HEAT SHOCK PROTEINS: NOVEL THERAPEUTIC TARGETS AGAINST INSULIN RESISTANCE AND TYPE 2 DIABETES

Impaired insulin action, termed insulin resistance, is characteristic of type 2 diabetes, obesity and aging. Given the rising epidemic of diabetes, efforts to understand the mechanisms of insulin resistance and discover effective therapeutic interventions are urgent. Considerable evidence now implicates oxidative stress in the patho-physiology of insulin resistance, a condition prevalent in the elderly and obese. Oxidative stress is known to activate several signaling cascades. This includes pathways that activate the stress kinases c-Jun N-terminal kinase (JNK) and the inhibitor of kappa B kinase beta (IKK beta), which interact with and inhibit the insulin signaling cascade. The heat shock proteins HSP72 and HSP25 have been recently identified as natural inhibitors of JNK and IKK beta, respectively, and therefore represent novel therapeutic targets against insulin resistance. Overexpression of HSPs has been shown to protect against obesity-induced insulin resistance as well as age-related muscle damage. Skeletal muscle, the largest glucose disposing tissue, also contains large amounts of inducible HSPs. We hypothesized that heat shock protein overexpression in skeletal muscle could protect against insulin resistance in obesity and aging. We tested this hypothesis using aged male Fischer 344 rats (24-month-old) as the aging model of insulin resistance and male Wistar rats given a high fat diet (60% calories from fat) as the model of diet induced-insulin resistance. We examined the role of HSPs in insulin resistance by inducing HSP expression with both in vitro and in vivo heat treatments and anti-oxidant administration. Our results showed that reduced HSP expression in the aging muscles is associated with a higher degree of stress kinase activation and insulin resistance in fast-twitch muscles compared to slow-twitch muscles. Increasing HSP72 expression in the muscles of young and old animals via heat treatment inhibited JNK activation. Heat-mediated JNK inhibition was specific to HSP72 induction, as determined by HSP72-inhibition studies, and was mediated by a direct interaction between HSP72 and JNK. In contrast to the muscle, brain sections from aging rats showed a robust increase in HSP25 expression, suggesting a tissue-specific regulation of HSPs in aging. In the high fat diet model, alpha-lipoic acid (LA), a potent antioxidant, was administered to relieve oxidative stress associated with high fat feeding. LA treatment improved insulin signaling and glucose transport, reduced stress kinase activation and increased HSP expression. As another method of HSP-induction, heat treatment, given in parallel with a high fat diet, improved glucose tolerance, reduced hyperinsulinemia, and reduced epididymal fat storage. In skeletal muscles, heat treatment induced HSP72 expression, improved insulin sensitivity, and reduced stress kinase activities. Heat treatment also enhanced mitochondrial function in fast-twitch muscles, normalizing the compensatory changes in mitochondrial protein expression seen with high fat feeding. Studies in L6 myotubes showed that heat treatment improved oxygen consumption and fatty acid oxidation. Mechanistically, our results indicate that heat shock proteins can 1). improve insulin sensitivity, 2). directly inhibit stress kinase activities, and 3). protect and enhance mitochondrial function. Our studies provide strong evidence that HSP induction in skeletal muscle could be a potential therapeutic treatment for age-related and obesity-induced insulin resistance

The Role of Calcium Signaling in Melanoma

Calcium signaling plays important roles in physiological and pathological conditions, including cutaneous melanoma, the most lethal type of skin cancer. Intracellular calcium concentration ([Ca2+]i), cell membrane calcium channels, calcium related proteins (S100 family, E-cadherin, and calpain), and Wnt/Ca2+ pathways are related to melanogenesis and melanoma tumorigenesis and progression. Calcium signaling influences the melanoma microenvironment, including immune cells, extracellular matrix (ECM), the vascular network, and chemical and physical surroundings. Other ionic channels, such as sodium and potassium channels, are engaged in calcium-mediated pathways in melanoma. Calcium signaling serves as a promising pharmacological target in melanoma treatment, and its dysregulation might serve as a marker for melanoma prediction. We documented calcium-dependent endoplasmic reticulum (ER) stress and mitochondria dysfunction, by targeting calcium channels and influencing [Ca2+]i and calcium homeostasis, and attenuated drug resistance in melanoma management

