Pregnane X receptor (PXR) deficiency protects against spinal cord injury by activating NRF2/HO-1 pathway.

INTRODUCTION: As a devastating neurological disease, spinal cord injury (SCI) results in severe tissue loss and neurological dysfunction. Pregnane X receptor (PXR) is a ligand-activated nuclear receptor with a major regulatory role in xenobiotic and endobiotic metabolism and recently has been implicated in the central nervous system. In the present study, we aimed to investigate the role and mechanism of PXR in SCI. METHODS: The clip-compressive SCI model was performed in male wild-type C57BL/6 (PXR+/+ ) and PXR-knockout (PXR-/- ) mice. The N2a H2 O2 -induced injury model mimicked the pathological process of SCI in vitro. Pregnenolone 16α-carbonitrile (PCN), a mouse-specific PXR agonist, was used to activate PXR in vivo and in vitro. The siRNA was applied to knock down the PXR expression in vitro. Transcriptome sequencing analysis was performed to discover the relevant mechanism, and the NRF2 inhibitor ML385 was used to validate the involvement of PXR in influencing the NRF2/HO-1 pathway in the SCI process. RESULTS: The expression of PXR decreased after SCI and reached a minimum on the third day. In vivo, PXR knockout significantly improved the motor function of mice after SCI, meanwhile, inhibited apoptosis, inflammation, and oxidative stress induced by SCI. On the contrary, activation of PXR by PCN negatively influenced the recovery of SCI. Mechanistically, transcriptome sequencing analysis revealed that PXR activation downregulated the mRNA level of heme oxygenase-1 (HO-1) after SCI. We further verified that PXR deficiency activated the NRF2/HO-1 pathway and PXR activation inhibited this pathway in vitro. CONCLUSION: PXR is involved in the recovery of motor function after SCI by regulating NRF2/HO-1 pathway.

Myeloid-specific deficiency of pregnane X receptor decreases atherosclerosis in LDL receptor-deficient mice.

The pregnane X receptor (PXR) is a nuclear receptor that can be activated by numerous drugs and xenobiotic chemicals. PXR thereby functions as a xenobiotic sensor to coordinately regulate host responses to xenobiotics by transcriptionally regulating many genes involved in xenobiotic metabolism. We have previously reported that PXR has pro-atherogenic effects in animal models, but how PXR contributes to atherosclerosis development in different tissues or cell types remains elusive. In this study, we generated an LDL receptor-deficient mouse model with myeloid-specific PXR deficiency (PXRΔMyeLDLR-/-) to elucidate the role of macrophage PXR signaling in atherogenesis. The myeloid PXR deficiency did not affect metabolic phenotypes and plasma lipid profiles, but PXRΔMyeLDLR-/- mice had significantly decreased atherosclerosis at both aortic root and brachiocephalic arteries compared with control littermates. Interestingly, the PXR deletion did not affect macrophage adhesion and migration properties, but reduced lipid accumulation and foam cell formation in the macrophages. PXR deficiency also led to decreased expression of the scavenger receptor CD36 and impaired lipid uptake in macrophages of the PXRΔMyeLDLR-/- mice. Further, RNA-Seq analysis indicated that treatment with a prototypical PXR ligand affects the expression of many atherosclerosis-related genes in macrophages in vitro. These findings reveal a pivotal role of myeloid PXR signaling in atherosclerosis development and suggest that PXR may be a potential therapeutic target in atherosclerosis management.

STAT3 is involved in IL-6-Mediated Downregulation of Hepatic Transporters in Mice.

Interleukin (IL)-6 decreases hepatic expression of numerous transporters. Although IL-6 signaling occurs through STAT3, the extent of the involvement of the STAT3 signaling pathway has not been elucidated. PURPOSE: Our objective was to investigate whether IL-6-mediated effects occur through STAT3, and whether PXR plays a role in this regulation. METHOD: PXR null (-/-) or wild-type (+/+) male mice were pre-dosed with a selective STAT3 inhibitor S3I-201 (7.5 mg/kg ip) or vehicle (n=5-8/group) 30 minutes before receiving a single dose of IL-6 (1 µg ip) or saline. Animals were sacrificed after 6 hours and liver samples were analyzed using qRT-PCR and western blotting. RESULTS: As compared to saline controls, IL-6 decreased the expression of Cyp3a, Abcb1a, Abcc3, and Slco1a4 20-70% similarly in PXR (+/+) and (-/-) mice at 6 hr, while downregulation of Abcb11, Abcc2, Slc10a1and Slco2b1 was only seen in PXR (+/+). Pre-administration of S3I-201 attenuated IL-6-mediated changes of most transporters in PXR (+/+) and PXR (-/-) mice. At early times after IL-6 administration (10-120 minutes), transcript levels of Socs3, PXR, Abcb1a, Abcc3, Abcb11, Slco1a4 and Slco2b1were increased in PXR (+/+) mice. CONCLUSIONS: Our findings demonstrate that IL-6 imposes a significant downregulation of numerous ABC and SLC transporters in liver primarily through activation of the STAT3 signaling pathway. Based on time-dependent changes in transporter expression, downregulation likely occurs downstream of STAT3 activation.  As IL-6 is elevated in many diseases, understanding the underlying mechanism(s) involved in transporter dysregulation will allow us to predict potential drug-disease interactions.

