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H-Factors in Dense Graphs
Rheumatol Int (2012) 32:1705–1710 DOI 10.1007/s00296-011-1874-2
ORIGINAL ARTICLE
Activation of farnesoid X receptor attenuates liver injury in systemic lupus erythematosus Fan Lian • Yu Wang • Jie Chen • Hanshi Xu • Xiuyan Yang • Liuqin Liang • Zhongping Zhan Yujin Ye • Minhu Chen
•
Received: 9 December 2010 / Accepted: 18 February 2011 / Published online: 24 March 2011 Ó Springer-Verlag 2011
Abstract To investigate the expression and effect of farnesoid X receptor (FXR) on systemic lupus erythematosus (SLE) liver dysfunction and indicate its hepatoprotective role and the immunomodulatory property. mRNA and protein levels of FXR were determined on the liver specimens of SLE patients with liver injury as well as MRL/lpr rodent models. The FXR agonist chenodeoxycholic acid (CDCA) was administrated to MRL/lpr mice and the control BALB/C with concanavalin A (ConA)induced liver injury. Blood samples were taken 0, 4, 8, 12, 16, and 24 h after ConA injection for the detection of serum ALT, AST, IFN-c, TNF-a, and IL-6. FXR was down-regulated at both mRNA and protein levels in the liver specimens of SLE patients with liver injury as well as MRL/lpr mice. MRL/lpr was more susceptible to ConA than BALB/C indicated by significantly higher levels of aminotransferase and inflammatory cytokines. Activation of FXR by CDCA significantly reduced aminotransferase and inflammatory cytokines IFN-c, TNF-a, and IL-6
F. Lian and Y. Wang equally contributed to this publication. F. Lian H. Xu X. Yang L. Liang Z. Zhan Y. Ye Department of Rheumatology and Clinical Immunology, The First Affiliated Hospital of Sun Yat-Sen University, Guangzhou, China Y. Wang Department of Oncology and Interventional Radiology, The First Affiliated Hospital of Sun Yat-Sen University, Guangzhou, China J. Chen M. Chen (&) Department of Gastroenterology, The First Affiliated Hospital of Sun Yat-Sen University, Guangzhou, China e-mail: [email protected]
caused by ConA injection in MRL/lpr mice. FXR was down-regulated in SLE patients as well as MRL/lpr lupus models with liver dysfunction. FXR activation ameliorated liver injury and suppressed inflammatory cytokines, thereby showing its protective function in SLE. Our findings raised the promising potential target for the treatment of SLE liver injury. Keywords Farnesoid X receptor Systemic lupus erythematosus Liver injury MRL/lpr
Introduction Liver dysfunction is commonly seen in systemic lupus erythematosus (SLE). Hepatic pathology related to SLE included fatty liver, portal inflammation, chronic active hepatitis, cirrhosis, cholestasis, and hepatic necrosis associated with antiphospholipid antibody syndrome [1–4]. For the patients who had no cause for the liver enzyme elevation other than SLE, dysfunction of the liver should be considered a primary disorder associated with SLE [2]. Farnesoid X receptor (FXR), a member of the ligandactivated nuclear receptor superfamily, is a bile sensor highly expressed in the liver [5–7]. Nuclear receptors (NRs) are regulatory factors that play an important role at the interface between nutrient metabolism and innate immunity. Activation of NRs provides counterregulatory signals for macrophages [8–11] and protects rodent models from immune dysregulation [12, 13]. Previous studies have linked FXR to immune-mediated liver diseases [14]. FXR and its ligands are important for the immune modulation in entero-hepatic tissues. FXR-deficient mice tended to lose homeostasis of innate immunity [15]. Chenodeoxycholic acid (CDCA), a primary bile acid and FXR ligand, has
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been known to down-regulate IL-1b, IL-6, and TNF-a released from LPS-primed macrophages [16, 17]. In the present study, we have investigated the expression and effect of FXR on SLE liver dysfunction, and whether its activation involves in the regulation of inflammationrelated cytokines in rodent models of SLE.
Materials and methods
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after ConA injection for the detection of serum ALT, AST, IFN-c, TNF-a, and IL-6. Determination of metabolites Serum alanine transaminase (ALT) and aspartate aminotransferase (AST) levels were determined with a commercial kit (Roche Diagnostics) using an Automated Chemical Analyzer (7600; Hitachi, Tokyo, Japan) according to the manufacturer’s instructions.
