Pulmonary arterial remodelling by deficiency of peroxisome proliferator-activated receptor-γ in murine vascular smooth muscle cells occurs independently of obesity-related pulmonary hypertension.

BACKGROUND: Obesity is associated with cardiovascular complications, including pulmonary hypertension (PH). Reports suggest that peroxisome proliferator-activated receptor-γ (PPARγ) has direct action in preventing vascular remodelling in PH. Here we dissected the specific role of high-fat-diet (HFD)-induced obesity and vascular smooth muscle cell (VSMC)-PPARγ for remodelling of small pulmonary arteries. METHODS: Wild-type (WT) and VSMC-specific PPARγ-knockout (SmPparγ-/-) mice were fed a low-fat-diet (LFD, 10% kcal from fat) or HFD (60% kcal from fat) for 24 weeks. Mice were metabolically phenotyped (e.g. weight development, insulin/glucose tolerance) at the beginning, and after 12 and 24 weeks, respectively. At 24 weeks additionally pulmonary pressure, heart structure, pulmonary vascular muscularization together with gene and protein expression in heart and lung tissues were determined. RESULTS: HFD increased right ventricular systolic pressure (RVSP) to a similar extent in WT and SmPparγ-/- mice. HFD decreased glucose tolerance and insulin sensitivity in both WT and SmPparγ-/- mice. Importantly, the increase in RVSP correlated with the degree of insulin resistance. However, VSMC-PPARγ deficiency increased pulmonary vascular muscularization independently of the diet-induced rise in RVSP. This increase was associated with elevated expression of early growth response protein 1 in heart and osteopontin in lung tissue. CONCLUSIONS: Here we demonstrate a correlation of insulin resistance and pulmonary pressure. Further, deficiency of PPARγ in VSMCs diet-independently leads to increased pulmonary vascular muscularization.

Pioglitazone alleviates cardiac and vascular remodelling and improves survival in monocrotaline induced pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is a fatal disease with limited therapeutic options. Pathophysiological changes comprise obliterative vascular remodelling of small pulmonary arteries, elevated mean pulmonary arterial systolic pressure (PASP) due to elevated resistance of pulmonary vasculature, adverse right ventricular remodelling, and heart failure. Recent findings also indicate a role of increased inflammation and insulin resistance underlying the development of PAH. We hypothesized that treatment of this condition with the peroxisome proliferator-activated receptor-γ (PPARγ) activator pioglitazone, known to regulate the expression of different genes addressing insulin resistance, inflammatory changes, and vascular remodelling, could be a beneficial approach. PAH was induced in adult rats by a single subcutaneous injection of monocrotaline (MCT). Pioglitazone was administered for 2 weeks starting 3 weeks after MCT-injection. At day 35, hemodynamics, organ weights, and -indices were measured. We performed morphological and molecular characterization of the pulmonary vasculature, including analysis of the degree of muscularization, proliferation rates, and medial wall thickness of the small pulmonary arteries. Furthermore, markers of cardiac injury, collagen content, and cardiomyocyte size were analyzed. Survival rates were monitored throughout the experimental period. Pioglitazone treatment improved survival, reduced PASP, muscularization of small pulmonary arteries, and medial wall thickness. Further, MCT-induced right ventricular hypertrophy and fibrosis were attenuated. This was accompanied with reduced cardiac expression of brain natriuretic peptide, as well as decreased cardiomyocyte size. Finally, pulmonary macrophage content and osteopontin gene expression were attenuated. Based on the beneficial impact of pioglitazone, activation of PPARγ might be a promising treatment option in PAH.

Enhanced insulin signaling in density-enhanced phosphatase-1 (DEP-1) knockout mice.

