Increased dendrite branching in AbetaPP/PS1 mice and elongation of dendrite arbors by fasudil administration

Rock inhibitors in Alzheimer's disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disease and cause of dementia. AD pathology primarily involves the formation of amyloid β (Aβ) plaques and neurofibrillary tangles containing hyperphosphorylated tau (p-tau). While Aβ targeted treatments have shown clinical promise, other aspects of AD pathology such as microgliosis, astrocytosis, synaptic loss, and hypometabolism may be viable targets for treatment. Among notable novel therapeutic approaches, the Ras homolog (Rho)-associated kinases (ROCKs) are being investigated as targets for AD treatment, based on the observations that ROCK1/2 levels are elevated in AD, and activation or inhibition of ROCKs changes dendritic/synaptic structures, protein aggregate accumulation, inflammation, and gliosis. This review will highlight key findings on the effects of ROCK inhibition in Aβ and ptau pathologies, as well as its effects on neuroinflammation, synaptic density, and potentially metabolism and bioenergetics.

RTP801 interacts with the tRNA ligase complex and dysregulates its RNA ligase activity in Alzheimer's disease

RTP801/REDD1 is a stress-responsive protein overexpressed in neurodegenerative diseases such as Alzheimer's disease (AD) that contributes to cognitive deficits and neuroinflammation. Here, we found that RTP801 interacts with HSPC117, DDX1 and CGI-99, three members of the tRNA ligase complex (tRNA-LC), which ligates the excised exons of intron-containing tRNAs and the mRNA exons of the transcription factor XBP1 during the unfolded protein response (UPR). We also found that RTP801 modulates the mRNA ligase activity of the complex in vitro since RTP801 knockdown promoted XBP1 splicing and the expression of its transcriptional target, SEC24D. Conversely, RTP801 overexpression inhibited the splicing of XBP1. Similarly, in human AD postmortem hippocampal samples, where RTP801 is upregulated, we found that XBP1 splicing was dramatically decreased. In the 5xFAD mouse model of AD, silencing RTP801 expression in hippocampal neurons promoted Xbp1 splicing and prevented the accumulation of intron-containing pre-tRNAs. Finally, the tRNA-enriched fraction obtained from 5xFAD mice promoted abnormal dendritic arborization in cultured hippocampal neurons, and RTP801 silencing in the source neurons prevented this phenotype. Altogether, these results show that elevated RTP801 impairs RNA processing in vitro and in vivo in the context of AD and suggest that RTP801 inhibition could be a promising therapeutic approach.

Early chronic fasudil treatment rescues hippocampal alterations in the Ts65Dn model for down syndrome

Down syndrome (DS) is the most common genetic disorder associated with intellectual disability. To study this syndrome, several mouse models have been developed. Among the most common is the Ts65Dn model, which mimics most of the alterations observed in DS. Ts65Dn mice, as humans with DS, show defects in the structure, density, and distribution of dendritic spines in the cerebral cortex and hippocampus. Fasudil is a potent inhibitor of the RhoA kinase pathway, which is involved in the formation and stabilization of dendritic spines. Our study analysed the effect of early chronic fasudil treatment on the alterations observed in the hippocampus of the Ts65Dn model. We observed that treating Ts65Dn mice with fasudil induced an increase in neural plasticity in the hippocampus: there was an increment in the expression of PSA-NCAM and BDNF, in the dendritic branching and spine density of granule neurons, as well as in cell proliferation and neurogenesis in the subgranular zone. Finally, the treatment reduced the unbalance between excitation and inhibition present in this model. Overall, early chronic treatment with fasudil increases cell plasticity and eliminates differences with euploid animals.

Effect of the ROCK inhibitor fasudil on the brain proteomic profile in the tau transgenic mouse model of Alzheimer's disease

Introduction

The goal of this study is to explore the pharmacological potential of the amyloid-reducing vasodilator fasudil, a selective Ras homolog (Rho)-associated kinases (ROCK) inhibitor, in the P301S tau transgenic mouse model (Line PS19) of neurodegenerative tauopathy and Alzheimer's disease (AD).

Methods

We used LC-MS/MS, ELISA and bioinformatic approaches to investigate the effect of treatment with fasudil on the brain proteomic profile in PS19 tau transgenic mice. We also explored the efficacy of fasudil in reducing tau phosphorylation, and the potential beneficial and/or toxic effects of its administration in mice.

Results

Proteomic profiling of mice brains exposed to fasudil revealed the activation of the mitochondrial tricarboxylic acid (TCA) cycle and blood-brain barrier (BBB) gap junction metabolic pathways. We also observed a significant negative correlation between the brain levels of phosphorylated tau (pTau) at residue 396 and both fasudil and its metabolite hydroxyfasudil.

Conclusions

Our results provide evidence on the activation of proteins and pathways related to mitochondria and BBB functions by fasudil treatment and support its further development and therapeutic potential for AD.

ROCK Inhibitor Fasudil Attenuates Neuroinflammation and Associated Metabolic Dysregulation in the Tau Transgenic Mouse Model of Alzheimer's Disease

BACKGROUND

The pathological manifestations of Alzheimer's disease (AD) include not only brain amyloid β protein (Aβ) containing neuritic plaques and hyperphosphorylated tau (p-- tau) containing neurofibrillary tangles but also microgliosis, astrocytosis, and neurodegeneration mediated by metabolic dysregulation and neuroinflammation.

METHODS

While antibody-based therapies targeting Aβ have shown clinical promise, effective therapies targeting metabolism, neuroinflammation, and p-tau are still an urgent need. Based on the observation that Ras homolog (Rho)-associated kinases (ROCK) activities are elevated in AD, ROCK inhibitors have been explored as therapies in AD models. This study determines the effects of fasudil, a ROCK inhibitor, on neuroinflammation and metabolic regulation in the P301S tau transgenic mouse line PS19 that models neurodegenerative tauopathy and AD. Using daily intraperitoneal (i.p.) delivery of fasudil in PS19 mice, we observed a significant hippocampal-specific decrease of the levels of phosphorylated tau (pTau Ser202/Thr205), a decrease of GFAP+ cells and glycolytic enzyme Pkm1 in broad regions of the brain, and a decrease in mitochondrial complex IV subunit I in the striatum and thalamic regions.

