Rhotekin modulates differentiation of cultured neural stem cells to neurons

Novel cardiovascular protective effects of RhoA signaling and its therapeutic implications

Ras homolog gene family member A (RhoA) belongs to the Rho GTPase superfamily, which was first studied in cancers as one of the essential regulators controlling cellular function. RhoA has long attracted attention as a key molecule involved in cell signaling and gene transcription, through which it affects cellular processes. A series of studies have demonstrated that RhoA plays crucial roles under both physiological states and pathological conditions in cardiovascular diseases. RhoA has been identified as an important regulator in cardiac remodeling by regulating actin stress fiber dynamics and cytoskeleton formation. However, its underlying mechanisms remain poorly understood, preventing definitive conclusions being drawn about its protective role in the cardiovascular system. In this review, we outline the characteristics of RhoA and its related signaling molecules, and present an overview of RhoA classical function and the corresponding cellular responses of RhoA under physiological and pathological conditions. Overall, we provide an update on the novel signaling under RhoA in the cardiovascular system and its potential clinical and therapeutic targets in cardiovascular medicine.

Transplanted embryonic retinal stem cells have the potential to repair the injured retina in mice

Background

Stem cell transplantation has been reported as one of the promising strategies to treat retinal degenerative diseases. But, the application and the role of retina stem cells (RSCs) in the treatment of patients with retinal degenerative diseases have not been fully revealed. This study aimed to investigate the potential role of transplantation of the embryo-derived RSCs into the vitreous cavity in repairing the damaged retina in mice.

Methods

RSCs were isolated from Kunming mice E17 embryonic retina and ciliary body tissues, and labeled with 5-bromo-2’-deoxyuridin (BrdU). Retinal optic nerve crush injury was induced in left eyes in male Kunming mice by ring clamping the optic nerve. The 6th -generation of BrdU-labeled RSCs were transplanted into the damaged retina by the intravitreal injection, and saline injected eyes were used as the control. Hematoxylin and eosin histological staining, and BrdU, Nestin and Pax6 immunostaining were performed. Electroretinogram (ERG) was used for assessing the electrical activity of the retina.

Results

Embryo-derived RSCs were identified by the positive stains of Pax6 and Nestin. BrdU incorporation was detected in the majority of RSCs. The damaged retina showed cellular nuclear disintegration and fragmentation in the retinal tissue which progressed over the periods of clamping time, and decreased amplitudes of a and b waves in ERG. In the damaged retina with RSCs transplantation, the positive staining for BrdU, Pax6 and Nestin were revealed on the retinal surface. Notably, RSCs migrated into the retinal ganglion cell layer and inner nuclear. Transplanted RSCs significantly elevated the amplitudes of a waves in retina injured eyes.

Conclusions

Embryonic RSCs have similar characteristics to neural stem cells. Transplantation of RSCs by intravitreal injection would be able to repair the damaged retina.

Lysophosphatidic acid levels in cerebrospinal fluid and plasma samples in patients with major depressive disorder

Major depressive disorder (MDD) is the most common psychiatric disorders. However, a biochemical marker has yet to be established for clinical purposes. It is proposed that lysophosphatidic acid (LPA, 1-acyl-2-sn-glycerol-3-phosphoate) plays some important roles in emotional regulation of experimental animals. Therefore, in this study, we measured LPA levels using enzyme-linked immunosorbent assays of cerebrospinal fluid (CSF) and plasma samples from patients with MDD. The participants were 52 patients and 49 normal healthy controls for CSF study, and 47 patients and 44 controls for plasma study. We used the Japanese version of the GRID Hamilton Depression Rating Scale (17-item version) for the assessment of depressive symptoms. We found no associations between LPA levels (CSF or plasma) and either diagnosis or severity of MDD, or with psychotropic medication. In conclusion, our data suggest that LPA levels likely would not serve as a practical biomarker of MDD.

Functions of Rhotekin, an Effector of Rho GTPase, and Its Binding Partners in Mammals

Rhotekin is an effector protein for small GTPase Rho. This protein consists of a Rho binding domain (RBD), a pleckstrin homology (PH) domain, two proline-rich regions and a C-terminal PDZ (PSD-95, Discs-large, and ZO-1)-binding motif. We, and other groups, have identified various binding partners for Rhotekin and carried out biochemical and cell biological characterization. However, the physiological functions of Rhotekin, per se, are as of yet largely unknown. In this review, we summarize known features of Rhotekin and its binding partners in neuronal tissues and cancer cells.

