Long‐term deprivation of ovarian hormones via ovariectomy alters functional connectivity, brain neurochemistry and white matter integrity in a mouse model of Alzheimer's disease: Neuroimaging: Sex and ethnoracial differences – biomarkers.

Background: The abrupt loss of ovarian hormones before menopause, induced by oophorectomy, has been associated with accelerated aging, multimorbidity, and Alzheimer's disease (AD). We investigated the impact of prolonged loss of ovarian hormones on AD progression in a transgenic mouse model of amyloid pathology using in vivo diffusion tensor MRI, resting‐state functional MRI (rsfMRI) and spectroscopy (MRS). Method: Female 3.5‐month‐old TG2576 (TG) (N=27) and wild‐type (WT) (N=27) mice were ovariectomized (TGOVX) or sham‐operated (TGSHAM). When they became 18‐month‐old, 1‐H MRS (ROIs: hypothalamus, hippocampus, and cerebral cortex), DTI and rsfMRI was performed. ROI based analysis was performed on rsfMRI and DTI (Fractional anisotropy (FA), axial diffusivity (AxD), mean diffusivity, and radial diffusivity). The brain samples were then evaluated by histology and ELISA to assess Aβ load and activated glial cells. The loss of ovarian hormones via OVX was validated with elevated plasma luteinizing hormone level: OVX>SHAM (p<0.05). Two‐way ANOVA and post‐hoc (Student's‐t) tests were used for statistical analysis. P values were adjusted for multiple comparisons (FDR‐p). Result: The multimodel imaging data showed that there was a significant increase in taurine and total creatine (markers for inflammation and energy metabolism) in the hypothalamus, decrease in FA and AxD (markers for white matter integrity) in the white matter regions, and decrease in the functional connectivity between the prefrontal cortex and the hippocampus and dorsal and ventral hippocampus regions (a neural marker of network activity and integrity) (FDR‐p <0.05 (Figure 1)) in TGOVX mice compared to TGSHAM mice (post‐hoc t‐test). rsFMRI showed a significant increase in rsfMRI connectivity in WTOVX mice compared to WTSHAM mice. Complementary histological (and ELISA) analysis revealed no differences in Aβ load (plaque and soluble) and activated glial cells between the TG groups. Conclusion: The MRI results suggest that inflammatory response was elevated, energy metabolism was disrupted and white matter and network integrity decreased after prolonged ovarian hormone loss. These MRI results support other data from human and animal studies suggesting that abrupt hormonal changes associated with premenopausal removal of ovaries may increase the risk factors of AD, and accelerate the disease progression by causing abnormalities in brain structure, function and metabolism. [ABSTRACT FROM AUTHOR]