Modulators of the structural dynamics of the retinoid X receptor to reveal receptor function

Retinoid X receptors (RXRalpha, -beta, and -gamma) occupy a central position in the nuclear receptor superfamily, because they form heterodimers with many other family members and hence are involved in the control of a variety of (patho)physiologic processes. Selective RXR ligands, referred to as rexinoids, are already used or are being developed for cancer therapy and have promise for the treatment of metabolic diseases. However, important side effects remain associated with existing rexinoids. Here we describe the rational design and functional characterization of a spectrum of RXR modulators ranging from partial to pure antagonists and demonstrate their utility as tools to probe the implication of RXRs in cell biological phenomena. One of these ligands renders RXR activity particularly sensitive to coactivator levels and has the potential to act as a cell-specific RXR modulator. A combination of crystallographic and fluorescence anisotropy studies reveals the molecular details accounting for the agonist-to-antagonist transition and provides direct experimental evidence for a correlation between the pharmacological activity of a ligand and its impact on the structural dynamics of the activation helix H12. Using RXR and its cognate ligands as a model system, our correlative analysis of 3D structures and dynamic data provides an original view on ligand actions and enables the establishment of mechanistic concepts, which will aid in the development of selective nuclear receptor modulators.     

A proinflammatory chemokine, CCL3, sensitizes the heat- and capsaicin-gated ion channel TRPV1

Pain, a critical component of host defense, is one hallmark of the inflammatory response. We therefore hypothesized that pain might be exacerbated by proinflammatory chemokines. To test this hypothesis, CCR1 was cotransfected into human embryonic kidney (HEK)293 cells together with transient receptor potential vanilloid 1 (TRPV1), a cation channel required for certain types of thermal hyperalgesia. In these cells, capsaicin and anandamide induced Ca(2+) influx mediated by TRPV1. When CCR1:TRPV1/HEK293 cells were pretreated with CCL3, the sensitivity of TRPV1, as indicated by the Ca(2+) influx, was increased approximately 3-fold. RT-PCR analysis showed that a spectrum of chemokine and cytokine receptors is expressed in rat dorsal root ganglia (DRG). Immunohistochemical staining of DRG showed that CCR1 is coexpressed with TRPV1 in >85% of small-diameter neurons. CCR1 on DRG neurons was functional, as demonstrated by CCL3-induced Ca(2+) ion influx and PKC activation. Pretreatment with CCL3 enhanced the response of DRG neurons to capsaicin or anandamide. This sensitization was inhibited by pertussis toxin, U73122, or chelerythrine chloride, inhibitors of Gi-protein, phospholipase C, and protein kinase C, respectively. Intraplantar injection of mice with CCL3 decreased their hot-plate response latency. That a proinflammatory chemokine, by interacting with its receptor on small-diameter neurons, sensitizes TRPV1 reveals a previously undescribed mechanism of receptor cross-sensitization that may contribute to hyperalgesia during inflammation.     

Definition of a mouse microglial subset that regulates neuronal development and proinflammatory responses in the brain

Expression of Itgax (encoding the CD11c surface protein) and Spp1 (encoding osteopontin; OPN) has been associated with activated microglia that can develop in healthy brains and some neuroinflammatory disorders. However, whether CD11c and OPN expression is a consequence of microglial activation or represents a portion of the genetic program expressed by a stable microglial subset is unknown. Here, we show that OPN production in the brain is confined to a small CD11c⁺ microglial subset that differentiates from CD11c⁻ precursors in perinatal life after uptake of apoptotic neurons. Our analysis suggests that coexpression of OPN and CD11c marks a microglial subset that is expressed at birth and persists into late adult life, independent of environmental activation stimuli. Analysis of the contribution of OPN to the intrinsic functions of this CD11c⁺ microglial subset indicates that OPN is required for subset stability and the execution of phagocytic and proinflammatory responses, in part through OPN-dependent engagement of the αVβ3-integrin receptor. Definition of OPN-producing CD11c⁺ microglia as a functional microglial subset provides insight into microglial differentiation in health and disease.

