Gender differences in neurotrophin and glutamate receptor expression in cholinergic nucleus basalis neurons during the progression of Alzheimer's disease

Abstract

The higher incidence rate of Alzheimer's disease (AD) in elderly women indicates that gender plays a role in AD pathogenesis. Evidence from clinical and pharmacologic studies, neuropathological examinations, and models of hormone replacement therapy suggest that cholinergic basal forebrain (CBF) cortical projection neurons within the nucleus basalis (NB), which mediate memory and attention and degenerate in AD, may be preferentially vulnerable in elderly women compared to men. CBF neurons depend on nerve growth factor (NGF) and their cognate receptors (trkA and p75(NTR)) for their survival and maintenance. We recently demonstrated a shift in the balance of NGF and its receptors toward cell death mechanisms during the progression of AD. To address whether gender affects NGF signaling system expression within the CBF, we used single cell RNA amplification and custom microarray technologies to compare gene expression profiles of single cholinergic NB neurons in tissue specimens from male and female members of the Religious Orders Study who died with a clinical diagnosis of no cognitive impairment (NCI), mild cognitive impairment (MCI), or mild/moderate AD. p75(NTR) expression within male cholinergic NB neurons was unchanged across clinical diagnosis, whereas p75(NTR) mRNA levels in female NB neurons exhibited a ∼40% reduction in AD compared to NCI. Male AD subjects displayed a ∼45% reduction in trkA mRNA levels within NB neurons compared to NCI and MCI. In contrast, NB neuronal trkA expression in females was reduced ∼50% in both MCI and AD compared to NCI. Reduced trkA mRNA levels were associated with poorer global cognitive performance and higher Braak scores in the female subjects. In addition, we found a female-selective reduction in GluR2 AMPA glutamate receptor subunit expression in NB neurons in AD. These data suggest that cholinergic NB neurons in females may be at greater risk for degeneration during the progression of AD and support the concept of gender-specific therapeutic interventions during the preclinical stages of the disease.

Figure 1

Expression profiling of p75^NTR and trkA NGF receptors within male and female cholinergic NB neurons during the progression of AD. A, C) p75^NTR mRNA levels measured in single NB neurons microaspirated from male (A) and female (C) subjects with an ante mortem diagnosis of NCI, MCI, or mild/moderate AD. B, D) trkA mRNA levels measured in single NB neurons microaspirated from male (A) and female (C) subjects with NCI, MCI, or AD. *, p < 0.05 vs. MCI; **, p < 0.01 vs. NCI; p < 0.001 vs. NCI.

Figure 2

qPCR validation of the microarray analysis demonstrating down regulation of trkA expression. A, B) trkA mRNA levels within the anterior NB in male (A) and female (B) subjects.*, p < 0.05 and **, p < 0.01 vs. NCI.

Figure 3

Expression profiling of AMPA glutamate receptor subunits within male and female cholinergic NB neurons during the progression of AD. A) Representative array hybridization data for GluR1 (GRIA1), GluR2 (GRIA2), GluR3 (GRIA3), and GluR4 (GRIA4) AMPA receptor transcripts from NB neurons of male (M) and female (F) NCI, MCI, and AD subjects. B, C) Heatmaps show relative hybridization signal intensities for GRIA1-4 mRNAs in cholinergic NB neurons from male (B) and female (C) subjects (white to black = decreasing mRNA levels).*, p < 0.05 vs. NCI, MCI.