Distinct and complementary functions of rho kinase isoforms ROCK1 and ROCK2 in prefrontal cortex structural plasticity

Social experience in adolescence shapes prefrontal cortex structure and function in adulthood

During adolescence, the prefrontal cortex (PFC) undergoes dramatic reorganization. PFC development is profoundly influenced by the social environment, disruptions to which may prime the emergence of psychopathology across the lifespan. We investigated the neurobehavioral consequences of isolation experienced in adolescence in mice, and in particular, the long-term consequences that were detectable even despite normalization of the social milieu. Isolation produced biases toward habit-like behavior at the expense of flexible goal seeking, plus anhedonic-like reward deficits. Behavioral phenomena were accompanied by neuronal dendritic spine over-abundance and hyper-excitability in the ventromedial PFC (vmPFC), which was necessary for the expression of isolation-induced habits and sufficient to trigger behavioral inflexibility in socially reared controls. Isolation activated cytoskeletal regulatory pathways otherwise suppressed during adolescence, such that repression of constituent elements prevented long-term isolation-induced neurosequelae. Altogether, our findings unveil an adolescent critical period and multi-model mechanism by which social experiences facilitate prefrontal cortical maturation.

ROCK2 regulates microglia proliferation and neuronal survival after traumatic brain injury

Traumatic brain injury (TBI) results in prolonged and non-resolving activation of microglia. Forced turnover of these cells during the acute phase of TBI aids recovery, but the cell-intrinsic pathways that underpin the pro-repair phenotype of these repopulating microglia remain unclear. Here, we show that selective targeting of ROCK2 with the small molecule inhibitor KD025 impairs the proliferative response of microglia after TBI as well as during genetically induced turnover of microglia. KD025 treatment abolished the substantial neuroprotective and cognitive benefits conferred by repopulating microglia, preventing these cells from replenishing the depleted niche during the early critical time window post-injury. Delaying KD025 treatment to the subacute phase of TBI allowed microglial repopulation to occur, but this did not enhance the benefits conferred by repopulating microglia. Taken together, our data indicate that ROCK2 mediates neuronal survival and microglial population dynamics after TBI, including the emergence of repopulating microglia with a pro-repair phenotype.

Cross-Platform Synaptic Network Analysis of Human Entorhinal Cortex Identifies TWF2 as a Modulator of Dendritic Spine Length

Proteomic studies using postmortem human brain tissue samples have yielded robust assessments of the aging and neurodegenerative disease(s) proteomes. While these analyses provide lists of molecular alterations in human conditions, like Alzheimer's disease (AD), identifying individual proteins that affect biological processes remains a challenge. To complicate matters, protein targets may be highly understudied and have limited information on their function. To address these hurdles, we sought to establish a blueprint to aid selection and functional validation of targets from proteomic datasets. A cross-platform pipeline was engineered to focus on synaptic processes in the entorhinal cortex (EC) of human patients, including controls, preclinical AD, and AD cases. Label-free quantification mass spectrometry (MS) data (n = 2260 proteins) was generated on synaptosome fractionated tissue from Brodmann area 28 (BA28; n = 58 samples). In parallel, dendritic spine density and morphology was measured in the same individuals. Weighted gene co-expression network analysis was used to construct a network of protein co-expression modules that were correlated with dendritic spine metrics. Module-trait correlations were used to guide unbiased selection of Twinfilin-2 (TWF2), which was the top hub protein of a module that positively correlated with thin spine length. Using CRISPR-dCas9 activation strategies, we demonstrated that boosting endogenous TWF2 protein levels in primary hippocampal neurons increased thin spine length, thus providing experimental validation for the human network analysis. Collectively, this study describes alterations in dendritic spine density and morphology as well as synaptic proteins and phosphorylated tau from the entorhinal cortex of preclinical and advanced stage AD patients.SIGNIFICANCE STATEMENT Proteomic studies can yield vast lists of molecules that are altered under various experimental or disease conditions. Here, we provide a blueprint to facilitate mechanistic validation of protein targets from human brain proteomic datasets. We conducted a proteomic analysis of human entorhinal cortex (EC) samples spanning cognitively normal and Alzheimer's disease (AD) cases with a comparison of dendritic spine morphology in the same samples. Network integration of proteomics with dendritic spine measurements allowed for unbiased discovery of Twinfilin-2 (TWF2) as a regulator of dendritic spine length. A proof-of-concept experiment in cultured neurons demonstrated that altering Twinfilin-2 protein level induced corresponding changes in dendritic spine length, thus providing experimental validation for the computational framework.