RESULTS

Although no overt detrimental phenotype was observed, mice dosed with 100 mg/kg/day for 2 weeks exhibited significantly decreased mitochondrial outer membrane and electron transport chain (ETC) protein abundance, as well as ETC activities.

CONCLUSION

Our results provide insights into dose-dependent neuroinflammatory and metabolic responses to fasudil and support further refinement of ROCK inhibitors for the treatment of AD.

Neurodegenerative Disease Associated Pathways in the Brains of Triple Transgenic Alzheimer's Model Mice Are Reversed Following Two Weeks of Peripheral Administration of Fasudil

The pan Rho-associated coiled-coil-containing protein kinase (ROCK) inhibitor fasudil acts as a vasodilator and has been used as a medication for post-cerebral stroke for the past 29 years in Japan and China. More recently, based on the involvement of ROCK inhibition in synaptic function, neuronal survival, and processes associated with neuroinflammation, it has been suggested that the drug may be repurposed for neurodegenerative diseases. Indeed, fasudil has demonstrated preclinical efficacy in many neurodegenerative disease models. To facilitate an understanding of the wider biological processes at play due to ROCK inhibition in the context of neurodegeneration, we performed a global gene expression analysis on the brains of Alzheimer's disease model mice treated with fasudil via peripheral IP injection. We then performed a comparative analysis of the fasudil-driven transcriptional profile with profiles generated from a meta-analysis of multiple neurodegenerative diseases. Our results show that fasudil tends to drive gene expression in a reverse sense to that seen in brains with post-mortem neurodegenerative disease. The results are most striking in terms of pathway enrichment analysis, where pathways perturbed in Alzheimer's and Parkinson's diseases are overwhelmingly driven in the opposite direction by fasudil treatment. Thus, our results bolster the repurposing potential of fasudil by demonstrating an anti-neurodegenerative phenotype in a disease context and highlight the potential of in vivo transcriptional profiling of drug activity.

p120-catenin subfamily members have distinct as well as shared effects on dendrite morphology during neuron development in vitro

Dendritic arborization is essential for proper neuronal connectivity and function. Conversely, abnormal dendrite morphology is associated with several neurological pathologies like Alzheimer's disease and schizophrenia. Among major intrinsic mechanisms that determine the extent of the dendritic arbor is cytoskeletal remodeling. Here, we characterize and compare the impact of the four proteins involved in cytoskeletal remodeling-vertebrate members of the p120-catenin subfamily-on neuronal dendrite morphology. In relation to each of their own distributions, we find that p120-catenin and delta-catenin are expressed at relatively higher proportions in growth cones compared to ARVCF-catenin and p0071-catenin; ARVCF-catenin is expressed at relatively high proportions in the nucleus; and all catenins are expressed in dendritic processes and the soma. Through altering the expression of each p120-subfamily catenin in neurons, we find that exogenous expression of either p120-catenin or delta-catenin correlates with increased dendritic length and branching, whereas their respective depletion decreases dendritic length and branching. While increasing ARVCF-catenin expression also increases dendritic length and branching, decreasing expression has no grossly observable morphological effect. Finally, increasing p0071-catenin expression increases dendritic branching, but not length, while decreasing expression decreases dendritic length and branching. These distinct localization patterns and morphological effects during neuron development suggest that these catenins have both shared and distinct roles in the context of dendrite morphogenesis.

Reduction of Phosphorylated Tau in Alzheimer's Disease Induced Pluripotent Stem Cell-Derived Neuro-Spheroids by Rho-Associated Coiled-Coil Kinase Inhibitor Fasudil

BACKGROUND

Alzheimer's disease (AD) is the most predominant form of dementia. Rho-associated coiled coil kinase (ROCK) inhibitor, fasudil, is one of the candidate drugs against the AD progression.

OBJECTIVE

We aimed to investigate possible changes of AD associated markers in three-dimensional neuro-spheroids (3D neuro-spheroids) generated from induced pluripotent stem cells derived from AD patients or healthy control subjects (HC) and to determine the impact of pharmacological intervention with the ROCK inhibitor fasudil.

METHODS

We treated 3D neuro-spheroids with fasudil and tested the possible effect on AD markers by ELISA, transcriptomic and proteomic analyses.

RESULTS

Transcriptomic analysis revealed a reduction in the expression of AKT serine/threonine-protein kinase 1 (AKT1) in AD neuro-spheroids, compared to HC. This decrease was reverted in the presence of fasudil. Proteomic analysis showed up- and down-regulation of proteins related to AKT pathway in fasudil-treated neuro-spheroids. We found an evident increase of phosphorylated tau at four different residues (pTau181, 202, 231, and 396) in AD compared to HC-derived neuro-spheroids. This was accompanied by a decrease of secreted clusterin (clu) and an increase of intracellular clu levels in AD patient-derived neuro-spheroids. Increases of phosphorylated tau in AD patient-derived neuro-spheroids were suppressed in the presence of fasudil.

CONCLUSIONS

Fasudil modulates clu protein levels and enhances AKT1 that results in the suppression of AD associated tau phosphorylation.

