17-DMAG, an Hsp90 inhibitor, ameliorates ovariectomy-induced obesity in rats

Hsp90: From Cellular to Organismal Proteostasis

Assuring a healthy proteome is indispensable for survival and organismal health. Proteome disbalance and the loss of the proteostasis buffer are hallmarks of various diseases. The essential molecular chaperone Hsp90 is a regulator of the heat shock response via HSF1 and a stabilizer of a plethora of signaling proteins. In this review, we summarize the role of Hsp90 in the cellular and organismal regulation of proteome maintenance.

Role of HSP90α in osteoclast formation and osteoporosis development

Osteoporosis (OP) is a systemic metabolic bone disease that occurs most frequently in the elderly. The main pathogenesis of OP is excessive proliferation and differentiation of osteoclasts, in which the peroxisome proliferator-activated receptor γ (PPARγ) pathway has a pivotal role. Recently, heat shock protein (HSP)90α has been identified as an important molecular chaperone with PPARγ, which regulates the effect of the PPARγ pathway. The aim of the present study was to investigate the role of HSP90α involved in the regulation of osteoclast formation and the process of osteoporosis. Firstly, the expression of HSP90α in osteoclast differentiation was detected by western blotting in vitro, then the effect of HSP90α inhibition on the formation and differentiation of osteoclasts was examined. Furthermore, the nuclear import of PPARγ was also assessed to confirm the synergistic effect of HSP90α. Finally, the inhibitory effect of HSP90α in vivo was explored, using a mouse model of osteoporosis. As a result, in the process of osteoclast differentiation and proliferation, the expression of HSP90α was upregulated. Inhibition of HSP90α could block the formation and differentiation of osteoclasts, and remit osteoporosis in mice. Regarding the underlying mechanism, inhibition of HSP90α could block the nuclear import of PPARγ to inhibit osteoclast differentiation and proliferation. In conclusion, these data indicated that the inhibition of HSP90α could block osteoclast formation and remit osteoporosis by reducing the nuclear import of PPARγ.

HSP90 inhibitors reduce cholesterol storage in Niemann-Pick type C1 mutant fibroblasts

Niemann-Pick type C1 (NPC1) disease is a lysosomal lipid storage disorder caused by mutations of the NPC1 gene. More than 300 disease-associated mutations are reported in patients, resulting in abnormal accumulation of unesterified cholesterol, glycosphingolipids, and other lipids in late endosomes and lysosomes (LE/Ly) of many cell types. Previously, we showed that treatment of many different NPC1 mutant fibroblasts with histone deacetylase inhibitors resulted in reduction of cholesterol storage, and we found that this was associated with enhanced exit of the NPC1 protein from the endoplasmic reticulum and delivery to LE/Ly. This suggested that histone deacetylase inhibitors may work through changes in protein chaperones to enhance the folding of NPC1 mutants, allowing them to be delivered to LE/Ly. In this study, we evaluated the effect of several HSP90 inhibitors on NPC1I1061T skin fibroblasts. We found that HSP90 inhibition resulted in clearance of cholesterol from LE/Ly, and this was associated with enhanced delivery of the mutant NPC1I1061T protein to LE/Ly. We also observed that inhibition of HSP90 increased the expression of HSP70, and overexpression of HSP70 also reduced cholesterol storage in NPC1I1061T fibroblasts. However, we did not see correction of cholesterol storage by arimoclomol, a drug that is reported to increase HSP70 expression, at doses up to 0.5 mM. The increase in other chaperones as a consequence of HSP90 improves folding of NPC1 protein and relieves cholesterol accumulation in NPC1 mutant fibroblasts.

In vitro model of perimenopausal depression implicates steroid metabolic and proinflammatory genes

