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Abstract Context Growth hormone (GH) and IGF-1 help regulate hepatic glucose and lipid metabolism, and reductions in these hormones may contribute to development of nonalcoholic fatty liver disease (NAFLD). Objective To assess relationships between hepatic expression of IGF1 and IGF-binding proteins (IGFBPs) and measures of glycemia and liver disease in adults with NAFLD. Secondarily to assess effects of GH-releasing hormone (GHRH) on circulating IGFBPs. Design Analysis of data from a randomized clinical trial of GHRH. Setting Two US academic medical centers. Participants Participants were 61 men and women 18 to 70 years of age with HIV-infection, ≥5% hepatic fat fraction, including 39 with RNA-Seq data from liver biopsy. Main Outcome Measures Hepatic steatosis, inflammation, and fibrosis by histopathology and measures of glucose homeostasis. Results Hepatic IGF1 mRNA was significantly lower in individuals with higher steatosis and NAFLD Activity Score (NAS) and was inversely related to glucose parameters, independent of circulating IGF-1. Among the IGFBPs, IGFBP2 and IGFBP4 were lower and IGFBP6 and IGFBP7 (also known as IGFBP-related protein 1) were higher with increasing steatosis. Hepatic IGFBP6 and IGFBP7 mRNA levels were positively associated with NAS. IGFBP7 mRNA increased with increasing fibrosis. Hepatic IGFBP1 mRNA was inversely associated with glycemia and insulin resistance, with opposite relationships present for IGFBP3 and IGFBP7. GHRH increased circulating IGFBP-1 and IGFBP-3, but decreased IGFBP-2 and IGFBP-6. Conclusions These data demonstrate novel relationships of IGF-1 and IGFBPs with NAFLD severity and glucose control, with divergent roles seen for different IGFBPs. Moreover, the data provide new information on the complex effects of GHRH on IGFBPs.

Vascular endothelial growth factors (VEGFs) regulate blood and lymph vessel formation through activation of three receptor tyrosine kinases, VEGFR-1, -2, and -3. The extracellular domain of VEGF receptors consists of seven immunoglobulin homology domains, which, upon ligand binding, promote receptor dimerization. Dimerization initiates transmembrane signaling, which activates the intracellular tyrosine kinase domain of the receptor. VEGF-C stimulates lymphangiogenesis and contributes to pathological angiogenesis via VEGFR-3. However, proteolytically processed VEGF-C also stimulates VEGFR-2, the predominant transducer of signals required for physiological and pathological angiogenesis. Here we present the crystal structure of VEGF-C bound to the VEGFR-2 high-affinity-binding site, which consists of immunoglobulin homology domains D2 and D3. This structure reveals a symmetrical 2:2 complex, in which left-handed twisted receptor domains wrap around the 2-fold axis of VEGF-C. In the VEGFs, receptor specificity is determined by an N-terminal alpha helix and three peptide loops. Our structure shows that two of these loops in VEGF-C bind to VEGFR-2 subdomains D2 and D3, while one interacts primarily with D3. Additionally, the N-terminal helix of VEGF-C interacts with D2, and the groove separating the two VEGF-C monomers binds to the D2/D3 linker. VEGF-C, unlike VEGF-A, does not bind VEGFR-1. We therefore created VEGFR-1/VEGFR-2 chimeric proteins to further study receptor specificity. This biochemical analysis, together with our structural data, defined VEGFR-2 residues critical for the binding of VEGF-A and VEGF-C. Our results provide significant insights into the structural features that determine the high affinity and specificity of VEGF/VEGFR interactions.

Fibroblast growth factor receptor (FGFR) signalling is a crucial regulator of endothelial metabolism and vascular development. The role of fibroblasts in vascular development The development of blood vessel networks involves the growth and spread of endothelial cells. Recent studies suggest that these processes are affected by changes in cellular metabolism, but the role of fibroblast growth factors (FGFs) is poorly understood. Michael Simons and colleagues identify FGF receptor signalling as a crucial regulator of vascular development andendothelial cell proliferation in adult tissues. They explore the molecular basis of this effect and find that FGFs control endothelial cell glycolysis through MYC-dependent regulation of hexokinase 2 expression. The authors suggest that understanding this pathway may guide investigations into targeted therapies for diseases associated with irregular vascular growth. Blood and lymphatic vasculatures are intimately involved in tissue oxygenation and fluid homeostasis maintenance. Assembly of these vascular networks involves sprouting, migration and proliferation of endothelial cells. Recent studies have suggested that changes in cellular metabolism are important to these processes 1 . Although much is known about vascular endothelial growth factor (VEGF)-dependent regulation of vascular development and metabolism 2 , 3 , little is understood about the role of fibroblast growth factors (FGFs) in this context 4 . Here we identify FGF receptor (FGFR) signalling as a critical regulator of vascular development. This is achieved by FGF-dependent control of c-MYC (MYC) expression that, in turn, regulates expression of the glycolytic enzyme hexokinase 2 (HK2). A decrease in HK2 levels in the absence of FGF signalling inputs results in decreased glycolysis, leading to impaired endothelial cell proliferation and migration. Pan-endothelial- and lymphatic-specific Hk2 knockouts phenocopy blood and/or lymphatic vascular defects seen in Fgfr1 / Fgfr3 double mutant mice, while HK2 overexpression partly rescues the defects caused by suppression of FGF signalling. Thus, FGF-dependent regulation of endothelial glycolysis is a pivotal process in developmental and adult vascular growth and development.