The RhoA-ROCK1/ROCK2 Pathway Exacerbates Inflammatory Signaling in Immortalized and Primary Microglia

Neuroinflammation is a unifying factor among all acute central nervous system (CNS) injuries and chronic neurodegenerative disorders. Here, we used immortalized microglial (IMG) cells and primary microglia (PMg) to understand the roles of the GTPase Ras homolog gene family member A (RhoA) and its downstream targets Rho-associated coiled-coil-containing protein kinases 1 and 2 (ROCK1 and ROCK2) in neuroinflammation. We used a pan-kinase inhibitor (Y27632) and a ROCK1- and ROCK2-specific inhibitor (RKI1447) to mitigate a lipopolysaccharide (LPS) challenge. In both the IMG cells and PMg, each drug significantly inhibited pro-inflammatory protein production detected in media (TNF-α, IL-6, KC/GRO, and IL-12p70). In the IMG cells, this resulted from the inhibition of NF-κB nuclear translocation and the blocking of neuroinflammatory gene transcription (iNOS, TNF-α, and IL-6). Additionally, we demonstrated the ability of both compounds to block the dephosphorylation and activation of cofilin. In the IMG cells, RhoA activation with Nogo-P4 or narciclasine (Narc) exacerbated the inflammatory response to the LPS challenge. We utilized a siRNA approach to differentiate ROCK1 and ROCK2 activity during the LPS challenges and showed that the blockade of both proteins may mediate the anti-inflammatory effects of Y27632 and RKI1447. Using previously published data, we show that genes in the RhoA/ROCK signaling cascade are highly upregulated in the neurodegenerative microglia (MGnD) from APP/PS-1 transgenic Alzheimer's disease (AD) mice. In addition to illuminating the specific roles of RhoA/ROCK signaling in neuroinflammation, we demonstrate the utility of using IMG cells as a model for primary microglia in cellular studies.

Integrated Proteomics to Understand the Role of Neuritin (NRN1) as a Mediator of Cognitive Resilience to Alzheimer's Disease

The molecular mechanisms and pathways enabling certain individuals to remain cognitively normal despite high levels of Alzheimer's disease (AD) pathology remain incompletely understood. These cognitively normal people with AD pathology are described as preclinical or asymptomatic AD (AsymAD) and appear to exhibit cognitive resilience to the clinical manifestations of AD dementia. Here we present a comprehensive network-based approach from cases clinically and pathologically defined as asymptomatic AD to map resilience-associated pathways and extend mechanistic validation. Multiplex tandem mass tag MS (TMT-MS) proteomic data (n = 7787 proteins) was generated on brain tissue from Brodmann area 6 and Brodmann area 37 (n = 109 cases, n = 218 total samples) and evaluated by consensus weighted gene correlation network analysis. Notably, neuritin (NRN1), a neurotrophic factor previously linked to cognitive resilience, was identified as a hub protein in a module associated with synaptic biology. To validate the function of NRN1 with regard to the neurobiology of AD, we conducted microscopy and physiology experiments in a cellular model of AD. NRN1 provided dendritic spine resilience against amyloid-β (Aβ) and blocked Aβ-induced neuronal hyperexcitability in cultured neurons. To better understand the molecular mechanisms of resilience to Aβ provided by NRN1, we assessed how exogenous NRN1 alters the proteome by TMT-MS (n = 8238 proteins) of cultured neurons and integrated the results with the AD brain network. This revealed overlapping synapse-related biology that linked NRN1-induced changes in cultured neurons with human pathways associated with cognitive resilience. Collectively, this highlights the utility of integrating the proteome from the human brain and model systems to advance our understanding of resilience-promoting mechanisms and prioritize therapeutic targets that mediate resilience to AD.

Involvement of miR-135a-5p Downregulation in Acute and Chronic Stress Response in the Prefrontal Cortex of Rats

Stress is a key risk factor in the onset of neuropsychiatric disorders. The study of the mechanisms underlying stress response is important to understand the etiopathogenetic mechanisms and identify new putative therapeutic targets. In this context, microRNAs (miRNAs) have emerged as key regulators of the complex patterns of gene/protein expression changes in the brain, where they have a crucial role in the regulation of neuroplasticity, neurogenesis, and neuronal differentiation. Among them, miR-135a-5p has been associated with stress response, synaptic plasticity, and the antidepressant effect in different brain areas. Here, we used acute unavoidable foot-shock stress (FS) and chronic mild stress (CMS) on male rats to study whether miR-135a-5p was involved in stress-induced changes in the prefrontal cortex (PFC). Both acute and chronic stress decreased miR-135a-5p levels in the PFC, although after CMS the reduction was induced only in animals vulnerable to CMS, according to a sucrose preference test. MiR-135a-5p downregulation in the primary neurons reduced dendritic spine density, while its overexpression exerted the opposite effect. Two bioinformatically predicted target genes, Kif5c and Cplx1/2, were increased in FS rats 24 h after stress. Altogether, we found that miR-135a-5p might play a role in stress response in PFC involving synaptic mechanisms.

