Reelin expression is upregulated following ocular tissue injury

Purpose Reelin is important in the guidance of neuronal stem cells in the central nervous system during normal development. We wished to determine whether reelin is expressed in the retina and cornea after injury. Methods Mice underwent laceration of their retina as well as corneal epithelial debridement. The mice were sacrificed at 3 days, and eyes were fixed and stained for reelin expression and reelin messenger ribonucleic acid (mRNA). Results In normal eyes, reelin was expressed only at very low levels in the ganglion cell layer of the retina and the endothelial cell layer of the cornea. In injured eyes, there was marked expression in reelin immunoreactivity in the retina and cornea. Reelin gene expression was seen in the retina and cornea. Conclusions Reelin is expressed during normal retinogenesis. This study shows that reelin is also upregulated following injury to the retina and cornea. The expression of reelin following injury suggests that reelin may play an important role in regulating stem cell trafficking in neuronal and nonneuronal tissues following injury similar to its role in normal organogenesis. For consideration of publication in Graefe’s Archive for Clinical and Experimental Ophthalmology.     

结肠癌细胞表达的细胞外基质Reelin在淋巴结转移中的作用

探讨一种由结肠癌细胞表达的细胞外基质Reelin在淋巴结转移中的作用.构建了99例结肠癌及其癌旁组织的组织芯片进行免疫组织化学染色,探测其表达强度并结合临床资料进行分析.结果显示,Duke's A,B,C,D分期与结肠癌细胞Reelin表达强度无关,结肠癌细胞Reelin表达强度与其淋巴结转移潜能相关,结肠癌细胞Reelin表达强度每增加一个单位,其转移进入淋巴结的能力将增加3.523倍.结肠癌细胞表达Reelin与其淋巴结转移密切相关,Reelin可以作为结肠癌淋巴结转移预测的一个新指标.     

A key requirement for synaptic Reelin signaling in ketamine-mediated behavioral and synaptic action

Ketamine is a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist that produces rapid antidepressant action in some patients with treatment-resistant depression. However, recent data suggest that ∼50% of patients with treatment-resistant depression do not respond to ketamine. The factors that contribute to the nonresponsiveness to ketamine’s antidepressant action remain unclear. Recent studies have reported a role for secreted glycoprotein Reelin in regulating pre- and postsynaptic function, which suggests that Reelin may be involved in ketamine’s antidepressant action, although the premise has not been tested. Here, we investigated whether the disruption of Reelin-mediated synaptic signaling alters ketamine-triggered synaptic plasticity and behavioral effects. To this end, we used mouse models with genetic deletion of Reelin or apolipoprotein E receptor 2 (Apoer2), as well as pharmacological inhibition of their downstream effectors, Src family kinases (SFKs) or phosphoinositide 3-kinase. We found that disruption of Reelin, Apoer2, or SFKs blocks ketamine-driven behavioral changes and synaptic plasticity in the hippocampal CA1 region. Although ketamine administration did not affect tyrosine phosphorylation of DAB1, an adaptor protein linked to downstream signaling of Reelin, disruption of Apoer2 or SFKs impaired baseline NMDA receptor–mediated neurotransmission. These results suggest that maintenance of baseline NMDA receptor function by Reelin signaling may be a key permissive factor required for ketamine’s antidepressant effects. Taken together, our results suggest that impairments in Reelin-Apoer2-SFK pathway components may in part underlie nonresponsiveness to ketamine’s antidepressant action.