CD11c, also termed integrin alpha X (encoded by Itgax), is a defining marker for dendritic cells (DCs). When paired with β2-integrin, the heterodimeric receptor binds to complement iC3b and mediates phagocytosis (1). A subpopulation of central nervous system (CNS)–resident microglia that also expresses CD11c develops early in life and is a feature of microglial development in healthy brains and in murine models of neurodegenerative disease, including Alzheimer’s disease (AD) (2–4). Genes expressed by CD11c⁺ microglia include the Spp1 gene, which encodes osteopontin (OPN), a cytokine-like phosphoprotein that is a prominent feature of both protective and pathogenic immune responses in peripheral lymphoid tissues (4–8).OPN is expressed as a secreted (OPN-s) or intracellular (OPN-i) isoform that originated from a single OPN messenger RNA (mRNA) precursor (9) after activation of immune cells. Regulation of immune responses by OPN includes promotion of proinflammatory responses following ligation of its canonical receptor, the αVβ3-integrin expressed on macrophages (10–12). Production of OPN by DCs also regulates the differentiation of T helper (TH) cell subsets (8), including TH17 cells, which contribute to the development of murine experimental autoimmune encephalomyelitis (13). More recently, microglial production of OPN has been implicated in diverse CNS pathologic disorders, including multiple sclerosis (3), spinal cord injury (14), and neurodegenerative disorders, including AD and amyotrophic lateral sclerosis (ALS) (4, 15). Although CD11c⁺ microglia are a major source of OPN production by activated microglia, whether coexpression of CD11c and OPN is a feature of microglial activation or marks a subset-specific genetic program is not known. This represents a central question in understanding microglial development, since it involves a choice between genetic mechanisms that regulate subset-specific differentiation rather than markers of a transient activation phenotype.Here, we report that OPN-producing CD11c⁺ microglia represent a small (<5%) subset that differentiates from CD11c⁻OPN⁻ precursors after engulfment of apoptotic neurons (ANs) in perinatal life and represent the sole microglial producers of OPN throughout life. The CD11c⁺OPN⁺ subset displays a stable phenotype in the steady state and expresses a core genetic program that is independent of microglial activation. Analysis of the contribution of OPN to CD11c⁺ microglial function indicates that OPN regulates microglial engulfment of synaptic proteins, proliferation and the development of a proinflammatory phenotype. Definition of OPN-producing CD11c⁺ microglia as a functional subset rather than a transient activation phenotype provides insight into the contribution of microglial differentiation to brain development and function in health and disease.     

促炎细胞因子在细菌性肺炎老龄大鼠多器官损伤中的作用

目的探讨促炎细胞因子肿瘤坏死因子-α（TNF-α）、白细胞介素-1（IL-1）、IL-6在老年感染性多器官损伤中的意义。方法将大鼠随机分为青年对照组、青年模型组和老龄对照组、老龄模型组;采用气管插管法注入肺炎克雷们杆菌,由肺炎导致多器官损伤;应用光学显微镜、免疫组织化学技术,观察肺、心、小肠及肾脏组织病理改变与促炎细胞因子TNF-α、IL-1、IL-6变化情况。结果与同龄对照组比较,老龄模型组和青年模型组肺、心、肾、小肠组织TNF-α、IL-1、IL-6表达水平明显增高及脏器组织病理学改变明显（P〈0.01或P〈0.05）;而老龄模型组肺IL-1、心TNF-α、IL-6和小肠IL-1、IL-6表达水平又较青年模型组显著增高（P〈0.01或P〈0.05）,脏器损伤亦较重（P〈0.05）。结论促炎细胞因子TNF-α、IL-1、IL-6参与了老年感染性多器官损伤,并在其中发挥了重要作用。     

Pharmacological inhibition of the chemokine receptor CX3CR1 attenuates disease in a chronic-relapsing rat model for multiple sclerosis

