Protective effect of cannabidiol against cadmium hepatotoxicity in rats

The protective effect of cannabidiol, the non-psychoactive component of Cannabis sativa, against liver toxicity induced by a single dose of cadmium chloride (6.5 mg kg^?1 i.p.) was investigated in rats. Cannabidiol treatment (5 mg kg^?1/day, i.p.) was applied for five days starting three days before cadmium administration. Cannabidiol significantly reduced serum alanine aminotransferase, and suppressed hepatic lipid peroxidation, prevented the depletion of reduced glutathione and nitric oxide, and catalase activity, and attenuated the elevation of cadmium level in the liver tissue resulted from cadmium administration. Histopathological examination showed that cadmium-induced liver tissue injury was ameliorated by cannabidiol treatment. Immunohistochemical analysis revealed that cannabidiol significantly decreased the cadmium-induced expression of tumor necrosis factor-α, cyclooxygenase-2, nuclear factor-κB, caspase-3, and caspase-9, and increased the expression of endothelial nitric oxide synthase in liver tissue. It was concluded that cannabidiol may represent a potential option to protect the liver tissue from the detrimental effects of cadmium toxicity.     

Manganese pre-treatment attenuates cadmium induced hepatotoxicity in Swiss albino mice

Cadmium (Cd) is a soft, malleable bluish-white metal with low melting point, a ubiquitous heavy metal and an environmental pollutant, found in soil, water and air. The presence of Cd in the components of the environment such as air, soil and groundwater is to a large part due to human activity, and the general population is exposed mainly by contaminated drinking water or food. Manganese (Mn) is a component in many enzymes, which play an important role in counteracting oxidative stress. In vitro experiments have revealed the ability of Mn to scavenge oxygen free radicals generated in differently mediated lipid peroxidation (LPO) conditions. The aim of the present study was to investigate the in vivo preventive effect of Mn²⁺ pre-treatment on acute Cd-intoxication with regard to oxidative stress biomarker and antioxidant defense system in liver of Swiss albino mice. On exposure to Cd a significant increase in LPO levels, decrease in thiol content and induction in glutathione metabolizing enzyme were observed. Mn pre-treatment attenuated the modulation caused in the above-mentioned parameters due to acute Cd exposure in mice. In conclusion, the results from this study demonstrate that the protective effect of Mn in Cd-induced systemic toxicity in mice. Further investigations are required on the relation between Mn accumulation and resistance to oxidative stress and on the factors influencing Mn/Cd transport in rodents are needed to elucidate the molecular basis of this protective effect.     

Receptor tyrosine kinase Tie-1 overexpression in endothelial cells upregulates adhesion molecules

Tie-1 is an endothelial specific cell surface protein whose biology remains poorly understood. Using an overexpression system in vitro, we examined whether Tie-1 activity in endothelial cells in vitro would elicit a proinflammatory response. We found that when overexpressed in endothelial cells in vitro, Tie-1 is tyrosine-phosphorylated. We also showed that Tie-1 upregulates VCAM-1, E-selectin, and ICAM-1, partly through a p38-dependent mechanism. Interestingly, upregulation of VCAM-1 and E-selectin by Tie-1 is significantly higher in human aortic endothelial cells than in human umbilical vein endothelial cells. Additionally, attachment of cells of monocytic lineage to endothelial cells is also enhanced by Tie-1 expression. Collectively, our data show that Tie-1 has a proinflammatory property and may play a role in the endothelial inflammatory diseases such as atherosclerosis.     

Circulating adhesion molecules in apoE-deficient mouse strains with different atherosclerosis susceptibility

Recruitment of inflammatory cells in the arterial wall by vascular adhesion molecules plays a key role in development of atherosclerosis. Apolipoprotein E-deficient (apoE(-/-)) mice have spontaneous hyperlipidemia and develop all phases of atherosclerotic lesions. We sought to examine plasma levels of soluble vascular cell adhesion molecule-1 (sVCAM-1) and sP-selectin in two apoE(-/-) strains C57BL/6 (B6) and BALB/c with early or advanced lesions. Mice were fed chow or a Western diet containing 42% fat, 0.15% cholesterol, and 19.5% casein. On either diet, BALB/c.apoE(-/-) mice developed much smaller atherosclerotic lesions and displayed significantly lower levels of sVCAM-1 and sP-selectin than B6.apoE(-/-) mice. The Western diet significantly elevated sVCAM-1 levels in both strains and sP-selectin levels in B6.apoE(-/-) mice. BALB/c.apoE(-/-) mice exhibited 2-fold higher HDL cholesterol levels on the chow diet and 15-fold higher HDL levels on the Western diet than B6.apoE(-/-) mice, although the two strains had comparable levels of total cholesterol and triglyceride. Thus, increased atherosclerosis is accompanied by increases in circulating VCAM-1 and P-selectin levels in the two apoE(-/-) mouse strains, and the high HDL level may protect against atherosclerosis by inhibiting the expression of adhesion molecules in BALB/c.apoE(-/-) mice.     