Advantages of Rho-associated kinases and their inhibitor fasudil for the treatment of neurodegenerative diseases

Ras homolog (Rho)-associated kinases (ROCKs) belong to the serine-threonine kinase family, which plays a pivotal role in regulating the damage, survival, axon guidance, and regeneration of neurons. ROCKs are also involved in the biological effects of immune cells and glial cells, as well as the development of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Previous studies by us and others confirmed that ROCKs inhibitors attenuated the symptoms and progression of experimental models of the abovementioned neurodegenerative diseases by inhibiting neuroinflammation, regulating immune imbalance, repairing the blood-brain barrier, and promoting nerve repair and myelin regeneration. Fasudil, the first ROCKs inhibitor to be used clinically, has a good therapeutic effect on neurodegenerative diseases. Fasudil increases the activity of neural stem cells and mesenchymal stem cells, thus optimizing cell therapy. This review will systematically describe, for the first time, the effects of abnormal activation of ROCKs on T cells, B cells, microglia, astrocytes, oligodendrocytes, and pericytes in neurodegenerative diseases of the central nervous system, summarize the therapeutic potential of fasudil in several experimental models of neurodegenerative diseases, and clarify the possible cellular and molecular mechanisms of ROCKs inhibition. This review also proposes that fasudil is a novel potential treatment, especially in combination with cell-based therapy. Findings from this review add support for further investigation of ROCKs and its inhibitor fasudil for the treatment of neurodegenerative diseases.

miR-29a and the PTEN-GSK3β axis are involved in aluminum-induced damage to primary hippocampal neuronal networks

We previously reported that aluminum (Al) can cause a range of neurotoxic injuries including progressive irreversible synaptic structural damage and synaptic dysfunction, and eventually neuronal deaths. Mechanism of Al-induced electrophysiological and neuronal connectivity changes in neurons may indicate damage to the neuronal network. Here, mouse primary hippocampal neurons were cultured on micro-electrode array (MEA)- and high-content analysis (HCA)-related plates, showing that Al exposure significantly inhibited hippocampal neuronal electrical spike activity and neurite outgrowth characterized by a reduction in neurite branching and a decrease in the average total neurite length in relation to both Al dose and time of incubation. In recent years, miR-29a/ phosphatase and tensin homolog (PTEN) have been found to play pivotal roles in the morphogenesis of neurons, it has been confirmed in vitro and in vivo that the PTEN-Glycogen synthase kinase-3β (GSK-3β) axis regulates neurite outgrowth. The present study demonstrated that increases in Al exposure and dose gradually reduce miR-29a expression. Up-regulation of miR-29a in the hippocampal neurons by lentivirus transfection reversed the decrease in electrical spike activity and the reduction in both neurite branching and length induced by Al. Moreover, miR-29a suppressed the expression of PTEN and increased the level of phosphorylated Protein Kinase B (p-AKT) and p-GSK-3β which were inhibited by the Al treatment. This suggests that miR-29a is critically involved in the functional and structural neuronal damage induced by Al and is a potential target for Al neurotoxicity. Moreover, the reduction of neurite length and branching induced by Al exposure was regulated by miR-29a and its target neuronal PTEN-GSK3β signaling pathway, which also represents a possible mechanism of Al-induced the inhibition of the electrical activity. Collectively, Al-induced damage to the neuronal network occurred through miR-29a-mediated alterations of the PTEN-GSK3β signaling pathway.

Pharmacological Modulators of Small GTPases of Rho Family in Neurodegenerative Diseases

Classical Rho GTPases, including RhoA, Rac1, and Cdc42, are members of the Ras small GTPase superfamily and play essential roles in a variety of cellular functions. Rho GTPase signaling can be turned on and off by specific GEFs and GAPs, respectively. These features empower Rho GTPases and their upstream and downstream modulators as targets for scientific research and therapeutic intervention. Specifically, significant therapeutic potential exists for targeting Rho GTPases in neurodegenerative diseases due to their widespread cellular activity and alterations in neural tissues. This study will explore the roles of Rho GTPases in neurodegenerative diseases with focus on the applications of pharmacological modulators in recent discoveries. There have been exciting developments of small molecules, nonsteroidal anti-inflammatory drugs (NSAIDs), and natural products and toxins for each classical Rho GTPase category. A brief overview of each category followed by examples in their applications will be provided. The literature on their roles in various diseases [e.g., Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), Frontotemporal dementia (FTD), and Multiple sclerosis (MS)] highlights the unique and broad implications targeting Rho GTPases for potential therapeutic intervention. Clearly, there is increasing knowledge of therapeutic promise from the discovery of pharmacological modulators of Rho GTPases for managing and treating these conditions. The progress is also accompanied by the recognition of complex Rho GTPase modulation where targeting its signaling can improve some aspects of pathogenesis while exacerbating others in the same disease model. Future directions should emphasize the importance of elucidating how different Rho GTPases work in concert and how they produce such widespread yet different cellular responses during neurodegenerative disease progression.

Drug repositioning and repurposing for Alzheimer disease

Drug repositioning and repurposing can enhance traditional drug development efforts and could accelerate the identification of new treatments for individuals with Alzheimer disease (AD) dementia and mild cognitive impairment. Transcriptional profiling offers a new and highly efficient approach to the identification of novel candidates for repositioning and repurposing. In the future, novel AD transcriptional signatures from cells isolated at early stages of disease, or from human neurons or microglia that carry mutations that increase the risk of AD, might be used as probes to identify additional candidate drugs. Phase II trials assessing repurposed agents must consider the best target population for a specific candidate therapy as well as the mechanism of action of the treatment. In this Review, we highlight promising compounds to prioritize for clinical trials in individuals with AD, and discuss the value of Delphi consensus methodology and evidence-based reviews to inform this prioritization process. We also describe emerging work, focusing on the potential value of transcript signatures as a cost-effective approach to the identification of novel candidates for repositioning.

