Lack of reelin modifies the gene expression in the small intestine of mice

Molecular Mechanisms of Reelin in the Enteric Nervous System and the Microbiota-Gut-Brain Axis: Implications for Depression and Antidepressant Therapy

Current pharmacological treatments for depression fail to produce adequate remission in a significant proportion of patients. Increasingly, other systems, such as the microbiome-gut-brain axis, are being looked at as putative novel avenues for depression treatment. Dysbiosis and dysregulation along this axis are highly comorbid with the severity of depression symptoms. The endogenous extracellular matrix protein reelin is present in all intestinal layers as well as in myenteric and submucosal ganglia, and its receptors are also present in the gut. Reelin secretion from subepithelial myofibroblasts regulates cellular migration along the crypt-villus axis in the small intestine and colon. Reelin brain expression is downregulated in mood and psychotic disorders, and reelin injections have fast antidepressant-like effects in animal models of depression. This review seeks to discuss the roles of reelin in the gastrointestinal system and propose a putative role for reelin actions in the microbiota-gut-brain axis in the pathogenesis and treatment of depression, primarily reflecting on alterations in gut epithelial cell renewal and in the clustering of serotonin transporters.

The Inflammation-Induced Dysregulation of Reelin Homeostasis Hypothesis of Alzheimer's Disease

Alzheimer's disease (AD) accounts for most dementia cases, but we lack a complete understanding of the mechanisms responsible for the core pathology associated with the disease (e.g., amyloid plaque and neurofibrillary tangles). Inflammation has been identified as a key contributor of AD pathology, with recent evidence pointing towards Reelin dysregulation as being associated with inflammation. Here we describe Reelin signaling and outline existing research involving Reelin signaling in AD and inflammation. Research is described pertaining to the inflammatory and immunological functions of Reelin before we propose a mechanism through which inflammation renders Reelin susceptible to dysregulation resulting in the induction and exacerbation of AD pathology. Based on this hypothesis, it is predicted that disorders of both inflammation (including peripheral inflammation and neuroinflammation) and Reelin dysregulation (including disorders associated with upregulated Reelin expression and disorders of Reelin downregulation) have elevated risk of developing AD. We conclude with a description of AD risk in various disorders involving Reelin dysregulation and inflammation.

Intravenous Reelin Treatment Rescues Atrophy of Spleen White Pulp and Correlates to Rescue of Forced Swim Test Immobility and Neurochemical Alterations Induced by Chronic Stress

Reelin, an extracellular matrix protein with putative antidepressant-like properties, becomes dysregulated by chronic stress. Improvement in cognitive dysfunction and depression-like behavior induced by chronic stress has been reported with both intrahippocampal and intravenous Reelin treatment but the mechanisms responsible are not clear. To determine if treatment with Reelin modifies chronic stress-induced dysfunction in immune organs and whether this relates to behavioral and/or neurochemical outcomes, spleens were collected from both male (n = 62) and female (n = 53) rats treated with daily corticosterone injections for three weeks that received Reelin or vehicle. Reelin was intravenously administered once on the final day of chronic stress, or repeatedly, with weekly treatments throughout chronic stress. Behavior was assessed during the forced swim test and the object-in-place test. Chronic corticosterone caused significant atrophy of the spleen white pulp, but treatment with a single shot of Reelin restored white pulp in both males and females. Repeated Reelin injections also resolved atrophy in females. Correlations were observed between recovery of white pulp atrophy and recovery of behavioral deficits and expression of both Reelin and glutamate receptor 1 in the hippocampus, supporting a role of the peripheral immune system in the recovery of chronic stress-induced behaviors following treatment with Reelin. Our data adds to research indicating Reelin could be a valuable therapeutic target for chronic stress-related disorders including major depression.

Nonneuronal roles for the reelin signaling pathway

The reelin signaling pathway has been established as an important regulator of cell migration during development of the central nervous system, and disruptions in reelin signaling alter the positioning of many types of neurons. Reelin is a large extracellular matrix glycoprotein and governs cell migration through activation of multiple intracellular signaling events by means of the receptors ApoE receptor 2 (ApoER2) and very low density lipoprotein receptor (VLDLR), and the intracellular adaptor protein Disabled-1 (Dab1). Earlier studies reported expression of reelin in nonneuronal tissues, but the functions of this signaling pathway outside of the nervous system have not been studied until recently. A large body of evidence now suggests that reelin functions during development and disease of multiple nonneuronal tissues. This review addresses recent advances in the field of nonneuronal reelin signaling. Developmental Dynamics 246:217-226, 2017. © 2016 Wiley Periodicals, Inc.

