The cell adhesion molecule L1 regulates the expression of FGF21 and enhances neurite outgrowth

doi:10.1016/j.brainres.2013.07.043

Brain Research

Volume 1530, 12 September 2013, Pages 13-21

https://doi.org/10.1016/j.brainres.2013.07.043 Get rights and content

Highlights

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L1 promotes the expression and secretion of FGF21.
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Activation of L1 promotes neurite outgrowth, expression and secretion of FGF21 in L1wt mice, but not L1ko mice.
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FGF21 promotes the neurite outgrowth of neurons isolated from L1wt mice and L1ko mice.
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Both FGF21 shRNA and inhibitor of FGF receptor block the neurite outgrowth induced by L1 antibody.
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FGF21/FGFR signaling is involved in the L1 enhanced neurite outgrowth.

Abstract

L1 plays a role in neural development. However, it remains unclear how L1 plays this role. In the present study, we have shown extensive outgrowth of long neurites in cerebellar neurons after treatment with either L1 or L1 antibody. Notably, the mRNA level of FGF21 was significantly increased in both L1 and L1 antibody treated neurons compared to control group. Consistently, the neurite outgrowth promoted by L1 was strongly inhibited by siRNA against FGF21 gene or a treatment of cells with FGFR inhibitor. These results demonstrate that FGF21/FGFR signaling promotes the neurite outgrowth in a L1-dependent manner.

Introduction

Neurites outgrowth is the fundamental basis of neural communication. Many neurodegenerative diseases are defined by the destruction of neurites (Noorbakhsh et al., 2009). It is known that appropriate neurite outgrowth and neuronal differentiation in a timely and ordered manner are decisive in developing therapies to promote axon regeneration after nerve injury in neurodegenerative diseases. Thus, there is a need for identifying molecules that affect the differentiation of neurons and neurite outgrowth to represent a promising strategy for neural regeneration. The neural cell adhesion molecule L1 is a member of the immunoglobulin superfamily predominantly expressed by postmitotic neurons in the central nervous system (CNS) (Wright et al., 2007, Rathjen and Schachner, 1984). During CNS development, L1 is targeted to the surface of developing axons and growth cones, and mediates outgrowth, adhesion, fasciculation and guidance of axons as well as neuronal migration and survival (Noorbakhsh et al., 2009, Wright et al., 2007, Rathjen and Schachner, 1984, Hortsch, 2003). Various human genetic disorders with prominent nervous system defects are caused by mutations in L1 at human chromosomal locus Xq28 (Kenwrick et al., 2000). Recently, using a murine embryonic stem cell line that constitutively expressed L1 at all stages of neural differentiation, we have shown L1 promotes neurogenesis in vitro (data not published). However, it remains unknown how L1 regulates neurite outgrowth.

Fibroblast growth factor (FGF) 21 is a FGF family member produced by liver and other tissues such as white adipose tissue (WAT), skeletal muscle, and pancreatic β cells (Kharitonenkov et al., 2005, Itoh, 2010). Although FGF21 possesses a canonical ‘FGF-like’ domain and shares significant sequence homology with the other FGFs (Kharitonenkov et al., 2005, Itoh, 2010), it is unable to act on fibroblasts, and FGF21 does not promote growth in vivo. Indeed, FGF21 transgenic mice or delivery of pharmacological doses of FGF21 to rodents and primates had no effect on tissue growth (Kharitonenkov et al., 2005, Itoh, 2010, Badman et al., 2009, Wu et al., 2010). Hence, FGF21 is considered to be a metabolic hormone rather than a traditional growth factor (Kharitonenkov et al., 2005, Itoh, 2010, Wu et al., 2010). Various studies on FGF21 suggested that FGF21 regulates energy balance and improves glucose homeostasis (Kharitonenkov et al., 2005, Adams et al., 2012). The important metabolic effects of FGF21 include increase of glucose uptake in adipocytes, reduction of glucose and triglyceride levels in obese mice (Kharitonenkov and Shanafelt, 2008), increase of energetic waste and induction of weight loss (Kharitonenkov et al., 2005, Badman et al., 2009), promotion of fatty acid oxidation and increment on ketone bodies formation (Badman et al., 2009, Kharitonenkov and Shanafelt, 2008, Coskun et al., 2008, Badman et al., 2007). Sarruf et al. showed the central FGF21 action in the brain for the first time (Sarruf et al., 2010). Accumulated evidence indicates that the CNS changes levels of key hormones and nutrients in adaptive adjustment to insulin sensitivity in the circulation (Schwartz and Porte, 2005). In this study, we have investigated the role of FGF21 in L1 regulated neurite outgrowth by comparatively analyzing the differential expression of FGF21 between L1 wild type (wt) mice and knockout (ko) mice, which may be important to neurite outgrowth. We demonstrate that L1 can promote the expression and secretion of FGF21, thereby enhancing neurite outgrowth through the activation of FGF21/FGFR signaling.