Non-Muscle Myosin 2A (NM2A): Structure, Regulation and Function

Non-muscle myosin 2A (NM2A) is a motor cytoskeletal enzyme with crucial importance from the early stages of development until adulthood. Due to its capacity to convert chemical energy into force, NM2A powers the contraction of the actomyosin cytoskeleton, required for proper cell division, adhesion and migration, among other cellular functions. Although NM2A has been extensively studied, new findings revealed that a lot remains to be discovered concerning its spatiotemporal regulation in the intracellular environment. In recent years, new functions were attributed to NM2A and its activity was associated to a plethora of illnesses, including neurological disorders and infectious diseases. Here, we provide a concise overview on the current knowledge regarding the structure, the function and the regulation of NM2A. In addition, we recapitulate NM2A-associated diseases and discuss its potential as a therapeutic target.

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.

Rho-kinase inhibition has antidepressant-like efficacy and expedites dendritic spine pruning in adolescent mice

Adolescence represents a critical period of neurodevelopment, defined by structural and synaptic pruning within the prefrontal cortex. While characteristic of typical development, this structural instability may open a window of vulnerability to developing neuropsychiatric disorders, including depression. Thus, therapeutic interventions that support or expedite neural remodeling in adolescence may be advantageous. Here, we inhibited the neuronally-expressed cytoskeletal regulatory factor Rho-kinase (ROCK), focusing primarily on the clinically-viable ROCK inhibitor fasudil. ROCK inhibition had rapid antidepressant-like effects in adolescent mice, and its efficacy was comparable to ketamine and fluoxetine. It also modified levels of the antidepressant-related signaling factors, tropomyosin/tyrosine receptor kinase B and Akt, as well as the postsynaptic marker PSD-95, in the ventromedial prefrontal cortex (vmPFC). Meanwhile, adolescent-typical dendritic spine pruning on excitatory pyramidal neurons in the vmPFC was expedited. Further, vmPFC-specific shRNA-mediated reduction of ROCK2, the dominant ROCK isoform in the brain, had antidepressant-like consequences. We cautiously suggest that ROCK inhibitors may have therapeutic potential for adolescent-onset depression.

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

Rho-associated protein kinases (ROCK) 1 and 2 are attractive drug targets for a range of neurologic disorders; however, a critical barrier to ROCK-based therapeutics is ambiguity over whether there are isoform-specific roles for ROCKs in neuronal structural plasticity. Here, we used a genetics approach to address this long-standing question by analyzing both male and female adult ROCK1+/- and ROCK2+/- mice compared to littermate controls. Individual pyramidal neurons in the medial prefrontal cortex (mPFC) were targeted for iontophoretic microinjection of fluorescent dye, followed by high-resolution confocal microscopy and neuronal 3D reconstructions for morphometry analysis. Increased apical and basal dendritic length and intersections were observed in ROCK1+/- but not ROCK2+/- mice. Although dendritic spine densities were comparable among genotypes, apical spine length was decreased in ROCK1+/- but increased in ROCK2+/- mice. Spine head and neck diameter were reduced similarly in ROCK1+/- and ROCK2+/- mice; however, certain spine morphologic subclasses were more affected than others in a genotype-dependent manner. Biochemical analyses of ROCK substrates in synaptic fractions revealed that phosphorylation of LIM kinase and cofilin were reduced in ROCK1+/- and ROCK2+/- mice, while phosphorylation of myosin light chain was decreased exclusively in ROCK1+/- mice. Collectively, these observations implicate ROCK1 as a novel regulatory factor of neuronal dendritic structure and detail distinct and complementary roles of ROCKs in mPFC dendritic spine structure.

A role for APP in Wnt signalling links synapse loss with β-amyloid production

In Alzheimer's disease (AD), the canonical Wnt inhibitor Dickkopf-1 (Dkk1) is induced by β-amyloid (Aβ) and shifts the balance from canonical towards non-canonical Wnt signalling. Canonical (Wnt-β-catenin) signalling promotes synapse stability, while non-canonical (Wnt-PCP) signalling favours synapse retraction; thus Aβ-driven synapse loss is mediated by Dkk1. Here we show that the Amyloid Precursor Protein (APP) co-activates both arms of Wnt signalling through physical interactions with Wnt co-receptors LRP6 and Vangl2, to bi-directionally modulate synapse stability. Furthermore, activation of non-canonical Wnt signalling enhances Aβ production, while activation of canonical signalling suppresses Aβ production. Together, these findings identify a pathogenic-positive feedback loop in which Aβ induces Dkk1 expression, thereby activating non-canonical Wnt signalling to promote synapse loss and drive further Aβ production. The Swedish familial AD variant of APP (APP_Swe) more readily co-activates non-canonical, at the expense of canonical Wnt activity, indicating that its pathogenicity likely involves direct effects on synapses, in addition to increased Aβ production. Finally, we report that pharmacological inhibition of the Aβ-Dkk1-Aβ positive feedback loop with the drug fasudil can restore the balance between Wnt pathways, prevent dendritic spine withdrawal in vitro, and reduce Aβ load in vivo in mice with advanced amyloid pathology. These results clarify a relationship between Aβ accumulation and synapse loss and provide direction for the development of potential disease-modifying treatments.

Therapeutic effect of Rho kinase inhibitor FSD-C10 in a mouse model of Alzheimer's disease

Fasudil, a Rho kinase (ROCK) inhibitor, effectively inhibits disease severity in a mouse model of Alzheimer's disease (AD). However, given its significant limitations, including a relatively narrow safety window and poor oral bioavailability, Fasudil is not suitable for long-term use. Thus, screening for ROCK inhibitor(s) that are more efficient, safer, can be used orally and suitable for long-term use in the treatment of neurodegenerative disorders is required. The main purpose of the present study is to explore whether FSD-C10, a novel ROCK inhibitor, has therapeutic potential in amyloid precursor protein/presenilin-1 transgenic (APP/PS1 Tg) mice, and to determine possible mechanisms of its action. The results showed that FSD-C10 effectively improved learning and memory impairment, accompanied by reduced expression of amyloid-β 1-42 (Aβ_1-42), Tau protein phosphorylation (P-tau) and β-site APP-cleaving enzyme in the hippocampus and cortex area of brain. In addition, FSD-C10 administration boosted the expression of synapse-associated proteins, such as postynaptic density protein 95, synaptophsin, α-amino 3-hydroxy-5-methyl-4-isoxa-zolep-propionate receptor and neurotrophic factors, e,g., brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor. Taken together, our results demonstrate that FSD-C10 has therapeutic potential in the AD mouse model, possibly through inhibiting the formation of Aβ_1-42 and P-tau, and promoting the generation of synapse-associated proteins and neurotrophic factors.

