Localization of endogenous amyloid-β to the coeruleo-cortical pathway: consequences of noradrenergic depletion

Abstract The locus coeruleus (LC)–norepinephrine (NE) system is an understudied circuit in the context of Alzheimer’s disease (AD), and is thought to play an important role in neurodegenerative and neuropsychiatric diseases involving catecholamine neurotransmitters. Understanding the expression and...
Ausführliche Beschreibung

Abstract The locus coeruleus (LC)–norepinephrine (NE) system is an understudied circuit in the context of Alzheimer’s disease (AD), and is thought to play an important role in neurodegenerative and neuropsychiatric diseases involving catecholamine neurotransmitters. Understanding the expression and distribution of the amyloid beta (Aβ) peptide, a primary component of AD, under basal conditions and under conditions of NE perturbation within the coeruleo-cortical pathway may be important for understanding its putative role in pathological states. Thus, the goal of this study is to define expression levels and the subcellular distribution of endogenous Aβ with respect to noradrenergic profiles in the rodent LC and medial prefrontal cortex (mPFC) and, further, to determine the functional relevance of NE in modulating endogenous $ Aβ_{42} $ levels. We report that endogenous $ Aβ_{42} $ is localized to tyrosine hydroxylase (TH) immunoreactive somatodendritic profiles of the LC and dopamine-β-hydroxylase (DβH) immunoreactive axon terminals of the infralimbic mPFC (ILmPFC). Male and female naïve rats have similar levels of amyloid precursor protein (APP) cleavage products demonstrated by western blot, as well as similar levels of endogenous $ Aβ_{42} $ as determined by enzyme-linked immunosorbent assay. Two models of NE depletion, DSP-4 lesion and DβH knockout (KO) mice, were used to assess the functional relevance of NE on endogenous $ Aβ_{42} $ levels. DSP-4 lesioned rats and DβH-KO mice show significantly lower levels of endogenous $ Aβ_{42} $. Noradrenergic depletion did not change APP-cleavage products resulting from β-secretase processing. Thus, resultant decreases in endogenous $ Aβ_{42} $ may be due to decreased neuronal activity of noradrenergic neurons, or, by decreased stimulation of adrenergic receptors which are known to contribute to $ Aβ_{42} $ production by enhancing γ-secretase processing under normal physiological conditions. Ausführliche Beschreibung