Plasminogen activator inhibitor-1 (PAI-1) plays an important role in the pathogenesis of obesity-driven type 2 diabetes mellitus and associated cardiovascular complications. Here, we show that perturbation of caveolar microdomains leads to insulin resistance and concomitant up-regulation of PAI-1 in 3T3L1 adipocytes. We present several lines of evidence showing that the phosphatidylinositol 3-kinase (PI3K) pathway negatively regulates PAI-1 gene expression. Insulin-induced PAI-1 gene expression is up-regulated by a specific inhibitor of PI3K. In addition, serum PAI-1 level is elevated in protein kinase B␣-deficient mice, whereas it is reduced in p70 ribosomal S6 kinase 1-deficient mice. The PI3K pathway phosphorylates retinoblastoma protein (pRB), known to release free E2 (adenoviral protein) factor (E2F), which we have previously demonstrated to be a transcriptional repressor of PAI-1 gene expression. Accordingly, cell-penetrating peptides that disrupt pRB-E2F interaction, and thereby release free E2F, are able to suppress PAI-1 levels that are elevated during insulin-resistant conditions. This study identifies a caveolar-dependent signal pathway that up-regulates PAI-1 in insulin-resistant adipocytes and proposes a previously undescribed pharmacological paradigm of disrupting pRB-E2F interaction to suppress PAI-1 levels. diabetes T ype 2 diabetes mellitus (T2DM) is characterized by insulin resistance, where the insulin receptor (IR) fails to elicit the metabolic signaling that is required for glucose metabolism and energy homeostasis. In insulin-sensitive tissues, the IR transduces two main signaling cascades: a metabolic signaling that is responsible for glucose uptake and glycogen synthesis and a mitogenic signaling that is responsible for cell proliferation and growth. The IR substrate (IRS)-phosphatidylinositol 3-kinase (PI3K)-protein kinase B (PKB) and Cbl-CAP-Flotillin pathways represents the major metabolic signaling, whereas the Shc-Rasextracellular regulated kinase (Erk) pathway represents the major mitogenic signaling (1). Both in animal models and clinical T2DM subjects, a selective impairment of metabolic signaling has been observed, whereas mitogenic signaling is more or less unaffected (2-4).Obesity is prominent among the plethora of factors that leads to the development of T2DM, although the molecular mechanism underlying the pathogenesis of obesity-driven T2DM is not well understood. Comparative analysis of large and small fat cells within the same fat pad reveals a 2-fold reduction in the levels of plasma membrane cholesterol in large fat cells, suggesting that a decrease in membrane cholesterol is characteristic of adipocyte hypertrophy per se (5). Recently, it has been proposed that the protein levels of caveolin-1 and -3 are inversely correlated to the body-mass index. § Plasma membrane cholesterol (6) and caveolins (7) are indispensable for the structural and functional integrity of caveolar microdomains. We therefore reasoned that obesity might lead to caveolar dysfunction. Because the IR...

Obesity is characterized by elevated levels of circulating plasminogen activator inhibitor-1 (PAI-1), which contribute towards the development of secondary disorders such as type 2 diabetes mellitus and cardiovascular complications. This increase in plasma PAI-1 levels is attributed to an increase in PAI-1 derived from adipose tissue. This study shows that adipose tissue evolved into a major PAI-1 producing organ by gaining capacity during adipocyte differentiation to respond to inducers of PAI-1 transcription. This is mediated by a decrease in E2F1 protein levels, an increase in pRB levels and a decrease in pRB phosphorylation, all leading to a decrease in levels of free E2F, a known transcriptional repressor of PAI-1. Depletion of E2F1-3 was sufficient for inducers such as insulin to potently induce PAI-1 gene expression in pre-adipocytes. Conversely, forced release of pRB-bound endogenous E2F using cell-penetrating peptides can suppress PAI-1 gene expression in adipocytes. This study describes the novel paradigm of cellular differentiation-associated increase in PAI-1 gene expression which is mediated by a decrease in repressor activity, and describes a way of desensitising terminally differentiated cells to PAI-1 inducing agents by restoring endogenous repressor activity.

In recent years, biomedical science has witnessed the emergence of peptide biochemicals as significant topics of research. Some of these peptides are of little potential clinical use, while others, of which cardiac natriuretic peptides are an example, appear to be promising. This particular group of peptides (i.e. ANP, BNP and CNP) shows promising diagnostic as well as therapeutic potential for various pathological conditions. In the case of acute myocardial infarction, these peptides have significant diagnostic and predictive properties, more so than other biochemicals such as adrenaline, renin and aldosterone. In addition, ANP is found to have significant benefits over the classical anti-anginal drug glyceryl trinitrate. However, as is the case with other peptides, applying these benefits clinically may not be easy because of the structure of the compounds, but various strategies are now being applied to solve this problem. These include the use of non-peptide receptor ligands, inhibitors of ANP metabolism, gene therapy and so on. The development of drugs in clinical practice, which exploits the natriuretic peptides system therefore seems to be promising, and this article reviews advances in our understanding of these compounds.

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In recent years, biomedical science has witnessed the emergence of peptide biochemicals as significant topics of research. Some of these peptides are of little potential clinical use, while others, of which cardiac natriuretic peptides are an example, appear to be promising. This particular group of peptides (i.e. ANP, BNP and CNP) shows promising diagnostic as well as therapeutic potential for various pathological conditions. In the case of acute myocardial infarction, these peptides have significant diagnostic and predictive properties, more so than other biochemicals such as adrenaline, renin and aldosterone. In addition, ANP is found to have significant benefits over the classical anti‐anginal drug glyceryl trinitrate. However, as is the case with other peptides, applying these benefits clinically may not be easy because of the structure of the compounds, but various strategies are now being applied to solve this problem. These include the use of non‐peptide receptor ligands, inhibitors of ANP metabolism, gene therapy and so on. The development of drugs in clinical practice, which exploits the natriuretic peptides system therefore seems to be promising, and this article reviews advances in our understanding of these compounds.

"Bound" and "free" RNA polymerase activities were assessed in the nuclear fraction of cerebral cortical, neuronal, astroglial, and oligodendroglial cells obtained from rats of young, adult, and old ages. Significant decreases in both the bound and free polymerase II activities were noticed in old brain, as compared to adult brain, in neuronal and oligodendroglial nuclei. In astroglia, only the free polymerase II was found to be affected. No effect of aging could be seen on the activity of bound RNA polymerase I + III. The free RNA polymerase I + III activity was increased from adult to old age in neuronal nuclei, but unchanged in oligodendroglial and astroglial nuclei. The age-dependent reduction in RNA polymerase II was maximum in oligodendroglial cells, whereas it was least, although still significant, in neuronal cells. DNA isolated from old brain was unable to enhance the transcriptional activity when added to chromatin preparations obtained from rat brains of any of the above ages and the "old" chromatin was unable to accept even the "young" DNA as additional exogenous template. It is concluded that the reduced gene expression noticed in old brain nuclei is due to both altered chromatin/DNA structure and inadequate levels of free RNA polymerase II.

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