OBJECTIVE: Insulin resistance can be triggered by enhanced dephosphorylation of the insulin receptor or downstream components in the insulin signaling cascade through protein tyrosine phosphatases (PTPs). Downregulating density-enhanced phosphatase-1 (DEP-1) resulted in an improved metabolic status in previous analyses. This phenotype was primarily caused by hepatic DEP-1 reduction. METHODS: Here we further elucidated the role of DEP-1 in glucose homeostasis by employing a conventional knockout model to explore the specific contribution of DEP-1 in metabolic tissues. Ptprj (-/-) (DEP-1 deficient) and wild-type C57BL/6 mice were fed a low-fat or high-fat diet. Metabolic phenotyping was combined with analyses of phosphorylation patterns of insulin signaling components. Additionally, experiments with skeletal muscle cells and muscle tissue were performed to assess the role of DEP-1 for glucose uptake. RESULTS: High-fat diet fed-Ptprj (-/-) mice displayed enhanced insulin sensitivity and improved glucose tolerance. Furthermore, leptin levels and blood pressure were reduced in Ptprj (-/-) mice. DEP-1 deficiency resulted in increased phosphorylation of components of the insulin signaling cascade in liver, skeletal muscle and adipose tissue after insulin challenge. The beneficial effect on glucose homeostasis in vivo was corroborated by increased glucose uptake in skeletal muscle cells in which DEP-1 was downregulated, and in skeletal muscle of Ptprj (-/-) mice. CONCLUSION: Together, these data establish DEP-1 as novel negative regulator of insulin signaling.

Inhibition of protein tyrosine phosphatases enhances cerebral collateral growth in rats.

UNLABELLED: Arteriogenesis involves the rapid proliferation of preexisting arterioles to fully functional arteries as a compensatory mechanism to overcome circulatory deficits. Stimulation of arteriogenesis has therefore been considered a treatment concept in arterial occlusive disease. Here, we investigated the impact of inhibition of protein tyrosine phosphatases (PTPs) on cerebral arteriogenesis in rats. Arteriogenesis was induced by occlusion of one carotid and both vertebral arteries (three-vessel occlusion (3-VO)). Collateral growth and functional vessel perfusion was assessed 3-35 days following 3-VO. Furthermore, animals underwent 3-VO surgery and were treated with the pan-PTP inhibitor BMOV, the SHP-1 inhibitor sodium stibogluconate (SSG), or the PTP1B inhibitor AS279. Cerebral vessel diameters and cerebrovascular reserve capacity (CVRC) were determined, together with immunohistochemistry analyses and proximity ligation assays (PLA) for determination of tissue proliferation and phosphorylation patterns after 7 days. The most significant changes in vessel diameter increase were present in the ipsilateral posterior cerebral artery (PCA), with proliferative markers (PCNA) being time-dependently increased. The CVRC was lost in the early phase after 3-VO and partially recovered after 21 days. PTP inhibition resulted in a significant increase in the ipsilateral PCA diameter in BMOV-treated animals and rats subjected to PTP1B inhibition. Furthermore, CVRC was significantly elevated in AS279-treated rats compared to control animals, along with hyperphosphorylation of the platelet-derived growth factor-ß receptor in the vascular wall in vivo. In summary, our data indicate PTPs as hitherto unrecognized negative regulators in cerebral arteriogenesis. Further, PTP inhibition leading to enhanced collateral growth and blood perfusion suggests PTPs as novel targets in anti-ischemic treatment. KEY MESSAGES: PTPs exhibit negative regulatory function in cerebral collateral growth in rats. Inhibition of pan-PTP/PTP1B increases vessel PDGF-ß receptor phosphorylation. PTP1B inhibition enhances arteriogenesis and cerebrovascular reserve capacity.

Targeting density-enhanced phosphatase-1 (DEP-1) with antisense oligonucleotides improves the metabolic phenotype in high-fat diet-fed mice.