AIBP Regulates Metabolism of Ketone and Lipids but Not Mitochondrial Respiration

Accumulating evidence indicates that the APOA1 binding protein (AIBP)—a secreted protein—plays a profound role in lipid metabolism. Interestingly, AIBP also functions as an NAD(P)H-hydrate epimerase to catalyze the interconversion of NAD(P)H hydrate [NAD(P)HX] epimers and is renamed as NAXE. Thus, we call it NAXE hereafter. We investigated its role in NAD(P)H-involved metabolism in murine cardiomyocytes, focusing on the metabolism of hexose, lipids, and amino acids as well as mitochondrial redox function. Unbiased metabolite profiling of cardiac tissue shows that NAXE knockout markedly upregulates the ketone body 3-hydroxybutyric acid (3-HB) and increases or trends increasing lipid-associated metabolites cholesterol, α-linolenic acid and deoxycholic acid. Paralleling greater ketone levels, ChemRICH analysis of the NAXE-regulated metabolites shows reduced abundance of hexose despite similar glucose levels in control and NAXE-deficient blood. NAXE knockout reduces cardiac lactic acid but has no effect on the content of other NAD(P)H-regulated metabolites, including those associated with glucose metabolism, the pentose phosphate pathway, or Krebs cycle flux. Although NAXE is present in mitochondria, it has no apparent effect on mitochondrial oxidative phosphorylation. Instead, we detected more metabolites that can potentially improve cardiac function (3-HB, adenosine, and α-linolenic acid) in the Naxe−/− heart; these mice also perform better in aerobic exercise. Our data reveal a new role of NAXE in cardiac ketone and lipid metabolism

Enhanced Succinate Oxidation with Mitochondrial Complex II Reactive Oxygen Species Generation in Human Prostate Cancer

The transformation of prostatic epithelial cells to prostate cancer (PCa) has been characterized as a transition from citrate secretion to citrate oxidation, from which one would anticipate enhanced mitochondrial complex I (CI) respiratory flux. Molecular mechanisms for this transformation are attributed to declining mitochondrial zinc concentrations. The unique metabolic properties of PCa cells have become a hot research area. Several publications have provided indirect evidence based on investigations using pre-clinical models, established cell lines, and fixed or frozen tissue bank samples. However, confirmatory respiratory analysis on fresh human tissue has been hampered by multiple difficulties. Thus, few mitochondrial respiratory assessments of freshly procured human PCa tissue have been published on this question. Our objective is to document relative mitochondrial CI and complex II (CII) convergent electron flow to the Q-junction and to identify electron transport system (ETS) alterations in fresh PCa tissue. The results document a CII succinate: quinone oxidoreductase (SQR) dominant succinate oxidative flux model in the fresh non-malignant prostate tissue, which is enhanced in malignant tissue. CI NADH: ubiquinone oxidoreductase activity is impaired rather than predominant in high-grade malignant fresh prostate tissue. Given these novel findings, succinate and CII are promising targets for treating and preventing PCa

Altered estrogen receptor expression in skeletal muscle and adipose tissue of female rats fed a high-fat diet

Estrogen receptors (ERs) are expressed in adipose tissue and skeletal muscle, with potential implications for glucose metabolism and insulin signaling. Previous studies examining the role of ERs in glucose metabolism have primarily used knockout mouse models of ERα and ERβ, and it is unknown whether ER expression is altered in response to an obesity-inducing high-fat diet (HFD). The purpose of the current study was to determine whether modulation of glucose metabolism in response to a HFD in intact and ovariectomized (OVX) female rats is associated with alterations in ER expression. Our results demonstrate that a 6-wk HFD (60% calories from fat) in female rats induces whole body glucose intolerance with tissue-specific effects isolated to the adipose tissue, and no observed differences in insulin-stimulated glucose uptake, GLUT4, or ERα protein expression levels in skeletal muscle. In chow-fed rats, OVX resulted in decreased ERα with a trend toward decreased GLUT4 expression in adipose tissue. Sham-treated and OVX rats fed a HFD demonstrated a decrease in ERα and GLUT4 in adipose tissue. The HFD also increased activation of stress kinases (c-jun NH2-terminal kinase and inhibitor of κB kinase β) in the sham-treated rats and decreased expression of the protective heat shock protein 72 (HSP72) in both sham-treated and OVX rats. Our findings suggest that decreased glucose metabolism and increased inflammation in adipose tissue with a HFD in female rats could stem from a significant decrease in ERα expression