Genetic deletion of ghrelin does not decrease food intake but influences metabolic fuel preference

Ghrelin is a recently identified growth hormone (GH) secretogogue whose administration not only induces GH release but also stimulates food intake, increases adiposity, and reduces fat utilization in mice. The effect on food intake appears to be independent of GH release and instead due to direct activation of orexigenic neurons in the arcuate nucleus of the hypothalamus. The effects of ghrelin administration on food intake have led to the suggestion that inhibitors of endogenous ghrelin could be useful in curbing appetite and combating obesity. To further study the role of endogenous ghrelin in appetite and body weight regulation, we generated ghrelin-deficient (ghrl(-/-)) mice, in which the ghrelin gene was precisely replaced with a lacZ reporter gene. ghrl(-/-) mice were viable and exhibited normal growth rates as well as normal spontaneous food intake patterns, normal basal levels of hypothalamic orexigenic and anorexigenic neuropeptides, and no impairment of reflexive hyperphagia after fasting. These results indicate that endogenous ghrelin is not an essential regulator of food intake and has, at most, a redundant role in the regulation of appetite. However, analyses of ghrl(-/-) mice demonstrate that endogenous ghrelin plays a prominent role in determining the type of metabolic substrate (i.e., fat vs. carbohydrate) that is used for maintenance of energy balance, particularly under conditions of high fat intake.     

Effects of gene delivery on collateral development in chronic hypoperfusion: diverse effects of angiopoietin-1 versus vascular endothelial growth factor

OBJECTIVES: The aim of this research was to test the effects of vascular endothelial growth factor (VEGF)/angiopoietin-1 (Ang-1) on adult hypoperfused tissues. BACKGROUND: Angiopoietin-1 and VEGF act separately and synergistically in vascular development during embryogenesis. However, little is known regarding their relative roles in collateral development after chronic arterial obstruction and tissue ischemia in the adult. METHODS: Central and caudal ear arteries of 32 rabbits were ligated to induce ischemia. At two months, when flow was about 65% of pre-ligation values, we injected intradermally 10(9) plaque-forming unit adenovirus with the following transgenes: Ang-1, VEGF, or a combination of both. Ear perfusion was followed up for four weeks, and vessel leakage was assessed by Evens Blue test. RESULTS: Before injection, flow was 65% of baseline, and endogenous VEGF levels in ischemic tissue were increased. Adenovirus-encoding VEGF gene (Ad.VEGF) at one week caused a visible inflammatory response associated with a 24% flow increase (p = 0.018). Adenovirus-encoding Ang-1 gene (Ad.Ang-1) increased flow 22% (p = 0.004) with no visible inflammation; Ad.VEGF caused three times as much vessel leakage as Ad.Ang-1 (142.5 +/- 38 vs. 49.5 +/- 9.8 ng Evens Blue/mg tissue; p < 0.001). However, at four weeks, compared with baseline, VEGF decreased flow 18% (p = 0.004), whereas Ang-1 increased tissue perfusion 26% (p < 0.001). This effect was abolished when Ad.Ang-1 was injected with soluble VEGF receptor [Ad.Flt(1-3)-Fc], which blocks VEGF-dependent signaling. Exogenous Ang-1 did not increase perfusion in a normally perfused ear, in which endogenous VEGF is not expressed. CONCLUSIONS: Exogenous Ang-1 enhances perfusion in hypoperfused tissues only in the presence of increased levels of endogenous VEGF. Overexpression of VEGF, however, after causing an inflammatory response, does not improve collateral blood flow.     

Efficacy and safety of rilonacept (interleukin-1 Trap) in patients with cryopyrin-associated periodic syndromes: results from two sequential placebo-controlled studies