One hallmark of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE) is infiltration of leukocytes into the CNS, where chemokines and their receptors play a major mediatory role. CX3CR1 is a chemokine receptor involved in leukocyte adhesion and migration and hence a mediator of immune defense reactions. The role of CX3CR1 in MS and EAE pathogenesis however remains to be fully assessed. Here, we demonstrate CX3CR1 mRNA expression on inflammatory cells within active plaque areas in MS brain autopsies. To test whether blocking CNS infiltration of peripheral leukocytes expressing CX3CR1 would be a suitable treatment strategy for MS, we developed a selective, high-affinity inhibitor of CX3CR1 (AZD8797). The compound is active outside the CNS and AZD8797 treatment in Dark Agouti rats with myelin oligodendrocyte glycoprotein-induced EAE resulted in reduced paralysis, CNS pathology, and incidence of relapses. The compound is effective when starting treatment before onset, as well as after the acute phase. This treatment strategy is mechanistically similar to, but more restricted than, current very late antigen-4–directed approaches that have significant side effects. We suggest that blocking CX3CR1 on leukocytes outside the CNS could be an alternative approach to treat MS.Multiple sclerosis (MS) is a chronic inflammatory, demyelinating and degenerative disease of the central nervous system (CNS). It was already discovered in the early 1900s that a similar disease could be induced in different animal species by injection of spinal cord extracts or myelin-derived proteins (1–3). This group of animal models for MS, called experimental autoimmune encephalomyelitis (EAE), has provided an experimental platform for building an extensive understanding of the pathology of MS, as well as discovering strategies for intervention of the disease. A typical feature of the pathogenesis in both MS and EAE is the infiltration of leukocytes from the blood stream into the CNS (3). Leukocyte adhesion and extravasation includes several well defined steps and various adhesion molecules, chemokines and their receptors are important mediators for this process. In line with this, the recently developed therapeutic drugs natalizumab and fingolimod, which broadly target leukocyte migration to the brain, exhibit efficacy in EAE models (4, 5), and they are now established therapies in MS (6).Natalizumab, blocking the interaction between very late antigen-4 (VLA-4) and CD106 (VCAM-1), is an effective treatment both on clinical endpoints and MRI biomarkers (7). Fingolimod, the first oral drug for relapsing remitting MS (RRMS), acts on S1P receptors preventing lymphocytes from moving out of lymphoid tissue (8). Natalizumab is only approved as a second-line monotherapy in RRMS or in patients with very active disease, because it carries increased risk of developing the often fatal progressive multifocal leukoencephalopathy (7, 9). Treatment with fingolimod is associated with side effects such as signs of immune suppression, including increased frequency of infections (8).Considering the pronounced presence of inflammatory cells in the brain of MS patients, the significant correlation between inflammation and axonal injury (10) and the efficiency of treatments that broadly block infiltration of immune cells, a similar but more restricted therapeutic approach is appealing. Chemokines are synthesized and released at sites of inflammation, where they act on specific receptors expressed by immune cells to mediate directed cell migration in synergy with adhesion molecules, such as VLA-4, from the blood stream and into the sites of inflammation. CX3CR1 is a unique member of the chemokine receptor family (11) and binds with high affinity to its ligand CX3CL1 [fractalkine (FKN)]. FKN is produced in a membrane bound form but can also be released following proteolytic cleavage, making it important for mediating both adhesion and migration of CX3CR1-expressing cells. In contrast to VLA-4, which is broadly expressed on most leukocytes except neutrophils (7, 12), the expression of CX3CR1 is restricted to subpopulations of monocytes, T lymphocytes, and natural killer (NK) cells (13–16). We have previously demonstrated intense accumulation of CX3CR1-expressing microglia/macrophages within inflammatory foci in the spinal cord of Dark Agouti (DA) rats with EAE induced by myelin oligodendrocyte glycoprotein (MOG) (17) and formed the hypothesis that CX3CR1 would be an attractive therapeutic target for treating MS.To test the hypothesis, we have developed a selective, high-affinity small-molecule inhibitor of CX3CR1 (AZD8797) (18). This molecule has the potential to be administered as an oral drug in humans. However, because of the decrease in potency to rat CX3CR1 and a modest oral bioavailability in rats (39%), we have chosen continuous s.c. dosing for the proof-of-concept studies in rats. The MOG_1-125–induced EAE model in DA rats was used, because it exhibits pathology very similar to MS with infiltration of inflammatory cells, demyelination, and axonal degeneration in the CNS, as well as a relapsing remitting disease course (19, 20). To further mimic the human treatment situation, we have not only treated rats before the onset of paralysis but also initiated treatment during ongoing disease. We present efficacy (reduced paralysis) versus exposure data, analysis of CNS pathology, and measurements of functional inhibition of CX3CR1. These data, in combination with an analysis for CX3CR1 expression within MS brain autopsy samples, clearly demonstrate the potential of CX3CR1 inhibition as an alternative and unique approach for treating MS.     

Hippo signaling regulates Drosophila intestine stem cell proliferation through multiple pathways

Intestinal stem cells (ISCs) in the Drosophila adult midgut are essential for maintaining tissue homeostasis and replenishing lost cells in response to tissue damage. Here we demonstrate that the Hippo (Hpo) signaling pathway, an evolutionarily conserved pathway implicated in organ size control and tumorigenesis, plays an essential role in regulating ISC proliferation. Loss of Hpo signaling in either midgut precursor cells or epithelial cells stimulates ISC proliferation. We provide evidence that loss of Hpo signaling in epithelial cells increases the production of cytokines of the Upd family and multiple EGFR ligands that activate JAK-STAT and EGFR signaling pathways in ISCs to stimulate their proliferation, thus revealing a unique non-cell-autonomous role of Hpo signaling in blocking ISC proliferation. Finally, we show that the Hpo pathway mediator Yorkie (Yki) is also required in precursor cells for injury-induced ISC proliferation in response to tissue-damaging reagent DSS.     