BACKGROUND: Insulin signaling is tightly controlled by tyrosine dephosphorylation of the insulin receptor through protein-tyrosine-phosphatases (PTPs). DEP-1 is a PTP dephosphorylating tyrosine residues in a variety of receptor tyrosine kinases. Here, we analyzed whether DEP-1 activity is differentially regulated in liver, skeletal muscle and adipose tissue under high-fat diet (HFD), examined the role of DEP-1 in insulin resistance in vivo, and its function in insulin signaling. RESULTS: Mice were fed an HFD for 10 weeks to induce obesity-associated insulin resistance. Thereafter, HFD mice were subjected to systemic administration of specific antisense oligonucleotides (ASOs), highly accumulating in hepatic tissue, against DEP-1 or control ASOs. Targeting DEP-1 led to improvement of insulin sensitivity, reduced basal glucose level, and significant reduction of body weight. This was accompanied by lower insulin and leptin serum levels. Suppression of DEP-1 in vivo also induced hyperphosphorylation in the insulin signaling cascade of the liver. Moreover, DEP-1 physically associated with the insulin receptor in situ, and recombinant DEP-1 dephosphorylated the insulin receptor in vitro. CONCLUSIONS: These results indicate that DEP-1 acts as an endogenous antagonist of the insulin receptor, and downregulation of DEP-1 results in an improvement of insulin sensitivity. DEP-1 may therefore represent a novel target for attenuation of metabolic diseases.

Cannabinoid receptor 1 inhibition improves cardiac function and remodelling after myocardial infarction and in experimental metabolic syndrome.

The cannabinoid receptors, CB1 and CB2, are expressed in the heart, but their role under pathological conditions remains controversial. This study examined the effect of CB1 receptor blockade on cardiovascular functions after experimental MI and in experimental metabolic syndrome. MI was induced in Wistar rats by permanent ligation of the left coronary artery. Treatment with the CB1 receptor antagonist rimonabant (10 mg/kg i.p. daily) started 7 days before or 6 h after MI and continued for 6 weeks. Haemodynamic parameters were measured via echocardiography and intracardiac Samba catheter. CB1 blockade improved systolic and diastolic heart function, decreased cardiac collagen and hydroxyproline content and down-regulated TGF-ß1. Additionally, rimonabant decreased arterial stiffness, normalised QRS complex duration and reduced brain natriuretic peptide levels in serum. In primary cardiac fibroblasts, rimonabant decreased MMP-9 activity and TGF-ß1 expression. Furthermore, rimonabant improved depressed systolic function of spontaneously hypertensive obese rats and reduced weight gain. Blocking of CB1 receptor with rimonabant improves cardiac functions in the early and late stages after MI, decreases arterial stiffness and reduces cardiac remodelling. Rimonabant also has cardioprotective actions in rats characterised by the metabolic syndrome. Inhibition of proteolysis and TGF-ß1 expression and reduced collagen content by rimonabant may attenuate destruction of the extracellular matrix and decrease fibrosis after MI.

Histone deacetylase 6 (HDAC6) is an essential modifier of glucocorticoid-induced hepatic gluconeogenesis.

In the current study, we investigated the importance of histone deacetylase (HDAC)6 for glucocorticoid receptor-mediated effects on glucose metabolism and its potential as a therapeutic target for the prevention of glucocorticoid-induced diabetes. Dexamethasone-induced hepatic glucose output and glucocorticoid receptor translocation were analyzed in wild-type (wt) and HDAC6-deficient (HDAC6KO) mice. The effect of the specific HDAC6 inhibitor tubacin was analyzed in vitro. wt and HDAC6KO mice were subjected to 3 weeks' dexamethasone treatment before analysis of glucose and insulin tolerance. HDAC6KO mice showed impaired dexamethasone-induced hepatic glucocorticoid receptor translocation. Accordingly, dexamethasone-induced expression of a large number of hepatic genes was significantly attenuated in mice lacking HDAC6 and by tubacin in vitro. Glucose output of primary hepatocytes from HDAC6KO mice was diminished. A significant improvement of dexamethasone-induced whole-body glucose intolerance as well as insulin resistance in HDAC6KO mice compared with wt littermates was observed. This study demonstrates that HDAC6 is an essential regulator of hepatic glucocorticoid-stimulated gluconeogenesis and impairment of whole-body glucose metabolism through modification of glucocorticoid receptor nuclear translocation. Selective pharmacological inhibition of HDAC6 may provide a future therapeutic option against the prodiabetogenic actions of glucocorticoids.