Locus Coeruleus Degeneration Induces Forebrain Vascular Pathology in a Transgenic Rat Model of Alzheimer’s Disease

Article type: Research Article

Authors: Kelly, Sarah C.^{a; b} | McKay, Erin C.^{a; c} | Beck, John S.^a | Collier, Timothy J.^{a; b; c} | Dorrance, Anne M.^{c; d} | Counts, Scott E.^{a; b; c; e; f; g; *}

Affiliations: [a] Department of Translational Science and Molecular Medicine, Michigan State University, Grand Rapids, MI, USA | [b] Cell and Molecular Biology Program, Michigan State University, East Lansing, MI, USA | [c] Neuroscience Program, Michigan State University, East Lansing, MI, USA | [d] Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI, USA | [e] Department of Family Medicine, Michigan State University, Grand Rapids, MI, USA | [f] Hauenstein Neurosciences Center, Mercy Health Saint Mary’s Hospital, Grand Rapids, MI, USA | [g] Michigan Alzheimer’s Disease Core Center, Ann Arbor, MI, USA

Correspondence: [*] Correspondence to: Scott E. Counts, PhD, Department of Translational Science and Molecular Medicine, Department of Family Medicine, College of Human Medicine, Michigan State University, 400 Monroe Ave NW, Grand Rapids, MI 49503 USA. Tel.: +1 616 234 0997; Fax: +1 616 234 0991; E-mail: scott.counts@hc.msu.edu.

Abstract: Noradrenergic locus coeruleus (LC) neuron loss is a significant feature of mild cognitive impairment and Alzheimer’s disease (AD). The LC is the primary source of norepinephrine in the forebrain, where it modulates attention and memory in vulnerable cognitive regions such as prefrontal cortex (PFC) and hippocampus. Furthermore, LC-mediated norepinephrine signaling is thought to play a role in blood-brain barrier (BBB) maintenance and neurovascular coupling, suggesting that LC degeneration may impact the high comorbidity of cerebrovascular disease and AD. However, the extent to which LC projection system degeneration influences vascular pathology is not fully understood. To address this question in vivo, we stereotactically lesioned LC projection neurons innervating the PFC of six-month-old Tg344-19 AD rats using the noradrenergic immunotoxin, dopamine-β-hydroxylase IgG-saporin (DBH-sap), or an untargeted control IgG-saporin (IgG-sap). DBH-sap-lesioned animals performed significantly worse than IgG-sap animals on the Barnes maze task in measures of both spatial and working memory. DBH-sap-lesioned rats also displayed increased amyloid and inflammation pathology compared to IgG-sap controls. However, we also discovered prominent parenchymal albumin extravasation with DBH-sap lesions indicative of BBB breakdown. Moreover, microvessel wall-to-lumen ratios were increased in the PFC of DBH-sap compared to IgG-sap rats, suggesting that LC deafferentation results in vascular remodeling. Finally, we noted an early emergence of amyloid angiopathy in the DBH-sap-lesioned Tg344-19 AD rats. Taken together, these data indicate that LC projection system degeneration is a nexus lesion that compromises both vascular and neuronal function in cognitive brain areas during the prodromal stages of AD.

Keywords: Alzheimer’s disease, blood-brain barrier, cerebral amyloid angiopathy, locus coeruleus, vascular remodeling

DOI: 10.3233/JAD-190090

Journal: Journal of Alzheimer's Disease, vol. 70, no. 2, pp. 371-388, 2019