Inhibition of interaction between ROCK1 and Rubicon restores autophagy in endothelial cells and attenuates brain injury after prolonged ischemia

Acute ischemic stroke (AIS) induces cerebral endothelial cell death resulting in the breakdown of the blood-brain barrier (BBB). Endothelial cell autophagy acts as a protective mechanism against cell death. Autophagy is activated in the very early stages of ischemic stroke and declines after prolonged ischemia. Previous studies have shown that Rubicon can inhibit autophagy. The current study aimed to investigate whether continuous long-term ischemia can inhibit autophagy in endothelial cells after ischemic stroke by regulating the function of Rubicon and its underlying mechanism. Wild-type male C57BL/6J mice were subjected to transient middle cerebral artery occlusion (tMCAO). ROCK1, ROCK2, and NOX2 inhibitors were injected into male mice 1 h before the onset of tMCAO. Disease severity and BBB permeability were evaluated. bEnd.3 cells were cultured in vitro and subjected to oxygen-glucose deprivation (OGD). bEnd.3 cells were pretreated with or without ROCK1, ROCK2, or NOX2 inhibitors overnight and then subjected to OGD. Cell viability and permeability were also evaluated. The expression of Rubicon, ROCK1, and autophagy-related proteins were analyzed. Increased BBB permeability was correlated with Rubicon expression in tMCAO mice and Rubicon was upregulated in endothelial cells subjected to OGD. Autophagy was inhibited in endothelial cells after long-term OGD treatment and knockdown of Rubicon expression restored autophagy and viability in endothelial cells subjected to 6-h OGD. ROCK1 inhibition decreased the interaction between Beclin1 and Rubicon and restored cell viability and autophagy suppressed by 6-h OGD treatment in endothelial cells. Additionally, ROCK1 inhibition suppressed Rubicon, attenuated BBB disruption, and brain injury induced by prolonged ischemia in 6-h tMCAO mice. Prolonged ischemia induced the death of brain endothelial cells and the breakdown of the BBB, thus aggravating brain injury by increasing the interaction of ROCK1 and Rubicon with Beclin1 while inhibiting canonical autophagy. Inhibition of ROCK1 signaling in endothelial cells could be a promising therapeutic strategy to prolong the therapeutic time window in AIS.

Comparison of Golgi-Cox and Intracellular Loading of Lucifer Yellow for Dendritic Spine Density and Morphology Analysis in the Mouse Brain

Dendritic spines are small protrusions on dendrites that serve as the postsynaptic site of the majority of excitatory synapses. These structures are important for normal synaptic transmission, and alterations in their density and morphology have been documented in various disease states. Over 130 years ago, Ramón y Cajal used Golgi-stained tissue sections to study dendritic morphology. Despite the array of technological advances, including iontophoretic microinjection of Lucifer yellow (LY) fluorescent dye, Golgi staining continues to be one of the most popular approaches to visualize dendritic spines. Here, we compared dendritic spine density and morphology among pyramidal neurons in layers 2/3 of the mouse medial prefrontal cortex (mPFC) and pyramidal neurons in hippocampal CA1 using three-dimensional digital reconstructions of (1) brightfield microscopy z-stacks of Golgi-impregnated dendrites and (2) confocal microscopy z-stacks of LY-filled dendrites. Analysis of spine density revealed that the LY microinjection approach enabled detection of approximately three times as many spines as the Golgi staining approach in both brain regions. Spine volume measurements were larger using Golgi staining compared to LY microinjection in both mPFC and CA1. Spine length was mostly comparable between techniques in both regions. In the mPFC, head diameter was similar for Golgi staining and LY microinjection. However, in CA1, head diameter was approximately 50% smaller on LY-filled dendrites compared to Golgi staining. These results indicate that Golgi staining and LY microinjection yield different spine density and morphology measurements, with Golgi staining failing to detect dendritic spines and overestimating spine size.

Effects of RhoA on depression-like behavior in prenatally stressed offspring rats

Depression is a common mental disease that can lead to suicide when severe. Exposure to prenatal stress (PS) can lead to depression-like behavior in offspring, but the mechanism is unclear. RhoA (Ras homology family member A) plays an important role in stress-induced changes in synaptic plasticity, participating in the development of depression by activating the downstream effector ROCK (Rho-associated protein kinase). This study explored the influence in the expression of RhoA and downstream molecules ROCK1/2 in prenatally stressed rats, and the effect of RhoA inhibitor simvastatin on depression-like behavior induced by PS. Depression-like behavior in offspring was detected by sucrose preference test, forced swimming test, and open-field test. The mRNA and protein expression of RhoA and ROCK1/2 in the hippocampus and prefrontal cortex of offspring rats were detected by qRT-PCR and western blotting, respectively. Our results showed that PS causes depression-like behavior in offspring rats, associated with elevated expression of RhoA, ROCK1/2 in the hippocampus and prefrontal cortex. After administration of simvastatin to PS rats, the expression of RhoA and ROCK2 was significantly reduced, alleviating depression-like behavior. Our study demonstrated that RhoA participates in the depression-like behavior in prenatally stressed offspring rats, which may be a potential target for antidepressant therapy.