Patients and liver samples Cytokine detection SLE diagnosis was defined by the 1997 revised ACR classification criteria [18]. All of the patients were at the first diagnosis and not treated with corticosteroids or immunosuppressors before. No treatment was taken for at least 1 week before biopsies were taken. Liver samples were obtained from patients with unexplained abnormal liver biochemistry other than SLE. Normal liver samples as control were obtained by surgical resection from liver cancer patients without autoimmune diseases, and the tumor-free locations devoid of tumor cell infiltrates were at least 2 cm apart from the tumorous area. The study was approved by the institutional ethics committee of Sun Yat-sen University. Informed consent was obtained from all patients and control subjects. Animals and treatment protocols Female MRL/lpr and age-matched BALB/C mice (18 weeks old) were purchased from Slac Laboratory Animal (Shanghai, China) and housed in the animal facility under controlled conditions (22–24°C, 55% humidity, 12-h day/night cycle with free access to food and water). All experiments were approved by the Animal Experiment Committee of Sun Yat-sen University, following the Guide for the Care and Use of Laboratory Animals (National Academic Press, USA, 1996). To induce liver injury, concanavalin A (ConA, type V, Jack bean, Sigma–Aldrich, St. Louis, MO, USA) was intravenously injected through the tail vein at a dose of 20 mg/kg. Untreated mice received 0.5 ml of 0.9% (w/v) NaCl. To analyze the effect of FXR on ConA-induced liver injury in MRL/lpr mice, experimental animals were injected with ConA in the presence or absence of the FXR agonist chenodeoxycholic acid (CDCA, oral administration for 14 days before ConA injection, a chow diet with 1% (w/w) CDCA, from Chemos GmbH, Regenstauf, Germany). To collaborate the progression of ConA-induced liver injury, blood samples were taken 0, 4,8,12, 16, and 24 h
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Cytokines IFN-c (interferon-c), TNF-a (tumor necrosis factor-a), and IL-6 (interleukin-6) in serum were detected by fluorimetry using Bio-Plex Suspension Array System (Cytokine Assay) according to the manufacturer’s instructions (Bio-Rad). RT-qPCR and western blot analysis Total RNA was isolated from snap-frozen human and mouse tissues, first-strand DNA was synthesized as previously described [19], and qPCR was performed (in triplicate reactions) using the SYBRÒ-Green PCR Master Mix (Applied Biosystems, Applera Deutschland GmbH, Darmstadt, Germany) in the thermocycler ABI PRISM TM7700. For the analysis of the FXR, RT-qPCR was used to detect FXR mRNA level. Primer sequence for FXR was designed according to previous reports [20, 21]. Western blot analysis was performed as previously described [22]. The relative amounts of each protein were determined in total extracts with the antibodies FXR and b-actin. Antibodies were from Cell Signaling (Boston, MA, USA) and Santa Cruz Laboratories (Santa Cruz, CA, USA). Statistical analysis Student’s t test or ANOVA were performed on numerical data. All values are presented as the mean ± S.E.M. P \ 0.05 was considered significant. Software: SPSS 13.0.
Results FXR expression in liver specimens of SLE patients with liver injury Fifteen liver samples of SLE-related liver injury and normal controls were analyzed, respectively. RT-qPCR and western blotting (representative pictures of three patients) showed that FXR was reduced in SLE-related liver injury at both mRNA level (Fig. 1a) and protein level (Fig. 1b).