Detecting cadmium during ultrastructural characterization of hepatotoxicity

BackgroundThe threat of cadmium (Cd), which is the cause of itai-itai disease in Japan, is still complicated and confusing, especially for digestive system, such as liver disease. One of the most keys of this problem is demonstrating that the hepatotoxicity is indeed induced by Cd. Therefore, we attempt detecting Cd at microscale during ultrastructural imaging of liver tissue.Methods12 rats were divided randomly into two experimental groups: control and Cd-treated. Treated rats were intraperitoneal injected with 1 mg/kg body weight cadmium chloride (CdCl₂) for 4 weeks (5 P.M each day for 6 days/week). At the end of the exposure period, liver tissue samples were processed into ultrathin sections for analysis of advanced analytical transmission electron microscopy and X-ray energy dispersive spectroscopy (TEM/X-EDS) investigations. Ultrastructural images and X-ray energy dispersive spectrum were acquired at microscale.ResultsCd can cause changes in the structure of the organelle, including the collapse of the membrane structure in the cell, the destruction of the internal structure of the organelle, the mitochondrial swelling, the expansion of the endoplasmic reticulum, and the appearance of inclusions. Cadmium bioaccumulation is detected in the mitochondria at microscale by TEM/X-EDS, which is the visual evidence of morphological changes of mitochondria related to Cd.ConclusionThe combination of detailed ultrastructure and microscale X-ray energy dispersive spectroscopy (X-EDS) characterization of cadmium hepatotoxicity demonstrate that cadmium indeed leads to mitochondrial damage, which is helpful for further investigation of the pathological mechanism of cadmium hepatotoxicity.     

Protective effect of zinc against cadmium hepatotoxicity depends on this bioelement intake and level of cadmium exposure: a study in a rat model

It was estimated, in a rat model of moderate and relatively high chronic human exposure to cadmium (Cd), whether enhanced zinc (Zn) consumption may prevent Cd-induced liver injury and if the possible protective effect of this bioelement depends on its intake. For this purpose, the structure and function of the liver of the rats that received Zn (30 and 60 mg/l) or/and Cd (5 and 50 mg/l) for 6 months were evaluated. The treatment with Cd led to, dependent on the exposure level, pathological changes in the liver, including enhanced apoptosis and induction of inflammatory and necrotic processes. Moreover, the serum activities of hepatic marker enzymes (alanine transaminase and aspartate transaminase) and the concentration of proinflammatory cytokine – tumor necrosis factor α were increased. The supplementation with 30 and 60 mg Zn/l (enhancing daily Zn intake by 79% and 151%, respectively) partially or totally prevented from some of the Cd-induced changes in the liver structure and function; however, it provided no protection from necrosis, and the administration of 60 mg Zn/l during the higher Cd exposure even intensified this process. At both levels of Cd treatment, the use of 30 mg Zn/l was more effective in preventing liver injury than that of 60 mg Zn/l. The hepatoprotective impact of Zn may be explained, at least partly, by its antioxidative, antiapoptotic and anti-inflammatory action, ability to stimulate regenerative processes in the liver tissue, and indirect action resulting in a decrease in the liver pool of the non-metallothionein-bound Cd²⁺ ions able to exert toxic action. The results provide strong evidence that enhanced Zn consumption may be beneficial in protection from Cd hepatotoxicity; however, its excessive intake at relatively high exposure to Cd may intensify liver injury.     

Expression of adhesion molecules during normal pregnancy

We review the available information regarding the role of adhesive molecules as potential participants in the complex events of fertilization, embryogenesis, implantation and placentation. Studies that specifically relate to the expression and modulation of adhesive molecules in fertilization, embryogenesis, and implantation have been identified in the literature and by Medline searches. Cell-cell and cell-extracellular matrix interactions play a critical role in various developmental processes and in the cascade of events that lead to implantation and to the normal development of the fetus during pregnancy. Adhesion molecules influence, directly or indirectly, numerous aspects of cell behaviour, cell migration, cell growth, cell survival, cell proliferation, angiogenesis, invasion and metastasis.     