Bortezomib reduces serum dickkopf-1 and receptor activator of nuclear factor-kappaB ligand concentrations and normalises indices of bone remodelling in patients with relapsed multiple myeloma

The effect of bortezomib on bone remodelling was evaluated in 34 relapsed myeloma patients. At baseline, patients had increased serum concentrations of dickkopf-1 (DKK-1), soluble receptor activator of nuclear factor-kappaB ligand (sRANKL), sRANKL/osteoprotegerin ratio, C-telopeptide of type-I collagen (CTX) and tartrate-resistant acid phosphatase isoform-5b (TRACP-5b); bone-alkaline phosphatase and osteocalcin were reduced. Serum DKK-1 correlated with CTX and severe bone disease. Bortezomib administration significantly reduced serum DKK-1, sRANKL, CTX, and TRACP-5b after four cycles, and dramatically increased bone-alkaline phosphatase and osteocalcin, irrespective of treatment response. This is the first study showing that bortezomib reduces DKK-1 and RANKL serum levels, leading to the normalisation of bone remodelling in relapsed myeloma.     

Homocysteine-lowering therapy does not affect inflammatory markers of atherosclerosis in patients with stable coronary artery disease

OBJECTIVES: A high level of total homocysteine (tHcy) is a risk marker for cardiovascular disease (CVD), and is related to inflammation. We wanted to test the effect of homocysteine-lowering B-vitamin therapy, as used in the Western Norway B-vitamin Intervention Trial (WENBIT), on inflammatory markers associated with atherosclerosis. DESIGN: Single centre, prospective double-blind clinical interventional study, randomised in a 2 x 2 factorial design. SUBJECTS AND METHODS: Ninety patients (21 female) with suspected coronary artery disease (CAD), aged 38-80 years, were blindly randomised into one of four groups of daily oral treatment with (A) folic acid (0.8 mg)/vitamin B12 (0.4 mg)/vitamin B6 (40 mg), (B) folic acid/vitamin B12, (C) vitamin B6 alone or (D) placebo. Blood samples were collected before and after 6 months of treatment. RESULTS: Before intervention, median levels of the analytes were: tHcy 11.0 micromol L(-1), neopterin 8.1 nmol L(-1), soluble CD40 ligand (sCD40L) 3.9 ng mL(-1), interleukin (IL)-6 1.9 pg mL(-1), C-reactive protein (CRP) 1.9 mg L(-1) and low-density lipoprotein (LDL) cholesterol 3.3 mmol L(-1). tHcy was significantly associated with neopterin (r = 0.49, P < 0.001) and with IL-6 (r = 0.29, P = 0.01), but not with CRP or sCD40L. Neither treatment with folic acid/B12 nor with B6 induced significant changes in any of these inflammatory biomarkers (P >or= 0.14). In patients receiving folic acid/B12 (groups A and B), tHcy was reduced with 33% (P < 0.001). CONCLUSIONS: In patients with stable CAD, homocysteine-lowering therapy with B-vitamins does not affect levels of inflammatory markers associated with atherogenesis. Failure to reverse inflammatory processes, may partly explain the negative results in clinical secondary B-vitamin intervention trials.     

The organic solute transporter alpha-beta, Ostalpha-Ostbeta, is essential for intestinal bile acid transport and homeostasis

The apical sodium-dependent bile acid transporter (Asbt) is responsible for transport across the intestinal brush border membrane; however, the carrier(s) responsible for basolateral bile acid export into the portal circulation remains to be determined. Although the heteromeric organic solute transporter Ostalpha-Ostbeta exhibits many properties predicted for a candidate intestinal basolateral bile acid transporter, the in vivo functions of Ostalpha-Ostbeta have not been investigated. To determine the role of Ostalpha-Ostbeta in intestinal bile acid absorption, the Ostalpha gene was disrupted by homologous recombination in mice. Ostalpha(-/-) mice were physically indistinguishable from wild-type mice. In everted gut sac experiments, transileal transport of taurocholate was reduced by >80% in Ostalpha(-/-) vs. wild-type mice; the residual taurocholate transport was further reduced to near-background levels in gut sacs prepared from Ostalpha(-/-)Mrp3(-/-) mice. The bile acid pool size was significantly reduced (>65%) in Ostalpha(-/-) mice, but fecal bile acid excretion was not elevated. The decreased pool size in Ostalpha(-/-) mice resulted from reduced hepatic Cyp7a1 expression that was inversely correlated with ileal expression of fibroblast growth factor 15 (FGF15). These data indicate that Ostalpha-Ostbeta is essential for intestinal bile acid transport in mice. Unlike a block in intestinal apical bile acid uptake, genetic ablation of basolateral bile acid export disrupts the classical homeostatic control of hepatic bile acid biosynthesis.     

