Transforming Growth Factor-β Signaling Alters Substrate Permeability and Tight Junction Protein Expression at the Blood-Brain Barrier during Inflammatory Pain

Abstract

Our laboratory has shown that peripheral inflammatory pain induced by λ-carrageenan (CIP) can increase blood–brain barrier (BBB) permeability and alter tight junction (TJ) protein expression leading to changes in BBB functional integrity. However, the intracellular signaling mechanisms involved in this pathophysiologic response have not been elucidated. Transforming growth factor (TGF)-β signaling pathways are known to regulate vascular integrity and permeability. Therefore, we examined the function of TGF-β signaling at the BBB in rats subjected to CIP. During CIP, serum TGF-β1 and protein expression of the TGF-β receptor activin receptor-like kinase-5 (ALK5) were reduced. Brain permeability to 14C-sucrose was increased and expression of TJ proteins (i.e., claudin-5, occludin, zonula occluden (ZO-1)) were also altered after 3 h CIP. Pharmacological inhibition of ALK5 with the selective inhibitor SB431542 further enhanced brain uptake of 14C-sucrose, increased TJ protein expression (i.e., claudin-3, claudin-5, occludin, ZO-1), and decreased nuclear expression of TGF-β/ALK5 signaling molecules (i.e., Smad2, Smad3), which suggests a role for TGF-β/ALK5 signaling in the regulation of BBB integrity. Interestingly, administration of exogenous TGF-β1 before CIP activated the TGF-β/ALK5 pathway and reduced BBB permeability to 14C-sucrose. Taken together, our data show that TGF-β/ALK5 signaling is, in part, involved in the regulation of BBB functional integrity.

Hypoxia/Reoxygenation Stress Signals an Increase in Organic Anion Transporting polypeptide 1a4 (Oatp1a4) at the Blood–Brain Barrier: Relevance to CNS Drug Delivery

“…21 Furthermore, we have shown that SB431542 does not affect TGF-b/ALK1 signaling, data that emphasize the specificity of this small molecule for the TGF-b/ALK5 signaling pathway. 21 Our current study also identifies TGF-b/ALK5 signaling as a target for pharmacological manipulation of brain microvascular permeability to neuroprotective and/or antioxidant drugs for treatment of diseases with an H/R component. Targeting the TGF-b signaling pathway may enable 'tighter control' of Oatp1a4 functional expression, thereby enabling increased delivery of drugs to the brain.…”

“…At the BBB, only two ALK receptors (i.e., ALK1 and ALK5) have been identified. 21 We have previously shown that pharmacological inhibition of TGF-b/ALK5 signaling can increase Oatp1a4 functional expression. 19 Therefore, targeting of TGF-b/ ALK5 signaling during H/R provides an opportunity to control Oatp1a4 expression/activity at the BBB for optimization of CNS drug delivery.…”

Transforming Growth Factor-β1 Regulates Cdk5 Activity in Primary Sensory Neurons

“…5B). Because TGF-␤ signaling is deregulated during inflammatory pain (44,45), we assessed whether thermal pain response in Tgfbr1 cKO mice are affected after experimental inflammation induced by intraplantar carrageenan injection. We injected carrageenan into the left and vehicle into the right hind paws of 1-month-old Tgfbr1 cKO and control mice, and then we measured paw withdrawal latency at 5 and 24 h after injection.…”

Stromal regulation of vessel stability by MMP14 and TGFβ

“…In the brain, the inhibition of TGFb type I ALK5 receptors also increases leakage (of the blood brain barrier), accompanied by changes in the expression of tight junction adhesion proteins (Ronaldson et al, 2009).…”