Major depressive disorder (MDD) is a serious disorder that affects ∼20.6% of the US population and is a leading cause of suicide (1). One crucial problem in treating patients with MDD is an incomplete response rate to medications, where a large fraction of patients do not show a response to primary antidepressant medications (2, 3). Recent clinical findings demonstrate that a subanesthetic dose of ketamine, a noncompetitive N-methyl-d-aspartate receptor (NMDAR) antagonist, produces rapid antidepressant effects within hours in some patients with treatment-resistant depression or MDD (4–6). However, ∼50% of patients with treatment-resistant depression do not respond to ketamine (7), and factors involved in the nonresponsiveness to ketamine remain unclear.The hippocampus is a brain region that has been linked to the pathophysiological changes in MDD. Patients with MDD show a decrease in hippocampal volume and function (8–12). In contrast, MDD patients treated with classic antidepressants have a reversal in hippocampal volume changes along with an improvement in hippocampus-dependent cognitive function (13–15). Previous preclinical studies have shown animal models of depression also exhibit a decrease in hippocampal volume and function (13), and hippocampal synaptic functional enhancement is required to mediate antidepressant responses (16–18). This enhancement of hippocampal function has been suggested to be a key requirement to exert an antidepressant response.Ketamine induces rapid molecular changes that elicit synaptic plasticity in the hippocampus (16, 19–22). Specifically, ketamine rapidly generates synaptic potentiation of field excitatory postsynaptic potentials (fEPSPs) in CA3–CA1 synapses in the hippocampus (ketamine potentiation) by inducing the rapid translation of brain-derived neurotrophic factor (BDNF) and trafficking of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) onto the postsynaptic surface (16, 19, 23, 24). Recent studies have shown that if key factors for the antidepressant effects of ketamine, such as BDNF (16, 25, 26) or AMPA receptors (16, 27), are deleted or blocked, the synaptic potentiation in the hippocampus concurrently disappears, suggesting that the synaptic potentiation underlies ketamine’s antidepressant effects (16, 19).Ketamine-mediated potentiation of fEPSPs in CA3–CA1 synapses has been shown to require a block of NMDAR activation by spontaneous glutamate release. Ketamine produces synaptic potentiation in the presence of tetrodotoxin, which blocks sodium channels, and thereby the generation of action potentials, suggesting that blocking NMDARs activated by the spontaneous presynaptic release is key to producing the synaptic potentiation (19, 21, 28, 29). In agreement with this premise, deletion of Vps10p-tail-interactor-1a (Vti1a) and vesicle-associated membrane protein 7 (VAMP7), which are soluble N-ethylmaleimide–sensitive factor attachment protein receptor proteins selectively involved in spontaneous neurotransmitter release (30, 31) in the CA3 hippocampal region, occluded the ketamine potentiation (32). Collectively, these lines of evidence suggest spontaneous glutamate release, and NMDARs are important factors for ketamine potentiation. Thus, it is possible that if these pre- or postsynaptic components are impaired, ketamine may not produce the synaptic potentiation and antidepressant effects.Reelin is a secreted glycoprotein and acts as a neuromodulator in the adult brain by regulating pre- and postsynaptic machinery. Reelin binds to its receptors, apolipoprotein E receptor 2 (Apoer2) and very-low-density lipoprotein receptor (VLDLR) and increases tyrosine phosphorylation in Disabled-1 (DAB1) (33–35). The Reelin pathway regulates pre- or postsynaptic function through its downstream signaling pathways in the adult brain. In presynaptic terminals, the Reelin-Apoer2 pathway activates phosphoinositide 3-kinase (PI3K) and increases Ca²⁺ release from intracellular stores, which in turn mobilizes VAMP7-containing synaptic vesicles and augments spontaneous release (31). At the postsynaptic sites, Reelin’s binding to Apoer2 reciprocally activates DAB1 and Src family kinases (SFKs). Subsequently, the activated SFKs increase tyrosine phosphorylation in NMDAR subunits, GluN2A and GluN2B (34–37), and increase NMDAR open probability (37–39). Since pre- and postsynaptic components regulated by Reelin have been suggested to be important for ketamine potentiation (16, 19–21, 32), it is conceivable that disrupted Reelin signaling may abrogate the antidepressant action and synaptic plasticity of ketamine.To examine this premise, we used genetically modified mice with a deletion of either Reelin or Apoer2 and investigated changes in antidepressant-like behaviors and synaptic potentiation in the CA1 hippocampal region following ketamine treatment. We also used pharmacological inhibitors to examine the effects of signaling molecules downstream of Reelin-Apoer2, specifically SFKs and PI3K, on ketamine-induced behavioral changes and synaptic plasticity. Lastly, we investigated whether the disruption of ketamine’s effects is due to a requirement for the activation of Reelin-dependent signaling or the impairment of NMDAR function by the disruption of Reelin-dependent signaling. Our results suggest that disruption of the Reelin-Apoer2-SFKs pathway depresses NMDAR function and diminishes ketamine’s use-dependent NMDAR antagonism, thereby rendering synapses nonresponsive to ketamine’s action as well as subsequent antidepressant responses. Taken together, these results provide insight into understanding the cellular and molecular mechanisms underlying ketamine’s antidepressant effects.     