The Outcomes of Small-Molecule Kinase Inhibitors and the Role of ROCK2 as a Molecular Target for the Treatment of Alzheimer's Disease

BACKGROUND

Alzheimer's disease is rapidly becoming a major threat to public health, with an increasing number of individuals affected as the world's population ages. In this sense, studies have been carried out aiming at the identification of new small-molecule kinase inhibitors useful for the treatment of Alzheimer's disease.

OBJECTIVE

In the present study, we investigated the compounds developed as inhibitors of different protein kinases associated with the pathogenesis of Alzheimer's disease.

METHODS

The applied methodology was the use of the Clarivate Analytics Integrity and ClinicalTrials. com databases. Moreover, we highlight ROCK2 as a promising target despite being little studied for this purpose. A careful structure-activity relationship analysis of the ROCK2 inhibitors was performed to identify important structural features and fragments for the interaction with the kinase active site, aiming to rationally design novel potent and selective inhibitors.

RESULTS

We were able to notice some structural characteristics that could serve as the basis to better guide the rational design of new ROCK2 inhibitors as well as some more in-depth characteristics regarding the topology of the active site of both isoforms of these enzymes, thereby identifying differences that could lead to planning more selective compounds.

CONCLUSION

We hope that this work can be useful to update researchers working in this area, enabling the emergence of new ideas and a greater direction of efforts for designing new ROCK2 inhibitors to identify new therapeutic alternatives for Alzheimer's disease.

Conditional deletion of ROCK2 induces anxiety-like behaviors and alters dendritic spine density and morphology on CA1 pyramidal neurons

Rho-associated kinase isoform 2 (ROCK2) is an attractive drug target for several neurologic disorders. A critical barrier to ROCK2-based research and therapeutics is the lack of a mouse model that enables investigation of ROCK2 with spatial and temporal control of gene expression. To overcome this, we generated ROCK2fl/fl mice. Mice expressing Cre recombinase in forebrain excitatory neurons (CaMKII-Cre) were crossed with ROCK2fl/fl mice (Cre/ROCK2fl/fl), and the contribution of ROCK2 in behavior as well as dendritic spine morphology in the hippocampus, medial prefrontal cortex (mPFC), and basolateral amygdala (BLA) was examined. Cre/ROCK2fl/fl mice spent reduced time in the open arms of the elevated plus maze and increased time in the dark of the light-dark box test compared to littermate controls. These results indicated that Cre/ROCK2fl/fl mice exhibited anxiety-like behaviors. To examine dendritic spine morphology, individual pyramidal neurons in CA1 hippocampus, mPFC, and the BLA were targeted for iontophoretic microinjection of fluorescent dye, followed by high-resolution confocal microscopy and neuronal 3D reconstructions for morphometry analysis. In dorsal CA1, Cre/ROCK2fl/fl mice displayed significantly increased thin spine density on basal dendrites and reduced mean spine head volume across all spine types on apical dendrites. In ventral CA1, Cre/ROCK2fl/fl mice exhibited significantly increased spine length on apical dendrites. Spine density and morphology were comparable in the mPFC and BLA between both genotypes. These findings suggest that neuronal ROCK2 mediates spine density and morphology in a compartmentalized manner among CA1 pyramidal cells, and that in the absence of ROCK2 these mechanisms may contribute to anxiety-like behaviors.

Wnt5a modulates dendritic spine dynamics through the regulation of Cofilin via small Rho GTPase activity in hippocampal neurons

