Heat Shock Protein 90β1 Is Essential for Polyunsaturated Fatty Acid-induced Mitochondrial Ca2+ Efflux

Abstract

Defective mitochondrial function has been observed in type 2 diabetes and is proposed to be a major contributing factor in the pathogenesis and progression of the disease (1, 2). Although the mechanism leading to mitochondrial dysfunction in diabetes remains under intensive investigation, a critical role for nonesterified fatty acids (NEFA) 2 and/or fatty acid metabolites is emphasized by an increasing body of evidence (3-5). NEFA may influence mitochondrial function by alterations in gene expression (6), metabolism (7), and/or mitochondrial Ca 2ϩ homeostasis (8, 9). Ionic Ca 2ϩ in the mitochondria regulates substrate oxidation by activation of mitochondrial dehydrogenases (9). Deficiency of pyruvate dehydrogenase (PDH) activity in pancreatic islet ␤-cells (10), cardiomyocytes (11), and skeletal muscles (7, 12, 13) has been demonstrated in diabetes. The degree to which PDH is dephosphorylated (i.e. the balance between phosphorylation and dephosphorylation) determines the level of enzyme activity. The concentration of mitochondrial Ca 2ϩ ([Ca 2ϩ ] m ) is an important activator of PDH phosphatase, which dephosphorylates and activates PDH. Additionally, [Ca 2ϩ ] m has been shown to activate at least three other mitochondrial dehydrogenases (i.e. glycerol 3-phosphate dehydrogenase, NAD-linked isocitrate dehydrogenase, and 2-oxoglutarate dehydrogenase), all of which play important roles in substrate oxidation (9). NEFA, which are chronically elevated in type 2 diabetes, inhibit PDH by mechanisms thought to involve FA oxidation and elevation of acetyl-CoA. We have previously reported that polyunsaturated fatty acids (PUFA) induce Ca 2ϩ efflux from mitochondria (8), an action that could deplete [Ca 2ϩ ] m and thus contribute to NEFA-responsive reduction of PDH activity and mitochondrial dysfunction. The PUFA-induced mitochondrial Ca 2ϩ efflux (PIMCE) cannot be blocked with cyclosporine A and bongkrekic acid, two inhibitors of the mitochondrial permeability transition pore. However, the pathway(s) underlying PIMCE has not previously been defined.In the current work, we have used proteomic analysis to demonstrate a parallel reduction in PIMCE and the level of heat shock protein 90␤1 (hsp90␤1) in NT2 cells treated with retinoic acid (RA). Further studies with pharmacological inhibitors and RNA interference (RNAi) indicate that hsp90␤1 plays an essential role in PIMCE in NT2 cells.

Geldanamycin Derivative Ameliorates High Fat Diet-Induced Renal Failure in Diabetes

“…Linoleic acid (LA), a major component of PUFA in the plasma, interacts with hsp90β1 to cause mitochondrial Ca 2+ ([Ca 2+ ] m ) efflux and peroxynitrite generation in cell cultures [25], [26]. These pathways may contribute to HFD-induced decline of kidney functions in db/db mice by increasing oxidative stress.…”

“…In the second phase of HFD challenge (Figure 1), db/db mice were treated with or without 17-DMAG (6.5 µg/kg bodyweight injected intraperitoneally once daily) to test the involvement of hsp90. The dose of 17-DMAG was chosen based on our previous studies showing 17-DMAG at that concentration exerting maximal inhibition on PUFA-induced [Ca 2+ ] m efflux but not producing apparent toxicity to cells [26]. In db/db mice without 17-DMAG treatment [injected with saline (vehicle) db/db-HF-S group, Figure 1 D], a dramatic increase in urine albumin excretion was observed following two weeks on HFD in the second phase of HFD challenge, mirroring the results in the first phase of HFD feeding (Figure 1B).…”

“…Treatment of cells with 17-DMAG downregulates hsp90β1 and inhibits LA-induced [Ca 2+ ] m efflux [25], [26]. We thus determined whether the beneficial effect of 17-DMAG on HFD-fed db/db mice involved the regulation of the same pathways in the kidney.…”

“…Our previous studies indicate that polyunsaturated fatty acids (PUFA) induce peroxynitrite generation in various cell types including primary human mesangial cells [24], [25]. The increasing peroxynitrite formation in response to PUFA requires heat shock protein 90β1 (HSP90β1) and is associated with Ca 2+ efflux from the mitochondria [25], [26]. In the current work, we investigated the role of hsp90 in high fat diet (HFD)-induced renal failure in db/db mice.…”

Effects of Dietary Polyunsaturated Fatty Acids on Mitochondria

“…PUFAs influenced the activity of a variety of ion channels and transporters located at the sarcolemma or the sarcoplasmic reticulum [111][112][113]. In particular, PUFAs (AA, LA, EPA, DHA) but not monounsaturated or saturated fatty acids induced calcium efflux from mitochondria, involving the calcium uniporter and required heat shock protein Hsp90b1 [114,115]. Increased mitochondrial calcium resulted in Krebs' cycle stimulation and activation of calcium-depen-dent mitochondrial dehydrogenases such as pyruvate dehy-drogenase (PDH) or isocitrate dehydrogenase [116,117].…”