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Fig. 1 FXR expression in liver specimens of SLE patients with liver injury. Liver specimens of SLE patients and normal controls were detected for FXR at mRNA level (a) and protein level (b). *P \ 0.05, SLE patients compared with normal controls
FXR expression in liver specimens of MRL/lpr mice Ten MRL/lpr and BALB/C were analyzed. Three of 10 MRL/lpr mice exhibited asymptomatic hepatomegaly, and 5 had slight liver fatty change (data not shown). RT-qPCR and western blotting (representative pictures of three mice and controls) showed that FXR was reduced in MRL/lpr mice at both mRNA level (Fig. 2a) and protein level (Fig. 2b). FXR activation attenuates ConA-induced liver injury in MRL/lpr mice Fifteen MRL/lpr mice and 15 BALB/C mice were injected with the same dose of ConA (20 mg/kg). Another 15 MRL/ lpr mice and BALB/C were fed with 1% CDCA before ConA injection for the activation of FXR. Mice received saline alone or CDCA alone were taken as controls. Liver injury induced by ConA injection exhibited in histopathology as confluent hepatocellular necrosis, mononuclear cell infiltrates throughout the parenchyma, and sinusoidal hyperemia (data not shown). Liver structures of the untreated mice were normal. Mice received CDCA administration alone did not develop liver injury. All BALB/C mice survived the ConA injection. Nine of 15 MRL/lpr mice fed with normal food survived and 6 died within 24 h, while 14 of 15 MRL/lpr mice fed with 1% CDCA survived the same dose of ConA. We found no significance in the aminotransferase of MRL/lpr and BALB/C at baseline. Both MRL/lpr and
BALB/C injected with ConA developed hepatitis that was indicated by the elevation of serum liver enzymes. Liver enzyme levels peaked at approximately 12 h and started to subside afterward. The increased levels of aminotransferases observed in MRL/lpr were much higher than in BALB/C. CDCA administration significantly attenuated liver injury and lowered rise in the aminotransferase levels in MRL/lpr mice (Figs. 3, 4). BALB/C mice treated with CDCA diet showed the same tendency of reduced aminotransferases, but no significance was found compared with BALB/C treated with ConA alone (data not shown). FXR activation suppresses inflammatory cytokines induced by ConA in MRL/lpr mice Serum levels of the inflammatory cytokines TNF-a, IFN-c, and IL-6 significantly increased after ConA injection, especially in MRL/lpr mice. Lower levels of cytokines in MRL/lpr were correlated with pretreated CDCA.
Discussion Systemic lupus erythematosus often presents multiple organ involvement. Liver abnormalities in SLE were commonly seen. Some studies showed that it was more clinically important than previously estimated [1, 23]. However, it has not been widely investigated. The underlying mechanism of SLE-related liver injury remains unclear and requires further research. In the present study,
Fig. 2 FXR expression in liver specimens of MRL/lpr mice. Liver specimens of MRL/lpr mice and normal controls were detected for FXR at mRNA level (a) and protein level (b). *P \ 0.05, SLE patients compared with normal controls
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Fig. 3 Protection of liver injury in MRL/lpr mice by FXR activation. MRL/lpr mice and BALB/C controls were injected with ConA in the presence or absence of CDCA. *P \ 0.05, MRL/lpr administrated with ConA in the presence of CDCA versus MRL/lpr treated with ConA alone
Fig. 4 Suppression of inflammatory-related cytokines in MRL/lpr mice that received CDCA. MRL/lpr and BALB/C mice were injected with ConA in the presence or absence of CDCA. *P \ 0.05, MRL/lpr
administrated with ConA in the presence of CDCA diet versus MRL/ lpr or BALB/C treated with ConA alone
we sought to examine the expression and effect of farnesoid X receptor (FXR) on SLE liver dysfunction and indicate its hepatoprotective role and the immunomodulatory property. The physiological function of FXR has been described in the previous studies. FXR is the major bile acid nuclear receptor in the liver and possibly associated with the expression of proinflammatory cytokines [24, 25]. FXR causes a SHP-mediated regulation of liver NKT cells [14]. FXR activation reduced inflammatory cytokines IL-1beta, IL-2, IL-6, TNF-alpha, and IFN-gamma in intestine and attenuated colitis [26]. The present study provided the evidence that FXR expression was significantly reduced in the liver specimens
of SLE patients with hepatic involvements. Since no other causes than SLE was related to the liver enzyme abnormalities in our patients, FXR down-regulation may have resulted from the immune dysregulation of SLE. The MRL/lpr mouse is a genetic model which spontaneously develops autoimmune diseases that highly resemble systemic lupus erythematosus (SLE). We observed hepatobiliary enzymes at baseline and found no significance of MRL/lpr mice and the control BALB/C, which was consistent with Ohba K et al’s report [27]. Interestingly, FXR was down-regulated at both mRNA and protein levels in the liver specimens of MRL/lpr mice, though these mice presented normal level of liver enzymes. Our data suggested that FXR may be a negative mediator of