Reelin activates the small GTPase TC10 and VAMP7 to promote neurite outgrowth and regeneration of dorsal root ganglia (DRG) neurons

Axonal outgrowth is a fundamental process during the development of central (CNS) and peripheral (PNS) nervous system as well as in nerve regeneration and requires accurate axonal navigation and extension to the correct target. These events need proper coordination between membrane trafficking and cytoskeletal rearrangements and are under the control of the small GTPases of the Rho family, among other molecules. Reelin, a relevant protein for CNS development and synaptic function in the adult, is also present in the PNS. Upon sciatic nerve damage, Reelin expression increases and, on the other hand, mice deficient in Reelin exhibit an impaired nerve regeneration. However, the mechanism(s) involved the Reelin‐dependent axonal growth is still poorly understood. In this work, we present evidence showing that Reelin stimulates dorsal root ganglia (DRG) regeneration after axotomy. Moreover, dissociated DRG neurons express the Reelin receptor Apolipoprotein E‐receptor 2 and also require the presence of TC10 to develop their axons. TC10 is a Rho GTPase that promotes neurite outgrowth through the exocytic fusion of vesicles at the growth cone. Here, we demonstrate for the first time that Reelin controls TC10 activation in DRG neurons. Besides, we confirmed that the known CNS Reelin target Cdc42 is also activated in DRG and controls TC10 activity. Finally, in the process of membrane addition, we found that Reelin stimulates the fusion of membrane carriers containing the v‐SNARE protein VAMP7 in vesicles that contain TC10. Altogether, our work shows a new role of Reelin in PNS, opening the option of therapeutic interventions to improve the regeneration process.     

Reelin在小鼠穿通纤维及大脑连合纤维寻径中的作用

目的通过对比野生型小鼠和Reeler小鼠穿通通路及连合纤维的发育,探讨Reelin在穿通通路及连合纤维寻径中的作用。方法共取野生型小鼠(WT)和Reelin基因缺失小鼠(Reeler),从胚龄16 d(E16)至出生7d(P7)各年龄点,共123例。采用Di I/Di O离体示踪技术对不同年龄点的WT小鼠及Reeler小鼠的穿通通路及连合纤维进行顺行和逆行示踪。结果 1.穿通通路主要由内嗅皮质第Ⅱ层和第Ⅳ层神经元所发出,在E16时进入海马腔隙分子层,P1时穿通纤维出现在齿状回,P7时穿通纤维形成致密纤维束终止于齿状回外分子层2/3;Reeler小鼠的穿通通路出现明显的发育延迟并且投射纤维分布紊乱;2.穹隆连合纤维主要由海马CA3锥体细胞,门细胞及内嗅皮质Ⅱ~Ⅳ层神经元发出,在E16时形成;Reeler小鼠穹隆纤维与WT小鼠在发育中无明显区别;3.胼胝体连合纤维主要由新皮质Ⅱ~Ⅳ层神经元及纹状体神经元所投射,在E18时形成并向对侧皮质进行纤维投射,并且投射部位出现对称分布,P3时一侧胼胝体纤维到达对侧纹状体。Reeler小鼠胼胝体投射的皮质神经元向对侧新皮质投射出现延迟。结论 Reelin可能是穿通通路及连合纤维发育的导向因子。Reelin的缺失导致穿通通路发育延迟,并且连合纤维在皮质的细胞来源及穿通通路细胞来源紊乱。     

Reelin immunoreactivity in dissociated cultures of the postnatal hippocampus

Reelin is an extracellular matrix glycoprotein expressed in different nerve cell populations in the developing, early postnatal and adult central nervous system. During histogenesis of the neocortex and hippocampus, reelin is present in Cajal-Retzius cells and other early neurons and contributes to correct layering of these regions. During early postnatal life, pioneer neurons disappear and reelin expression establishes in a subpopulation of cortical and hippocampal GABAergic interneurons, where it is maintained throughout adult life. We studied the developmental distribution pattern of reelin in dissociated cultures obtained from the early postnatal hippocampus to verify whether or not such a maturation phenomenon is maintained in vitro. Reelin is expressed both in Cajal-Retzius cells and multipolar and pyramidal neurons in younger cultures. The density of reelin-positive Cajal-Retzius cells dropped drastically by about 84% in 4-week-old cultures. Multipolar and pyramidal neurons containing reelin represented 12% of the total cell population in younger cultures and decreased by about 25% after 3 to 4 weeks of cultivation. Their density was significantly lower in cultures of the same age treated with glutamate receptor antagonists. These reelin-positive multipolar and pyramidal neurons were heterogeneous, including a larger amount of non-GABAergic, and 30-40% of GABAergic neurons. Cells double labeled for reelin and the GABA synthesizing enzyme glutamic acid decarboxylase represented about 4% of the total neuron population in culture and their density remained constant with age. It is thus possible that the decrease in the total reelin population may selectively be of importance to the larger non-GABAergic fraction of reelin cells. This study shows that reelin-expressing neurons are maintained in dissociated cultures of the neonatal hippocampus and their distribution and age-dependent changes in density resemble those of the early postnatal hippocampus in vivo.     

