Endogenously eliminating the hematoma is a favorable strategy in addressing intracerebral hemorrhage (ICH). This study sought to determine the role of retinoid X receptor-α (RXR-α) in the context of hematoma absorption after ICH. Our results showed that pharmacologically activating RXR-α with bexarotene significantly accelerated hematoma clearance and alleviated neurological dysfunction after ICH. RXR-α was expressed in microglia/macrophages, neurons, and astrocytes. Mechanistically, bexarotene promoted the nuclear translocation of RXR-α and PPAR-γ, as well as reducing neuroinflammation by modulating microglia/macrophage reprograming from the M1 into the M2 phenotype. Furthermore, all the beneficial effects of RXR-α in ICH were reversed by the PPAR-γ inhibitor GW9662. In conclusion, the pharmacological activation of RXR-α confers robust neuroprotection against ICH by accelerating hematoma clearance and repolarizing microglia/macrophages towards the M2 phenotype through PPAR-γ-related mechanisms. Our data support the notion that RXR-α might be a promising therapeutic target for ICH.
Anilides/pharmacology* ; Cerebral Hemorrhage/drug therapy* ; Hematoma/drug therapy* ; Humans ; Macrophages ; Microglia ; Neuroprotection ; PPAR gamma ; Retinoid X Receptor alpha

OBJECTIVETo investigate the effects of carnitine on cardiac function, collagen contents, peroxisome proliferator-activated receptor alpha (PPARalpha) and retinoid X receptor alpha (RXRct) expressions in a rat alcoholic cardiomyopathy modeL.

METHODSAdult male Wistar rats were randomly divided into alcohol group (A) , alcohol/carnitine group (B) and control group. Six months later, protein expressions of collagen I, collagen III, matrix metalloproteinase-9 (MMP-9) and Smad-3 were determined by immunohistochemical staining. Protein expressions of PPARalpha and RXRalpha were detected by Western blot.

RESULTSExpressions of collagen I, collagen III, MMP-9 and Smad-3 were significantly increased in groups A and B compared to group C (P < 0.01 or P < 0.05). Expressions of PPARalpha and RXRalpha (0.156 and 0.192, respectively, in group A; 0.248 and 0.385, respectively, in group B) were decreased compared to group C (P < 0.01 or P < 0.05). These changes were significantly attenuated by carnitine (all P < 0.05, group B vs. group A). Moreover, PPARalpha and RXRalpha positively correlated with EF and FS, and negatively correlated LVEDd, collagen I , collagen III, MMP-9 and Smad-3 (all P < 0.01).

CONCLUSIONPPARalpha and RXRalpha downregulation is significantly correlated with cardiac dysfunction in this alcoholic cardiomyopathy model, carnitine ameliorated the cardiac fibrosis and remodeling possibly through upregulating the metabolic pathways of PPARalpha and RXRalpha.

Animals ; Cardiomyopathy, Alcoholic ; metabolism ; pathology ; prevention & control ; Carnitine ; therapeutic use ; Male ; Myocardium ; metabolism ; pathology ; PPAR alpha ; metabolism ; Rats ; Rats, Wistar ; Retinoid X Receptor alpha ; metabolism

The mechanisms by which emodin induces apoptosis and inhibits proliferation of cancer cells remain unclear. In this study, we investigated whether the proapoptotic effect of emodin on human NIH-H460 lung cancer cells and SMMC-7721 liver cancer cells was related to regulating RXR expression and function. MTT assay and DAPI staining were used to detect the anti-proliferative and apoptotic effects of emodin with or without 9-cis-retinoid acid on H460 and SMMC-7721. The reporter assay was used to detect the effect of emodin on RXR homo- and hetero-dimer transactivation. Competitive ligand binding assay was carried out to detect whether emodin could directly bind to RXR. The result showed that emodin could strongly inhibit the proliferation and induce apoptosis of both cancer cell lines, which could be antagonized by 9-cis-RA. The reporter assay showed that emodin could inhibit the transcriptional effect of the homo- and hetero-dimer transactivation of RXRalpha dose-dependently. However, in vitro binding assay did not show that emodin bind to RXRalpha-LBD directly. The findings suggest that exhibition of emodin its anti-cancer activity may be associated with involvement of RXRalpha signal transduction pathways.
Apoptosis ; drug effects ; Cell Line, Tumor ; Cell Proliferation ; drug effects ; Dose-Response Relationship, Drug ; Emodin ; metabolism ; pharmacology ; Humans ; Retinoid X Receptor alpha ; metabolism ; Signal Transduction ; drug effects ; Transcriptional Activation ; drug effects ; Tretinoin ; antagonists & inhibitors

Retinoid X receptor α (RXRα) and its N-terminally truncated version tRXRα play important roles in tumorigenesis, while some RXRα ligands possess potent anti-cancer activities by targeting and modulating the tumorigenic effects of RXRα and tRXRα. Here we describe NSC-640358 (N-6), a thiazolyl-pyrazole derived compound, acts as a selective RXRα ligand to promote TNFα-mediated apoptosis of cancer cell. N-6 binds to RXRα and inhibits the transactivation of RXRα homodimer and RXRα/TR3 heterodimer. Using mutational analysis and computational study, we determine that Arg316 in RXRα, essential for 9-cis-retinoic acid binding and activating RXRα transactivation, is not required for antagonist effects of N-6, whereas Trp305 and Phe313 are crucial for N-6 binding to RXRα by forming extra π-π stacking interactions with N-6, indicating a distinct RXRα binding mode of N-6. N-6 inhibits TR3-stimulated transactivation of Gal4-DBD-RXRα-LBD by binding to the ligand binding pocket of RXRα-LBD, suggesting a strategy to regulate TR3 activity indirectly by using small molecules to target its interacting partner RXRα. For its physiological activities, we show that N-6 strongly inhibits tumor necrosis factor α (TNFα)-induced AKT activation and stimulates TNFα-mediated apoptosis in cancer cells in an RXRα/tRXRα dependent manner. The inhibition of TNFα-induced tRXRα/p85α complex formation by N-6 implies that N-6 targets tRXRα to inhibit TNFα-induced AKT activation and to induce cancer cell apoptosis. Together, our data illustrate a new RXRα ligand with a unique RXRα binding mode and the abilities to regulate TR3 activity indirectly and to induce TNFα-mediated cancer cell apoptosis by targeting RXRα/tRXRα.
Apoptosis ; drug effects ; Cell Line, Tumor ; Enzyme Activation ; drug effects ; Humans ; Ligands ; Molecular Docking Simulation ; Nuclear Receptor Subfamily 4, Group A, Member 1 ; genetics ; metabolism ; Oximes ; metabolism ; pharmacology ; Protein Conformation ; Proto-Oncogene Proteins c-akt ; metabolism ; Pyrazoles ; metabolism ; pharmacology ; Retinoid X Receptor alpha ; chemistry ; genetics ; metabolism ; Thiazoles ; metabolism ; pharmacology ; Transcription, Genetic ; drug effects ; Transcriptional Activation ; drug effects ; Tumor Necrosis Factor-alpha ; metabolism