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immune response, which contributed to the progression of SLE, even before the appearance of prominent liver damage. Since there was no significance in the aminotransferase of MRL/lpr and BLAB/C mice at baseline, we injected concanavalin A (ConA) intravenously to exacerbate the autoimmune-related liver injury. ConA-induced hepatitis, caused by T-cell activation [28], is marked by the release of a broad spectrum of cytokines and shared many features with SLE. MRL/lpr mice showed enhanced susceptibility to ConA and presented higher levels of aminotransferase upon ConA administration compared with the control BALB/C. These mice could be rendered resistant to ConA by pretreatment of the FXR agonist chenodeoxycholic acid (CDCA) and presented lower levels of aminotransferase compared with the MRL/lpr mice treated with ConA alone, which indicated the protective function of FXR activation. TNF-a, IFN-c, and IL-6 play crucial roles in autoimmune diseases including SLE and ConA-induced hepatitis [29–31]. The balance between protective cytokines IL-6 and the aggressive cytokines TNF-a and IFN-c could be responsible for the severity of liver injury. The presented data showed that the inflammatory cytokines elevated much higher in MRL/lpr mice than in BALB/C after ConA administration, suggesting the susceptibility of MRL/lpr to the T-cell mitogen ConA. This could be due to the defective expression of the Fas apoptotic gene in MRL/lpr mice. FXR activation significantly decreased the susceptibility to ConA in MRL/lpr mice indicated by lowering the levels of all the inflammatory cytokines mentioned above. It was suggested that CDCA increased tolerance in T cell-mediated hepatitis. FXR was expressed and may be co-regulated in CD4, CD8, CD19, and CD14 immune cells [32]. FXR gene expression/function in macrophages was regulated by IFN-gamma [6]. It is possible that the protective function of FXR is mediated by inflammatory cytokines. MRL/lpr mice had the tendency to develop autoimmune cholangitis, especially in their old age [27], which supported that MRL/lpr might be much more susceptible to liver injury enhancers compared with the normal control, even though they did not present much abnormal biochemical findings at baseline. FXR, as an immune and metabolic modulator, might take an important part in the regulation of liver injury in MRL/lpr mice. Taken together, our data suggested that FXR was downregulated in SLE patients as well as MRL/lpr lupus models with liver dysfunction. FXR activation ameliorated liver injury and suppressed inflammatory cytokines, thereby showing its protective function in SLE. Our findings raised the promising potential target for the treatment of SLE liver injury.
1709 Conflict of interest of interest.
The authors declare that they have no conflict
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ORIGINAL ARTICLE
Activation of farnesoid X receptor attenuates liver injury in systemic lupus erythematosus Fan Lian • Yu Wang • Jie Chen • Hanshi Xu • Xiuyan Yang • Liuqin Liang • Zhongping Zhan Yujin Ye • Minhu Chen
•
Received: 9 December 2010 / Accepted: 18 February 2011 / Published online: 24 March 2011 Ó Springer-Verlag 2011
Abstract To investigate the expression and effect of farnesoid X receptor (FXR) on systemic lupus erythematosus (SLE) liver dysfunction and indicate its hepatoprotective role and the immunomodulatory property. mRNA and protein levels of FXR were determined on the liver specimens of SLE patients with liver injury as well as MRL/lpr rodent models. The FXR agonist chenodeoxycholic acid (CDCA) was administrated to MRL/lpr mice and the control BALB/C with concanavalin A (ConA)induced liver injury. Blood samples were taken 0, 4, 8, 12, 16, and 24 h after ConA injection for the detection of serum ALT, AST, IFN-c, TNF-a, and IL-6. FXR was down-regulated at both mRNA and protein levels in the liver specimens of SLE patients with liver injury as well as MRL/lpr mice. MRL/lpr was more susceptible to ConA than BALB/C indicated by significantly higher levels of aminotransferase and inflammatory cytokines. Activation of FXR by CDCA significantly reduced aminotransferase and inflammatory cytokines IFN-c, TNF-a, and IL-6
F. Lian and Y. Wang equally contributed to this publication. F. Lian H. Xu X. Yang L. Liang Z. Zhan Y. Ye Department of Rheumatology and Clinical Immunology, The First Affiliated Hospital of Sun Yat-Sen University, Guangzhou, China Y. Wang Department of Oncology and Interventional Radiology, The First Affiliated Hospital of Sun Yat-Sen University, Guangzhou, China J. Chen M. Chen (&) Department of Gastroenterology, The First Affiliated Hospital of Sun Yat-Sen University, Guangzhou, China e-mail: [email protected]
caused by ConA injection in MRL/lpr mice. FXR was down-regulated in SLE patients as well as MRL/lpr lupus models with liver dysfunction. FXR activation ameliorated liver injury and suppressed inflammatory cytokines, thereby showing its protective function in SLE. Our findings raised the promising potential target for the treatment of SLE liver injury. Keywords Farnesoid X receptor Systemic lupus erythematosus Liver injury MRL/lpr
