Nrf2 Upregulates ATP Binding Cassette Transporter Expression and Activity at the Blood-Brain and Blood-Spinal Cord Barriers

Abstract

Activation of nuclear factor E2-related factor-2 (Nrf2), a sensor of oxidative stress, is neuroprotective in animal models of cerebral ischemia, traumatic brain injury, subarachnoid hemorrhage, and spinal cord injury. We show here that Nrf2 activation with sulforaphane (SFN) in vivo or in vitro increases expression and transport activity of three ATP-driven drug efflux pumps at the blood-brain barrier [P-glycoprotein, ATP binding cassette b1 (Abcb1); multidrug resistance-associated protein-2 (Mrp2), Abcc2; and breast cancer resistance protein (Bcrp), Abcg2]. Dosing rats with SFN increased protein expression of all three transporters in brain capillaries and decreased by 50% brain accumulation of the P-glycoprotein substrate verapamil. Exposing rat or mouse brain capillaries to SFN increased P-glycoprotein, Bcrp, and Mrp2 transport activity and protein expression; SFN increased P-glycoprotein activity in mouse spinal cord capillaries. Inhibiting transcription or translation abolished upregulation of P-glycoprotein activity. No such effects were seen in brain capillaries from Nrf2-null mice, indicating Nrf2 dependence. Nrf2 signaled indirectly to increase transporter activity/expression. The p53 inhibitor pifithrin abolished the SFN-induced increase in transporter activity/expression, and the p53-activator nutlin-3 increased P-glycoprotein activity. SFN did not alter P-glycoprotein transport activity in brain and spinal cord capillaries from p53-null mice. Inhibitors of p38 MAPK and nuclear factor B (NF-B) blocked the effects of SFN and nutlin-3 on P-glycoprotein activity. These results implicate Nrf2, p53, and NF-B in the upregulation of P-glycoprotein, Bcrp, and Mrp2 at blood-CNS barriers. They imply that the barriers are tightened selectively (efflux transporter upregulation) by oxidative stress, providing increased neuroprotection, but also reduced penetration of many therapeutic drugs.

Selective induction of P-glycoprotein at the CNS barriers during symptomatic stage of an ALS animal model

“…(Figures 2B&C). As shown in our previous publications, NFkB is a nuclear transcription factor known to induce P-gp expression in rat brain capillaries [23]. Using immunohistochemistry, we observed no significant difference of NFkB nuclear localization in brain and spinal cord capillaries from SOD rats compared among all three ALS stages (Figure 2D).…”

“…Next, we examined the role of NFκB for P-gp induction in SOD rats, because this transcription factor was shown to increase P-gp at the rat BBB [23] and was recently shown to play a role in microglia-induced motor neuron death in an ALS mouse model with SOD1-G93A mutation [10]. We observed no major changes of NFκB nuclear localization in capillaries of the brain and spinal cords from SOD rats at all ALS stages compared to wildtype.…”

Regulation of ABC Transporters Blood–Brain Barrier

“…Second, we previously showed that the blood-spinal cord barrier is similar to the blood-brain barrier with respect to ABC transporter expression and regulation by ligandactivated transcription factors, such as, PXR, CAR, AhR, and Nrf2/p53 Wang et al, 2014). Using mouse spinal cord capillaries, we found that basal P-glycoprotein transport activity was regulated by the same signaling pathway described in brain capillaries (Cartwright et al, 2013).…”

Glutamate-Mediated Upregulation of the Multidrug Resistance Protein 2 in Porcine and Human Brain Capillaries

“…The majority of these studies focused on the mechanisms of xenobiotic-induced upregulation of MRP2, indicating that diesel exhaust particles can induce MRP2 expression and that the pregnane X receptor, the constitutive androstane receptor, the farnesyl X receptor, and the activation of the transcription factor NF-E2-related factor-2 (Nrf2) can contribute to the impact of xenobiotic exposure on MRP2 expression and transport function (Maher et al, 2005;Miller, 2010;Wang et al, 2014). However, to our knowledge no study has been conducted exploring the signaling mechanisms of disease-associated MRP2 regulation on a cellular level.…”