Reelin-Dab1 signaling system in human colorectal cancer

Reelin is an extracellular matrix protein that plays a critical role in neuronal migration. Here we show that the mucosa of human colon expresses reelin, its receptors ApoER2 and VLDLR, and its effector protein Dab1. Immunohistochemical analyses reveal that reelin expression is restricted to pericryptal myofibroblasts; Dab1 is detected at myofibroblasts, the apical domain of surface epithelial and crypt cells, and a strong linear staining is observed at the basement membrane; VLDLR and ApoER2 are in the cytoplasm of surface epithelium and myofibroblasts, and VLDLR is also detected in the cytoplasm of the crypt cells. Human colorectal cancer downregulates reelin without change in vimentin or N-cadherin mRNA levels. Decreased Reelin mRNA expression is accompanied by decreased HIC1 mRNA levels, increased mRNA levels of ApoER2 and DNMT1, increased reelin hypermethylation and no change in either Cask or TGF-β1 mRNAs, suggesting that reelin repression results from a DNMT1-mediated hypermethylation of the reelin gene promoter. Decreased HIC1 expression may repress reelin transcription via increasing ApoER2 transcription. We conclude that the mucosa of human colon expresses the reelin-Dab1 signaling system and that reelin is repressed in colorectal cancer before epithelial-mesenchymal transition has occurred. The significant down-regulation of reelin expression makes this gene a promising biomarker for colorectal cancers. © 2016 Wiley Periodicals, Inc.

RAS signalling through PI3-Kinase controls cell migration via modulation of Reelin expression

RAS signalling through phosphoinositide 3-kinase (PI3-Kinase) has been shown to have an essential role in tumour initiation and maintenance. RAS also regulates cell motility and tumour invasiveness, but the role of direct RAS binding to PI3-Kinase in this remains uncertain. Here, we provide evidence that disruption of RAS interaction with PI3-Kinase p110α decreases cell motility and prevents activation of Rac GTPase. Analysis of gene expression in cells lacking RAS interaction with p110α reveals increased levels of the extracellular matrix glycoprotein Reelin and activation of its downstream pathway resulting in upregulation of E-cadherin expression. Induction of the Reelin/E-cadherin axis is also observed in Kras mutant lung tumours that are regressing due to blockade of RAS interaction with PI3-Kinase. Furthermore, loss of Reelin correlates with decreased survival of lung and breast cancer patients. Reelin thus plays a role in restraining RAS and PI3-kinase promotion of cell motility and potentially tumour metastasis.

Dab1 and reelin participate in a common signal pathway that controls intestinal crypt/villus unit dynamics

BACKGROUND INFORMATION

The myofibroblasts placed underneath the epithelium of the rodent small intestine express reelin, and the reelin absence modifies both the morphology and the cell renewal processes of the crypt-villus unit. In the developing central nervous system, the reelin effects are mediated by the disabled-1 (Dab1) protein. The present work explores whether Dab1 mediates the reelin control of the crypt-villus unit dynamics by examining in the mouse small intestine the consequences of the absence of (i) Dab1 (scrambler mutation) on crypt-villus unit cell renewal processes and morphology and (ii) reelin (reeler mutation) on the intestinal expression of Dab1.

RESULTS

The effects of the scrambler mutation on the crypt-villus unit renewal processes are remarkably similar to those caused by the lack of reelin. Thus, both mutations significantly reduce epithelial cell proliferation, migration and apoptosis, and the number of Paneth cells; affect the morphology of the villus, and expand the intercellular space of the adherens junctions and desmosomes. The Western blot assays reveal that the Dab1 isoform present in the enterocytes has a molecular weight of ∼63 kDa and that in the brain of ∼82 kDa. They also reveal that the absence of reelin increases Dab1 abundance in both brain and enterocytes.

CONCLUSIONS

All together, the current findings link reelin with Dab1 and suggest that Dab1 functions downstream of reelin action on the homeostasis of the crypt-villus unit.

Reelin is involved in the crypt-villus unit homeostasis

Intestinal myofibroblasts secrete substances that control organogenesis and wound repair of the intestine. The myofibroblasts of the rat small intestine express reelin and the present work explores whether reelin regulates crypt-villus unit homeostasis using normal mice and mice with the reelin gene disrupted (reeler). The results reveal that mouse small intestine expresses reelin, its receptors apolipoprotein E receptor 2 (ApoER2) and very low-density lipoprotein receptor (VldlR) and the reelin effector protein Disabled-1 (Dab1) and that reelin expression is restricted to myofibroblasts. The absence of reelin significantly reduces epithelial cell proliferation, migration, and apoptosis and the number of Paneth cells. These effects are observed during the suckling, weaning, and adult periods. The number of Goblet cells is increased in the 2-month-old reeler mice. The absence of reelin also expands the extracellular space of the adherens junctions and desmosomes without significantly affecting either the tight-junction structure or the epithelial paracellular permeability. In conclusion, this is the first in vivo work showing that the absence of reelin alters intestinal epithelium homeostasis.