Introduction The effects of caloric restriction (CR) on the skeleton are well studied in adult rodents, and include lower cortical bone mass but higher trabecular bone volume. Much less is known about how CR affects bone mass in young, rapidly growing animals. This is an important problem because low caloric intake during skeletal acquisition in humans, as in anorexia nervosa, is associated with low bone mass, increased fracture risk, and osteoporosis in adulthood. To explore this question, we tested the effect of caloric restriction on bone mass and microarchitecture during rapid skeletal growth in young mice. Methods At 3 wks of age we weaned male C57Bl/6J mice onto 30% caloric restriction (CR, 10% Kcal/fat) or normal diet (N, 10% Kcal/fat). Outcomes at 6 (N=4/group) and 12 wks of age (N=8/group) included body mass, femur length, serum leptin and IGF-1, whole body bone mineral density (WBBMD, g/cm2), cortical and trabecular bone architecture at the midshaft and distal femur, bone formation and cellularity, and marrow fat measurement. Results Compared to N, CR mice had 52% and 88% lower serum leptin and 33% and 39% lower serum IGF-1 at 6 and 12 wks of age (p<0.05 for all). CR mice were smaller, with lower bone mineral density, trabecular and cortical bone properties. Bone formation indices were lower, while bone resorption indices were higher (p<0.01 for all) in CR vs. N. Despite having lower %body fat, bone marrow adiposity was dramatically elevated in CR vs. N (p<0.05). Conclusion Caloric restriction in young, growing mice is associated with impaired skeletal acquisition, low leptin and IGF-1 levels, and high marrow adiposity. These results support the hypothesis that caloric restriction during rapid skeletal growth is deleterious to cortical and trabecular bone mass and architecture, in contrast to potential skeletal benefits of CR in aging animals.

Abstract-Glycolysis increases in hypertrophied hearts but the mechanisms are unknown. We studied the regulation of glycolysis in hearts with pressure-overload LV hypertrophy (LVH), a model that showed marked increases in the rates of glycolysis (by 2-fold) and insulin-independent glucose uptake (by 3-fold). Although the V max of the key glycolytic enzymes was unchanged in this model, concentrations of free ADP, free AMP, inorganic phosphate (P i ), and fructose-2,6-bisphosphate (F-2,6-P 2 ), all activators of the rate-limiting enzyme phosphofructokinase (PFK), were increased (up to 10-fold). Concentrations of the inhibitors of PFK, ATP, citrate, and H ϩ were unaltered in LVH. Thus, our findings show that increased glucose entry and activation of the rate-limiting enzyme PFK both contribute to increased flux through the glycolytic pathway in hypertrophied hearts. Moreover, our results also suggest that these changes can be explained by increased intracellular free [ADP] and [AMP], due to decreased energy reserve in LVH, activating the AMP-activated protein kinase cascade. This, in turn, results in enhanced synthesis of F-2,6-P 2 and increased sarcolemma localization of glucose transporters, leading to coordinated increases in glucose transport and activation of PFK. Key Words: cardiac function Ⅲ hypertrophy Ⅲ protein kinases Ⅲ cardiac metabolism Ⅲ cyclic AMP G lucose utilization is increased in hypertrophied and failing hearts, 1-4 but the underlying mechanisms are poorly understood. Increased glycolytic flux in the hypertrophied myocardium is important because ATP synthesis via glucose utilization may compensate for decreased capacity for ATP synthesis via other pathways. 5,6 In hearts with chronic pressure overload hypertrophy, it was recently reported that chronic depletion of the energy reserve compound PCr coupled with large changes in the ratio of PCr to free creatine led to activation of AMP-activated protein kinase (AMPK) by elevated AMP concentrations. 7 AMPK acts as a low-on-fuel sensor and, when the cytosolic AMP concentration increases, AMPK activates enzymes in pathways that synthesize ATP and inhibits enzymes in pathways that use ATP. 8,9 Among the many consequences of activated AMPK is increased localization of glucose transporters in the sarcolemma and hence increased glucose uptake by an insulinindependent mechanism. 10,11 In addition, in a study of acute myocardial ischemia, AMPK was found to phosphorylate and thereby activate heart phosphofructokinase-2 (PFK-2), leading to increased production of fructose-2,6-bisphosphate (F-2,6-P 2 ), a potent activator of the rate-limiting glycolytic enzyme phosphofructokinase (PFK). 12 In the present study, we tested the hypothesis that increased glycolysis in hypertrophied hearts occurs as a consequence of chronic decreases in the energy reserve and activation of AMPK.Using a model of pressure overload left ventricular hypertrophy (LVH) of the rat heart, in which reduced energy reserve, increased AMPK activity, and increased insulin-independent glucose upt...

