Gene–Dose–Dependent ReductionFshrExpression Improves Spatial Memory Deficits in Alzheimer’s Mice

Abstract

ABSTRACTAlzheimer’s disease (AD) is a major progressive neurodegenerative disorder of the aging population. High post–menopausal levels of the pituitary gonadotropin follicle–stimulating hormone (FSH) are strongly associated with the onset of AD, and we have shown recently that FSH directly activates the hippocampalFshrto drive AD–like pathology and memory loss in mice. To establish a role for FSH in memory loss, we used female3xTg;Fshr+/+, 3xTg;Fshr+/–and3xTg;Fshr-/-mice that were either left unoperated or underwent sham surgery or ovariectomy at 8 weeks of age. Unoperated and sham–operated3xTg;Fshr-/-mice were implanted with 17β-estradiol pellets to normalize estradiol levels. Morris Water Maze and Novel Object Recognition behavioral tests were performed to study deficits in spatial and recognition memory, respectively, and to examine the effects ofFshrdepletion.3xTg;Fshr+/+mice displayed impaired spatial memory at 5 months of age; both the acquisition and retrieval of the memory were ameliorated in3xTg;Fshr-/-mice and, to a lesser extent, in3xTg;Fshr+/-mice–– thus documenting a clear gene–dose–dependent prevention of hippocampal–dependent spatial memory impairment. At 5 and 10 months, sham–operated3xTg;Fshr-/-mice showed better memory performance during the acquisition and/or retrieval phases, suggesting thatFshrdeletion prevented the progression of spatial memory deficits with age. However, this prevention was not seen when mice were ovariectomized, except in the 10–month–old3xTg;Fshr-/-mice. In the Novel Object Recognition test performed at 10 months, all groups of mice, except ovariectomized3xTg;Fshr-/-mice showed a loss of recognition memory. Consistent with the neurobehavioral data, there was a gene–dose–dependent reduction mainly in the amyloid β40 isoform in whole brain extracts. Finally, serum FSH levels <8 ng/mL in 16–month–oldAPP/PS1mice were associated with better retrieval of spatial memory. Collectively, the data provide compelling genetic evidence for a protective effect of inhibiting FSH signaling on the progression of spatial and recognition memory deficits in mice, and lay a firm foundation for the use of an FSH–blocking agent for the early prevention of cognitive decline in postmenopausal women.