1,25-dihydroxyvitamin D3 attenuates NPSLE in MRL/lpr mice through a meliorating BCSFB activating PPARγ/NF-κB/TNF-α and lessening TGF-β 1/Smads
Authors: Li Xuewei , Liu Jie , Zhao Yingzhe , Han Huirong , Li Xiangling , Wang Yanqiang 
Published: March 2022

Abstract
Backgrounds: Systemic lupus erythematosus encephalopathy (NPSLE) is a serious complication of systemic lupus erythematosus (SLE) involving the nervous system with high morbidity and mortality. A key hypothesis in NPSLE is that a disrupted barrier allowed autoantibodies and immune components of peripheral blood to penetrate into the central nervous system (CNS), resulting in inflammation and damage. The blood cerebrospinal fluid barrier (BCSFB), which consists of the choroid plexus and the hypothalamic tanycytes, has long been regarded as an immunological sanctuary site. 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) is the active form of vitamin D, which plays multiple roles in inflammation and immunoregulation. In this study, we investigate the possible protective effects of 1,25-dihydroxyvitamin D3 on BCSFB dysfunction of NPSLE in MRL/lpr mice and explore the mechanism of 1,25-dihydroxyvitamin D3 inhibiting the progression of NPSLE.Methods：40 MRL/lpr mice at 11-week-old were included in this study and the mice were divided into VitD3-treated group and control group. Mice in the VitD3-treated groups received 4μg/kg 1,25-dihydroxyvitamin D3 in 1％ dimethyl sulfoxide（DMSO）intraperitoneal injection twice a week for 3 weeks. Mice in the control groups received 1% DMSO intraperitoneal injections for 3 weeks. The mice were anesthetized at 0 weeks (T1), 2 weeks (T2), 4 weeks (T3), and 6 weeks (T4) after treatment, and the mice were executed to collect blood and brain tissue samples. During this period, the skin lesions and neuropsychiatric manifestations of mice were observed continuously. The expressions of serum anti-double-stranded DNA (dsDNA) antibody and C3 complement were analyzed by ELISA. Then we evaluated the effect of 1,25-dihydroxyvitamin D3 on BCSFB integrity with time in terms of histopathological changes, neurological deficit, and the expression of brain-derived neurotrophic factor (BDNF) in MRL/lpr mice. BCSFB permeability and the expression of permeability-related proteins with time in the brain were also analyzed by immunofluorescence and western blotting respectively. To determine the possible mechanism underlying the role of 1,25-dihydroxyvitamin D3 in BCSFB maintenance, the effects of peroxisome proliferator-activated receptor-gamma (PPARγ) on BCSFB integrity and the expression of TGF-β/Smads on BCSFB integrity with time were detected.Results: The skin lesions, neuropsychiatric manifestations, and pathology of mice in the VitD3-treated group were significantly improved compared with those in the control group. The levels of A-dsDNA in the VitD3-treated group were significantly lower than those in the control group (P＜0.05). The C3 in the VitD3-treated group was significantly higher than those in the control group (P＜0.05). The expressions of occluding and claudin-2 in the VitD3-treated group were significantly higher than those in the control group (P＜0.05). 1,25-dihydroxyvitamin D3 treatment modulated the PPARγ/TNF-α/NF-κB axis and increased BDNF expression levels (P＜0.05). There were significant differences in TGF-β/Smads pathway expression between the two groups (P＜0.05). The TGF-β1, TβR-1, Smad2/3, and P-Smad2/3 in the VitD3-treated group were significantly lower than those in the control group (P＜0.05). Furthermore, these results presented the descending or increasing tendency in the VitD3-treated group or the control group.Conclusion: Our findings support the positive effect of 1,25-dihydroxyvitamin D3 on NPSLE in MRL/lpr mice, which may be related to the protection of BCSFB disruption through the activation of the anti-inflammatory PPARγ/NF-κB/TNF-α pathway as well as upregulation of BDNF and the inhibition of TGF-β/Smads signaling pathway.