OBJECTIVE: To assess the efficacy and safety of rilonacept (Interleukin-1 [IL-1] Trap), a long-acting and potent inhibitor of IL-1, in patients with cryopyrin-associated periodic syndromes (CAPS), including familial cold autoinflammatory syndrome (FCAS) and Muckle-Wells syndrome (MWS). METHODS: Forty-seven adult patients with CAPS, as defined by mutations in the causative NLRP3 (CIAS1) gene and pathognomonic symptoms, were enrolled in 2 consecutive phase III studies. Study 1 involved a 6-week randomized double-blind comparison of weekly subcutaneous injections of rilonacept (160 mg) versus placebo. Study 2 consisted of 9 weeks of single-blind treatment with rilonacept (part A), followed by a 9-week, randomized, double-blind, placebo-controlled withdrawal procedure (part B). Primary efficacy was evaluated using a validated composite key symptom score. RESULTS: Forty-four patients completed both studies. In study 1, rilonacept therapy reduced the group mean composite symptom score by 84%, compared with 13% with placebo therapy (primary end point; P < 0.0001 versus placebo). Rilonacept also significantly improved all other efficacy end points in study 1 (numbers of multisymptom and single-symptom disease flare days, single-symptom scores, physician's and patient's global assessments of disease activity, limitations in daily activities, and C-reactive protein and serum amyloid A [SAA] levels). In study 2 part B, rilonacept was superior to placebo for maintaining the improvements seen with rilonacept therapy, as shown by all efficacy parameters (primary end point; P < 0.0001 versus placebo). Rilonacept was generally well tolerated; the most common adverse events were injection site reactions. CONCLUSION: Treatment with weekly rilonacept provided marked and lasting improvement in the clinical signs and symptoms of CAPS, and normalized the levels of SAA from those associated with risk of developing amyloidosis. Rilonacept exhibited a generally favorable safety and tolerability profile.     

Human thrombopoietin knockin mice efficiently support human hematopoiesis in vivo

Hematopoietic stem cells (HSCs) both self-renew and give rise to all blood cells for the lifetime of an individual. Xenogeneic mouse models are broadly used to study human hematopoietic stem and progenitor cell biology in vivo. However, maintenance, differentiation, and function of human hematopoietic cells are suboptimal in these hosts. Thrombopoietin (TPO) has been demonstrated as a crucial cytokine supporting maintenance and self-renewal of HSCs. We generated RAG2(-/-)γ(c)(-/-) mice in which we replaced the gene encoding mouse TPO by its human homolog. Homozygous humanization of TPO led to increased levels of human engraftment in the bone marrow of the hosts, and multilineage differentiation of hematopoietic cells was improved, with an increased ratio of myelomonocytic verus lymphoid lineages. Moreover, maintenance of human stem and progenitor cells was improved, as demonstrated by serial transplantation. Therefore, RAG2(-/-)γ(c)(-/-) TPO-humanized mice represent a useful model to study human hematopoiesis in vivo.     

Identification and characterisation of chicken cDNAs encoding the endothelial cell-specific receptor tyrosine kinase Tie2 and its ligands, the angiopoietins

The angiopoietins represent a recently discovered family of angiogenic factors that recognise and specifically bind to the endothelial cell-specific Tie2 receptor tyrosine kinase. The specific biological functions of the angiopoietins have not yet been elucidated, although transgenic technology has shown the critical roles that these proteins have in vascularisation. The chicken vasculature, and more particularly the chorioallantoic membrane, is an important tool in the study of angiogenesis and has been previously used to study the functions of angiogenic factors such as vascular endothelial growth factor. We have undertaken the identification of the chicken orthologs of the angiopoietins and the Tie2 receptor. cDNA clones that encompass the full coding sequence of chicken Tie2 show features typical of this family of receptor tyrosine kinases. Chicken angiopoietin-1 and angiopoietin-2 show a high degree of homology to their human counterparts, 91% and 87% respectively, a reflection of the critical role of this signalling pathway. This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinase domain of the muscle-specific receptor tyrosine kinase (MuSK) is sufficient for phosphorylation but not clustering of acetylcholine receptors: Required role for the MuSK ectodomain?

Formation of the neuromuscular junction (NMJ) depends upon a nerve-derived protein, agrin, acting by means of a muscle-specific receptor tyrosine kinase, MuSK, as well as a required accessory receptor protein known as MASC. We report that MuSK does not merely play a structural role by demonstrating that MuSK kinase activity is required for inducing acetylcholine receptor (AChR) clustering. We also show that MuSK is necessary, and that MuSK kinase domain activation is sufficient, to mediate a key early event in NMJ formation—phosphorylation of the AChR. However, MuSK kinase domain activation and the resulting AChR phosphorylation are not sufficient for AChR clustering; thus we show that the MuSK ectodomain is also required. These results indicate that AChR phosphorylation is not the sole trigger of the clustering process. Moreover, our results suggest that, unlike the ectodomain of all other receptor tyrosine kinases, the MuSK ectodomain plays a required role in addition to simply mediating ligand binding and receptor dimerization, perhaps by helping to recruit NMJ components to a MuSK-based scaffold.     

