Mutations Y493G and K546D in human HSP90 disrupt binding of celastrol and reduce interaction with Cdc37

Heat shock protein 90 inhibition and multi-target approach to maximize cardioprotection in ischaemic injury

Despite several advances in medicine, ischaemic heart disease remains a major cause of morbidity and mortality. The unravelling of molecular mechanisms underlying disease pathophysiology has revealed targets for pharmacological interventions. However, transfer of these pharmcological possibilities to clinical use has been disappointing. Considering the complexity of ischaemic disease at the cellular and molecular levels, an equally multifaceted treatment approach may be envisioned. The pharmacological principle of 'one target, one key' may fall short in such contexts, and optimal treatment may involve one or many agents directed against complementary targets. Here, we introduce a 'multi-target approach to cardioprotection' and propose heat shock protein 90 (HSP90) as a target of interest. We report on a member of a distinct class of HSP90 inhibitor possessing pleiotropic activity, which we found to exhibit potent infarct-sparing effects.

Novel heat shock protein 90 inhibitor improves cardiac recovery in a rodent model of donation after circulatory death

OBJECTIVE

Organ donation after circulatory death (DCD) is a potential solution for the shortage of suitable organs for transplant. Heart transplantation using DCD donors is not frequently performed due to the potential myocardial damage following warm ischemia. Heat shock protein (HSP) 90 has recently been investigated as a novel target to reduce ischemia/reperfusion injury. The objective of this study is to evaluate an innovative HSP90 inhibitor (HSP90i) as a cardioprotective agent in a model of DCD heart.

METHODS

A DCD protocol was initiated in anesthetized Lewis rats by discontinuation of ventilation and confirmation of circulatory death by invasive monitoring. Following 15 minutes of warm ischemia, cardioplegia was perfused for 5 minutes at physiological pressure. DCD hearts were mounted on a Langendorff ex vivo heart perfusion system for reconditioning and functional assessment (60 minutes). HSP90i (0.01 μmol/L) or vehicle was perfused in the cardioplegia and during the first 10 minutes of ex vivo heart perfusion reperfusion. Following assessment, pro-survival pathway signaling was evaluated by western blot or polymerase chain reaction.

RESULTS

Treatment with HSP90i preserved left ventricular contractility (maximum + dP/dt, 2385 ± 249 vs 1745 ± 150 mm Hg/s), relaxation (minimum -dP/dt, -1437 ± 97 vs 1125 ± 85 mm Hg/s), and developed pressure (60.7 ± 5.6 vs 43.9 ± 4.0 mm Hg), when compared with control DCD hearts (All P = .001). Treatment abrogates ischemic injury as demonstrated by a significant reduction of infarct size (2,3,5-triphenyl-tetrazolium chloride staining) of 7 ± 3% versus 19 ± 4% (P = .03), troponin T release, and mRNA expression of Bax/Bcl-2 (P < .05).

CONCLUSIONS

The cardioprotective effects of HSP90i when used following circulatory death might improve transplant organ availability by expanding the use of DCD hearts.

Therapeutic Potential of the Hsp90/Cdc37 Interaction in Neurodegenerative Diseases

Alzheimer's, Huntington's, and Parkinson's are devastating neurodegenerative diseases that are prevalent in the aging population. Patient care costs continue to rise each year, because there is currently no cure or disease modifying treatments for these diseases. Numerous efforts have been made to understand the molecular interactions governing the disease development. These efforts have revealed that the phosphorylation of proteins by kinases may play a critical role in the aggregation of disease-associated proteins, which is thought to contribute to neurodegeneration. Interestingly, a molecular chaperone complex consisting of the 90 kDa heat shock protein (Hsp90) and Cell Division Cycle 37 (Cdc37) has been shown to regulate the maturation of many of these kinases as well as regulate some disease-associated proteins directly. Thus, the Hsp90/Cdc37 complex may represent a potential drug target for regulating proteins linked to neurodegenerative diseases, through both direct and indirect interactions. Herein, we discuss the broad understanding of many Hsp90/Cdc37 pathways and how this protein complex may be a useful target to regulate the progression of neurodegenerative disease.

Celastrol-type HSP90 modulators allow for potent cardioprotective effects

AIMS

Cardiac ischemic conditioning has been shown to decrease ischemic injury in experimental models and clinically. Activation of survival pathways leading to heat shock proteins (HSP) modulation is an important contributor to this effect. We have previously shown that celastrol, an HSP90 modulator, achieves cardioprotection through activation of cytoprotective HSP's and heme-oxygenase-1 (HO-1). This is the first comparative evaluation of several modulators of HSP90 activity for cardioprotection. Furthermore, basic celastrol structure-activity relationship was characterized in order to develop novel potent infarct sparing agents suitable for clinical development.

MAIN METHODS

Combining in vitro cell culture using rat myocardial cell line exposed to ischemic and ischemia/reperfusion (I/R) stresses, and ex vivo Langendorff rat heart perfusion I/R model, we evaluated cardioprotective effects of various compounds. Selected signalling pathways were evaluated by western blot and reporter gene activation.

