24-REOX, p-TrkB expression increased 20% in both male and female ERα neurons. However, with 3 µM 7,8-DHF treatment p-TrkB expression increased further in female neurons by 2.81 ± 0.79-fold and was ERα dependent. 4-OGD/24-REOX resulted in a 56% increase in cell death, but only female cells were rescued with 3 µM 7,8-DHF, again in an ERα dependent manner. Following 4-OGD/3-REOX, ERα mRNA increased ~ 3 fold in female neurons. This increase was blocked with either the TrkB antagonist ANA-12 or pre-treatment with T. Pre-treatment with T also blocked the 7,8-DHF- dependent sex-specific neuronal survival in female neurons following 4-OGD/24-REOX. OGD/REOX results in sex-dependent TrkB phosphorylation in female neurons that increases further with 7,8-DHF treatment. TrkB phosphorylation by 7,8-DHF increased ERα mRNA expression and promoted cel