Stromal cells expressing ephrin-B2 promote the growth and sprouting of ephrin-B2(+) endothelial cells

Ephrin-B2 is a transmembrane ligand that is specifically expressed on arterial endothelial cells (ECs) and surrounding cells and interacts with multiple EphB class receptors. Conversely, EphB4, a specific receptor for ephrin-B2, is expressed on venous ECs, and both ephrin-B2 and EphB4 play essential roles in vascular development. The bidirectional signals between EphB4 and ephrin-B2 are thought to be specific for the interaction between arteries and veins and to regulate cell mixing and the making of particular boundaries. However, the molecular mechanism during vasculogenesis and angiogenesis remains unclear. Manipulative functional studies were performed on these proteins in an endothelial cell system. Using in vitro stromal cells (OP9 cells) and a paraaortic splanchnopleura (P-Sp) coculture system, these studies found that the stromal cells expressing ephrin-B2 promoted vascular network formation and ephrin-B2(+) EC proliferation and that they also induced the recruitment and proliferation of alpha-smooth muscle actin (alpha-SMA)-positive cells. Stromal cells expressing EphB4 inhibited vascular network formation, ephrin-B2(+) EC proliferation, and alpha-SMA(+) cell recruitment and proliferation. Thus, these data suggest that ephrin-B2 and EphB4 mediate reciprocal interactions between arterial and venous ECs and surrounding cells to form each characteristic vessel. (Blood. 2001;98:1028-1037)     

Interleukin-22 but not interleukin-17 provides protection to hepatocytes during acute liver inflammation

The cytokine interleukin-22 (IL-22) is primarily expressed by T helper 17 (Th17) CD4(+) T cells and is highly upregulated during chronic inflammatory diseases. IL-22 receptor expression is absent on immune cells, but is instead restricted to the tissues, providing signaling directionality from the immune system to the tissues. However, the role of IL-22 in inflammatory responses has been confounded by data suggesting both pro- and anti-inflammatory functions. Herein, we provide evidence that during inflammation, IL-22 played a protective role in preventing tissue injury. Hepatocytes from mice deficient in IL-22 were highly sensitive to the detrimental immune response associated with hepatitis. Additionally, IL-22-expressing Th17 cells provided protection during hepatitis in IL-22-deficient mice. On the other hand, interleukin-17 (IL-17), which is coexpressed with IL-22 and can induce similar cellular responses, had no observable role in liver inflammation. Our data suggest that IL-22 serves as a protective molecule to counteract the destructive nature of the immune response to limit tissue damage.     

B cell receptors in TCL1 transgenic mice resemble those of aggressive, treatment-resistant human chronic lymphocytic leukemia

B cell chronic lymphocytic leukemia (B-CLL) is a clonal overgrowth of CD5(+) B lymphocytes. In this disease, the B cell antigen receptor (BCR) is intimately linked to disease severity, because patients with BCRs, comprised of unmutated V(H) genes, follow a much more aggressive course. This and related observations suggest that B-CLL derives from a B cell subset comprised of restricted BCR structural diversity and that antigen-selection and drive are major factors promoting the disease. Nevertheless, the initiating event(s) that lead to the development of B-CLL are still unclear, in part because of the lack of an animal model that spontaneously evolves the molecular abnormalities that occur in the human disease. Because overexpression of the TCL1 gene in murine B cells leads to a CD5(+) B cell lymphoproliferative disorder with many of the features of human B-CLL, we studied leukemias emerging in these mice to examine the extent to which their BCRs resemble those in B-CLL. Our data indicate that the immunoglobulin heavy and light chain rearrangements in TCL1 mice display minimal levels of somatic mutations and exhibit several molecular features found in the human disease. Like human B-CLL, TCL1 leukemic rearrangements from different mice can be very similar structurally and closely resemble autoantibodies and antibodies reactive with microbial antigens. Antigen-binding analyses confirm that selected TCL1 clones react with glycerophospholipid, lipoprotein, and polysaccharides that can be autoantigens and be expressed by microbes. This (auto)antigen-driven mouse model reliably captures the BCR characteristics of aggressive, treatment-resistant human B-CLL.