Comparison of the hepatic and thyroid gland effects of sodium phenobarbital in wild type and constitutive androstane receptor (CAR) knockout rats and pregnenolone-16α-carbonitrile in wild type and pregnane X receptor (PXR) knockout rats.

A number of chemicals produce liver and thyroid gland tumours in rodents by nongenotoxic modes of action (MOAs). In this study the hepatic and thyroid gland effects of the constitutive androstane receptor (CAR) activator sodium phenobarbital (NaPB) were examined in male Sprague-Dawley wild type (WT) rats and in CAR knockout (CAR KO) rats and the effects of the pregnane X receptor (PXR) activator pregnenolone-16α-carbonitrile (PCN) were examined in WT and PXR knockout (PXR KO) rats. Rats were either fed diets containing 0 (control) or 500 ppm NaPB or were dosed with 0 (control) or 100 mg/kg/day PCN orally for 7 days. The treatment of WT rats with NaPB and PCN for 7 days resulted in increased relative liver weight, increased hepatocyte replicative DNA synthesis (RDS) and the induction of cytochrome P450 CYP2B and CYP3A subfamily enzyme, mRNA and protein levels. In marked contrast, the treatment of CAR KO rats with NaPB and PXR KO rats with PCN did not result in any increases in liver weight and induction of CYP2B and CYP3A enzymes. The treatment of CAR KO rats with NaPB had no effect on hepatocyte RDS, while PCN produced only a small increase in hepatocyte RDS in PXR KO rats. Treatment with NaPB had no effect on thyroid gland weight in WT and CAR KO rats, whereas treatment with PCN resulted in an increase in relative thyroid gland weight in WT, but not in PXR KO, rats. Thyroid gland follicular cell RDS was increased by the treatment of WT rats with NaPB and PCN, with NaPB also producing a small increase in thyroid gland follicular cell RDS in CAR KO rats. Overall, the present study with CAR KO rats demonstrates that a functional CAR is required for NaPB-mediated increases in liver weight, stimulation of hepatocyte RDS and induction of hepatic CYP enzymes. The studies with PXR KO rats demonstrate that a functional PXR is required for PCN-mediated increases in liver weight and induction of hepatic CYP enzymes; with induction of hepatocyte RDS also being largely mediated through PXR. The hepatic effects of NaPB in CAR KO rats and of PCN in PXR KO rats are in agreement with those observed in other recent literature studies. These results suggest that CAR KO and PXR KO rats are useful experimental models for liver MOA studies with rodent CAR and PXR activators and may also be useful for thyroid gland MOA studies.

Pregnane X Receptor Deletion Modifies Recognition Memory and Electroencephalographic Activity.

Nuclear receptors (NR) are emerging as key players in the central nervous system (CNS) with reported implications in physiological and pathophysiological conditions. While a number of NR has been studied, it is unknown whether invalidation of the pregnane xenobiotic receptor (PXR, NR1I2) corresponds to neurological modifications in the adult brain. PXR-/- C57BL/6J and wild-type mice were used to investigate: (i) recognition memory, motor coordination, and anxiety-like behaviors; (ii) longitudinal video-electroencephalographic (EEG) recordings and frequency wave analysis; (iii) neurovascular structures by histological evaluation and expression of the cerebrovascular tight junctions ZO1 and CLDN5. Absence of PXR was associated with anxiety-like behavior and recognition memory impairment in adult mice. The latter was simultaneous to an EEG signature of lower theta frequency during sleep and abnormal delta waves. Neurophysiological changes did not correspond to significant structural changes in the adult brain, expect for a localized and minor increase in the fronto-parietal neurovascular density and reduced ZO1, but not CLDN5, expression in isolated brain capillaries. Our results converge with existing evidence supporting a link between NR expression and brain physiology. Although the exact modalities remain to be elucidated, the possibility that extra-physiological modulation of PXR may constitute a pathophysiological entry point or a molecular target for brain diseases is proposed.