The Impact of Nociception on Central Microvessel Permeability and Neuroinflammation

Nociceptive insults (nerve injury or inflammation) alter blood spinal cord barrier (BSCB) integrity, allowing immune cell infiltration and plasma leakage into the parenchyma (Varatharaj & Galea 2016; Echeverry et al. 2011). Endothelial cells are said to become "activated" after nociceptive insults, upregulating adhesion molecules such as ICAM-1 and VCAM-1, which are involved in immune cell transmigration across the BSCB (Lawson & Wolf 2009). Endothelial cells can also release cytokines and prostaglandins that have the potential to sensitise neurones and glial cells (Varatharaj & Galea 2016). Tight junction expression is also altered in endothelial cells after nociceptive insults (Echeverry et al. 2011; Huber et al. 2001). However, barrier integrity and endothelial activation after nociceptive insults have not been extensively researched.

Microglia are "activated" after peripheral inflammation and nerve injury, and inhibition of microglia prevents chronic pain development (Calvo & Bennett 2012; Raghavendra et al. 2003). Microglia also play an integral role in the maintenance of blood-CNS (central nervous system) barriers (da Fonseca et al. 2014; Abbott et al. 2010), but the effect of microglia phenotype on spinal cord endothelial cells has rarely been investigated.
Astrocytes are involved in the BSCB and directly signal with neurones, so they may therefore be fundamental in overseeing alterations in barrier functions as they directly signal with both neurones and endothelial cells. Astrocytes are known to be involved with the maintenance of chronic pain (Chiang et al. 2012) and blood brain barrier integrity (Willis 2011), but it is unclear whether this is in part due astrocytes activating the endothelium to alter blood vessel permeability, which then sets up a positive feedback loop to exacerbate non-neuronal cell infiltration, astrocyte activation and subsequent neuronal activation, therefore maintaining pain.

Plan of investigation and procedures
1.1 To determine whether nerve injury or inflammation alters BSCB integrity in vivo.
Employ nerve injury or peripheral inflammation and monitor pain behaviour in at least two animal models of altered nociception.
Immunofluorescence/Western blots directed towards endothelial cell molecules involved in vascular "activation" (phospho-STAT3, ICAM-1, VCAM-1), tight junction proteins (occludin, claudin-5, ZO-1), and glia (GFAP, OX-42/IBA1)
Extravasation of exogenous substances (e.g. Evans Blue)
Effect of known analgesics on pain and spinal cord endothelial activation to determine associations between analgesic effect and spinal cord barrier alteration.

1.2 To determine molecular/functional responses of endothelial cells in vitro (this will inform 1.1 above)
Culture endothelial cells and alter e.g. ICAM-1/up/downstream signalling (and monitor following responses)
Mechanisms of monocyte migration across endothelial cell monolayer
Involvement of cell adhesion molecules (e.g.ICAM-1), signalling/regulatory molecules (e.g. pSTAT3) in cellular function and phenotypic alteration (ELISAs, Westerns, RNA seq)
Trans-endothelial electrical resistance (TEER) to determine endothelial monolayer integrity.

2. To determine the role of glia on endothelial "activation" in vitro
Culture endothelial cells and introduce media from "activated" astrocytes or microglia AND/OR introduce different molecules into endothelial cell culture that are known to be released from activated glia/neurones (e.g. glutamate, IL-6, TNF-a) and compare the effects on endothelial function and phenotype.
Control of monocyte migration across endothelial cell monolayer and contributions of glial-derived modulators.
Expression of key molecules in endothelial cells (ICAM-1, pSTAT3 etc. ELISAs, Westerns)
Effect of glial-derived modulators on endothelial monolayer integrity