Renal activity of Akt kinase in experimental Type 1 diabetes.

Akt kinase regulates numerous cell functions including glucose metabolism, cell growth, survival, protein synthesis, and control of local hemodynamics. mTOR is one of down-stream effectors of Akt involved in the initiation of protein translation. However, renal Akt signaling in Type 1 diabetes (DM) in vivo, in particular under the conditions reflecting differences in metabolic control, has received less attention. Renal cortical activity and expression of Akt and mTOR (kinase assay, western blotting) were determined in streptozotocin-diabetic rats (D) with different levels of glycemic control (blood glucose 22.0+/-1.0, 13.4+/-1.5, 8.1+/-0.4 mmol/l, p<0.05 between the groups), achieved by varying insulin treatment (0, 4 and 12 IU/day), and in control rats with (C4) or without (C) chronic insulin administration. Renal Akt activity was reduced in D rats without insulin treatment and severe hyperglycemia (D-0, -62 %, p<0.01 vs. C), partially restored in moderately hyperglycemic rats (D-4, -30 %, p<0.05 vs. C), and normalized in D rats with intensive insulin and tight metabolic control (D-12). Expression of active mTOR paralleled Akt activity in D-0 (-51 %, p<0.01 vs. C), but not in D-4 and D-12 that demonstrated increases in active mTOR (+55 %, +80 % resp., p<0.05) as compared to C. Moreover, insulin activated renal Akt (+82 %, p<0.01), but not mTOR in C4. In conclusion, glycemic control and intensity of insulin treatment are important modulators of renal Akt and mTOR activity in diabetes. While Akt activity is reversible by tight metabolic control, combination of hyperglycemia and insulin treatment resulted in enhancement of mTOR activity. In addition to Akt, other signaling pathways likely contribute to regulation of renal mTOR activity in diabetes.

Pro-inflammatory gene expression in adipose tissue of patients with atherosclerosis.

Inflammatory changes, both in the arterial wall and adipose tissue, play a crucial role in the development of atherosclerosis. We measured the gene expression of tumor necrosis factor-alpha (TNFalpha), monocyte chemoattractant protein-1 (MCP-1), and interleukin 6 (IL-6) in adipose tissue (AT) of living kidney donors (LKD) and patients with peripheral arterial disease (PAD). Quantitative polymerase chain reaction (qPCR) and flow cytometry analyses were performed in subcutaneous (SAT), visceral (VAT), and perivascular adipose tissue (PVAT). Data of PAD patients showed significantly higher expression in VAT in all three genes (TNFalpha 5-fold, p<0.05; MCP-1 3.6-fold, p<0.05; IL-6 18.8-fold, p<0.001). The differences in PVAT and SAT were less significant. Total body pro-inflammatory status was documented by higher TNFalpha concentration in patients (4.86+/-1.4 pg/ml) compared to LKDs (2.14+/-0.9 pg/ml; p<0.001), as was hsCRP (11.8+/-7.0 in PAD; 1.5+/-0.48 in LKDs; p=0.017). We found no age-dependent relationship between gene expression vs. TNFalpha and hsCRP concentrations in both compared groups. No effect of the atherosclerosis score on gene expression and circulating inflammatory markers within the PAD group was observed. Our results suggest that the AT of PAD patients infiltrated with macrophages produces more cytokines involved in the development of inflammation and atherosclerosis.

Emerging role of Akt kinase/protein kinase B signaling in pathophysiology of diabetes and its complications.

In addition to a number of deleterious effects on cellular integrity and functions, diabetic metabolic milieu has been implicated in a rapidly growing number of alterations in signal transduction. In this review we focus on Akt kinase physiology, its alterations in diabetes mellitus (DM), and on the emerging role of this signaling system in the pathophysiology of diabetic microvascular complications. Studies focusing on Akt in diabetes suggest both decrease and increase of Akt activity in DM. Alterations of Akt activity have been found in various tissues and cells in diabetes depending on experimental and clinical contexts. There is convincing evidence suggesting defective Akt signaling in the development of insulin resistance. Similar defects, as in insulin-sensitive tissues, have been reported in endothelia of DM Type 2 models, possibly contributing to the development of endothelial dysfunction under these conditions. In contrast, Akt activity is increased in some tissues and vascular beds affected by complications in DM Type 1. Identification of the role of this phenomenon in DM-induced growth and hemodynamic alterations in affected vascular beds remains one of the major challenges for future research in this area. Future studies should include the evaluation of therapeutical benefits of pharmacological modulators of Akt activity.