Dendritic spines are small, actin-rich protrusions that act as the receiving sites of most excitatory inputs in the central nervous system. The remodeling of the synapse architecture is mediated by actin cytoskeleton dynamics, a process precisely regulated by the small Rho GTPase family. Wnt ligands exert their presynaptic and postsynaptic effects during formation and consolidation of the synaptic structure. Specifically, Wnt5a has been identified as an indispensable synaptogenic factor for the regulation and organization of the postsynaptic side; however, the molecular mechanisms through which Wnt5a induces morphological changes resulting from actin cytoskeleton dynamics within dendritic spines remain unclear. In this work, we employ primary rat hippocampal cultures and HT22 murine hippocampal neuronal cell models, molecular and pharmacological tools, and fluorescence microscopy (laser confocal and epifluorescence) to define the Wnt5a-induced molecular signaling involved in postsynaptic remodeling mediated via the regulation of the small Rho GTPase family. We report that Wnt5a differentially regulates the phosphorylation of Cofilin in neurons through both Ras-related C3 botulinum toxin substrate 1 and cell division cycle 42 depending on the subcellular compartment and the extracellular calcium levels. Additionally, we demonstrate that Wnt5a increases the density of dendritic spines and promotes their maturation via Ras-related C3 botulinum toxin substrate 1. Accordingly, we find that Wnt5a requires the combined activation of small Rho GTPases to increase the levels of filamentous actin, thus promoting the stability of actin filaments. Altogether, these results provide evidence for a new mechanism by which Wnt5a may target actin dynamics, thereby regulating the subsequent morphological changes in dendritic spine architecture.

Neuronal Cytoskeleton in Intellectual Disability: From Systems Biology and Modeling to Therapeutic Opportunities

Intellectual disability (ID) is a pathological condition characterized by limited intellectual functioning and adaptive behaviors. It affects 1–3% of the worldwide population, and no pharmacological therapies are currently available. More than 1000 genes have been found mutated in ID patients pointing out that, despite the common phenotype, the genetic bases are highly heterogeneous and apparently unrelated. Bibliomic analysis reveals that ID genes converge onto a few biological modules, including cytoskeleton dynamics, whose regulation depends on Rho GTPases transduction. Genetic variants exert their effects at different levels in a hierarchical arrangement, starting from the molecular level and moving toward higher levels of organization, i.e., cell compartment and functions, circuits, cognition, and behavior. Thus, cytoskeleton alterations that have an impact on cell processes such as neuronal migration, neuritogenesis, and synaptic plasticity rebound on the overall establishment of an effective network and consequently on the cognitive phenotype. Systems biology (SB) approaches are more focused on the overall interconnected network rather than on individual genes, thus encouraging the design of therapies that aim to correct common dysregulated biological processes. This review summarizes current knowledge about cytoskeleton control in neurons and its relevance for the ID pathogenesis, exploiting in silico modeling and translating the implications of those findings into biomedical research.

Dendritic Spine Remodeling and Synaptic Tau Levels in PS19 Tauopathy Mice

Synapse or dendritic spine loss is the strongest correlate of cognitive decline in Alzheimer's disease (AD), and neurofibrillary tangles (NFTs), but not amyloid-β plaques, associate more closely with transition to mild cognitive impairment. Yet, how dendritic spine architecture is affected by hyperphosphorylated tau is still an ongoing question. To address this, we combined cell and biochemical analyses of the Tau P301S mouse line (PS19). Individual pyramidal neurons in the hippocampus and medial prefrontal cortex (mPFC) were targeted for iontophoretic microinjection of fluorescent dye, followed by high-resolution confocal microscopy and 3D morphometry analysis. In the hippocampus, PS19 mice and non-transgenic (NTG) littermates displayed equivalent spine density at 6 and 9 months, but both genotypes exhibited age-related thin spine loss. PS19 mice exhibited significant increases in synaptic tau protein levels and mean dendritic spine head diameter with age. This suggests that CA1 pyramidal neurons in PS19 mice may undergo spine remodeling in response to tau accumulation and age. In the mPFC, spine density was similar among PS19 mice and NTG littermates at 6 and 9 months, but age-related reductions in synaptic tau levels were observed among PS19 mice. Collectively, these studies reveal brain region-specific changes in dendritic spine density and morphology in response to age and the presence of hyperphosphorylated tau in the PS19 mouse line.

Myosin II isoforms promote internalization of spatially distinct clathrin-independent endocytosis cargoes through modulation of cortical tension downstream of ROCK2

Although the actomyosin cytoskeleton has been implicated in clathrin-mediated endocytosis, a clear requirement for actomyosin in clathrin-independent endocytosis (CIE) has not been demonstrated. We discovered that the Rho-associated kinase ROCK2 is required for CIE of MHCI and CD59 through promotion of myosin II activity. Myosin IIA promoted internalization of MHCI and myosin IIB drove CD59 uptake in both HeLa and polarized Caco2 intestinal epithelial cells. In Caco2 cells, myosin IIA localized to the basal cortex and apical brush border and mediated MHCI internalization from the basolateral domain, while myosin IIB localized at the basal cortex and apical cell–cell junctions and promoted CD59 uptake from the apical membrane. Atomic force microscopy demonstrated that myosin IIB mediated apical epithelial tension in Caco2 cells. Thus, specific cargoes are internalized by ROCK2-mediated activation of myosin II isoforms to mediate spatial regulation of CIE, possibly by modulation of local cortical tension.

