Zexie Tang targeting FKBP38/mTOR/SREBPs pathway improves hyperlipidemia

ETHNOPHARMACOLOGICAL RELEVANCE

Zexie Tang (ZXT), only two consists with Alismatis Rhizoma (AR) and Atractylodes macrocephala Rhizoma (AM), a classical Chinese medicine formula from Synopsis of the Golden Chamber with a history of 2000 years. Clinical observation in recent years has found that ZXT has excellent lipid-lowering effect.

AIM OF THE STUDY

To explore the potential mechanism of ZXT ameliorates hyperlipidemia based on FKBP38/mTOR/SREBPs pathway.

MATERIALS AND METHODS

WD-induced hyperlipidemia mice and oleic acid induced cell lipid accumulation model were used to investigate pharmacodynamic. The effect of ZXT on the transcriptional activity of SREBPs was detected by reporter gene assay. Proteins and downstream genes of mTOR/SREBPs pathway were detected in vivo and in vitro. Combined with network pharmacology and HPLC-Q-TOF/MS, the active ingredients were screened and identified. The interaction between active compounds of ZXT and FKBP38 protein were analyzed by docking analysis.

RESULTS

ZXT decreased TC, TG and LDL-c levels in blood of WD-induced hyperlipidemia mouse model, and improved insulin resistance in vivo. ZXT also reduced TC, TG and lipid accumulation in cells line, and inhibited SREBPs luciferase activity, protein and its target genes expression such as FASN, HMGCR, etc. Meanwhile, ZXT inhibited protein expression levels of p-mTOR, p-S6K, etc in vitro and in vivo. Combined with network pharmacology and HPLC-Q-TOF/MS, 16 active ingredients were screened and identified. Docking results showed that active compounds of ZXT binding to FKBP38 and formed hydrogen bond.

CONCLUSION

Our findings highlighted that ZXT ameliorates hyperlipidemia, in which FKBP/mTOR/SREBPs pathway might be the potential regulatory mechanism.

FKBP5 mRNA Expression Is a Biomarker for GR Antagonism

CONTEXT

Endogenous Cushing's syndrome is caused by chronically elevated levels of cortisol. Mifepristone, a glucocorticoid receptor (GR) antagonist, is approved for the treatment of Cushing's syndrome. Currently there is an unmet clinical need for a direct biochemical method for monitoring the immediate effectiveness of mifepristone in patients with Cushing's syndrome. The glucocorticoid induction of FK506-binding protein 5 (FKBP5) expression is rapid and has been shown to be attenuated by GR antagonists in a range of in vitro and in vivo models.

OBJECTIVE

The objective of the study was to develop a quantitative PCR assay for FKBP5 mRNA expression in blood and apply it to measure the inhibition of glucocorticoid-induced FKBP5 expression by GR antagonists in healthy human subjects.

METHODS

Briefly, blood samples were acquired from a phase I study in which healthy human subjects were administered either a single dose of the GR agonist prednisone with and without coadministration of a single oral dose of mifepristone or glucocorticoid receptor antagonist (CORT125134) or multiple daily doses of CORT125134 over 14 days with coadministration of prednisone with the final dose. FKBP5 mRNA levels were analyzed by quantitative PCR in blood samples collected at selected time points.

SETTING

The study was conducted at Quotient Clinical (Nottingham, United Kingdom).

RESULTS

Oral administration of the glucocorticoid prednisone to healthy human subjects resulted in a time-dependent increase of FKBP5 mRNA to peak levels of approximately 12-fold compared with unstimulated levels within 4 hours of steroid administration, followed by a reduction to baseline levels within 24 hours. Furthermore, oral administration of mifepristone or the selective GR antagonist CORT125134 had the desired effect of inhibiting prednisone-mediated activation of GR as seen by a reduction of FKBP5 mRNA levels.

CONCLUSIONS

The inhibition of FKBP5 mRNA expression by a selective GR antagonist is a potential clinical biomarker of GR antagonism.

Male-specific effects of lipopolysaccharide on glucocorticoid receptor nuclear translocation in the prefrontal cortex of depressive rats

RATIONALE

Inflammation plays a key role in the pathogenesis of major depressive disorder (MDD) for a subset of depressed individuals. One of the possible routes by which cytokines can induce depressive symptoms is by promoting the dysregulation of hypothalamic-pituitary-adrenal (HPA) axis via altering glucocorticoid receptor (GR) function.