Inhibition of RhoA reduces propofol-mediated growth cone collapse, axonal transport impairment, loss of synaptic connectivity, and behavioural deficits

BACKGROUND

Exposure of the developing brain to propofol results in cognitive deficits. Recent data suggest that inhibition of neuronal apoptosis does not prevent cognitive defects, suggesting mechanisms other than neuronal apoptosis play a role in anaesthetic neurotoxicity. Proper neuronal growth during development is dependent upon growth cone morphology and axonal transport. Propofol modulates actin dynamics in developing neurones, causes RhoA-dependent depolymerisation of actin, and reduces dendritic spines and synapses. We hypothesised that RhoA inhibition prevents synaptic loss and subsequent cognitive deficits. The present study tested whether RhoA inhibition with the botulinum toxin C3 (TAT-C3) prevents propofol-induced synapse and neurite loss, and preserves cognitive function.

METHODS

RhoA activation, growth cone morphology, and axonal transport were measured in neonatal rat neurones (5-7 days in vitro) exposed to propofol. Synapse counts (electron microscopy), dendritic arborisation (Golgi-Cox), and network connectivity were measured in mice (age 28 days) previously exposed to propofol at postnatal day 5-7. Memory was assessed in adult mice (age 3 months) previously exposed to propofol at postnatal day 5-7.

RESULTS

Propofol increased RhoA activation, collapsed growth cones, and impaired retrograde axonal transport of quantum dot-labelled brain-derived neurotrophic factor, all of which were prevented with TAT-C3. Adult mice previously treated with propofol had decreased numbers of total hippocampal synapses and presynaptic vesicles, reduced hippocampal dendritic arborisation, and infrapyramidal mossy fibres. These mice also exhibited decreased hippocampal-dependent contextual fear memory recall. All anatomical and behavioural changes were prevented with TAT-C3 pre-treatment.

CONCLUSION

Inhibition of RhoA prevents propofol-mediated hippocampal neurotoxicity and associated cognitive deficits.

MicroRNA-16 targets mRNA involved in neurite extension and branching in hippocampal neurons during presymptomatic prion disease

The mechanisms that lead to neuronal death in neurodegenerative diseases are poorly understood. Prion diseases, like many more common disorders such as Alzheimer's and Parkinson's diseases, are characterized by the progressive accumulation of misfolded disease-specific proteins. The earliest changes observed in brain tissue include a reduction in synaptic number and retraction of dendritic spines, followed by reduced length and branching of neurites. These pathologies are observable during presymptomatic stages of disease and are accompanied by altered expression of transcripts that include miRNAs. Here we report that miR-16 localized within hippocampal CA1 neurons is increased during early prion disease. Modulating miR-16 expression in mature murine hippocampal neurons by expression from a lentivirus, thus mimicking the modest increase seen in vivo, was found to induce neurodegeneration. This was characterized by retraction of neurites and reduced branching. We performed immunoprecipitation of the miR-16 enriched RISC complex, and identified associated transcripts from the co-immunoprecipitated RNA (Ago2 RIP-Chip). These transcripts were enriched with predicted binding sites for miR-16, including the validated miR-16 targets APP and BCL2, as well as numerous novel targets. In particular, genes within the neurotrophin receptor mediated MAPK/ERK pathway were potentially regulated by miR-16; including TrkB (NTRK2), MEK1 (MAP2K1) and c-Raf (RAF). Increased miR-16 expression in neurons during presymptomatic prion disease and reduction in proteins involved in MAPK/ERK signaling represents a possible mechanism by which neurite length and branching are decreased during early stages of disease.

Inhibiting Rho kinase promotes goal-directed decision making and blocks habitual responding for cocaine

The prelimbic prefrontal cortex is necessary for associating actions with their consequences, enabling goal-directed decision making. We find that the strength of action–outcome conditioning correlates with dendritic spine density in prelimbic cortex, suggesting that new action–outcome learning involves dendritic spine plasticity. To test this, we inhibited the cytoskeletal regulatory factor Rho kinase. We find that the inhibitor fasudil enhances action–outcome memory, resulting in goal-directed behavior in mice that would otherwise express stimulus-response habits. Fasudil transiently reduces prelimbic cortical dendritic spine densities during a period of presumed memory consolidation, but only when paired with new learning. Fasudil also blocks habitual responding for cocaine, an effect that persists over time, across multiple contexts, and depends on actin polymerization. We suggest that Rho kinase inhibition promotes goal-oriented action selection by augmenting the plasticity of prelimbic cortical dendritic spines during the formation of new action–outcome memories.

Action-outcome learning requires the prelimbic prefrontal cortex. Here the authors report that fasudil, a Rho kinase inhibitor, reduces dendritic spine densities on prelimbic neurons in an activity-dependent manner, stimulating goal-directed actions, and reducing habitual responding for cocaine.

