Joseph W. Zagorski

The Nrf2 activator tBHQ inhibits T cell activation of primary human CD4 T cells

The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) regulates a battery of antioxidant, detoxification, and cell stress genes. It is activated by oxidative stress and a number of exogenous compounds, one of which is tert-butylhydroquinone (tBHQ), a widely used food preservative. Nrf2 modulates immune responses in numerous rodent models of inflammation, but its effects on human immune cells are not well characterized. The purpose of these studies was to evaluate the effects of the Nrf2 activator tBHQ on early events of T cell activation in primary human cells. Treatment with tBHQ induced mRNA expression of the Nrf2 target genes HMOX-1, GCLC, and NQO1, and also increased NRF2 mRNA expression, albeit to a lesser extent than the other target genes. tBHQ decreased production of the cytokines IL-2 and IFN-γ at both the protein and mRNA levels after stimulation with anti-CD3/anti-CD28 in human peripheral blood mononuclear cells and to an even greater extent in isolated CD4 T cells. Likewise, tBHQ decreased induction of CD25 and CD69 in peripheral blood mononuclear cells (PBMCs) and this decrease was even more marked in isolated CD4 T cells. In addition, tBHQ inhibited induction of NFκB DNA binding in anti-CD3/anti-CD28-activated PBMCs. Collectively, these data suggest that tBHQ inhibits activation of primary human CD4 T cells, which correlates with activation of Nrf2 and inhibition of NFκB DNA binding. Although these studies suggest the food additive tBHQ negatively impacts T cell activation, further studies will be needed to fully elucidate the effect of tBHQ on human immune responses.

The Nrf2 Activator, tBHQ, Differentially Affects Early Events Following Stimulation of Jurkat Cells

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that is activated by cellular stresses, such as oxidative compounds. After activation, Nrf2 induces transcription of its target genes, many of which have cytoprotective functions. Previously, we have shown that activation of Nrf2 by tert-butylhydroquinone (tBHQ) skews murine CD4⁺ T-cell differentiation. Although the role of Nrf2 in murine T cells is somewhat characterized, it is largely uncharacterized in human T cells. Therefore, the aim of the current studies was to characterize the effects of the Nrf2 activator, tBHQ, on the early events of human CD4⁺ T-cell activation. Pretreatment of Jurkat T cells with tBHQ, prior to activation with anti-CD3/anti-CD28, diminished the production of interleukin-2 (IL-2) at both the transcript and protein levels. Similarly, the expression of CD25 also diminished, albeit to a lesser degree than IL-2, after pretreatment with tBHQ. The decrease in IL-2 production was not due to decreased nuclear translocation of c-fos or c-jun. Although tBHQ caused both a delay and a decrease in Ca²⁺ influx in activated Jurkat cells, no decrease in nuclear factor of activated T cells (NFAT) DNA binding or transcriptional activity was observed. In contrast to NFAT, tBHQ significantly decreased NFκB transcriptional activity. Collectively, our studies show that the Nrf2 activator, tBHQ, inhibits IL-2 and CD25 expression, which correlates with decreased NFκB transcriptional activity in activated Jurkat cells. Overall, our studies suggest that Nrf2 represents a novel mechanism for the regulation of both human and mouse T cell function.

Differential effects of the Nrf2 activators tBHQ and CDDO-Im on the early events of T cell activation

ABSTRACT We previously demonstrated that activation of the transcription factor, nuclear factor erythroid 2‐related factor 2 (Nrf2) promotes CD4+ Th2 differentiation. In the current study, we assessed the role of Nrf2 in early events following T cell activation. The Nrf2 activators, tBHQ (tert‐butylhydroquinone) and CDDO‐Im (the imidazolide derivative of the triterpenoid CDDO), were used in conjunction with splenocytes derived from wild‐type and Nrf2‐null mice to distinguish between Nrf2‐specific and off‐target effects. CDDO‐Im inhibited early IFN&ggr; production in a largely Nrf2‐dependent manner. In contrast, tBHQ and CDDO‐Im had little effect on expression of CD25 or CD69. Furthermore, tBHQ inhibited GM‐CSF and IL‐2 production in both wild‐type and Nrf2‐null T cells, suggesting this effect is Nrf2‐independent. Conversely, CDDO‐Im caused a concentration‐dependent increase in IL‐2 secretion in wild‐type, but not Nrf2‐null, splenocytes, suggesting that Nrf2 promotes IL‐2 production. Interestingly, both compounds inhibit NF&kgr;B DNA binding, where the suppression by tBHQ is Nrf2‐independent and CDDO‐Im is Nrf2‐dependent. Surprisingly, as compared to wild‐type splenocytes, Nrf2‐null splenocytes showed lower nuclear accumulation of c‐Jun, a member of the AP‐1 family of transcription factors, which have been shown to drive multiple immune genes, including IL‐2. Both Nrf2 activators caused a Nrf2‐dependent trend toward increased nuclear accumulation of c‐Jun. These data suggest that modulation of cytokine secretion by tBHQ likely involves multiple pathways, including AP‐1, NF&kgr;B, and Nrf2. Overall, the data suggest that Nrf2 activation inhibits secretion of the Th1 cytokine IFN&ggr;, and increases early production of IL‐2, which has been shown to promote Th2 differentiation, and may support the later occurrence of Th2 polarization.