BMP9 signaling has been implicated in hereditary hemorrhagic telangiectasia (HHT) and vascular remodeling, acting via the HHT target genes, endoglin and ALK1. This study sought to identify endothelial BMP9-regulated proteins that could affect the HHT phenotype. Gene ontology analysis of cDNA microarray data obtained after BMP9 treatment of primary human endothelial cells indicated regulation of chemokine, adhesion, and inflammation pathways. These responses included the up-regulation of the chemokine CXCL12/SDF1 and down-regulation of its receptor CXCR4. Quantitative mass spectrometry identified additional secreted proteins, including the chemokine CXCL10/IP10. RNA knockdown of endoglin and ALK1 impaired SDF1/CXCR4 regulation by BMP9. Because of the association of SDF1 with ischemia, we analyzed its expression under hypoxia in response to BMP9 in vitro, and during the response to hindlimb ischemia, in endoglin-deficient mice. BMP9 and hypoxia were additive inducers of SDF1 expression. Moreover, the data suggest that endoglin deficiency impaired SDF1 expression in endothelial cells in vivo. Our data implicate BMP9 in regulation of the SDF1/CXCR4 chemokine axis in endothelial cells and point to a role for BMP9 signaling via endoglin in a switch from an SDF1-responsive autocrine phenotype to an SDF1 nonresponsive paracrine state that represses endothelial cell migration and may promote vessel maturation. IntroductionEndoglin directly interacts with the TGF-␤ receptors, 1 including ALK1, 2 and modulates TGF-␤ and bone morphogenetic protein (BMP) signaling. 3 Mutations in either endoglin 4 or ALK1 5 increase the risk of hereditary hemorrhagic telangiectasia (HHT1 and HHT2, respectively), whose symptoms include arteriovenous malformation, tissue ischemia, and reperfusion defects. 6 The ALK1-endoglin signaling complex in endothelial cells is activated by BMP9, 7 a circulating cytokine produced in the liver reticuloendothelium 8 and endothelial cells, including those lining the mouse aorta. 9 BMP9 interacts with endoglin and ALK1 to activate signaling pathways 7 that promote endothelial cell quiescence 10 and vessel maturation. 11 Several endothelial cell-derived factors, including BMP9, are known to regulate vessel maturation via paracrine recruitment of other cell types. 12 Moreover, our recent work using nonendothelial cells implicates endoglin in the regulation of tumor neoangiogenesis via the secreted insulin-like growth factor binding protein 4. 13 Therefore, elucidation of the role of BMP9 signaling, specifically in terms of its effects on the expression of endothelial cell-secreted factors, is needed to better understand the mechanisms by which BMP9 affects vessel maturation, integrity, the vascular response to injury, and how deficiency in either endoglin or ALK1 impacts vessel integrity and cause HHT.Stromal-derived factor 1 (SDF1, CXCL12) is a chemokine that signals via the chemokine receptor, CXCR4, to modulate hypoxiainduced angiogenesis. 14 SDF1 regulates both endothelial cellmediated paracrine signaling ...