Soluble intercellular adhesion molecules, soluble vascular cell adhesion molecules, and risk of coronary heart disease

Objective: We examined the association of circulating levels of soluble intercellular adhesion molecules (sICAM‐1) and soluble vascular cell adhesion molecules (sVCAM‐1) with coronary heart disease (CHD) risk factors and whether the adhesion molecules alone, and in combination, can serve as predictors of coronary CHD. Research Methods and Procedures: Among 18,225 men from the Health Professional Follow‐up Study who provided blood in 1994, we documented 266 incidents of non‐fatal myocardial infarction or fatal CHD during 6 years of follow‐up. The cases were matched 1:2 with non‐cases on age, smoking, and month of blood draw. We found both adhesion molecules directly associated with BMI, inflammatory biomarkers, and triglycerides and inversely associated with high‐density lipoprotein and alcohol intake (p < 0.05). After adjustment for C‐reactive protein, cholesterol‐to‐high‐density lipoprotein ratio, age, smoking, BMI, physical activity, alcohol intake, history of diabetes, parental history of CHD, aspirin use, antihypertensive drug use, and fasting status, the relative risk of CHD was 1.69 [95% confidence interval (CI), 1.14 to 2.51] for sICAM‐1 and 1.34 (95% CI, 0.91 to 1.96) for sVCAM‐1, when comparing the top quintile with the lower four quintiles. Control for other inflammatory or lipid biomarkers did not appreciably attenuate the associations. When we cross‐classified participants based on their sICAM‐1 and sVCAM‐1 levels, only the men in the top quintile of both biomarkers [relative risk = 2.39 (95% CI, 1.45 to 3.91)] had a significantly elevated risk of CHD (P interaction = 0.01, multivariate model). Discussion: sICAM‐1 and sVCAM‐1 are directly associated with obesity and other CHD risk factors. The combination of high levels of both adhesion molecules might be associated with the development of CHD, independent of other CHD risk factors.     

Expression of cell adhesion molecules in the adriamycin-induced esophageal atresia rat model

Cell adhesion molecules are well-known membrane glycoproteins widely expressed during embryonic development that play a crucial role in cell division, migration and differentiation. We investigated the cell-matrix relationship using N-CAM and pan-cadherin adhesion molecules in the adriamycin-induced esophageal atresia (EA) rat model in the hope of finding a clue to the mechanisms of this unique anomaly.Time-mated pregnant Sprague-Dawley rats were given either saline or adriamycin on days 8 and 9 of gestation. Embryos were harvested on the 18th day of gestation. Esophageal specimens obtained from adriamycin-exposed embryos with (EA+) or without esophageal atresia (EA-) and from saline-exposed embryos were immunostained with N-CAM and pan-cadherin primary antisera.The esophageal specimens from control and EA- groups revealed similar immunostaining properties: weak N-CAM and pan-cadherin immunoreactivity. In contrast, the EA+ group showed intense immunoreactivity.Our study demonstrated an increased synthesis of N-CAM and pan-cadherin in the epithelial cells of the atretic esophagus and trachea. These results suggest that embryonic cell-cell and cell-matrix interactions may play a crucial role in the development of adriamycin-induced EA.     

Gene expression profile of adhesion and extracellular matrix molecules during early stages of skeletal muscle regeneration

Skeletal muscle regeneration implies the coordination of myogenesis with the recruitment of myeloid cells and extracellular matrix (ECM) remodelling. Currently, there are no specific biomarkers to diagnose the severity and prognosis of muscle lesions. In order to investigate the gene expression profile of extracellular matrix and adhesion molecules, as premises of homo‐ or heterocellular cooperation and milestones for skeletal muscle regeneration, we performed a gene expression analysis for genes involved in cellular cooperation, migration and ECM remodelling in a mouse model of acute crush injury. The results obtained at two early time‐points post‐injury were compared to a GSE5413 data set from two other trauma models. Third day post‐injury, when inflammatory cells invaded, genes associated with cell‐matrix interactions and migration were up‐regulated. After day 5, as myoblast migration and differentiation started, genes for basement membrane constituents were found down‐regulated, whereas genes for ECM molecules, macrophage, myoblast adhesion, and migration receptors were up‐regulated. However, the profile and the induction time varied according to the experimental model, with only few genes being constantly up‐regulated. Gene up‐regulation was higher, delayed and more diverse following more severe trauma. Moreover, one of the most up‐regulated genes was periostin, suggestive for severe muscle damage and unfavourable architecture restoration.     

