Characterisation of the in-vivo, cellular and gene expression changes in the neurovascular unit due to systemic inflammation

The neurovascular unit (NVU) plays a pivotal role in the maintenance of a healthy brain microenvironment, including the regulation of cerebral blood flow in accordance with dynamically changing metabolic demand. Systemic inflammation has deleterious effects on brain function and altered NVU function may be the primary pathway for these effects. The proposed PhD project will unify research carried out in the labs of Martin (Psychology, in-vivo neurovascular function) and Simpson (SITraN, neuroinflammation and neuropathology) to characterize the functional and histological changes in the NVU as a response to systemic inflammatory challenge. The student will benefit from multidisciplinary expertise and training in a range of techniques across both laboratories.

Work leading up to this PhD Project Proposal: Our preliminary studies have determined the acute effects of systemic inflammation upon NVU function with both in-vivo and immunohistological characterisation. Naïve rats were injected systemically with lipopolysaccharide (LPS, 2mg/kg i.p.) or saline before in-vivo multimodal imaging to determine acute changes in neurovascular function. After in-vivo data collection, brains were extracted in order to characterise immunohistochemical (IHC) changes in NVU cells which were associated with the observed functional in-vivo changes. Imaging results (Figure 1) demonstrate enhanced hemodynamic responses in rats just 4 hours after LPS treatment. Quantified IHC data obtained from the same animals as used in the in-vivo experiments show significant concomitant changes in gliosis (GFAP – astrogliosis), microglial morphology (IBA-1), endothelial activation (ICAM-1) and AQP4 upregulation in cortex indicating rapid changes to NVU cell status. These data demonstrate for the first time that an induced systemic inflammatory response acutely alters in-vivo hemodynamic function, in association with significant underlying changes in the status of cellular constituents of the NVU. An important next step is to extend this work into a chronic inflammation model to ascertain the neurovascular-inflammation interactions in contexts with greater relevance to their operation in the normal life course. Specifically, this project will ask 3 further questions: (i) What are the functional and histological NVU changes induced by a chronically administered systemic inflammatory stimulus? (ii) What alterations in the gene expression profile of the NVU are associated with these histopathological and in-vivo effects? (iii) What is the interaction of these effects with age?

Programme of Work / Timeline: The student will be trained to use our established rodent (rat) model to combine (i) multimodal, multiscale, in-vivo measurements of brain neurovascular function (imaging, electrophysiology [training in Martin’s lab]) with (ii) detailed characterisation of NVU pathology (histology [training in Simpson’s lab]) and (iii) associated changes in the gene expression profile (RNA-seq [training in Simpson’s lab and Bioinformatics Core]). We will determine effects in both young-adult (Study 1) and middle-aged (Study 2) animals. This will enable us to test a number of specific hypotheses:
Hypothesis 1: Exposure to a chronic systemic inflammatory stimulus produces changes in in-vivo neurovascular function with associated histopathological changes.
Hypothesis 2: There will be an interaction of age with the measured in-vivo and histopathological changes, such that these will be exacerbated in older adult animals.
Hypothesis 3: Exposure to a chronic systemic inflammatory stimulus leads to transcriptomic changes in the neurovascular unit (ECs, astrocyte endfeet, pericytes).
Hypothesis 4: The gene expression profiles in older adult animals will differ to those observed in young-adult animals.