TDP-43 misexpression causes defects in dendritic growth

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) share overlapping genetic causes and disease symptoms, and are linked neuropathologically by the RNA binding protein TDP-43 (TAR DNA binding protein-43 kDa). TDP-43 regulates RNA metabolism, trafficking, and localization of thousands of target genes. However, the cellular and molecular mechanisms by which dysfunction of TDP-43 contributes to disease pathogenesis and progression remain unclear. Severe changes in the structure of neuronal dendritic arbors disrupt proper circuit connectivity, which in turn could contribute to neurodegenerative disease. Although aberrant dendritic morphology has been reported in non-TDP-43 mouse models of ALS and in human ALS patients, this phenotype is largely unexplored with regards to TDP-43. Here we have employed a primary rodent neuronal culture model to study the cellular effects of TDP-43 dysfunction in hippocampal and cortical neurons. We show that manipulation of TDP-43 expression levels causes significant defects in dendritic branching and outgrowth, without an immediate effect on cell viability. The effect on dendritic morphology is dependent on the RNA-binding ability of TDP-43. Thus, this model system will be useful in identifying pathways downstream of TDP-43 that mediate dendritic arborization, which may provide potential new avenues for therapeutic intervention in ALS/FTD.

Differential expression of cytoskeletal regulatory factors in the adolescent prefrontal cortex: Implications for cortical development

The prevalence of depression, anxiety, schizophrenia, and drug and alcohol use disorders peaks during adolescence. Further, up to 50% of "adult" mental health disorders emerge in adolescence. During adolescence, the prefrontal cortex (PFC) undergoes dramatic structural reorganization, in which dendritic spines and synapses are refined, pruned, and stabilized. Understanding the molecular mechanisms that underlie these processes should help to identify factors that influence the development of psychiatric illness. Here we briefly discuss the anatomical connections of the medial and orbital prefrontal cortex (mPFC and OFC, respectively). We then present original findings suggesting that dendritic spines on deep-layer excitatory neurons in the mouse mPFC and OFC prune at different adolescent ages, with later pruning in the OFC. In parallel, we used Western blotting to define levels of several cytoskeletal regulatory proteins during early, mid-, and late adolescence, focusing on tropomyosin-related kinase receptor B (TrkB) and β1-integrin-containing receptors and select signaling partners. We identified regional differences in the levels of several proteins in early and midadolescence that then converged in early adulthood. We also observed age-related differences in TrkB levels, both full-length and truncated isoforms, Rho-kinase 2, and synaptophysin in both PFC subregions. Finally, we identified changes in protein levels in the dorsal and ventral hippocampus that were distinct from those in the PFC. We conclude with a general review of the manner in which TrkB- and β1-integrin-mediated signaling influences neuronal structure in the postnatal brain. Elucidating the role of cytoskeletal regulatory factors throughout adolescence may identify critical mechanisms of PFC development. © 2016 Wiley Periodicals, Inc.

Induction and Blockade of Adolescent Cocaine-Induced Habits

BACKGROUND

Cocaine use during adolescence increases vulnerability to drug dependence and decreases the likelihood that individuals will seek treatment as adults. Understanding how early-life cocaine exposure influences decision-making processes in adulthood is thus critically important.

METHODS

Adolescent or adult mice were exposed to subchronic cocaine, then behavioral sensitivity to changes in the predictive relationship between actions and their consequences was tested. Dendritic spines on the principal pyramidal neurons of the orbitofrontal prefrontal cortex (oPFC) were also imaged and enumerated. To determine whether cytoskeletal regulatory systems in the oPFC influenced decision-making strategies, we then inhibited the activity of Abl family and Rho kinases as well as NR2B-containing N-methyl-D-aspartate receptors. We also attempted to block the reinstatement of cocaine seeking in cocaine self-administering mice.

RESULTS

Adult mice with a history of subchronic cocaine exposure in adolescence engaged habit-based response strategies at the expense of goal-directed decision-making strategies and had fewer dendritic spines in the oPFC. Inhibition of the cytoskeletal regulatory Abl family kinases in the oPFC recapitulated these neurobehavioral deficiencies, whereas Rho kinase inhibition corrected response strategies. Additionally, the NR2B-selective N-methyl-D-aspartate receptor antagonists ifenprodil and CP-101,606 blocked cocaine-induced habits; this was dependent on Abl family signaling in the oPFC. Ifenprodil also mitigated cue-induced reinstatement of cocaine seeking in mice self-administering cocaine.

CONCLUSIONS

We suggest that adolescent cocaine exposure confers a bias toward habit-based behavior in adulthood via long-term cellular structural modifications in the oPFC. Treatments aimed at mitigating the durable consequences of early-life cocaine use may benefit from targeting cytoskeletal regulatory systems.

Non-muscle myosin II in disease: mechanisms and therapeutic opportunities

The actin motor protein non-muscle myosin II (NMII) acts as a master regulator of cell morphology, with a role in several essential cellular processes, including cell migration and post-synaptic dendritic spine plasticity in neurons. NMII also generates forces that alter biochemical signaling, by driving changes in interactions between actin-associated proteins that can ultimately regulate gene transcription. In addition to its roles in normal cellular physiology, NMII has recently emerged as a critical regulator of diverse, genetically complex diseases, including neuronal disorders, cancers and vascular disease. In the context of these disorders, NMII regulatory pathways can be directly mutated or indirectly altered by disease-causing mutations. NMII regulatory pathway genes are also increasingly found in disease-associated copy-number variants, particularly in neuronal disorders such as autism and schizophrenia. Furthermore, manipulation of NMII-mediated contractility regulates stem cell pluripotency and differentiation, thus highlighting the key role of NMII-based pharmaceuticals in the clinical success of stem cell therapies. In this Review, we discuss the emerging role of NMII activity and its regulation by kinases and microRNAs in the pathogenesis and prognosis of a diverse range of diseases, including neuronal disorders, cancer and vascular disease. We also address promising clinical applications and limitations of NMII-based inhibitors in the treatment of these diseases and the development of stem-cell-based therapies.