Expression of adhesion and activation molecules on circulating monocytes in children with Helicobacter pylori infection

Objectives: The aim of this study was to assess the cell surface expression of adhesion (CD11a, CD11b, CD11c, CD18, CD54, and CD58) and activation (CD14, HLA‐DR, and CD16) molecules on the circulating monocytes in Helicobacter pylori (H. pylori)‐infected and noninfected children with gastritis, with the goal of comparing the results with those obtained from the controls. Materials and Methods: Ninety‐four children were studied: 47 of them with H. pylori infection (of those 25 children after the failure of eradication therapy) and 26 children with gastritis where H. pylori infection was excluded, as well as 21 controls. H. pylori infection status was assessed based on [¹³C] urea breath test, rapid urease test, and histology. Analysis of the monocyte surface molecule expression was carried out by flow cytometry. Results: H. pylori‐infected children and children who experienced a failure of the eradication therapy differed significantly in the expression of adhesion and activation molecule on circulating monocytes. A decrease, both in the proportion of CD11c‐ and CD14‐bearing monocytes, and the expression of CD11c and CD14 molecules on circulating monocytes, was found in children in whom the eradication therapy failed (p < .05). Low expression of CD11b (p = .04) and CD18 (p = .02) integrins on monocytes was also observed. Additionally, the percentage of HLA‐DR‐bearing monocytes was decreased (p = .04), while the CD16 density receptor was increased (p = .02). Compared with the controls, low percentage of CD16‐positive monocytes was noted in noninfected children with gastritis (p = .01). Conclusion: H. pylori eradication therapy in children causes inhibition of inflammatory response via a reduction in CD11b, CD11c, and CD18 beta2 integrin monocyte expression.     

Co-stimulatory and adhesion molecules of dendritic cells in rheumatoid arthritis

Dendritic cells (DCs) in the rheumatoid arthritis (RA) joint mediate the immunopathological process and act as a potent antigen presenting cell. We compared the expression of co-stimulatory and adhesion molecules on DCs in RA patients versus controls with traumatic joint lesions and evalulated the correlation between the immunophenotypical presentation of DCs and the clinical status of the disease. Samples of peripheral venous blood, synovial fluid (SF) and synovial tissue (ST) were obtained from 10 patients with RA at the time of hip or knee replacement and from 9 control patients with knee arthroscopy for traumatic lesions. Clinical status was appreciated using the DAS28 score. Blood, SF and dissociated ST cell populations were separated by centrifugation and analyzed by flow cytometry. Cells phenotypes were identified using three-color flow cytometry analysis for the following receptors HLA-DR, CD80, CD83, CD86, CD11c, CD18, CD54, CD58, CD3, CD4, CD8, CD19, CD20, CD14, CD16, CD56. HLA-DR molecules, co-stimulatory receptors CD80, CD86, CD83 and adhesion molecules CD18, CD11c, CD54, CD58, were analyzed by two-color immunofluorescence microscopy on ST serial sections. In patients with active RA (DAS28>5.1) we found a highly differentiated subpopulation of DCs in the ST and SF that expressed an activated phenotype (HLA-DR, CD86+, CD80+, CD83+, CD11c+, CD54+, CD58+). No differences were found between circulating DCs from RA patients and control patients. Our data suggest an interrelationship between clinical outcome and the immunophenotypical presentation of DCs. Clinical active RA (DAS28>5.1) is associated with high incidence of activated DCs population in the ST and SF as demonstrated by expression of adhesion and co-stimulatory molecules.     