The Roles of Reelin, Bcl2, and Serotonin in Cerebellar Pathology in Autism

This review describes involvement of serotonin, Reelin, and Bcl2 in cerebellar pathology in autism. The literature regarding neurochemical, neuropathologic, and imaging aspects of autistic pathology as related to cerebellum is discussed. Where appropriate, relevant animal data are also presented to explain the impact of environmental and genetic influences on development of autism.     

Repeated exposure to corticosterone,but not restraint,decreases the number of reelin-positive cells in the adult rat hippocampus

Stress is an important risk factor for the emergence of depression, but little is known about the neurobiological mechanisms by which stress might promote depressive symptomatology. Much of the research on this topic has focused on stress-induced changes in hippocampal plasticity, specifically the idea that decreased hippocampal plasticity could be a precipitating factor for depression. Interestingly, recent evidence has described a regulatory role for the extracellular matrix protein reelin in important aspects of neural plasticity within the hippocampus and dentate gyrus. Given this association between reelin and hippocampal plasticity, we investigated whether repeated exposure to corticosterone or physical restraint might decrease reelin expression in specific hippocampal regions. Rats were subjected to either 21 days of corticosterone injections or physical restraint and then sacrificed so that the number of reelin-positive cells throughout the hippocampus and dentate gyrus could be quantified using immunohistochemistry. Our results revealed a significant decrease in the number of reelin-positive cells in the CA1 stratum lacunosum and the subgranular zone of the dentate gyrus in rats that received corticosterone, but not in rats that received restraint. Interestingly, these results parallel our previous observation that corticosterone increases depression-like behavior but physical restraint does not. These novel findings suggest that altered reelin signaling could play a role in the expression of depressive symptomatology after exposure to high levels of glucocorticoids.     

Histological study in the brain of the <Emphasis Type="Italic">reelin</Emphasis>/<Emphasis Type="Italic">Dab1</Emphasis>-compound mutant mouse

The Reelin (Reln)-deficient mouse (reeler) and the Dab1-deficient mouse (yotari) are autosomal recessive mutant mice characterized by cerebellar ataxia. Previously, we reported that Reelin and Dab1 proteins have slightly different functions during the development of the cerebral cortex. To analyze the functional roles of Reelin and Dab1 proteins in detail, we attempted to generate a reelin/Dab1 compound-mutant mouse by breeding heterozygote reeler and yotari mice. We examined the cytoarchitecture of the cerebral and cerebellar cortices and the hippocampus of wild-type (Reln ^+/+ ; Dab1 ^+/+ ), double-heterozygote (Reln ^rl/+ ; Dab1 ^yot/+ ), reeler (Reln ^rl/rl ; Dab1 ^+/+ , Reln ^rl/rl ; Dab1 ^yot/+ ), yotari (Reln ^+/+ ; Dab1 ^yot/yot , Reln ^rl/+ ; Dab1 ^yot/yot ), and double-compound-deficient (Reln ^rl/rl ; Dab1 ^yot/yot ) mice. Nissl staining demonstrated that no abnormality was recognized in the mice of reelin/Dab1 double-heterozygote (Reln ^rl/+ ; Dab1 ^yot/+ ). The reelin/Dab1-compound mutant mouse (Reln ^rl/rl ; Dab1 ^yot/yot ) showed histological abnormalities in the cerebral and cerebellar cortices and the hippocampus, in addition to those of reeler and yotari mice. We injected HRP into the lumbar cord of these animals with various gene compositions to examine the distribution pattern of corticospinal tract (CST) neurons. CST neurons of the reelin/Dab1-compound mutant mice were not confined to layer V, but scattered throughout the motor cortex. This quantitative and statistical analysis shows that the distribution pattern of CST neurons of the reelin/Dab1-compound mutant mouse differs from those of either of the reeler or yotari counterparts. Taken together, although Reelin/Dab1 signal transduction is a primary cascade in neurons during developmental periods, other signaling cascades (e.g., the Cdk-5/Dab1 pathway) may lie in a parallel fashion to Reelin/Dab1 signal transduction.