Introduction Liver dysfunction is commonly seen in systemic lupus erythematosus (SLE). Hepatic pathology related to SLE included fatty liver, portal inflammation, chronic active hepatitis, cirrhosis, cholestasis, and hepatic necrosis associated with antiphospholipid antibody syndrome [1–4]. For the patients who had no cause for the liver enzyme elevation other than SLE, dysfunction of the liver should be considered a primary disorder associated with SLE [2]. Farnesoid X receptor (FXR), a member of the ligandactivated nuclear receptor superfamily, is a bile sensor highly expressed in the liver [5–7]. Nuclear receptors (NRs) are regulatory factors that play an important role at the interface between nutrient metabolism and innate immunity. Activation of NRs provides counterregulatory signals for macrophages [8–11] and protects rodent models from immune dysregulation [12, 13]. Previous studies have linked FXR to immune-mediated liver diseases [14]. FXR and its ligands are important for the immune modulation in entero-hepatic tissues. FXR-deficient mice tended to lose homeostasis of innate immunity [15]. Chenodeoxycholic acid (CDCA), a primary bile acid and FXR ligand, has
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been known to down-regulate IL-1b, IL-6, and TNF-a released from LPS-primed macrophages [16, 17]. In the present study, we have investigated the expression and effect of FXR on SLE liver dysfunction, and whether its activation involves in the regulation of inflammationrelated cytokines in rodent models of SLE.
Materials and methods
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after ConA injection for the detection of serum ALT, AST, IFN-c, TNF-a, and IL-6. Determination of metabolites Serum alanine transaminase (ALT) and aspartate aminotransferase (AST) levels were determined with a commercial kit (Roche Diagnostics) using an Automated Chemical Analyzer (7600; Hitachi, Tokyo, Japan) according to the manufacturer’s instructions.
Patients and liver samples Cytokine detection SLE diagnosis was defined by the 1997 revised ACR classification criteria [18]. All of the patients were at the first diagnosis and not treated with corticosteroids or immunosuppressors before. No treatment was taken for at least 1 week before biopsies were taken. Liver samples were obtained from patients with unexplained abnormal liver biochemistry other than SLE. Normal liver samples as control were obtained by surgical resection from liver cancer patients without autoimmune diseases, and the tumor-free locations devoid of tumor cell infiltrates were at least 2 cm apart from the tumorous area. The study was approved by the institutional ethics committee of Sun Yat-sen University. Informed consent was obtained from all patients and control subjects. Animals and treatment protocols Female MRL/lpr and age-matched BALB/C mice (18 weeks old) were purchased from Slac Laboratory Animal (Shanghai, China) and housed in the animal facility under controlled conditions (22–24°C, 55% humidity, 12-h day/night cycle with free access to food and water). All experiments were approved by the Animal Experiment Committee of Sun Yat-sen University, following the Guide for the Care and Use of Laboratory Animals (National Academic Press, USA, 1996). To induce liver injury, concanavalin A (ConA, type V, Jack bean, Sigma–Aldrich, St. Louis, MO, USA) was intravenously injected through the tail vein at a dose of 20 mg/kg. Untreated mice received 0.5 ml of 0.9% (w/v) NaCl. To analyze the effect of FXR on ConA-induced liver injury in MRL/lpr mice, experimental animals were injected with ConA in the presence or absence of the FXR agonist chenodeoxycholic acid (CDCA, oral administration for 14 days before ConA injection, a chow diet with 1% (w/w) CDCA, from Chemos GmbH, Regenstauf, Germany). To collaborate the progression of ConA-induced liver injury, blood samples were taken 0, 4,8,12, 16, and 24 h
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Cytokines IFN-c (interferon-c), TNF-a (tumor necrosis factor-a), and IL-6 (interleukin-6) in serum were detected by fluorimetry using Bio-Plex Suspension Array System (Cytokine Assay) according to the manufacturer’s instructions (Bio-Rad). RT-qPCR and western blot analysis Total RNA was isolated from snap-frozen human and mouse tissues, first-strand DNA was synthesized as previously described [19], and qPCR was performed (in triplicate reactions) using the SYBRÒ-Green PCR Master Mix (Applied Biosystems, Applera Deutschland GmbH, Darmstadt, Germany) in the thermocycler ABI PRISM TM7700. For the analysis of the FXR, RT-qPCR was used to detect FXR mRNA level. Primer sequence for FXR was designed according to previous reports [20, 21]. Western blot analysis was performed as previously described [22]. The relative amounts of each protein were determined in total extracts with the antibodies FXR and b-actin. Antibodies were from Cell Signaling (Boston, MA, USA) and Santa Cruz Laboratories (Santa Cruz, CA, USA). Statistical analysis Student’s t test or ANOVA were performed on numerical data. All values are presented as the mean ± S.E.M. P \ 0.05 was considered significant. Software: SPSS 13.0.