Section snippets

Activated L1 promotes neurite outgrowth

L1 is predominantly expressed by postmitotic neurons of the CNS (Rathjen and Schachner, 1984, Maness and Schachner, 2006). By activating diverse signal transduction, L1 plays key roles during development and regeneration (Kiryushko et al., 2004). To further support this notion, we measured the neurite length to analyze the change of cell morphology with different concentrations of L1 (Supplementary Fig. 1A). Fc treatment was used as a control. The length of the longest neurite (Supplementary

Discussion

In the present study, we have shown that levels of both FGF21 mRNA and protein are significantly increased in neurons treated by either L1 or L1 antibody. The neurite outgrowth promoted by L1 is strongly inhibited by siRNA against FGF21 gene or the treatment with FGFR inhibitor. These results demonstrate that FGF21/FGFR signaling is involved in the L1 enhanced neurite outgrowth.

Several studies have documented that during CNS development, L1 is involved in developing axons and growth cones and

Antibodies and reagents

Anti-β-actin mouse IgG, anti-FGF21 rabbit IgG, goat anti-rabbit IgG-horseradish peroxidase and goat anti-mouse IgG-horseradish peroxidase were purchased from Santa Cruz Biotechnology. Anti-β-tubulin III antibody was purchased from Covance Inc. The monoclonal anti-mouse L1 antibody 557 and L1 molecule was produced and purified as previously described (Appel et al., 1995). FITC-conjugated rat anti-mouse IgM monoclonal antibodies were purchased from BD Biosciences. FGFR Inhibitor SU5402 was

Authors Contributions

XHH and JLH performed majority of the experiments. XHH and ZCX wrote the manuscript. YL performed some experiments. ZZYY, HMZ, KLM and LZ provided technical support and help. MS, ZCX and YLL participated actively in discussion of the project and editorial work of the manuscript.

Acknowledgments

This work was supported by grants to Y.L. Li from National Natural Science Foundation of China (31070728) and Liaoning Province education bureau (L2010103); and to Z.C. Xiao from Talent Program of Yunnan Province, China, and The Professorial Fellowship of Monash University.

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¹: These authors contributed equally to this work.

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Research ReportThe cell adhesion molecule L1 regulates the expression of FGF21 and enhances neurite outgrowth

Highlights

Abstract

Introduction

Section snippets

Activated L1 promotes neurite outgrowth

Discussion

Antibodies and reagents

Authors Contributions

Acknowledgments

Cell Metab.

J. Biol. Chem.

Cytokine Growth Factor Rev.

Trends Neurosci.

J. Biol. Chem.

Neuron

J. Biol. Chem.

Fundamentals of FGF19 & FGF21 action in vitro and in vivo

PLoS One

Several extracellular domains of the neural cell adhesion molecule L1 are involved in neurite outgrowth and cell body adhesion

J. Neurosci.

Identification of the border between fibronectin type III homologous repeats 2 and 3 of the neural cell adhesion molecule L1 as a neurite outgrowth promoting and signal transducing domain

J. Neurobiol.

Fibroblast growth factor 21-deficient mice demonstrate impaired adaptation to ketosis

Endocrinology

Adeno-associated virus-mediated L1 expression promotes functional recovery after spinal cord injury

Brain

Fibroblast growth factor 21 corrects obesity in mice

Endocrinology

Research resource: comprehensive expression atlas of the fibroblast growth factor system in adult mouse

Mol. Endocrinol.

Molecular insights into the klotho-dependent, endocrine mode of action of fibroblast growth factor 19 subfamily members

Mol. Cell. Biol.

Neurofilament protein synthesis and phosphorylation

J. Neurocytol.

Drosophila Echinoid is an antagonist of Egfr signalling, but is not a member of the L1-type family of cell adhesion molecules

Development

Research Report
The cell adhesion molecule L1 regulates the expression of FGF21 and enhances neurite outgrowth