Rho Kinases in Health and Disease: From Basic Science to Translational Research

Rho-associated kinases ROCK1 and ROCK2 are key regulators of actin cytoskeleton dynamics downstream of Rho GTPases that participate in the control of important physiologic functions, S including cell contraction, migration, proliferation, adhesion, and inflammation. Several excellent review articles dealing with ROCK function and regulation have been published over the past few years. Although a brief overview of general molecular, biochemical, and functional properties of ROCKs is included, an effort has been made to produce an original work by collecting and synthesizing recent studies aimed at translating basic discoveries from cell and experimental models into knowledge of human physiology, pathophysiological mechanisms, and medical therapeutics. This review points out the specificity and distinct roles of ROCK1 and ROCK2 isoforms highlighted in the last few years. Results obtained from genetically modified mice and genetic analysis in humans are discussed. This review also addresses the involvement of ROCKs in human diseases and the potential use of ROCK activity as a biomarker or a pharmacological target for specific inhibitors.

Merging advanced technologies with classical methods to uncover dendritic spine dynamics: A hot spot of synaptic plasticity

The structure of dendritic spines determines synaptic efficacy, a plastic process that mediates information processing in the vertebrate nervous system. Aberrant spine morphology, including alterations in shape, size, and number, are common in different brain diseases. Because of this, accurate and unbiased characterization of dendritic spine structure is vital to our ability to explore and understand their involvement in neuronal development, synaptic plasticity, and synaptic failure in neurological diseases. Investigators have attempted to elucidate the precise structure and function of dendritic spines for more than a hundred years, but their fundamental role in synaptic plasticity and neurological diseases remains elusive. Limitations and ambiguities in imaging techniques have exacerbated the challenges of acquiring accurate information about spines and spine features. However, recent advancements in molecular biology, protein engineering, immuno-labeling techniques, and the use of super-resolution nano-microscopy along with powerful image analysis software have provided a better understanding of dendritic spine architecture. Here we describe the pros and cons of the classical staining techniques used to study spine morphology, and the alteration of dendritic spines in various neuropathological conditions. Finally, we highlight recent advances in super-resolved nanoscale microscopy, and their potentials and pitfalls when used to explore dendritic spine dynamics.

Synaptic Cytoskeletal Plasticity in the Prefrontal Cortex Following Psychostimulant Exposure

Addiction is characterized by maladaptive decision-making, a loss of control over drug consumption and habit-like drug seeking despite adverse consequences. These cognitive changes may reflect the effects of drugs of abuse on prefrontal cortical neurobiology. Here, we review evidence that amphetamine and cocaine fundamentally remodel the structure of excitatory neurons in the prefrontal cortex. We summarize evidence in particular that these psychostimulants have opposing effects in the medial and orbital prefrontal cortices ('mPFC' and 'oPFC', respectively). For example, amphetamine and cocaine increase dendrite length and spine density in the mPFC, while dendrites are impoverished and dendritic spines are eliminated in the oPFC. We will discuss evidence that certain cytoskeletal regulatory proteins expressed in the oPFC and implicated in postnatal (adolescent) neural development also regulate behavioral sensitivity to cocaine. These findings potentially open a window of opportunity for the identification of novel pharmacotherapeutic targets in the treatment of drug abuse disorders in adults, as well as in drug-vulnerable adolescent populations. Finally, we will discuss the behavioral implications of drug-related dendritic spine elimination in the oPFC, with regard to reversal learning tasks and tasks that assess the development of reward-seeking habits, both used to model aspects of addiction in rodents.

Adolescent cocaine exposure simplifies orbitofrontal cortical dendritic arbors

Cocaine and amphetamine remodel dendritic spines within discrete cortico-limbic brain structures including the orbitofrontal cortex (oPFC). Whether dendrite structure is similarly affected, and whether pre-existing cellular characteristics influence behavioral vulnerabilities to drugs of abuse, remain unclear. Animal models provide an ideal venue to address these issues because neurobehavioral phenotypes can be defined both before, and following, drug exposure. We exposed mice to cocaine from postnatal days 31–35, corresponding to early adolescence, using a dosing protocol that causes impairments in an instrumental reversal task in adulthood. We then imaged and reconstructed excitatory neurons in deep-layer oPFC. Prior cocaine exposure shortened and simplified arbors, particularly in the basal region. Next, we imaged and reconstructed orbital neurons in a developmental-genetic model of cocaine vulnerability—the p190rhogap+/– mouse. p190RhoGAP is an actin cytoskeleton regulatory protein that stabilizes dendrites and dendritic spines, and p190rhogap+/– mice develop rapid and robust locomotor activation in response to cocaine. Despite this, oPFC dendritic arbors were intact in drug-naïve p190rhogap+/– mice. Together, these findings provide evidence that adolescent cocaine exposure has long-term effects on dendrite structure in the oPFC, and they suggest that cocaine-induced modifications in dendrite structure may contribute to the behavioral effects of cocaine more so than pre-existing structural abnormalities in this cell population.

Rho kinase: A new target for treatment of cerebral ischemia/reperfusion injury

Rho kinase inhibitor fasudil hydrochloride has been shown to reduce cerebral vasospasm, to inhibit inflammation and apoptosis and to promote the recovery of neurological function. However, the effect of fasudil hydrochloride on claudin-5 protein expression has not been reported after cerebral ischemia/reperfusion. Therefore, this study sought to explore the effects of fasudil hydrochloride on blood-brain barrier permeability, growth-associated protein-43 and claudin-5 protein expression, and to further understand the neuroprotective effect of fasudil hydrochloride. A focal cerebral ischemia/reperfusion model was established using the intraluminal suture technique. Fasudil hydrochloride (15 mg/kg) was intraperitoneally injected once a day. Neurological deficit was evaluated using Longa's method. Changes in permeability of blood-brain barrier were measured using Evans blue. Changes in RhoA, growth-associated protein-43 and claudin-5 protein expression were detected using immunohistochemistry and western blotting. Results revealed that fasudil hydrochloride noticeably contributed to the recovery of neurological function, improved the function of blood-brain barrier, inhibited RhoA protein expression, and upregulated growth-associated protein-43 and claudin-5 protein expression following cerebral ischemia/reperfusion. Results indicated that Rho kinase exhibits a certain effect on neurovascular damage following cerebral ischemia/reperfusion. Intervention targeted Rho kinase might be a new therapeutic target in the treatment of cerebral ischemia/reperfusion.