Isolation of progenitor cells from cord blood using adhesion matrices

The aim of this study was to develop optimal conditions for selective adhesion and isolation of mesenchymal progenitor cells (MPCs) from cord blood and to determine their potential for osteogenic differentiation. Mononuclear cells (MNCs) were isolated by Ficoll-Paque gradient and plated onto 48-well culture plates precoated with: human or bovine collagen type I, human collagen type IV, fibronectin or matrigel. Cultures were incubated in αMEM containing fetal calf serum. Viability of the adherent cells was determined by alamarBlue® assay after 2, 3, and 4 weeks. After 4 weeks in culture, cells were typsinized and replated. Primary cultures were analyzed by histochemistry and third passage cells by FACS. Isolated fibroblast-like cells were cultured in the presence of osteogenic factors and differentiation determined by Alizarin Red S staining, RT-PCR and electron dispersive spectroscopy (EDS). MNCs adhered to all types of matrices with the greatest adhesion rates on fibronectin. These cells were CD45⁺, CD105⁺, CD14⁺, CD49a⁺, CD49f⁺, CD44⁺ and CD34⁻. The highest incidence of progenitor cells (PC) was observed on fibronectin and polystyrene. Passages were CD45⁻, CD14⁻, CD34⁻ and weakly CD105⁺. Primary cultures expressed endothelial/macrophage RNA markers whether cultured on fibronectin or polystyrene and these markers decreased upon passage. The best osteogenic differentiation was observed in MPCs cultured in osteogenic medium containing vitamin D₃ and FGF9. These cells expressed the bone-related mRNA, collagen type I, core binding factor I (Cbfa I), osteocalcin and osteopontin. EDS of deposits produced by these cells demonstrated a calcium/phosphate ratio parallel to hydroxyapatite. It was concluded that fibronectin increased adhesion rates and isolation potential of cord blood mesenchymal progenitor cells.     

Isolation of progenitor cells from cord blood using adhesion matrices

The aim of this study was to develop optimal conditions for selective adhesion and isolation of mesenchymal progenitor cells (PCs) from cord blood and to determine their potential for osteogenic differentiation. Mononuclear cells (MNCs) were isolated by Ficoll-Paque gradient and plated onto 48-well culture plates precoated with: human or bovine collagen type I, human collagen type IV, fibronectin or matrigel. Cultures were incubated in αMEM containing fetal calf serum. Viability of the adherent cells was determined by alamarBlue® assay after 2, 3, and 4 weeks. After 4 weeks in culture, cells were typsinized and replated. Primary cultures were analyzed by histochemistry and third passage cells by FACS. Isolated fibroblast-like cells were cultured in the presence of osteogenic factors and differentiation determined by Alizarin Red S staining, RT-PCR and electron dispersive spectroscopy (EDS). MNCs adhered to all types of matrices with the greatest adhesion rates on fibronectin. These cells were CD45⁺, CD105⁺, CD14⁺, CD49a⁺, CD49f⁺, CD44⁺ and CD34⁻. The highest incidence of PCs was observed on fibronectin and polystyrene. Passages were CD45⁻, CD14⁻, CD34⁻ and weakly CD105⁺. Primary cultures expressed endothelial/macrophage RNA markers whether cultured on fibronectin or polystyrene and these markers decreased upon passage. The best osteogenic differentiation was observed in MPCs cultured in osteogenic medium containing Vit D₃ and FGF9. These cells expressed the bone-related mRNA, collagen type I, core binding factor I (Cbfa I), osteocalcin and osteopontin. EDS of deposits produced by these cells demonstrated a calcium/phosphate ratio parallel to hydroxyapatite. It was concluded that fibronectin increased adhesion rates and isolation potential of cord blood mesenchymal progenitor cells.     

Alcohol exposure alters the expression pattern of neural cell adhesion molecules during brain development

Neural cell adhesion molecules (NCAMs) play critical roles during development of the nervous system. The aim of this study is to investigate the possible effect of ethanol exposure on the pattern of expression and sialylation of NCAM isoforms during postnatal rat brain development because alterations in NCAM content and distribution have been associated with defects in cell migration, synapse formation, and memory consolidation, and deficits in these processes have been observed after in utero alcohol exposure. The expression of NCAM isoforms in the developing cerebral cortex of pups from control and alcohol-fed mothers was assessed by western blotting, ribonuclease protection assay, and immunocytochemistry. The highly sialylated form of NCAM [polysialic acid (PSA)-NCAM] is mainly expressed during the neonatal period and then is down-regulated in parallel with the appearance of NCAM 180 and NCAM 140. Ethanol exposure increases PSA-NCAM levels during the neonatal period, delays the loss of PSA-NCAM, decreases the amount of NCAM 180 and NCAM 140 isoforms, and reduces sialyltransferase activity during postnatal brain development. Neuraminidase treatment of ethanol-exposed neonatal brains leads to more intense band degradation products, suggesting a higher content of NCAM polypeptides carrying PSA in these samples. However, NCAM mRNA levels are not changed by ethanol. Immunocytochemical analysis demonstrates that ethanol triggers an increase in PSA-NCAM immunolabeling in the cytoplasm of astroglial cells, accompanied by a decrease in immunogold particles over the plasma membrane. These findings indicate that ethanol exposure during brain development alters the pattern of NCAM expression and suggest that modification of NCAM could affect neuronal-glial interactions that might contribute to the brain defects observed after in utero alcohol exposure.     