Macrophage phenotypes in the adipose tissue of postmenopausal women.

Atherosclerosis pathology is the interplay between high intravascular LDL particle concentration and monocyte/macrophage presence within the sub-endothelial space of the artery. In this project, phenotypes of macrophages connected with subclinical inflammation in adipose tissue of living kidney donors were studied. Samples of subcutaneous adipose tissue of living kidney donors (n=36) were exposed to collagenase. Stromal vascular fraction (SVF) was eluted from the samples, then labeled with monoclonal antibodies (anti-CD14 and anti-calprotectin), conjugated with fluorochromes and analyzed by flow cytometry. The positive correlation between the number of total macrophages and calprotectin-positive macrophages with BMI in the subcutaneous adipose tissue of postmenopausal women was demonstrated (p<0.05; R=0.43 and p<0.01; R=0.60), whereas no positive correlation in premenopausal women and men was shown. In conclusion, we documented a significant effect of BMI increase on the presence of total macrophages in adipose tissue of postmenopausal women, in contrast to premenopausal women. This difference was much more pronounced when proinflammatory macrophages with membrane-bound calprotectin were analyzed.

Co-cultivation of human aortic smooth muscle cells with epicardial adipocytes affects their proliferation rate.

The abnormal proliferation of vascular smooth muscle cells (VSMC) is thought to play a role in the pathogenesis of atherosclerosis. Adipocytes produce several bioactive paracrine substances that can affect the growth and migration of VSMCs. Our study focuses on the direct effect of the bioactive substances in conditioned media (CM) that was obtained by incubation with primary adipocyte-derived cell lines, including cell lines derived from both preadipocytes and from more mature cells, on the proliferation rate of human aortic smooth muscle cells (HAoSMCs). We used a Luminex assay to measure the adipokine content of the CM and showed that there was a higher concentration of monocyte chemoattractant protein-1 in renal preadipocyte-CM compared with the HAoSMC control (p<0.5). The addition of both renal preadipocyte- and epicardial adipocyte- CM resulted in the elevated production of vascular endothelial growth factor compared with the control HASoSMC CM (p<0.001). The adiponectin content in renal adipocyte-CM was increased compared to all the remaining adipocyte-CM (p<0.01). Moreover, the results showed a higher proliferation rate of HAoSMCs after co-culture with epicardial adipocyte-CM compared to the HAoSMC control (p<0.05). These results suggest that bioactive substances produced by adipocytes have a stimulatory effect on the proliferation of VSMCs.

Autophagy-lysosomal pathway is involved in lipid degradation in rat liver.

We present data supporting the hypothesis that the lysosomal-autophagy pathway is involved in the degradation of intracellular triacylglycerols in the liver. In primary hepatocytes cultivated in the absence of exogenous fatty acids (FFA), both inhibition of autophagy flux (asparagine) or lysosomal activity (chloroquine) decreased secretion of VLDL (very low density lipoproteins) and formation of FFA oxidative products while the stimulation of autophagy by rapamycine increased some of these parameters. Effect of rapamycine was completely abolished by inactivation of lysosomes. Similarly, when autophagic activity was influenced by cultivating the hepatocytes in "starving" (amino-acid poor medium) or "fed" (serum-supplemented medium) conditions, VLDL secretion and FFA oxidation mirrored the changes in autophagy being higher in starvation and lower in fed state. Autophagy inhibition as well as lysosomal inactivation depressed FFA and DAG (diacylglycerol) formation in liver slices in vitro. In vivo, intensity of lysosomal lipid degradation depends on the formation of autophagolysosomes, i.e. structures bringing the substrate for degradation and lysosomal enzymes into contact. We demonstrated that lysosomal lipase (LAL) activity in liver autophagolysosomal fraction was up-regulated in fasting and down-regulated in fed state together with the increased translocation of LAL and LAMP2 proteins from lysosomal pool to this fraction. Changes in autophagy intensity (LC3-II/LC3-I ratio) followed a similar pattern.