HIF-independent regulation of VEGF and angiogenesis by the transcriptional coactivator PGC-1alpha.

Ischaemia of the heart, brain and limbs is a leading cause of morbidity and mortality worldwide. Hypoxia stimulates the secretion of vascular endothelial growth factor (VEGF) and other angiogenic factors, leading to neovascularization and protection against ischaemic injury. Here we show that the transcriptional coactivator PGC-1alpha (peroxisome-proliferator-activated receptor-gamma coactivator-1alpha), a potent metabolic sensor and regulator, is induced by a lack of nutrients and oxygen, and PGC-1alpha powerfully regulates VEGF expression and angiogenesis in cultured muscle cells and skeletal muscle in vivo. PGC-1alpha-/- mice show a striking failure to reconstitute blood flow in a normal manner to the limb after an ischaemic insult, whereas transgenic expression of PGC-1alpha in skeletal muscle is protective. Surprisingly, the induction of VEGF by PGC-1alpha does not involve the canonical hypoxia response pathway and hypoxia inducible factor (HIF). Instead, PGC-1alpha coactivates the orphan nuclear receptor ERR-alpha (oestrogen-related receptor-alpha) on conserved binding sites found in the promoter and in a cluster within the first intron of the VEGF gene. Thus, PGC-1alpha and ERR-alpha, major regulators of mitochondrial function in response to exercise and other stimuli, also control a novel angiogenic pathway that delivers needed oxygen and substrates. PGC-1alpha may provide a novel therapeutic target for treating ischaemic diseases.

Bone marrow-derived CMPs and GMPs represent highly functional proangiogenic cells: implications for ischemic cardiovascular disease.

Clinical studies using bone marrow-derived proangiogenic cells (PACs) have demonstrated modest improvements of function and/or perfusion of ischemic myocardium or skeletal muscle. Because the identities of these PACs and their functional ability to promote neovascularization remain poorly understood, it is possible that a subset of robust PACs exists but is obscured by the heterogeneous nature of this cell population. Herein, we found that common myeloid progenitors (CMPs) and granulocyte-macrophage progenitors (GMPs) preferentially differentiate into PACs compared with megakaryocyte-erythrocyte progenitors, hematopoietic stem cells, and common lymphoid progenitors. In vivo hindlimb ischemia studies and Matrigel plug assays verified the enhanced neovascularization properties uniquely associated with PACs derived from CMPs and GMPs. Taken together, these observations identify CMPs and GMPs as key bone marrow progenitors for optimal PAC function in vitro and in vivo and provide a foundation for novel therapeutic approaches to modulate angiogenesis.

TGF-ß1 signaling and Krüppel-like factor 10 regulate bone marrow-derived proangiogenic cell differentiation, function, and neovascularization.

Emerging evidence demonstrates that proangiogenic cells (PACs) originate from the BM and are capable of being recruited to sites of ischemic injury where they contribute to neovascularization. We previously determined that among hematopoietic progenitor stem cells, common myeloid progenitors (CMPs) and granulocyte-macrophage progenitor cells (GMPs) differentiate into PACs and possess robust angiogenic activity under ischemic conditions. Herein, we report that a TGF-ß1-responsive Krüppel- like factor, KLF10, is strongly expressed in PACs derived from CMPs and GMPs, ∼ 60-fold higher than in progenitors lacking PAC markers. KLF10(-/-) mice present with marked defects in PAC differentiation, function, TGF-ß responsiveness, and impaired blood flow recovery after hindlimb ischemia, an effect rescued by wild-type PACs, but not KLF10(-/-) PACs. Overexpression studies revealed that KLF10 could rescue PAC formation from TGF-ß1(+/-) CMPs and GMPs. Mechanistically, KLF10 targets the VEGFR2 promoter in PACs which may underlie the observed effects. These findings may be clinically relevant because KLF10 expression was also found to be significantly reduced in PACs from patients with peripheral artery disease. Collectively, these observations identify TGF-ß1 signaling and KLF10 as key regulators of functional PACs derived from CMPs and GMPs and may provide a therapeutic target during cardiovascular ischemic states.

RTEF-1, an upstream gene of hypoxia-inducible factor-1α, accelerates recovery from ischemia.

The amount of available hypoxia-inducible factor (HIF)-1α has been considered to be largely a consequence of post-translational modification by multiple ubiquitin-proteasome pathways. However, the role of transcriptional regulation of HIF-1α is less certain, and the mechanisms of transcriptional regulation of HIF-1α require further investigation. Here we report that related transcriptional enhancer factor-1 (RTEF-1), a member of the TEF transcriptional factor family, transcriptionally regulates the HIF-1α gene under normoxic and hypoxic conditions. The expression of HIF-1α mRNA was decreased in endothelial cells in which RTEF-1 was knocked down with siRNA. Sequential deletional analysis of the HIF-1α promoter revealed that the MCAT-like element in the HIF-1α promoter was essential for HIF-1α transcription. Binding of RTEF-1 to the MCAT-like element was confirmed by ChIP. Treatment of endothelial cells with a HIF-1 inhibitor resulted in retardation of RTEF-1-induced proliferation and tube formation. Moreover, increased HIF-1α expression was observed in transgenic mice expressing RTEF-1 under the VE-cadherin promoter (VE-Cad/RTEF-1). VE-Cad/RTEF-1 mice subjected to hindlimb ischemia demonstrated increased levels of HIF-1α, accelerated recovery of blood flow, and increased capillary density compared with littermate controls. These results identify RTEF-1 as a regulator of HIF-1α transcription, which results in up-regulation of HIF-1α and acceleration of recovery from ischemia.

Response gene to complement 32, a novel hypoxia-regulated angiogenic inhibitor.