OBJECTIVES

We investigated the mechanisms that finely tune the GR functioning upon lipopolysaccharide (LPS), i.e., subcellular localization of the GR, the levels of its co-chaperones FK506 binding protein 52 (FKBP4) and FK506 binding protein 51 (FKBP5), the receptor phosphorylation status along with its upstream kinases, as well as mRNA levels of GR-regulated genes in the prefrontal cortex (PFC) of male and female Wistar rats.

RESULTS

We found that upon LPS treatment, animals of both sexes exhibited depressive-like behavior and elevated serum corticosterone. However, the nuclear translocation of the GR and both FKBPs was found only in males, together with elevated phosphorylation of the GR at serine 232 and 246 and the activation and nuclear translocation of all analyzed kinases. This activation of the GR in males was paralleled with altered expression of GR-related genes, particularly PTGS2 and BDNF.

CONCLUSION

Our data suggest that LPS treatment produced alterations in the mechanisms that control the GR nuclear translocation in the PFC of males, and that these mechanisms may contribute to the sex-specific dysfunction of GR-related neurotrophic and neuroinflammatory processes in inflammation-associated depression.

Intratympanic dexamethasone up-regulates Fkbp5 in the cochleae of mice in vivo

CONCLUSIONS

Quantitative, real-time RT-PCR demonstrated that intratympanic dexamethasone significantly up-regulates the expression of Fkbp5 in cochleae of mice in vivo. The immunohistochemistry results showed fundamentally ubiquitous expression of Fkbp5 in cochlear structures, with relatively strong expression in type 4 fibrocytes and weak signal in the inner hair cells. These data indicate that dexamethasone regulates gene expression at the level of transcription in vivo and that this process is basically ubiquitous in the cochlea.

OBJECTIVES

To demonstrate that intratympanically applied dexamethasone up-regulates Fkbp5 in the cochlea in vivo.

METHODS

Dexamethasone or control saline were intratympanically applied to adult C57/BL6 mice and dexamethasone-dependent changes in the levels of Fkbp5 expression in the cochlea were analyzed using quantitative real-time RT-PCR. The expression pattern of Fkbp5 in cochlea was investigated by immunohistochemistry in mice that were administered dexamethasone and in controls.

RESULTS

Quantitative real-time RT-PCR demonstrated significant increases of Fkbp5 expression levels in cochleae of dexamethasone-treated mice as compared with controls at 12 h after application (244.8 ± 155.5, n = 5 vs 100.0 ± 3.0, n = 6, p < 0.01). Immunohistochemistry showed fundamentally ubiquitous expression of Fkbp5 in cochlear structures, with some strongly positive fibrocytes in the spiral ligaments and weak immunoreactivity in the inner hair cells. Distribution of Fkbp5 signaling was not different between the dexamethasone-treated group and controls.

Hepatitis C virus NS5A activates the mammalian target of rapamycin (mTOR) pathway, contributing to cell survival by disrupting the interaction between FK506-binding protein 38 (FKBP38) and mTOR

Hepatitis C virus (HCV) often establishes a persistent infection that most likely involves a complex host-virus interplay. We previously reported that the HCV nonstructural protein 5A (NS5A) bound to cellular protein FKBP38 and resulted in apoptosis suppression in human hepatoma cell line Huh7. In the present research we further found that NS5A increased phosphorylation levels of two mTOR-targeted substrates, S6K1 and 4EBP1, in Huh7 in the absence of serum. mTOR inhibitor rapamycin or NS5A knockdown blocked S6K1 and 4EBP1 phosphorylation increase in NS5A-Huh7 and HCV replicon cells, suggesting that NS5A specifically regulated mTOR activation. Overexpression of NS5A and FKBP38 mutants or FKBP38 knockdown revealed this mTOR activation was dependent on NS5A-FKBP38 interaction. Phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 treatment in NS5A-Huh7 showed that the mTOR activation was independent of PI3K. Moreover, NS5A suppressed caspase 3 and poly(ADP-ribose) polymerase activation, which was abolished by NS5A knockdown or rapamycin, indicating NS5A inhibited apoptosis specifically through the mTOR pathway. Further analyses suggested that apoptotic inhibition exerted by NS5A via mTOR also required NS5A-FKBP38 interaction. Glutathione S-transferase pulldown and co-immunoprecipitation showed that NS5A disrupted the mTOR-FKBP38 association. Additionally, NS5A or FKBP38 mutants recovered the mTOR-FKBP38 interaction; this indicated that the impairment of mTOR-FKBP38 association was dependent on NS5A-FKBP38 binding. Collectively, our data demonstrate that HCV NS5A activates the mTOR pathway to inhibit apoptosis through impairing the interaction between mTOR and FKBP38, which may represent a pivotal mechanism for HCV persistence and pathogenesis.