Tea catechins improve left ventricular dysfunction, suppress myocardial inflammation and fibrosis, and alter cytokine expression in rat autoimmune myocarditis

BACKGROUND: Myocarditis is a clinically serious disease. Tea catechins have been shown to reduce inflammation; however the effects of catechins on the development of myocarditis have not been well studied. AIMS: To clarify the role of catechins, using an experimental autoimmune myocarditis (EAM) model. METHODS AND RESULTS: Lewis rats were immunized with porcine cardiac myosin to establish EAM. Tea catechins were administered orally from day 0 to day 21 (Group A, n=12), from day 14 to day 21 (Group B, n=8), or saline (Group C, n=9) daily. Rats were killed on day 21. Echocardiograms indicated that Group A showed significantly improved cardiac function compared to Group C. Pathologically, non-treated EAM hearts showed severe myocardial cell infiltration and fibrosis; however Group A showed significantly less area. Immunohistochemistry revealed enhanced expression of NF-kappaB and ICAM-1 in non-treated EAM hearts, which was suppressed by catechin administration in Group A. mRNA levels of TNF-alpha were decreased and Th2 cytokines were markedly enhanced in Group A compared with the control group. Late catechin administration (Group B) showed limited effects on EAM. CONCLUSION: The catechins suppressed ventricular remodelling in EAM; thus catechin treatment might be a promising option for the prevention of EAM myocarditis.     

Low-molecular weight and unfractionated heparins induce a downregulation of inflammation: decreased levels of proinflammatory cytokines and nuclear factor-kappaB in LPS-stimulated human monocytes

Unfractionated heparin (UFH) and low-molecular weight heparin (LMWH) are well defined anticoagulant agents. Recent data suggest that both LMWH and UFH may also have potent anti-inflammatory properties; however, their mechanism of action responsible for the anti-inflammatory effect is not yet fully elucidated. This study was designed to assess the effect of LMWH and UFH on human monocytes production of inflammatory markers and nuclear translocation of nuclear factor (NF)-kappaB. Cultured monocytes were pretreated for 15 min with LMWH or UFH (10 microg and 1 microg/million cells) before stimulation with lipopolysaccharide (LPS) at a dose of 1 ng/million cells. Proinflammatory cytokines tumour necrosis factor (TNF)-alpha, interleukin (IL)-8, IL-6 and IL-1beta release were subsequently measured by enzyme-linked immunosorbent assay at 6 h, and nuclear translocation of the proinflammatory NF-kappaB was assessed at 2 h. Treatment with pharmacological doses of LMWH and UFH significantly attenuated LPS-induced production of TNF-alpha, IL-8, IL-6 and IL-1beta as well as NF-kappaB translocation. These results indicate equivalent and significant heparin anti-inflammatory properties at low doses on monocyte-mediated immune response. The inhibition of NF-kappaB activation certainly represents one of the mechanisms by which heparin exerts its anti-inflammatory effect. LMWH and UFH therefore appear as potential therapeutic inhibitors of inflammation.     

Ghrelin receptor regulates HFCS-induced adipose inflammation and insulin resistance

Background and Objectives:

High fructose corn syrup (HFCS) is the most commonly used sweetener in the United States. Some studies show that HFCS consumption correlates with obesity and insulin resistance, while other studies are in disagreement. Owing to conflicting and insufficient scientific evidence, the safety of HFCS consumption remains controversial.

Subjects/Methods:

We investigated the metabolic consequences of mice fed a (a) regular diet, (b) ‘Western'' high-fat diet or (c) regular diet supplemented with 8% HFCS in drinking water (to mimic soft drinks) for 10 months. Adipose tissue macrophages (ATMs) have emerged as a major pathogenic factor for obesity and insulin resistance. ATMs consist of proinflammatory F4/80⁺CD11c⁺ macrophages and anti-inflammatory F4/80⁺CD11c⁻ macrophages. In this study, we assessed the effects of HFCS on ATMs in intra-abdominal fat.