The estimated 20-30% of women who develop perimenopausal depression (PMD) are at an increased risk of cardiovascular and all-cause mortality. The therapeutic benefits of estradiol (E2) and symptom-provoking effects of E2-withdrawal (E2-WD) suggest that a greater sensitivity to changes in E2 at the cellular level contribute to PMD. We developed an in vitro model of PMD with lymphoblastoid cell lines (LCLs) derived from participants of a prior E2-WD clinical study. LCLs from women with past PMD (n = 8) or control women (n = 9) were cultured in three experimental conditions: at vehicle baseline, during E2 treatment, and following E2-WD. Transcriptome analysis revealed significant differences in transcript expression in PMD in all experimental conditions, and significant overlap in genes that were changed in PMD regardless of experimental condition. Of these, chemokine CXCL10, previously linked to cardiovascular disease, was upregulated in women with PMD, but most so after E2-WD (p < 1.55 × 10-5). CYP7B1, an enzyme intrinsic to DHEA metabolism, was upregulated in PMD across experimental conditions (F(1,45) = 19.93, p < 0.0001). These transcripts were further validated via qRT-PCR. Gene networks dysregulated in PMD included inflammatory response, early/late E2-response, and cholesterol homeostasis. Our results provide evidence that differential behavioral responsivity to E2-WD in PMD reflects intrinsic differences in cellular gene expression. Genes such as CXCL10, CYP7B1, and corresponding proinflammatory and steroid biosynthetic gene networks, may represent biomarkers and molecular targets for intervention in PMD. Finally, this in vitro model allows for future investigations into the mechanisms of genes and gene networks involved in the vulnerability to, and consequences of, PMD.

FOXO3a regulates lipid accumulation and adipocyte inflammation in adipocytes through autophagy : Role of FOXO3a in obesity

BACKGROUND

FOXO3a is a widely studied transcription factor and plays an important role in a variety of biology. The purpose of this study was to explore the role and potential mechanism of FOXO3a on lipid accumulation and adipocyte inflammation in adipocytes through regulation of autophagy.

METHODS

The obese mouse model was successfully induced by high-fat diet. SiRNA targeting FOXO3a was transfected into differentiation of 3T3-L1 adipocytes to reduce the expression of FOXO3a. The culture medium of RAW264.7 cells was added to the differentiated 3T3-L1 adipocytes to form a co-culture system. Subsequently, ELISA or AdipoRed assay was performed to measure the expression of triglyceride (TG) and cholesterol (TC) in mouse adipose tissue or differentiation of 3T3-L1 adipocytes. Adipocyte differentiation was detected by Oil Red O-staining. Ad-mCherry-GFP-LC3II was used to detect the level of autophagy in differentiation of 3T3-L1 adipocytes. Western blotting or qRT-PCR was used to detect the expression of FOXO3a, autophagy-related proteins (beclin 1, CEBPβ, PPARγ, ACC1 and KLF4), inflammatory cytokines (TNF-α, IL-1β, IL-6 and MCP1), NF-κB signal pathway-related proteins or adipokines (Adiponectin, AdipoR1 and resistin) in differentiated 3T3-L1 or RAW264.7 cells.

RESULTS

The expression of FOXO3a and autophagy levels were significantly increased in visceral adipose tissue of obese mice and differentiation of 3T3-L1 adipocytes. Downregulation of FOXO3a significantly inhibited the autophagy and lipid accumulation in differentiation of 3T3-L1 adipocytes. In addition, FOXO3a knockdown significantly reduced Lipopolysaccharide (LPS)-induced inflammation and adipokines release in RAW264.7 cells treated with the culture medium of 3T3-L1 adipocytes. These above activity changes could be reversed by autophagy inducer rapamycin.

CONCLUSION

FOXO3a could promote lipid accumulation and inflammation in differentiated 3T3-L1 adipocytes by targeting autophagy. Our results provide a new theoretical basis for FOXO3a to regulate obesity.

Metformin ameliorates body mass gain and early metabolic changes in ovariectomized rats

Estradiol has been used to prevent metabolic diseases, bone loss and menopausal symptoms, even though it might raise the risk of cancer. Metformin is usually prescribed for type 2 diabetes mellitus and lowers food intake and body mass while improving insulin resistance and the lipid profile. Ovariectomized rats show increased body mass, insulin resistance and changes in the lipid profile. Thus, the aim of this work was to evaluate whether metformin could prevent the early metabolic dysfunction that occurs early after ovariectomy. Female Wistar rats were divided into the following groups: SHAM-operated (SHAM), ovariectomized (OVX), ovariectomized + estradiol (OVX + E2) and ovariectomized + metformin (OVX + M). Treatment with metformin diminished approximately 50% of the mass gain observed in ovariectomized animals and reduced both the serum and hepatic triglyceride levels. The hepatic levels of phosphorylated AMP-activated protein kinase (pAMPK) decreased after OVX, and the expression of the inactive form of hepatic acetyl-CoA carboxylase (ACC) was also reduced. Metformin was able to increase the levels of pAMPK in the liver of OVX animals, sustaining the balance between the inactive and total forms of ACC. Estradiol effects were similar to those of metformin but with different proportions. Our results suggest that metformin ameliorates the early alterations of metabolic parameters and rescues hepatic AMPK phosphorylation and ACC inactivation observed in ovariectomized rats.