Nrf2-Dependent and -Independent Effects of tert -Butylhydroquinone, CDDO-Im, and H 2 O 2 in Human Jurkat T Cells as Determined by CRISPR/Cas9 Gene Editing

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a stress-activated transcription factor activated by stimuli such as electrophilic compounds and other reactive xenobiotics. Previously, we have shown that the commonly used food additive and Nrf2 activator tert-butylhydroquinone (tBHQ) suppresses interleukin-2 (IL-2) production, CD25 expression, and NFκB activity in human Jurkat T cells. The purpose of the current studies was to determine whether these effects were dependent upon Nrf2 by developing a human Nrf2-null T cell model using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 technology. The current studies show that suppression of CD25 expression by tBHQ is partially dependent on Nrf2, whereas inhibition of IL-2 secretion is largely Nrf2-independent. Interestingly, tBHQ inhibited NFκB activation in an Nrf2-independent manner. This was an unexpected finding since Nrf2 inhibits NFκB activation in other models. These results led us to investigate another more potent Nrf2 activator, the synthetic triterpenoid 1[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Im). Treatment of wild-type and Nrf2-null Jurkat T cells with CDDO-Im resulted in an Nrf2-dependent suppression of IL-2. Furthermore, susceptibility to reactive oxygen species was significantly enhanced in the Nrf2-null clones as determined by decreased mitochondrial membrane potential and cell viability. Importantly, this study is the first to describe the generation of a human Nrf2-null model, which is likely to have multiple applications in immunology and cancer biology. Collectively, this study demonstrates a role for Nrf2 in the effects of CDDO-Im on CD25 and IL-2 expression, whereas the effect of tBHQ on these parameters is complex and likely involves modulation of multiple stress-activated transcription factors, including NFκB and Nrf2.

Inhibition of early T cell cytokine production by arsenic trioxide occurs independently of Nrf2.

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a stress-activated transcription factor that induces a variety of cytoprotective genes. Nrf2 also mediates immunosuppressive effects in multiple inflammatory models. Upon activation, Nrf2 dissociates from its repressor protein, Keap1, and translocates to the nucleus where it induces Nrf2 target genes. The Nrf2-Keap1 interaction is disrupted by the environmental toxicant and chemotherapeutic agent arsenic trioxide (ATO). The purpose of the present study was to determine the effects of ATO on early events of T cell activation and the role of Nrf2 in those effects. The Nrf2 target genes Hmox-1, Nqo-1, and Gclc were all upregulated by ATO (1–2 μM) in splenocytes derived from wild-type, but not Nrf2-null, mice, suggesting that Nrf2 is activated by ATO in splenocytes. ATO also inhibited IFNγ, IL-2, and GM-CSF mRNA and protein production in wild-type splenocytes activated with the T cell activator, anti-CD3/anti-CD28. However, ATO also decreased production of these cytokines in activated splenocytes from Nrf2-null mice, suggesting the inhibition is independent of Nrf2. Interestingly, ATO inhibited TNFα protein secretion, but not mRNA expression, in activated splenocytes suggesting the inhibition is due to post-transcriptional modification. In addition, c-Fos DNA binding was significantly diminished by ATO in wild-type and Nrf2-null splenocytes activated with anti-CD3/anti-CD28, consistent with the observed inhibition of cytokine production by ATO. Collectively, this study suggests that although ATO activates Nrf2 in splenocytes, inhibition of early T cell cytokine production by ATO occurs independently of Nrf2 and may instead be due to impaired AP-1 DNA binding.