Inhibition of endogenous MHC class II-restricted antigen presentation by tacrolimus (FK506) via FKBP51

The effect of tacrolimus (FK506) on down-regulation of IL-2 production by T cells is considered to be mainly responsible for its strong suppression of immunological events. In this study, we show that FK506 also has an affect on antigen presentation by antigen-presenting cells in vitro. FK506 was able to inhibit the presentation of endogenous MHC class II-restricted minor histocompatibility antigens in primary dendritic cells (DC) in vitro, but cyclosporine A (CsA) and rapamycin (RAP) were not. RNA interference (RNAi)-mediated reduction of endogenous FK506-binding protein (FKBP)51 expression resulted in a marked decrease in antigen presentation, suggesting that FKBP51 plays a role in endogenous MHC class II-restricted antigen presentation. Since our model used naturally expressed cytosolic antigens in primary DC, these effects might have been due to novel properties of the immunosuppressive drugs and may allow us to elucidate a new paradigm for the immunosuppressive mechanism of FK506.

Neuroprotective effects of tacrolimus (FK506) in a model of ischemic cortical cell cultures: role of glutamate uptake and FK506 binding protein 12 kDa

BACKGROUND

The mechanisms underlying the neuroprotective effects of the immunosuppressant tacrolimus, observed in vivo, remain unclear. Here we quantify these effects in vitro, and evaluate the potential involvement of the glutamate and/or immunophilin FK506 binding protein 12 kDa in tacrolimus-induced neuroprotection.

METHODS

Primary cultures of neurons and astrocytes from rat cerebral cortex were subjected to transient oxygen-glucose deprivation. Neuronal injury was evaluated by cell counting after immunostaining experiments, lactate dehydrogenase release and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction. The involvement of the immunophilin FK506 binding protein 12 kDa was explored using an anti-FK506 binding protein 12 kDa antibody, (3-3-pyridyl)-1-propyl(2 s)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidine carboxylate and rapamycin. Extracellular glutamate and glutamate uptake were respectively measured by high performance liquid chromatography and l-[3H]glutamate incorporation.

RESULTS

When added during either oxygen-glucose deprivation or reoxygenation, FK506 (50-500 pM) offered significant neuroprotection. During oxygen-glucose deprivation, it was able to reverse the oxygen-glucose deprivation-induced increase in extracellular glutamate and decrease in glutamate uptake and this effect was reversed in the presence of threo-3-methyl glutamate, a specific inhibitor of glutamate transporter-1. Blocking FK506 binding protein 12 kDa inhibited the neuroprotection induced by tacrolimus added during either oxygen-glucose deprivation or reoxygenation. Tacrolimus-induced neuroprotection was also reversed in the presence of rapamycin, an immunosuppressant FK506 binding protein 12 kDa ligand devoid of neuroprotective properties and (3-3-pyridyl)-1-propyl(2 s)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidine carboxylate, a non-immunosuppressant ligand of FK506 binding protein 12 kDa, exerteing neuroprotective effects.

CONCLUSION

The beneficial effects of tacrolimus during in vitro ischemia/reperfusion seem to indicate the restoration of a glutamate transporter-1-mediated activity and could be mediated by a FK506 binding protein 12 kDa pathway.

Regulated dimerization of the thyrotropin-releasing hormone receptor affects receptor trafficking but not signaling

To investigate the function of dimerization of the TRH receptor, a controlled dimerization system was developed. A variant FK506 binding protein (FKBP) domain was fused to the receptor C terminus and dimerization induced by incubating cells with dimeric FKBP ligand, AP20187. The TRH receptor-fusion bound hormone and signaled normally. Addition of dimerizer to cells expressing the receptor-FKBP fusion dramatically increased the fraction of receptor running as dimer on SDS-PAGE. AP20187 caused dimerization in a time- and concentration-dependent manner, acting within 1 min. Dimerizer had no effect on TRH receptors lacking the FKBP domain, and its effects were blocked by excess monomeric FKBP ligand. AP20187-induced dimerization did not cause receptor phosphorylation, inositol phosphate production, or ERK1/2 activation, and dimerizer did not alter signaling by TRH. Induced dimerization did, however, alter TRH receptor trafficking. TRH promoted greater receptor internalization in cells treated with AP20187 but not monomeric ligand, based on loss of surface binding sites and immunostaining. Dimerization increased the rate of internalization of TRH receptors and decreased the apparent rate of receptor recycling. AP20187 enhanced the small amount of TRH-induced receptor internalization when the receptor-FKBP fusion protein was expressed in cells lacking beta-arrestins. The results show that controlled dimerization of the TRH receptor potentiates hormone-induced receptor trafficking.

