17-AAG, a Hsp90 inhibitor, attenuates the hypoxia-induced expression of SDF-1alpha and ILK in mouse RPE cells

A simplified protocol to induce hypoxia in a standard incubator: A focus on retinal cells

Hypoxia chambers have traditionally been used to induce hypoxia in cell cultures. Cellular responses to hypoxia can also be mimicked with the use of chemicals such as cobalt chloride (CoCl2), which stabilizes hypoxia-inducible factor alpha-subunit proteins. In studies of ocular cells using primary cells and cell lines, such as Müller glial cell (MGC) lines, photoreceptor cell lines, retinal pigment epithelial (RPE) cell lines and retinoblastoma cell lines oxygen levels employed in hypoxia chambers range typically between 0.2% and 5% oxygen. For chemical induction of hypoxic response in these cells, the CoCl2 concentrations used typically range from 100 to 600 μM. Here, we describe simplified protocols for stabilizing cellular hypoxia-inducible factor-1α (HIF-1α) in cell culture using either a hypoxia chamber or CoCl2. In addition, we also provide a detailed methodology to confirm hypoxia induction by the assessment of protein levels of HIF-1α, which accumulates in response to hypoxic conditions. Furthermore, we provide a summary of conditions applied in previous studies of ocular cells.

Pharmacological Inhibition of the VCP/Proteasome Axis Rescues Photoreceptor Degeneration in RHOP23H Rat Retinal Explants

Rhodopsin (RHO) misfolding mutations are a common cause of the blinding disease autosomal dominant retinitis pigmentosa (adRP). The most prevalent mutation, RHO^P23H, results in its misfolding and retention in the endoplasmic reticulum (ER). Under homeostatic conditions, misfolded proteins are selectively identified, retained at the ER, and cleared via ER-associated degradation (ERAD). Overload of these degradation processes for a prolonged period leads to imbalanced proteostasis and may eventually result in cell death. ERAD of misfolded proteins, such as RHO^P23H, includes the subsequent steps of protein recognition, targeting for ERAD, retrotranslocation, and proteasomal degradation. In the present study, we investigated and compared pharmacological modulation of ERAD at these four different major steps. We show that inhibition of the VCP/proteasome activity favors cell survival and suppresses P23H-mediated retinal degeneration in RHO^P23H rat retinal explants. We suggest targeting this activity as a therapeutic approach for patients with currently untreatable adRP.

Effects of HSP90 inhibition on primordial germ cells migration: A study in the gonad of the chick embryo

INTRODUCTION

Primordial Germ Cells (PGCs) differentiate into spermatozoa or oocytes. They appear early during embryonic development before migrating to the gonadal ridges. Because of their long migration, PGCs have been proposed as a valuable model to study long distance cell migration. Some species also present a vascular phase in the migration of the germline and could therefore be compared to metastatic migration. HSP90 is a heat shock protein involved in the stabilization of several client-proteins, including oncoproteins. HSP90 inhibition has been proved to decrease PGCs migration in mouse and zebrafish.

MATERIAL AND METHODS

We investigated the effect of geldanamycin on PGCs migration in a species with a vascular phase, the chicken. Geldanamycin was injected in the egg at 48h of incubation, PGC's were detected in blood using of blood smears, and in the embryo by immunohistochemistry using anti-HSP90 antibody.

RESULTS

The effects of the treatment were similar to those observed in mouse and zebrafish. We show the presence of ectopic germs cells in the vasculature and in the dorsal mesentery, and some deformities of the gonads.

CONCLUSION

Inhibition of HSP90 decreases the migration of PGCs and proposed the migration of PGCs in the chick embryo as an interesting model to study metastatic invasion.

Hsp90 inhibition as a means to inhibit activation of the NLRP3 inflammasome

Once activated, the intracellular receptor NLRP3 assembles an inflammasome protein complex that facilitates the caspase-1-mediated maturation of IL-1β and IL-18. Inactive NLRP3 is guarded by a protein complex containing Hsp90. In response to stress stimuli, Hsp90 is released, and NLRP3 can be activated to promote inflammation. In this study, we blocked Hsp90 with geldanamycin and studied the fate of NLRP3 in human retinal pigment epithelial (RPE) cells. RPE cells play a central role in the development of age-related macular degeneration (AMD), a progressive eye disease causing severe vision loss in the elderly. IL-1α-primed ARPE-19 cells, human embryonal stem cell (hESC)-derived RPE cells, and primary human RPE cells were exposed to MG-132 and bafilomycin A to activate NLRP3 via the inhibition of proteasomes and autophagy, respectively. Additionally, RPE cells were treated with geldanamycin at different time points and the levels of NLRP3 and IL-1β were determined. Caspase-1 activity was measured using a commercial assay. Geldanamycin prevented the activation of the inflammasome in human RPE cells. NLRP3 released from its protective complex became degraded by autophagy or secreted from the cells. Controlled destruction of NLRP3 is a potential way to regulate the inflammation associated with chronic diseases, such as AMD.