Results:

We found that HFCS feeding in mice induced more severe adipose inflammation and insulin resistance than even the higher-calorie-containing ‘Western'' high-fat diet, and these HFCS-induced deleterious effects were independent of calorie intake or body fat content. We showed that similar to ‘Western'' high-fat diet, HFCS triggered a robust increase of both proinflammatory ATMs and anti-inflammatory ATMs in intra-abdominal fat. Remarkably, however, the anti-inflammatory ATMs were much less abundant in HFCS-fed mice than in high-fat-fed mice. Furthermore, we showed that deletion of the ghrelin receptor (growth hormone secretagogue receptor, GHS-R) ameliorates HFCS-induced adipose inflammation and insulin resistance. HFCS-fed GHS-R-null mice exhibit decreased proinflammatory ATMs in intra-abdominal fat, reduced adipose inflammation and attenuated liver steatosis.

Conclusion:

Our studies demonstrate that HFCS has detrimental effects on metabolism, suggesting that dietary guidelines on HFCS consumption for Americans may need to be revisited. GHS-R deletion mitigates the effects of HFCS on adipose inflammation and insulin resistance, suggesting that GHS-R antagonists may represent a novel therapy for insulin resistance.     

Regulatory T-cell immunity and its relevance to atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall where both innate and adaptive immune responses contribute to disease initiation and progression. Recent studies from several groups suggest that subtypes of T cells, called regulatory T cells, previously shown to maintain immunological tolerance, inhibit the development and progression of atherosclerosis. Here, we review the current knowledge on the regulatory T-cell response and the major cytokines involved in its modulation in the context of atherosclerosis.     

Specific binding of melatonin to purified cell nuclei from mammary gland of swiss mice: day-night variations and effect of continuous light

Melatonin binding sites were characterized in the nuclei of mouse mammary glands. The specific binding of 2-125I-iodomelatonin by homogenates of purified mammary gland cell nuclei was found to be rapid, reversible and saturable. Binding of 125I-melatonin exhibited day-night variations with the highest binding affinity observed during the dark period and the lowest affinity at midday. However, when the animals were maintained under continuous light exposure, binding of 125I-melatonin to cell nuclei showed a higher affinity than the daytime values found in animals maintained in normal photoperiod. Scatchard analysis of the binding data revealed the existence of a significant night-day variation in the binding kinetics, compatible with the existence of two classes of binding sites: a high-affinity binding site expressed during the night, with KD = 185 +/- 36 pm and a binding capacity of 6.24 +/- 0.4 fmol/mg protein, and a low-affinity site with KD = 562 +/- 57 nm and Bmax = 7.56 +/- 0.49 pmol/mg protein during the day. Interestingly, after 2 wk of continuous exposure to light, the animals killed at an equivalent midday time showed a significant increase in binding affinity, with KD = 1.43 +/- 0.2 nm and Bmax = 24.75 +/- 3.5 fmol/mg protein. Displacement experiments show an IC50 value compatible with the affinity constants obtained in the saturation experiments. These results indicate that the low-affinity binding site may be saturated by the high levels of melatonin found in the mouse mammary gland, and sustain the hypothesis of a circadian regulation of these melatonin binding sites by the photoperiod.     

A complex between contactin-1 and the protein tyrosine phosphatase PTPRZ controls the development of oligodendrocyte precursor cells

The six members of the contactin (CNTN) family of neural cell adhesion molecules are involved in the formation and maintenance of the central nervous system (CNS) and have been linked to mental retardation and neuropsychiatric disorders such as autism. Five of the six CNTNs bind to the homologous receptor protein tyrosine phosphatases gamma (PTPRG) and zeta (PTPRZ), but the biological roles of these interactions remain unclear. We report here the cocrystal structure of the carbonic anhydrase-like domain of PTPRZ bound to tandem Ig repeats of CNTN1 and combine these structural data with binding assays to show that PTPRZ binds specifically to CNTN1 expressed at the surface of oligodendrocyte precursor cells. Furthermore, analyses of glial cell populations in wild-type and PTPRZ-deficient mice show that the binding of PTPRZ to CNTN1 expressed at the surface of oligodendrocyte precursor cells inhibits their proliferation and promotes their development into mature oligodendrocytes. Overall, these results implicate the PTPRZ/CNTN1 complex as a previously unknown modulator of oligodendrogenesis.