Intronic hormone response elements mediate regulation of FKBP5 by progestins and glucocorticoids

Expression of FKBP51, a large molecular weight immunophilin, is strongly enhanced by glucocorticoids, progestins, and androgens. However, the activity of a 3.4-kb fragment of the FKBP51 gene (FKBP5) promoter was only weakly increased by progestin and we show here that it is unresponsive to glucocorticoids and androgens. The entire FKBP5 was scanned for consensus hormone response elements (HREs) using MatInspector. We found that 2 regions of intron E, which are conserved in rat and mouse FKBP5, contain HRE-like sequences with high match scores. Deoxyribonucleic acid fragments (approximately 1 kb in length) containing these regions were amplified and tested in reporter gene assays for steroid responsiveness. One region of intron E of FKBP5 (pIE2) conferred both glucocorticoid and progestin responsiveness to 2 heterologous reporter genes, whereas the other, less-conserved region of intron E (pIE1) was responsive only to progestins. The inclusion of pIE1 upstream of pIE2 (pIE1IE2) enhanced progestin but not glucocorticoid responsiveness. None of the constructs containing intronic sequences was responsive to androgens. Mutation of the putative HREs within pIE1 and pIE2 eliminated hormone responsiveness. Electrophoretic mobility shift assays demonstrated that progesterone receptors (PR) bound to the HRE in pIE1, whereas both PR and glucocorticoid receptors interacted with the HRE in pIE2. These data suggest that distal intronic elements significantly contribute to transcriptional regulation of FKBP5 by glucocorticoids and progestins.

Protection against ischemic brain damage in rats by immunophilin ligand GPI-1046

To determine the effect of immunophilin ligand GPI-1046 on ischemic brain injury, 90 min of transient middle cerebral artery occlusion (MCAO) was carried out in rat brains. In contrast to cases treated with vehicle, the infarct volume was reduced greatly and rotamase activity was inhibited significantly at 24 hr of reperfusion by treatment with GPI-1046. Immunoreactivity and the number of cells stained positively for FKBP12, FKBP52, caspase-8, cytochrome c, and caspase-3 were also reduced markedly in the brain after GPI-1046 treatment. The present results suggest that GPI-1046 significantly decreased infarct volume and provided neuroprotective effect on rats after transient focal cerebral ischemia by inhibiting the increase of rotamase activity and of the number of FKBP12-, FKBP52-, caspase-8-, cytochrome c-, and caspase-3-positive cells in the ischemic area.

Targeted chemical disruption of clathrin function in living cells

The accurate assignment of molecular roles in membrane traffic is frequently complicated by the lack of specific inhibitors that can work on rapid time scales. Such inhibition schemes would potentially avoid the complications arising from either compensatory gene expression or the complex downstream consequences of inhibition of an important protein over long periods (>12 h). Here, we developed a novel chemical tool to disrupt clathrin function in living cells. We engineered a cross-linkable form of clathrin by using an FK506-binding protein 12 (FKBP)-clathrin fusion protein that is specifically oligomerized upon addition of the cell-permeant cross-linker FK1012-A. This approach interrupts the normal assembly-disassembly cycle of clathrin lattices and results in a specific, rapid, and reversible approximately 70% inhibition of clathrin function. This approach should be applicable to a number of proteins that must go through an assembly-disassembly cycle for normal function.

FKBP ligands as novel therapeutics for neurological disorders

Given their clinical importance for the treatment of acute and chronic neurodegenerative diseases in humans including nerve injuries (e.g. Alzheimer's disease, Parkinson's disease, diabetic neuropathy) a number of different approaches were pursued to obtain selectively acting FK506-binding protein (FKBP) ligands: computational methods and target-oriented screening of natural compound and synthetic product libraries. The resulting monofunctional ligands, which inhibit the peptidyl prolyl cis/trans isomerase activity of FKBPs, highlight the role of these enzymes in neuronal signaling. The exploration of the mechanisms of neuroregenerative and neuroprotective action of some of these compounds is the main focus of ongoing neuropharmaceutical research.