Heat Shock Proteins in Vascular Diabetic Complications: Review and Future Perspective

Heat shock proteins (HSPs) are a large family of proteins highly conserved throughout evolution because of their unique cytoprotective properties. Besides assisting protein refolding and regulating proteostasis under stressful conditions, HSPs also play an important role in protecting cells from oxidative stress, inflammation, and apoptosis. Therefore, HSPs are crucial in counteracting the deleterious effects of hyperglycemia in target organs of diabetes vascular complications. Changes in HSP expression have been demonstrated in diabetic complications and functionally related to hyperglycemia-induced cell injury. Moreover, associations between diabetic complications and altered circulating levels of both HSPs and anti-HSPs have been shown in clinical studies. HSPs thus represent an exciting therapeutic opportunity and might also be valuable as clinical biomarkers. However, this field of research is still in its infancy and further studies in both experimental diabetes and humans are required to gain a full understanding of HSP relevance. In this review, we summarize current knowledge and discuss future perspective.

Hsp90 as a Potential Therapeutic Target in Retinal Disease

The molecular chaperone heat shock protein 90 (Hsp90) is a pivotal cellular regulator involved in the folding, activation and assembly of a wide range of proteins. Hsp90 has multiple roles in the retina and the use of different Hsp90 inhibitors has been shown to prevent retinal degeneration in models of retinitis pigmentosa and age-related macular degeneration. Hsp90 is also a potential target in uveal melanoma. Mechanistically, Hsp90 inhibition can evoke a dual response in the retina; stimulating a stress response with molecular chaperone expression. Thereby leading to an improvement in visual function and photoreceptor survival; however, prolonged inhibition can also stimulate the degradation of Hsp90 client proteins potentially deleteriously affect vision. Here, we review the multiple roles of Hsp90 in the retina and the therapeutic potential of Hsp90 as a target.

SDF-1/CXCR4 Axis Promotes MSCs to Repair Liver Injury Partially through Trans-Differentiation and Fusion with Hepatocytes

MSCs have become a popular target for developing end-stage liver therapies. In this study, two models of bone marrow chimeric mice were used to construct the liver failure models. Then it was found that MSCs can transdifferentiate into hepatocyte-like cells and these hepatocyte-like cells can significantly express albumin. Furthermore it was also found that MSCs can fuse with the hepatocytes and these cells had the proliferation activity. However, the percentage of transdifferentiation was significantly higher than fusion. So it was considered that MSCs which transdifferentiated into hepatocyte-likes cells played important roles for repairing the injuring liver function.

Integrin-linked kinase regulates vasomotor function by preventing endothelial nitric oxide synthase uncoupling: role in atherosclerosis

RATIONALE

Atherosclerotic lesions develop in regions of disturbed flow, whereas laminar flow protects from atherogenesis; however, the mechanisms involved are not completely elucidated. Integrins are mechanosensors of shear stress in endothelial cells, and integrin-linked kinase (ILK) is important for blood vessel integrity and cardiovascular development.

OBJECTIVES

To explore the role of ILK in vascular function by studying conditionally ILK-deficient (cKO) mice and human atherosclerotic arteries.

RESULTS

ILK expression was detected in the endothelial cell layer of nonatherosclerotic vessels but was absent from the endothelium of atherosclerotic arteries. Live ultrasound imaging revealed that acetylcholine-mediated vasodilatation was impaired in cKO mice. These mice exhibited lowered agonist-induced nitric oxide synthase (NOS) activity and decreased cyclic guanosine monophosphate and nitrite production. ILK deletion caused endothelial NOS (eNOS) uncoupling, reflected in reduced tetrahydrobiopterin (BH4) levels, increased BH2 levels, decreased dihydrofolate reductase expression, and increased eNOS-dependent generation of superoxide accompanied by extensive vascular protein nitration. ILK reexpression prevented eNOS uncoupling in cKO cells, whereas superoxide formation was unaffected by ILK depletion in eNOS-KO cells, indicating eNOS as a primary source of superoxide anion. eNOS and ILK coimmunoprecipitated in aortic lysates from control animals, and eNOS-ILK-shock protein 90 interaction was detected in human normal mammary arteries but was absent from human atherosclerotic carotid arteries. eNOS-ILK interaction in endothelial cells was prevented by geldanamycin, suggesting heat shock protein 90 as a binding partner.

CONCLUSIONS

Our results identify ILK as a regulatory partner of eNOS in vivo that prevents eNOS uncoupling, and suggest ILK as a therapeutic target for prevention of endothelial dysfunction related to shear stress-induced vascular diseases.

Inhibition of high glucose-induced VEGF and ICAM-1 expression in human retinal pigment epithelium cells by targeting ILK with small interference RNA

The aim of this study was to investigate the change of Integrin-linked kinase (ILK) expression of human retinal pigment epithelium (RPE) cells in response to high glucose, and the effect of targeting ILK with small interference RNA (siRNA) on the high glucose-induced expression of vascular endothelial growth factor (VEGF) and intercellular adhesion molecule-1 (ICAM-1). The ILK mRNA and protein expression in human RPE cells were analyzed with RT-PCR and western blot after exposure to 5.5, 30, 40, 50 mM glucose, or 5.5 mM glucose+45.5 mM mannitol for 48 h. The expression of VEGF and ICAM-1 was also determined. Cells were treated with ILK siRNA, to determine the effect of ILK on VEGF and ICAM-1 expression following treatment with high glucose. High concentrations of glucose significantly up-regulated ILK mRNA and protein expression, and the ILK expression increased along with the glucose concentration. The changes of VEGF and ICAM-1 expression were similar to that of ILK expression. Knocking down ILK gene expression with siRNA inhibited the elevation of VEGF and ICAM-1 induced by high glucose treatment. These results suggested that ILK was involved in the response of RPE cells to high glucose and may therefore play a role in the pathogenesis of diabetic ophthalmology.