Antipsychotic Drugs Reverse MK801-Inhibited Cell Migration and F-actin Condensation by Modulating the Rho Signaling Pathway in B35 Cells

Background and Aim. MK801-induced psychotic symptoms and also the Ras homolog family member A (RhoA) expression and cell division control protein 42 (cdc42) mRNA modulation in the rat brain have been investigated. Antipsychotic drugs (APDs) have been reported to induce Rho GDP-dissociation inhibitor (RhoGDI) pathway regulation related to cytoskeleton reorganization in neuronal cells. It will be necessary to clarify the effects of APDs on MK801-induced RhoGDI signaling regulation in neuronal cells. Methods. B35 neuronal cells were treated with MK801 for 7 days then treated with MK801 in combination with haloperidol or clozapine for a further 7 days. Cell migration, F-actin condensation, and RhoGDI signaling regulation were examined to investigate the regulatory effects of MK801, haloperidol, and clozapine in B35 neuronal cells. Results. MK801 reduced B35 cell migration, whereas both haloperidol and clozapine reversed the reduction in cell migration induced by MK801. Haloperidol and clozapine restored F-actin condensation after it was diminished by MK801 in B35 cell nuclei. MK801 increased the RhoGDI1 and RhoA expression, which was diminished by the addition of haloperidol and clozapine. MK801 reduced the CDC42 expression, which was restored by haloperidol and clozapine. MK801 reduced the Rho-associated coiled-coil containing protein kinase 1 (ROCK1), profilin1 (PFN1), and neuronal Wiskott–Aldrich Syndrome protein (N-WASP) expression, which was further reduced by haloperidol and clozapine. MK801 also increased the phosphorylated myosin light chain 2 (p-MLC2), postsynaptic density protein 95 (PSD-95), and c-jun expression, which was decreased by haloperidol and clozapine. p21 (RAC1-) activated kinase 1 (PAK1) expression was not affected by MK801.

Neuronal Protein Farnesylation Regulates Hippocampal Synaptic Plasticity and Cognitive Function

Protein prenylation is a post-translational lipid modification that governs a variety of important cellular signaling pathways, including those regulating synaptic functions and cognition in the nervous system. Two enzymes, farnesyltransferase (FT) and geranylgeranyltransferase type I (GGT), are essential for the prenylation process. Genetic reduction of FT or GGT ameliorates neuropathology but only FT haplodeficiency rescues cognitive function in transgenic mice of Alzheimer's disease. A follow-up study showed that systemic or forebrain neuron-specific deficiency of GGT leads to synaptic and cognitive deficits under physiological conditions. Whether FT plays different roles in shaping neuronal functions and cognition remains elusive. This study shows that in contrast to the detrimental effects of GGT reduction, systemic haplodeficiency of FT has little to no impact on hippocampal synaptic plasticity and cognition. However, forebrain neuron-specific FT deletion also leads to reduced synaptic plasticity, memory retention, and hippocampal dendritic spine density. Furthermore, a novel prenylomic analysis identifies distinct pools of prenylated proteins that are affected in the brain of forebrain neuron-specific FT and GGT knockout mice, respectively. Taken together, this study uncovers that physiological levels of FT and GGT in neurons are essential for normal synaptic/cognitive functions and that the prenylation status of specific signaling molecules regulates neuronal functions.

Upregulation of miR-496 Rescues Propofol-induced Neurotoxicity by Targeting Rho Associated Coiled-coil Containing Protein Kinase 2 (ROCK2) in Prefrontal Cortical Neurons

OBJECTIVE

Early exposure to general anesthesia in children might be a potentially highrisk factor for learning and behavioral disorders. The mechanism of neurotoxicity induced by general anesthesia was not defined. miR-496 could regulate cerebral injury, while the roles of miR- 496 in neurotoxicity were not elucidated. Therefore, we aimed to investigate the effects of miR- 496 in neurotoxicity induced by propofol.

METHODS

Primary Prefrontal Cortical (PFC) neurons were isolated from neonatal rats and treated with propofol to induce neurotoxicity. Cell viability was detected by (3-(4,5-Dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and cell apoptosis was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The target relationship of miR-496 and Rho Associated Coiled-Coil Containing Protein Kinase 2 (ROCK2) was explored using luciferase assays.

RESULTS

Propofol decreased cell viability, promoted cell apoptosis, and decreased the expression of miR-496 in PFC neurons in a dose-dependent manner. Overexpression of miR-496 attenuated neurotoxicity induced by propofol in PFC neurons. ROCK2 was a target of miR-496, and miR-496 oppositely modulated the expression of ROCK2. Besides, propofol increased the expression of ROCK2 through inhibiting miR-496 in PFC neurons. Overexpression of miR-496 attenuated propofol- induced neurotoxicity by targeting ROCK2 in PFC neurons.