Results FXR expression in liver specimens of SLE patients with liver injury Fifteen liver samples of SLE-related liver injury and normal controls were analyzed, respectively. RT-qPCR and western blotting (representative pictures of three patients) showed that FXR was reduced in SLE-related liver injury at both mRNA level (Fig. 1a) and protein level (Fig. 1b).
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Fig. 1 FXR expression in liver specimens of SLE patients with liver injury. Liver specimens of SLE patients and normal controls were detected for FXR at mRNA level (a) and protein level (b). *P \ 0.05, SLE patients compared with normal controls
FXR expression in liver specimens of MRL/lpr mice Ten MRL/lpr and BALB/C were analyzed. Three of 10 MRL/lpr mice exhibited asymptomatic hepatomegaly, and 5 had slight liver fatty change (data not shown). RT-qPCR and western blotting (representative pictures of three mice and controls) showed that FXR was reduced in MRL/lpr mice at both mRNA level (Fig. 2a) and protein level (Fig. 2b). FXR activation attenuates ConA-induced liver injury in MRL/lpr mice Fifteen MRL/lpr mice and 15 BALB/C mice were injected with the same dose of ConA (20 mg/kg). Another 15 MRL/ lpr mice and BALB/C were fed with 1% CDCA before ConA injection for the activation of FXR. Mice received saline alone or CDCA alone were taken as controls. Liver injury induced by ConA injection exhibited in histopathology as confluent hepatocellular necrosis, mononuclear cell infiltrates throughout the parenchyma, and sinusoidal hyperemia (data not shown). Liver structures of the untreated mice were normal. Mice received CDCA administration alone did not develop liver injury. All BALB/C mice survived the ConA injection. Nine of 15 MRL/lpr mice fed with normal food survived and 6 died within 24 h, while 14 of 15 MRL/lpr mice fed with 1% CDCA survived the same dose of ConA. We found no significance in the aminotransferase of MRL/lpr and BALB/C at baseline. Both MRL/lpr and
BALB/C injected with ConA developed hepatitis that was indicated by the elevation of serum liver enzymes. Liver enzyme levels peaked at approximately 12 h and started to subside afterward. The increased levels of aminotransferases observed in MRL/lpr were much higher than in BALB/C. CDCA administration significantly attenuated liver injury and lowered rise in the aminotransferase levels in MRL/lpr mice (Figs. 3, 4). BALB/C mice treated with CDCA diet showed the same tendency of reduced aminotransferases, but no significance was found compared with BALB/C treated with ConA alone (data not shown). FXR activation suppresses inflammatory cytokines induced by ConA in MRL/lpr mice Serum levels of the inflammatory cytokines TNF-a, IFN-c, and IL-6 significantly increased after ConA injection, especially in MRL/lpr mice. Lower levels of cytokines in MRL/lpr were correlated with pretreated CDCA.