Extending the release cycle of growth factors to match the cycle of bone remodeling is difficult. When using concentrated growth factors (CGFs), the release of growth factors is excessively rapid. In the present study, CGF samples were prepared by centrifugation. CGF samples were then lyophilized and grinded into a powder, which was termed freeze-dried CGF. The freeze-dried CGF samples were mixed with chitosan-alginate composite hydrogels, and the mixture was lyophilized. The result was a chitosan-alginate composite CGF membrane, which was called sustained-release CGF. This study investigated whether freeze-dried CGF in a chitosan-alginate composite gel can release CGF steadily to achieve effective osteogenesis. The proliferation and osteogenic expression of MC3T3-E1 cells induced by the supernatants from incubation with freeze-dried CGF and sustained-release CGF were evaluated. The concentrations of the growth factors, transforming growth factor β1 (TGF-β1), insulin-like growth factor-1 (IGF-1), platelet-derived growth factor-AB (PDGF-AB) and vascular endothelial growth factor (VEGF), in these two experimental groups at different times were determined by ELISA kits. The freeze-dried CGF showed better osteogenic performance than the sustained-release CGF in the early stages. At later stages, the sustained-release CGF had significant advantages over freeze-dried CGF in terms of promoting osteogenic mineralization. By characterizing the biologic properties of the CGF in the two different forms in vitro, we obtained a better understanding of their clinical effects.

Key Points Fibroblast growth factor (FGF) signalling controls a myriad of processes in embryonic development and in tissue homeostasis and metabolism in the adult. Recent structural studies have provided a glimpse of the complexity of molecular control that is in place to fine-tune this signalling system to enable it to produce specific signalling outputs in diverse biological contexts. The interaction of FGFs with heparan sulphate glycosaminoglycan chains of heparan sulphate proteoglycans in the pericellular and extracellular matrix defines their mode of action, that is, whether an FGF acts in a paracrine or endocrine fashion. It also determines the shape of gradient formed by a paracrine FGF ligand in the extracellular matrix, which in turn is a determinant of the biological response to that ligand. In addition to mechanisms common to all FGFs, such as the interaction with heparan sulphate, the biological activity of individual ligands or ligand subfamilies is regulated by mechanisms unique to these ligands: amino-terminal alternative splicing controls the activity of FGF8 subfamily ligands; homodimerization autoinhibits the activity of FGF9 subfamily ligands; and site-specific proteolytic cleavage inactivates the phosphaturic hormone FGF23. Alternative splicing in the extracellular immunoglobulin-like domain 3 (D3) of FGF receptor 1 (FGFR1), FGFR2 and FGFR3 primarily determines the ligand-binding specificity of these receptors. This splicing event is fundamental to the establishment of directional paracrine FGF signalling between the epithelium and the mesenchyme, which underlies the coordinated cellular processes that govern organ development. Klotho co-receptors convert FGFRs into specific receptors for endocrine FGFs by a dual mechanism; these co-receptors not only enhance the binding affinity of FGFRs for endocrine FGFs but concomitantly suppress the binding of paracrine FGFs to FGFRs. The finding that heparan sulphate is dispensable for signalling by endocrine FGFs implies that Klotho co-receptors also promote FGFR dimerization upon endocrine FGF binding, which is required for FGFR activation. The structural findings suggest that there may be no functional redundancy among FGF ligands, and genetic data support this conclusion. Hence, future studies should concentrate on identifying novel ligand-specific functions of FGF signalling. Structural data has provided insight into the molecular mechanisms that modulate fibroblast growth factor (FGF) signalling to generate distinct biological outputs in development, tissue homeostasis and metabolism. Mechanisms include alternative splicing of ligand and receptor, homodimerization and site-specific proteolytic cleavage of ligand, and interaction of ligand and receptor with heparan sulphate and Klotho co-receptors. Fibroblast growth factors (FGFs) mediate a broad range of functions in both the developing and adult organism. The accumulated wealth of structural information on the FGF signalling pathway has begun to unveil the underlying molecular mechanisms that modulate this system to generate a myriad of distinct biological outputs in development, tissue homeostasis and metabolism. At the ligand and receptor level, these mechanisms include alternative splicing of the ligand (FGF8 subfamily) and the receptor (FGFR1–FGFR3), ligand homodimerization (FGF9 subfamily), site-specific proteolytic cleavage of the ligand (FGF23), and interaction of the ligand and the receptor with heparan sulphate cofactor and Klotho co-receptor.