Expression and function of cell adhesion molecules during neural crest migration

Neural crest cells are highly migratory cells that give rise to many derivatives including peripheral ganglia, craniofacial structures and melanocytes. Neural crest cells migrate along defined pathways to their target sites, interacting with each other and their environment as they migrate. Cell adhesion molecules are critical during this process. In this review we discuss the expression and function of cell adhesion molecules during the process of neural crest migration, in particular cadherins, integrins, members of the immunoglobulin superfamily of cell adhesion molecules, and the proteolytic enzymes that cleave these cell adhesion molecules. The expression and function of these cell adhesion molecules and proteases are compared across neural crest emigrating from different axial levels, and across different species of vertebrates.     

Modulation of Adhesion Molecule Expression on Rat Cortical Astrocytes During Maturation

Abstract: During development of the vertebrate CNS the functional properties of astrocytes change significantly. Many of these functional changes result from modifications in the expression of cell surface adhesion molecules on astrocytes that mediate the interactions of astrocytes with other astrocytes, neurons, and growing axons. In this study we have compared the cell surface expression of HNK-1, NCAM, and laminin on rat cortical type-I-like astrocytes during maturation in vitro and in vivo. Both the proportion of immunoreactive cells and the relative levels of expression of these antigens on different aged astrocyte populations were assayed by flow cytometry. At birth, most cortical type-I astrocytes express high levels of HNK-1 and NCAM, while ∼50% of the cells express laminin. During maturation in vitro, the proportion of cortical astrocytes that expressed these surface molecules decreased over a period of 28 days, even though cell size and glial fibrillary acidic protein content increased. During maturation in vivo, a qualitatively and temporally similar decrease in antigen expression on astrocytes was observed. This reduction in the expression of specific cell surface molecules on maturing astrocytes results from maturation of a single population of astrocytes and not differential proliferation of a nonexpressing subpopulation of astrocytes, as shown by cell cycle analysis of both immunoreactive and nonimmunoreactive cell populations. These data indicate that during maturation of rat cortical type-I-like astrocytes, the expression of cell surface adhesion molecules is regulated. Furthermore, this regulation appears to be cell autonomous and not dependent on environmental factors. Such regulation of adhesion molecule expression may have profound consequences for the functional properties of astrocytes during CNS maturation.     

Tunable hydroxyapatite wettability: Effect on adhesion of biological molecules

Surface wettability modifications of biocompatible materials and wettability patterning are attractive methods for directed biological cells immobilization for tissue engineering, drug delivery, gene transfer, etc. Hydroxyapatite is known as an implantable biomimetic material and a substrate for effective adhesion of biological cells of various origins. Here we report the use of a low-energy electron irradiation to achieve tunable wettability of the hydroxyapatite in a wide range of contact angles, from 10° to 100°, with accuracy of ±3°. The incident electrons generate electron/hole pairs resulting in significant variation of the surface potential of the hydroxyapatite semiconductor and give rise to pronounced wettability modification. Tailoring the gradually varied wettability state in the hydroxyapatite nanoceramics enabled the differential binding of biological materials with different surface properties, such as bovine serum albumin (BSA) and deoxyribonucleic acid (DNA).     

Homophilic adhesion mechanism of neurofascin, a member of the L1 family of neural cell adhesion molecules

The L1 family neural cell adhesion molecules play key roles in specifying the formation and remodeling of the neural network, but their homophilic interaction that mediates adhesion is not well understood. We report two crystal structures of a dimeric form of the headpiece of neurofascin, an L1 family member. The four N-terminal Ig-like domains of neurofascin form a horseshoe shape, akin to several other immunoglobulin superfamily cell adhesion molecules such as hemolin, axonin, and Dscam. The neurofascin dimer, captured in two crystal forms with independent packing patterns, reveals a pair of horseshoes in trans-synaptic adhesion mode. The adhesion interaction is mediated mostly by the second Ig-like domain, which features an intermolecular β-sheet formed by the joining of two individual GFC β-sheets and a large but loosely packed hydrophobic cluster. Mutagenesis combined with gel filtration assays suggested that the side chain hydrogen bonds at the intermolecular β-sheet are essential for the homophilic interaction and that the residues at the hydrophobic cluster play supplementary roles. Our structures reveal a conserved homophilic adhesion mode for the L1 family and also shed light on how the pathological mutations of L1 affect its structure and function.