CONCLUSION

miR-496 was decreased in PFC neurons treated with propofol, and overexpression of miR-496 attenuated propofol-induced neurotoxicity by targeting ROCK2. miR-496 and ROCK2 may be promising targets for protecting propofol-induced neurotoxicity.

ROCK inhibitors upregulate the neuroprotective Parkin-mediated mitophagy pathway

The accumulation of damaged mitochondria causes the death of dopaminergic neurons. The Parkin-mediated mitophagy pathway functions to remove these mitochondria from cells. Targeting this pathway represents a therapeutic strategy for several neurodegenerative diseases, most notably Parkinson's disease. We describe a discovery pipeline to identify small molecules that increase Parkin recruitment to damaged mitochondria and ensuing mitophagy. We show that ROCK inhibitors promote the activity of this pathway by increasing the recruitment of HK2, a positive regulator of Parkin, to mitochondria. This leads to the increased targeting of mitochondria to lysosomes and removal of damaged mitochondria from cells. Furthermore, ROCK inhibitors demonstrate neuroprotective effects in flies subjected to paraquat, a parkinsonian toxin that induces mitochondrial damage. Importantly, parkin and rok are required for these effects, revealing a signaling axis which controls Parkin-mediated mitophagy that may be exploited for the development of Parkinson's disease therapeutics.

Fasudil or genetic depletion of ROCK1 or ROCK2 induces anxiety-like behaviors

Twenty-nine protein kinase inhibitors have been used to treat human diseases. Out of these, two are Rho-associated protein kinase (ROCK) 1 and 2 inhibitors. The ROCKs heavily influence neuronal architecture and structural plasticity, and ROCKs are putative drug targets for various brain disorders. While the pan-ROCK inhibitor Fasudil has been clinically approved to treat hypertension, heart failure, glaucoma, spinal cord injury, and stroke, a barrier to progress on this therapeutic avenue is the lack of experimental comparisons between pharmacologic and genetic manipulation of ROCKs. Our study begins to address this question using parallel approaches to study behavior in mice that were treated with Fasudil or were heterozygous for ROCK1 or ROCK2. Adult mice treated with Fasudil for thirty days displayed reduced time spent in the open arms of the elevated plus maze, whereas activity in the open field was more analogous to mock-treated animals. Both male and female adult ROCK1+/- and ROCK2+/- mice exhibited reduced time spent in open arms of the elevated plus maze compared to littermate controls. However, ROCK1 or ROCK2 heterozygosity did not alter performance in the open field or Y-maze. These results indicate that chronic treatment with Fasudil induces anxiety-like behaviors that are likely the consequence of ROCK1 and/or ROCK2 inhibition. Our findings may have implications for several ongoing clinical trials using Fasudil or other ROCK-based therapeutics.

Medial prefrontal cortex in neurological diseases

The medial prefrontal cortex (mPFC) is a crucial cortical region that integrates information from numerous cortical and subcortical areas and converges updated information to output structures. It plays essential roles in the cognitive process, regulation of emotion, motivation, and sociability. Dysfunction of the mPFC has been found in various neurological and psychiatric disorders, such as depression, anxiety disorders, schizophrenia, autism spectrum disorders, Alzheimer's disease, Parkinson's disease, and addiction. In the present review, we summarize the preclinical and clinical studies to illustrate the role of the mPFC in these neurological diseases.

Klotho deficiency affects the spine morphology and network synchronization of neurons

Klotho-deficient mice rapidly develop cognitive impairment and show some evidence of the onset of neurodegeneration. However, it is impossible to investigate the long-term consequences on the brain because of the dramatic shortening of lifespan caused by systemic klotho deficiency. As klotho expression is downregulated with advancing organismal age, understanding the mechanisms of klotho action is important for developing novel strategies to support healthy brain aging. Previously, we reported that klotho-deficient mice show enhanced long-term potentiation prior to the onset of cognitive impairment. To inform this unusual phenotype, herein, we examined neuronal structure and in vitro synaptic function. Our results indicate that klotho deficiency causes the population of dendritic spines to shift towards increased head diameter and decreased length consistent with mature, mushroom type spines. Multi-electrode array recordings from klotho-deficient neurons show increased synchronous firing and activity changes reflective of increased neuronal network activity. Supplementation of the neuronal growth media with recombinant shed klotho corrected some but not all of the activity changes caused by klotho deficiency. Last, in vivo we found that klotho-deficient mice have a decreased latency to induced seizure activity. Together these data show that klotho-deficient memory impairments are underpinned by structural and functional changes that may preclude ongoing normal cognition.