Identification and characterization of functional modules reflecting transcriptome transition during human neuron maturation

BACKGROUND

Neuron maturation is a critical process in neurogenesis, during which neurons gain their morphological, electrophysiological and molecular characteristics for their functions as the central components of the nervous system.

RESULTS

To better understand the molecular changes during this process, we combined the protein-protein interaction network and public single cell RNA-seq data of mature and immature neurons to identify functional modules relevant to the neuron maturation process in humans. Among the 109 functional modules in total, 33 showed significant gene expression level changes (discriminating modules) which participate in varied functions including energy consumption, synaptic functions and housekeeping functions such as translation and splicing. Based on the identified modules, we trained a neuron maturity index (NMI) model for the quantification of maturation states of single neurons or purified bulk neurons. Applied to multiple single neuron transcriptome data sets of neuron development in humans and mice, the NMI model made estimation of neuron maturity states which were significantly correlated with the neuron maturation trajectories in both species, implying the reproducibility and conservation of the identified transcriptome transition.

CONCLUSION

We identified 33 discriminating modules whose activities were significantly correlated with single neuron maturity states, which may play important roles in the neuron maturation process.

Lysophosphatidic acid induces anxiety-like behavior via its receptors in mice

Lysophosphatidic acid (LPA) is a potent bioactive lipid mediator with diverse biological properties. We previously found altered expression of the LPA-related genes in rodents after treatment with sertraline, which is widely used to treat anxiety disorders and depression. However, little is known about the behavioral effects of LPA. In the present study, we investigated the behavioral effects of intracerebroventricular injection of LPA in adult mice. LPA did not significantly affect spontaneous locomotor activity, suggesting that LPA does not induce hyperactivity, ataxia, or sedation. We next investigated the emotional effects of LPA via the hole-board test. LPA significantly increased the number of head-dips in a dose- and time-related manner. A significant induction of head-dip counts occurred 15 and 30 min after LPA administration. To clarify the involvement of LPA receptors, we examined the effect of the non-selective LPA1-4 receptor antagonist, 1-bromo-3(S)-hydroxy-4-(palmitoyloxy)butyl-phosphonate (BrP-LPA) co-administered with LPA. BrP-LPA dose-dependently inhibited LPA-induced head-dip counts. We next investigated anxiety-like behavior via the elevated plus-maze test. LPA significantly reduced the percentage of time spent in the open arms and BrP-LPA dose-dependently inhibited this anxiety-like behavior. In conclusion, LPA induced anxiety-like behavior in mice via LPA receptors. Our results suggest that LPA signaling plays an important role in regulating anxiety in mice.

Physiological roles of Rho and Rho effectors in mammals

Rho GTPase is a master regulator controlling cytoskeleton in multiple contexts such as cell migration, adhesion and cytokinesis. Of several Rho GTPases in mammals, the best characterized is the Rho subfamily including ubiquitously expressed RhoA and its homologs RhoB and RhoC. Upon binding GTP, Rho exerts its functions through downstream Rho effectors, such as ROCK, mDia, Citron, PKN, Rhophilin and Rhotekin. Until recently, our knowledge about functions of Rho and Rho effectors came mostly from in vitro studies utilizing cultured cells, and their physiological roles in vivo were largely unknown. However, gene-targeting studies of Rho and its effectors have now unraveled their tissue- and cell-specific roles and provide deeper insight into the physiological function of Rho signaling in vivo. In this article, we briefly describe previous studies of the function of Rho and its effectors in vitro and then review and discuss recent studies on knockout mice of Rho and its effectors.

Plasticity-related gene 1 is important for survival of neurons derived from rat neural stem cells

Plasticity-related gene 1 (Prg1) is a membrane-associated lipid phosphate phosphatase. In this study, we first investigated the role of Prg1 in the survival of neurons derived from rat neural stem cells (NSCs) using small interfering RNA (siRNA). Prg1 knock-down decreased the cell number. Interestingly, Prg1 knock-down increased genomic DNA fragmentation, suggesting the possible induction of apoptosis. Exogenously expressed Prg1 rescued the cells from death and restored the loss of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) activity induced with Prg1 siRNA. However, exogenously expressed mutated-Prg1 (the 253rd amino acid, histidine253, had been changed to alanine) did not rescue the cell death or restore the MTT activity. Histidine253 of Prg1 has been reported to be important for lipid phosphate phosphatase activity. These results suggest that Prg1 is important for survival of neurons through its dephosphorylation activity.