Discussion Systemic lupus erythematosus often presents multiple organ involvement. Liver abnormalities in SLE were commonly seen. Some studies showed that it was more clinically important than previously estimated [1, 23]. However, it has not been widely investigated. The underlying mechanism of SLE-related liver injury remains unclear and requires further research. In the present study,
Fig. 2 FXR expression in liver specimens of MRL/lpr mice. Liver specimens of MRL/lpr mice and normal controls were detected for FXR at mRNA level (a) and protein level (b). *P \ 0.05, SLE patients compared with normal controls
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Fig. 3 Protection of liver injury in MRL/lpr mice by FXR activation. MRL/lpr mice and BALB/C controls were injected with ConA in the presence or absence of CDCA. *P \ 0.05, MRL/lpr administrated with ConA in the presence of CDCA versus MRL/lpr treated with ConA alone
Fig. 4 Suppression of inflammatory-related cytokines in MRL/lpr mice that received CDCA. MRL/lpr and BALB/C mice were injected with ConA in the presence or absence of CDCA. *P \ 0.05, MRL/lpr
administrated with ConA in the presence of CDCA diet versus MRL/ lpr or BALB/C treated with ConA alone
we sought to examine the expression and effect of farnesoid X receptor (FXR) on SLE liver dysfunction and indicate its hepatoprotective role and the immunomodulatory property. The physiological function of FXR has been described in the previous studies. FXR is the major bile acid nuclear receptor in the liver and possibly associated with the expression of proinflammatory cytokines [24, 25]. FXR causes a SHP-mediated regulation of liver NKT cells [14]. FXR activation reduced inflammatory cytokines IL-1beta, IL-2, IL-6, TNF-alpha, and IFN-gamma in intestine and attenuated colitis [26]. The present study provided the evidence that FXR expression was significantly reduced in the liver specimens
of SLE patients with hepatic involvements. Since no other causes than SLE was related to the liver enzyme abnormalities in our patients, FXR down-regulation may have resulted from the immune dysregulation of SLE. The MRL/lpr mouse is a genetic model which spontaneously develops autoimmune diseases that highly resemble systemic lupus erythematosus (SLE). We observed hepatobiliary enzymes at baseline and found no significance of MRL/lpr mice and the control BALB/C, which was consistent with Ohba K et al’s report [27]. Interestingly, FXR was down-regulated at both mRNA and protein levels in the liver specimens of MRL/lpr mice, though these mice presented normal level of liver enzymes. Our data suggested that FXR may be a negative mediator of
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immune response, which contributed to the progression of SLE, even before the appearance of prominent liver damage. Since there was no significance in the aminotransferase of MRL/lpr and BLAB/C mice at baseline, we injected concanavalin A (ConA) intravenously to exacerbate the autoimmune-related liver injury. ConA-induced hepatitis, caused by T-cell activation [28], is marked by the release of a broad spectrum of cytokines and shared many features with SLE. MRL/lpr mice showed enhanced susceptibility to ConA and presented higher levels of aminotransferase upon ConA administration compared with the control BALB/C. These mice could be rendered resistant to ConA by pretreatment of the FXR agonist chenodeoxycholic acid (CDCA) and presented lower levels of aminotransferase compared with the MRL/lpr mice treated with ConA alone, which indicated the protective function of FXR activation. TNF-a, IFN-c, and IL-6 play crucial roles in autoimmune diseases including SLE and ConA-induced hepatitis [29–31]. The balance between protective cytokines IL-6 and the aggressive cytokines TNF-a and IFN-c could be responsible for the severity of liver injury. The presented data showed that the inflammatory cytokines elevated much higher in MRL/lpr mice than in BALB/C after ConA administration, suggesting the susceptibility of MRL/lpr to the T-cell mitogen ConA. This could be due to the defective expression of the Fas apoptotic gene in MRL/lpr mice. FXR activation significantly decreased the susceptibility to ConA in MRL/lpr mice indicated by lowering the levels of all the inflammatory cytokines mentioned above. It was suggested that CDCA increased tolerance in T cell-mediated hepatitis. FXR was expressed and may be co-regulated in CD4, CD8, CD19, and CD14 immune cells [32]. FXR gene expression/function in macrophages was regulated by IFN-gamma [6]. It is possible that the protective function of FXR is mediated by inflammatory cytokines. MRL/lpr mice had the tendency to develop autoimmune cholangitis, especially in their old age [27], which supported that MRL/lpr might be much more susceptible to liver injury enhancers compared with the normal control, even though they did not present much abnormal biochemical findings at baseline. FXR, as an immune and metabolic modulator, might take an important part in the regulation of liver injury in MRL/lpr mice. Taken together, our data suggested that FXR was downregulated in SLE patients as well as MRL/lpr lupus models with liver dysfunction. FXR activation ameliorated liver injury and suppressed inflammatory cytokines, thereby showing its protective function in SLE. Our findings raised the promising potential target for the treatment of SLE liver injury.
1709 Conflict of interest of interest.
The authors declare that they have no conflict
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