BACKGROUND: Response gene to complement 32 (RGC-32) is induced by activation of complement and regulates cell proliferation. To determine the mechanism of RGC-32 in angiogenesis, we examined the role of RGC-32 in hypoxia-related endothelial cell function. METHODS AND RESULTS: Hypoxia/ischemia is able to stimulate both angiogenesis and apoptosis. Hypoxia-inducible factor-1/vascular endothelial growth factor is a key transcriptional regulatory pathway for angiogenesis during hypoxia. We demonstrated that the increased RGC-32 expression by hypoxia was via hypoxia-inducible factor-1/vascular endothelial growth factor induction in cultured endothelial cells. However, overexpression of RGC-32 reduced the proliferation and migration and destabilized vascular structure formation in vitro and inhibited angiogenesis in Matrigel assays in vivo. Silencing RGC-32 had an opposing, stimulatory effect. RGC-32 also stimulated apoptosis as shown by the increased apoptotic cells and caspase-3 cleavage. Mechanistic studies revealed that the effect of RGC-32 on the antiangiogenic response was via attenuating fibroblast growth factor 2 expression and further inhibiting expression of cyclin E without affecting vascular endothelial growth factor and fibroblast growth factor 2 signaling in endothelial cells. In the mouse hind-limb ischemia model, RGC-32 inhibited capillary density with a significant attenuation in blood flow. Additionally, treatment with RGC-32 in the xenograft tumor model resulted in reduced growth of blood vessels that is consistent with reduced colon tumor size. CONCLUSIONS: We provide the first direct evidence for RGC-32 as a hypoxia-inducible gene and antiangiogenic factor in endothelial cells. These data suggest that RGC-32 plays an important homeostatic role in that it contributes to differentiating the pathways for vascular endothelial growth factor and fibroblast growth factor 2 in angiogenesis and provides a new target for ischemic disorder and tumor therapies.

Myostatin regulates cardiomyocyte growth through modulation of Akt signaling.

Myostatin is a highly conserved, potent negative regulator of skeletal muscle hypertrophy in many species, from rodents to humans, although its mechanisms of action are incompletely understood. Transcript profiling of hearts from a genetic model of cardiac hypertrophy revealed dramatic upregulation of myostatin, not previously recognized to play a role in the heart. Here we show that myostatin abrogates the cardiomyocyte growth response to phenylephrine in vitro through inhibition of p38 and the serine-threonine kinase Akt, a critical determinant of cell size in many species from drosophila to mammals. Evaluation of male myostatin-null mice revealed that their cardiomyocytes and hearts overall were slightly smaller at baseline than littermate controls but exhibited more exuberant growth in response to chronic phenylephrine infusion. The increased cardiac growth in myostatin-null mice corresponded with increased p38 phosphorylation and Akt activation in vivo after phenylephrine treatment. Together, these data demonstrate that myostatin is dynamically regulated in the heart and acts more broadly than previously appreciated to regulate growth of multiple types of striated muscle.

Feasibility of Serial 6-min Walk Tests in Patients with Acute Heart Failure.

BACKGROUND: Functional status assessment is common in many cardiovascular diseases but it has undergone limited study in the setting of acute heart failure (AHF). Accordingly, we performed a pilot study of the feasibility of the six-minute walk test (6MWT) at the emergency department (ED) presentation and through the hospitalization in patients with AHF. METHODS AND RESULTS: From November 2014 to February 2015, we conducted a multicenter, observational study of ED patients, aged 18-85 years, whose primary ED admission diagnosis was AHF. Other criteria for enrollment included a left ventricular ejection fraction ≤40%, systolic blood pressure between 90 and 170 mmHg, and verbal confirmation that the patient was able to walk >30 m at the baseline, prior to ED presentation. Study teams were uniformly trained to administer a 6MWT. Patients underwent a baseline 6MWT within 24 h of ED presentation (Day 1) and follow-up 6MWTs at 24 (Day 2), 48 (Day 3), and 120 h (Day 5). A total of 46 patients (65.2% male, 73.9% African American) had a day one mean walk distance of 137.3 ± 78 m, day 2 of 170.9 ± 100 m, and day 3 of 180.8 ± 98 m. The 6MWT demonstrated good reproducibility, as the distance walked on the first 6MWT on Day 3 was similar to the distance on the repeated 6MWT the same day. CONCLUSIONS: Our pilot study demonstrates the feasibility of the 6MWT as a functional status endpoint in AHF patients. A larger study in a more demographically diverse cohort of patients is necessary to confirm its utility and association with 30-day heart failure (HF) events.

Predictors for the development of elevated anti-heparin/platelet factor 4 antibody titers in patients undergoing cardiac catheterization.

A substantial proportion of patients who undergo cardiac catheterization develop antibodies directed against the heparin/platelet factor 4 (PF4) complex after the procedure, which have been implicated in the pathogenesis of heparin-induced thrombocytopenia. This study attempted to identify factors that predicted the development of these antibodies in a prospective cohort study. Antiheparin/PF4 antibody titers were measured at baseline and again 5 +/- 2 days after cardiac catheterization by enzyme-linked immunosorbent assay. A total of 311 patients who underwent cardiac catheterization were included in the analysis. Of these, 25 (8.0%) developed positive antibody levels after catheterization. Patients who had positive antibody test results after catheterization had significantly greater baseline antiheparin/PF4 antibody titers compared with those whose titers remained low (optical density 0.227 vs 0.158, p < 0.001). In a logistic regression model, greater baseline antibody titers, a history of heparin exposure, and a lower platelet count at enrollment were the strongest predictors of conversion to positive antiheparin/PF4 antibody titers after cardiac catheterization. It is possible to identify patients at high risk for developing elevated titers of antiheparin/PF4 antibodies on the basis of their baseline clinical characteristics.