KEY FINDINGS

From a variety of HSP90 modulator chemotypes, the celastrol family was most efficient in inducing cytoprotective HSP70 and HO-1 protein overexpression and cell survival in vitro. Celastrol and two synthetic analogs were protective against ischemia and prevented ischemia/reperfusion (I/R) injury when given as pre-treatment or at time of reperfusion, increasing viability and reducing mitochondrial permeability transition pore opening. Ex vivo experiments demonstrated that the two synthetic analogs show cardioprotective activity at lower concentrations compared to celastrol, with activation of multiple survival pathways.

SIGNIFICANCE

Celastrol backbone is essential for cardioprotection through HSP90 activity modulation. These compounds hold promise as novel adjunct treatment to improve outcome in the clinical management of I/R injury.

Celastrol Promotes Weight Loss in Diet-Induced Obesity by Inhibiting the Protein Tyrosine Phosphatases PTP1B and TCPTP in the Hypothalamus

Celastrol is a natural pentacyclic triterpene used in traditional Chinese medicine with significant weight-lowering effects. Celastrol-administered mice at 100 μg/kg decrease food consumption and body weight via a leptin-dependent mechanism, yet its molecular targets in this pathway remain elusive. Here, we demonstrate in vivo that celastrol-induced weight loss is largely mediated by the inhibition of leptin negative regulators protein tyrosine phosphatase (PTP) 1B (PTP1B) and T-cell PTP (TCPTP) in the arcuate nucleus (ARC) of the hypothalamus. We show in vitro that celastrol binds reversibly and inhibits noncompetitively PTP1B and TCPTP. NMR data map the binding site to an allosteric site in the catalytic domain that is in proximity of the active site. By using a panel of PTPs implicated in hypothalamic leptin signaling, we show that celastrol additionally inhibited PTEN and SHP2 but had no activity toward other phosphatases of the PTP family. These results suggest that PTP1B and TCPTP in the ARC are essential for celastrol's weight lowering effects in adult obese mice.

Celastrol-Induced Weight Loss Is Driven by Hypophagia and Independent From UCP1

Celastrol, a plant-derived constituent of traditional Chinese medicine, has been proposed to offer significant potential as an antiobesity drug. However, the molecular mechanism for this activity is unknown. We show that the weight-lowering effects of celastrol are driven by decreased food consumption. Although young Lep ^ob mice respond with a decrease in food intake and body weight, adult Lep ^db and Lep ^ob mice are unresponsive to celastrol, suggesting that functional leptin signaling in adult mice is required to elicit celastrol's catabolic actions. Protein tyrosine phosphatase 1 (PTP1B), a leptin negative-feedback regulator, has been previously reported to be one of celastrol's targets. However, we found that global PTP1B knockout (KO) and wild-type (WT) mice have comparable weight loss and hypophagia when treated with celastrol. Increased levels of uncoupling protein 1 (UCP1) in subcutaneous white and brown adipose tissue suggest celastrol-induced thermogenesis as a further mechanism. However, diet-induced obese UCP1 WT and KO mice have comparable weight loss upon celastrol treatment, and celastrol treatment has no effect on energy expenditure under ambient housing or thermoneutral conditions. Overall, our results suggest that celastrol-induced weight loss is hypophagia driven and age-dependently mediated by functional leptin signaling. Our data encourage reconsideration of therapeutic antiobesity strategies built on leptin sensitization.

Celastrol attenuates ventilator induced lung injury in mouse through inhibition of MAPK pathway

PURPOSE

Previous studies have shown that celastrol has anti-inflammatory, anti-oxidative and anti-tumor activities, but little is known about its protective effects on ventilator induced lung injury (VILI). This study is aimed to investigate the effects of celastrol on VILI and explore its potential mechanism.

METHODS

A total of 40 ICR male mice aged 7-9 weeks were randomly divided into 4 groups (n=10 per group): control group (Con), control + celastrol group (Con+Ce), mechanical ventilation group (Ven) and mechanical ventilation + celastrol group (Ven+Ce). The lungs were collected for histological examination, detection of W/D, and MPO, MDA, SOD, inflammatory cytokines (IL-1β, IL-6, IL-10 and TNF-α) by ELISA, p-P₃₈ and p-JNK 1/2 protein by Western blotting, and collagen-1 and TGF-β mRNA expression by RT-PCR.

RESULTS

The W/D in the Ven group was significantly higher than the W/D in the Con group and the Ven+Ce group (both P<0.01). Mechanical ventilation for 4 h markedly increased lung MPO and MDA activity, TNF-α, IL-1β and IL-6, but dramatically reduced SOD and IL-10 (all P<0.01). However, celastrol pre-treatment compromised the increased MPO, MDA, TNF-α, IL-1β, IL-6 (all P<0.01) and significantly increased SOD (P=0.035<0.05) and IL-10 (P<0.01). In addition, mRNA level of collagen-1 and TGF-β as well as p-P₃₈ and p-JNK 1/2 protein expression increased significantly (P<0.01) after mechanical ventilation, which however were markedly reduced in the presence of celastrol pre-treatment.

CONCLUSION

Celastrol pre-treatment may exert anti-oxidative and anti-inflammatory effects and related lung fibrosis to attenuate VILI in mice, which may be related to the inhibition of p-P₃₈ and p-JNK 1/2 by MAPK pathway.