Tissue engineering is a rapidly developing field with many potential clinical applications in tissue and organ regeneration. The development of a mature and stable vasculature within these engineered tissues (ET) remains a significant obstacle. Currently, several growth factors (GFs) have been identified to play key roles within in vivo angiogenesis, including vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF), FGF and angiopoietins. In this article we attempt to build on in vivo principles to review the single, dual and multiple GF release systems and their effects on promoting angiogenesis. We conclude that multiple GF release systems offer superior results compared to single and dual systems with more stable, mature and larger vessels produced. However, with more complex release systems this raises other problems such as increased cost and significant GF–GF interactions. Upstream regulators and pericyte-coated scaffolds could provide viable alternative to circumnavigate these issues.

Articular cartilage is formed at the end of epiphyses in the synovial joint cavity and permanently contributes to the smooth movement of synovial joints. Most skeletal elements develop from transient cartilage by a biological process known as endochondral ossification. Accumulating evidence indicates that articular and growth plate cartilage are derived from different cell sources and that different molecules and signaling pathways regulate these two kinds of cartilage. As the first sign of joint development, the interzone emerges at the presumptive joint site within a pre-cartilage tissue. After that, joint cavitation occurs in the center of the interzone, and the cells in the interzone and its surroundings gradually form articular cartilage and the synovial joint. During joint development, the interzone cells continuously migrate out to the epiphyseal cartilage and the surrounding cells influx into the joint region. These complicated phenomena are regulated by various molecules and signaling pathways, including GDF5, Wnt, IHH, PTHrP, BMP, TGF-β, and FGF. Here, we summarize current literature and discuss the molecular mechanisms underlying joint formation and articular development.

Fibroblast growth factors (FGFs) deliver extracellular signals that govern many developmental and regenerative processes, but the mechanisms regulating FGF signaling remain incompletely understood. Here, we explored the relationship between intrinsic stability of FGF proteins and their biological activity for all 18 members of the FGF family. We report that FGF1, FGF3, FGF4, FGF6, FGF8, FGF9, FGF10, FGF16, FGF17, FGF18, FGF20, and FGF22 exist as unstable proteins, which are rapidly degraded in cell cultivation media. Biological activity of FGF1, FGF3, FGF4, FGF6, FGF8, FGF10, FGF16, FGF17, and FGF20 is limited by their instability, manifesting as failure to activate FGF receptor signal transduction over long periods of time, and influence specific cell behavior in vitro and in vivo. Stabilization via exogenous heparin binding, introduction of stabilizing mutations or lowering the cell cultivation temperature rescues signaling of unstable FGFs. Thus, the intrinsic ligand instability is an important elementary level of regulation in the FGF signaling system.

α/βKlotho coreceptors simultaneously engage fibroblast growth factor (FGF) hormones (FGF19, FGF21 and FGF23) 1 , 2 and their cognate cell-surface FGF receptors (FGFR1–4) thereby stabilizing the endocrine FGF–FGFR complex 3 – 6 . However, these hormones still require heparan sulfate (HS) proteoglycan as an additional coreceptor to induce FGFR dimerization/activation and hence elicit their essential metabolic activities 6 . To reveal the molecular mechanism underpinning the coreceptor role of HS, we solved cryo-electron microscopy structures of three distinct 1:2:1:1 FGF23–FGFR–αKlotho–HS quaternary complexes featuring the ‘c’ splice isoforms of FGFR1 (FGFR1c), FGFR3 (FGFR3c) or FGFR4 as the receptor component. These structures, supported by cell-based receptor complementation and heterodimerization experiments, reveal that a single HS chain enables FGF23 and its primary FGFR within a 1:1:1 FGF23–FGFR–αKlotho ternary complex to jointly recruit a lone secondary FGFR molecule leading to asymmetric receptor dimerization and activation. However, αKlotho does not directly participate in recruiting the secondary receptor/dimerization. We also show that the asymmetric mode of receptor dimerization is applicable to paracrine FGFs that signal solely in an HS-dependent fashion. Our structural and biochemical data overturn the current symmetric FGFR dimerization paradigm and provide blueprints for rational discovery of modulators of FGF signalling 2 as therapeutics for human metabolic diseases and cancer. This study reveals how Klotho and heparan sulfate glycosaminoglycan coreceptors enable FGF hormones to induce asymmetric 1:2 FGF–FGFR dimerization mandatory for FGFR kinase activation and hence signalling.

Resistance to cancer therapy is a challenge because of innate tumor heterogeneity and constant tumor evolution. Since the pathway of resistance cannot be predicted, combination therapies may address this progression. We discovered that in addition to IGF1 and IGF2, IGFBP-3 binds bFGF, HGF, neuregulin, and PDGF AB with nanomolar affinity. Because growth factors drive resistance, simultaneous inhibition of multiple growth factor pathways may improve the efficacy of precision therapy. Growth factor sequestration by IGFBP-3-Fc enhances the activity of EGFR inhibitors by decreasing cell survival and inhibiting bFGF, HGF, and IGF1 growth factor rescue and also potentiates the activity of other cancer drugs. Inhibition of tumor growth in vivo with adjuvant IGFBP-3-Fc with erlotinib versus erlotinib after treatment cessation supports that the combination reduces cell survival. Inhibition of multiple growth factor pathways may postpone resistance and extend progression-free survival in many cancer indications.