Recombinant DNA vaccine against neurite outgrowth inhibitors attenuates behavioral deficits and decreases Abeta in an Alzheimer's disease mouse model

Alzheimer's disease (AD) is a chronic neurodegenerative disease that causes a progressive loss in learning and memory capabilities and eventually results in dementia. The non-renewable nature of neurons in the central nervous system leads to the basic pathological changes that are related to the various behavioral and psychological symptoms of AD. Oligodendrocyte- and myelin-related neurite outgrowth inhibitors (NOIs) tend to hinder the regeneration of neurons. We designed a recombinant DNA vaccine composed of multiple specific inhibitory domains of NOIs. Vaccination induced effective antibodies against the specific domains in the sera of mice treated with a DNA primed-vaccinia virus boost regimen. The vaccine attenuated neuronal degeneration in the mouse brain and protected the model mice from behavioral deficits. Vaccination also decreased the formation of soluble Aβ oligomer and amyloid plaques in the co-transgenic mice brain. What's more, astrocytosis in brains of APP/PS1 co-transgenic mice was also relieved. The results suggested that immunotherapy with multiple specific domains of myelin- and oligodendrocyte-related NOIs may be a promising approach for Alzheimer's disease and other degenerative central nervous system diseases.

Rho kinase inhibitor fasudil protects against β-amyloid-induced hippocampal neurodegeneration in rats

BACKGROUND AND PURPOSE

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, and Aβ-induced neuronal damage is the major pathology of AD. There is increasing evidence that neuroinflammation induced by Aβ is also involved in the pathogenesis of AD. Fasudil is a Rho kinase inhibitor and has been reported to have neuroprotective effects. In this study, the main purpose is to investigate whether fasudil has beneficial effects on cognitive impairment and neuronal toxicity induced by Aβ.

METHODS AND RESULTS

In the present study, intracerebroventricular injection of Aβ1-42 to rats resulted in marked cognitive impairment, severe neuronal damage, as well as increased IL-1β, tumor necrosis factor alpha (TNF-α) production, and NF-κB activation. Administration of fasudil significantly ameliorated the spatial learning and memory impairment, attenuated neuronal loss, and neuronal injury induced by Aβ1-42 . In addition, fasudil inhibited IL-1β and TNF-α production and NF-κB activation in the rat brain.

CONCLUSIONS

Fasudil can protect against Aβ-induced hippocampal neurodegeneration by suppressing inflammatory response, suggesting that fasudil might be a promising agent for the prevention and treatment of inflammation-related diseases, such as AD.

Developmentally divergent effects of Rho-kinase inhibition on cocaine- and BDNF-induced behavioral plasticity

Prefrontal cortical dendritic spine remodeling during adolescence may open a window of vulnerability to pathological stimuli that impact long-term behavioral outcomes, but causal mechanisms remain unclear. We administered the Rho-kinase inhibitor HA-1077 during three adolescent periods in mice to destabilize dendritic spines. In adulthood, cocaine-induced locomotor activity was exaggerated. By contrast, when administered in adulthood, HA-1077 had no psychomotor consequences and normalized food-reinforced instrumental responding after orbitofrontal-selective knockdown of Brain-derived neurotrophic factor, a potential factor in addiction. Thus, early-life Rho-kinase inhibition confers cocaine vulnerability, but may actually protect against pathological reward-seeking - particularly in cases of diminished neurotrophic support - in adulthood.

Molecular mechanisms of dendrite morphogenesis

Dendrites are key integrators of synaptic information in neurons and play vital roles in neuronal plasticity. Hence, it is necessary that dendrite arborization is precisely controlled and coordinated with synaptic activity to ensure appropriate functional neural network integrity. In the past several years, it has become increasingly clear that several cell intrinsic and extrinsic mechanisms contribute to dendritic arborization. In this review, we will discuss some of the molecular mechanisms that regulate dendrite morphogenesis, particularly in cortical and hippocampal pyramidal neurons and some of the implications of aberrant dendritic morphology for human disease. Finally, we will discuss the current challenges and future directions in the field.

Methods of dendritic spine detection: from Golgi to high-resolution optical imaging

Dendritic spines, the bulbous protrusions that form the postsynaptic half of excitatory synapses, are one of the most prominent features of neurons and have been imaged and studied for over a century. In that time, changes in the number and morphology of dendritic spines have been correlated to the developmental process as well as the pathophysiology of a number of neurodegenerative diseases. Due to the sheer scale of synaptic connectivity in the brain, work to date has merely scratched the surface in the study of normal spine function and pathology. This review will highlight traditional approaches to the imaging of dendritic spines and newer approaches made possible by advances in microscopy, protein engineering, and image analysis. The review will also describe recent work that is leading researchers toward the possibility of a systematic and comprehensive study of spine anatomy throughout the brain.

Cell adhesion signaling pathways: First responders to cocaine exposure?

The 100 billion neurons comprising the human brain are wired together using structural extensions termed axons, dendrites and dendritic spines. Addictive drugs remodel dendritic spine structure in certain brain regions and with repeated exposure, induce psychomotor sensitization and impair behavioral flexibility. We recently reported that low-dose cocaine exposure, in combination with knockout of Arg-an adhesion-regulated nonreceptor tyrosine kinase that stabilizes neuronal shape starting in adolescence-recapitulates both features of chronic drug exposure in rodents. In light of these and other recent findings in the field, we suggest that cell adhesion receptors and their downstream cytoskeletal effectors act as "first responders" to psychostimulant exposure. In this model, cell adhesion factors act to stabilize existing dendritic spines in response to cocaine, and reduced expression/function is expected to increase vulnerability. Moreover, this model anticipates that increased sensitivity to psychostimulants in adolescence relates to neuronal pruning processes that occur during this developmental period.