Pharmacologic inhibition of LIMK1 provides dendritic spine resilience against β-amyloid

Alzheimer's disease (AD) therapies predominantly focus on β-amyloid (Aβ), but Aβ effects may be maximal before clinical symptoms appear. Downstream of Aβ, dendritic spine loss correlates most strongly with cognitive decline in AD. Rho-associated kinases (ROCK1 and ROCK2) regulate the actin cytoskeleton, and ROCK1 and ROCK2 protein abundances are increased in early AD. Here, we found that the increased abundance of ROCK1 in cultured primary rat hippocampal neurons reduced dendritic spine length through a myosin-based pathway, whereas the increased abundance of ROCK2 induced spine loss through the serine and threonine kinase LIMK1. Aβ42 oligomers can activate ROCKs. Here, using static imaging studies combined with multielectrode array analyses, we found that the ROCK2-LIMK1 pathway mediated Aβ42-induced spine degeneration and neuronal hyperexcitability. Live-cell microscopy revealed that pharmacologic inhibition of LIMK1 rendered dendritic spines resilient to Aβ42 oligomers. Treatment of hAPP mice with a LIMK1 inhibitor rescued Aβ-induced hippocampal spine loss and morphologic aberrations. Our data suggest that therapeutically targeting LIMK1 may provide dendritic spine resilience to Aβ and therefore may benefit cognitively normal patients that are at high risk for developing dementia.

Wheel Running Improves Motor Function and Spinal Cord Plasticity in Mice With Genetic Absence of the Corticospinal Tract

Our previous studies showed that mutant mice with congenital absence of the corticospinal tract (CST) undergo spontaneous remodeling of motor networks to partially compensate for absent CST function. Here, we asked whether voluntary wheel running could further improve locomotor plasticity in CST-deficient mice. Adult mutant mice were randomly allocated to a “runners” group with free access to a wheel, or a “non-runners” group with no access to a wheel. In comparison with non-runners, there was a significant motor improvement including fine movement, grip strength, decreased footslip errors in runners after 8-week training, which was supported by the elevated amplitude of electromyography recording and increased neuromuscular junctions in the biceps. In runners, terminal ramifications of monoaminergic and rubrospinal descending axons were significantly increased in spinal segments after 12 weeks of exercise compared to non-runners. 5-ethynyl-2′-deoxyuridine (EDU) labeling showed that proliferating cells, 90% of which were Olig2-positive oligodendrocyte progenitors, were 4.8-fold more abundant in runners than in non-runners. In 8-week runners, RNAseq analysis of spinal samples identified 404 genes up-regulated and 398 genes down-regulated, and 69 differently expressed genes involved in signal transduction, among which the NF-κB, PI3K-Akt and cyclic AMP (cAMP) signaling were three top pathways. Twelve-week training induced a significant elevation of postsynaptic density protein 95 (PSD95), synaptophysin 38 and myelin basic protein (MBP), but not of brain derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) and insulin like growth factor-1 (IGF-1). Thus, locomotor training activates multiple signaling pathways, contributes to neural plasticity and functional improvement, and might palliate locomotor deficits in patients.

Cellular senescence is associated with reorganization of the microtubule cytoskeleton

Senescent cells undergo structural and functional changes that affect essentially every aspect of cell physiology. To date, the impact of senescence on the cytoskeleton is poorly understood. This study evaluated the cytoskeleton in two independent cellular models of kidney epithelium senescence. Our work identified multiple senescence-related alterations that impact microtubules and filamentous actin during interphase. Both filamentous systems reorganized profoundly when cells became senescent. As such, microtubule stability increased during senescence, making these filaments more resistant to disassembly in the cold or by nocodazole. Microtubule stabilization was accompanied by enhanced α-tubulin acetylation on lysine 40 and the depletion of HDAC6, the major deacetylase for α-tubulin lysine 40. Rho-associated kinase Rock1 is an upstream regulator that modulates key properties of the cytoplasmic cytoskeleton. Our research shows that Rock1 concentrations were reduced significantly in senescent cells, and we revealed a mechanistic link between microtubule stabilization and Rock1 depletion. Thus, Rock1 overexpression partially restored the cold sensitivity of microtubules in cells undergoing senescence. Additional components relevant to microtubules were affected by senescence. Specifically, we uncovered the senescence-related loss of the microtubule nucleating protein γ-tubulin and aberrant formation of γ-tubulin foci. Concomitant with the alterations of microtubule and actin filaments, senescent cells displayed functional changes. In particular, cell migration was impaired significantly in senescent cells. Taken together, our study identified new senescence-associated deficiencies of the microtubule and actin cytoskeleton, provided insights into the underlying molecular mechanisms and demonstrated functional consequences that are important to the physiology and function of renal epithelial cells.