Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. TBIs, which range in severity from mild to severe, occur when a traumatic event, such as a fall, a traffic accident, ...or a blow, causes the brain to move rapidly within the skull, resulting in damage. Long-term consequences of TBI can include motor and cognitive deficits and emotional disturbances that result in a reduced quality of life and work productivity. Recovery from TBI can be challenging due to a lack of effective treatment options for repairing TBI-induced neural damage and alleviating functional impairments. Central nervous system (CNS) injury and disease are known to induce the activation of the small GTPase RhoA and its downstream effector Rho kinase (ROCK). Activation of this signaling pathway promotes cell death and the retraction and loss of neural processes and synapses, which mediate information flow and storage in the brain. Thus, inhibiting RhoA-ROCK signaling has emerged as a promising approach for treating CNS disorders. In this review, we discuss targeting the RhoA-ROCK pathway as a therapeutic strategy for treating TBI and summarize the recent advances in the development of RhoA-ROCK inhibitors.
Abstract E6 associated protein is an E3 ubiquitin ligase encoded by the gene Ube3a . Deletion or loss of function of the maternally inherited allele of Ube3a leads to Angelman syndrome. In the ...present study, we show that maternal loss of Ube3a ( Ube3a m−/p+ ) in the mouse model leads to motor deficits that could be attributed to the dysfunction of the nigrostriatal pathway. The number of tyrosine hydroxylase positive neurons in the substantia nigra was significantly reduced in Ube3a m−/p+ mice as compared to the wild type counterparts. The Ube3a m−/p+ mice performed poorly in behavioural paradigms sensitive to nigrostriatal dysfunction. Even though the tyrosine hydroxylase staining was apparently the same in the striatum of both genotypes, the presynaptic and postsynaptic proteins were significantly reduced in Ube3a m−/p+ mice. These findings suggest that the abnormality in the nigrostriatal pathway along with the cerebellum produces the observed motor dysfunctions in Ube3a m−/p+ mice.
Clones of excitatory neurons derived from a common progenitor have been proposed to serve as elementary information processing modules in the neocortex. To characterize the cell types and circuit ...diagram of clonally related excitatory neurons, we performed multi-cell patch clamp recordings and Patch-seq on neurons derived from
-positive progenitors labeled by tamoxifen induction at embryonic day 10.5. The resulting clones are derived from two radial glia on average, span cortical layers 2-6, and are composed of a random sampling of transcriptomic cell types. We find an interaction between shared lineage and connection type: related neurons are more likely to be connected vertically across cortical layers, but not laterally within the same layer. These findings challenge the view that related neurons show uniformly increased connectivity and suggest that integration of vertical
-clonal input with lateral
-clonal input may represent a developmentally programmed connectivity motif supporting the emergence of functional circuits.
Traumatic brain injury (TBI) causes extensive neural damage, often resulting in long-term cognitive impairments. Unfortunately, effective treatments for TBI remain elusive. The RhoA-ROCK signaling ...pathway is a potential therapeutic target since it is activated by TBI and can promote the retraction of dendritic spines/synapses, which are critical for information processing and memory storage. To test this hypothesis, RhoA-ROCK signaling was blocked by RhoA deletion from postnatal neurons or treatment with the ROCK inhibitor fasudil. We found that TBI impairs both motor and cognitive performance and inhibiting RhoA-ROCK signaling alleviates these deficits. Moreover, RhoA-ROCK inhibition prevents TBI-induced spine remodeling and mature spine loss. These data argue that TBI elicits pathological spine remodeling that contributes to behavioral deficits by altering synaptic connections, and RhoA-ROCK inhibition enhances functional recovery by blocking this detrimental effect. As fasudil has been safely used in humans, our results suggest that it could be repurposed to treat TBI.
Synapses mediate information flow between neurons and undergo plastic changes in response to experience, which is critical for learning and memory. Conversely, synaptic defects impair information ...processing and underlie many brain pathologies. Rho-family GTPases control synaptogenesis by transducing signals from extracellular stimuli to the cytoskeleton and nucleus. The Rho-GTPases Rac1 and Cdc42 promote synapse development and the growth of axons and dendrites, while RhoA antagonizes these processes. Despite its importance, many aspects of Rho-GTPase signaling remain relatively unknown. Rho-GTPases are activated by guanine nucleotide exchange factors (GEFs) and inhibited by GTPase-activating proteins (GAPs). Though the number of both GEFs and GAPs greatly exceeds that of Rho-GTPases, loss of even a single GEF or GAP often has profound effects on cognition and behavior. Here, we explore how the actions of specific GEFs and GAPs give rise to the precise spatiotemporal activation patterns of Rho-GTPases in neurons. We consider the effects of coupling GEFs and GAPs targeting the same Rho-GTPase and the modular pathways that connect specific cellular stimuli with a given Rho-GTPase via different GEFs. We discuss how the creation of sharp borders between Rho-GTPase activation zones is achieved by pairing a GEF for one Rho-GTPase with a GAP for another and the extensive crosstalk between different Rho-GTPases. Given the importance of synapses for cognition and the fundamental roles that Rho-GTPases play in regulating them, a detailed understanding of Rho-GTPase signaling is essential to the progress of neuroscience.
Parkinson's disease (PD) is a common neurodegenerative disorder caused mainly because of the loss of dopaminergic neurons in the substantia nigra. Protein inclusions called Lewy bodies are the most ...common pathological hallmark of PD and other synucleinopathies. Because the main component of these inclusions is α-synuclein, aggregation of this protein is thought to be a key pathogenic event in this disease. In the present investigation we report that E6 associated protein (E6-AP), a HECT (homologous to E6-AP C-terminus) domain ubiquitin ligase is a component of Lewy bodies in post-mortem PD brain. In the cell culture model, we demonstrate that endogenous E6-AP colocalizes with α-synuclein in juxtanuclear aggregates. E6-AP is also recruited to the centrosome upon inhibition of the proteasome function suggesting its involvement in the degradation of misfolded proteins. Over-expression of E6-AP enhances the degradation of wild type as well as the mutant forms of α-synuclein in a proteasome-dependent manner. E6-AP also promotes the degradation of the more toxic oligomeric forms of α-synuclein. Our data suggests that E6-AP is involved in the clearance of α-synuclein.
The small GTPase Rac1 orchestrates actin-dependent remodeling essential for numerous cellular processes including synapse development. While precise spatiotemporal regulation of Rac1 is necessary for ...its function, little is known about the mechanisms that enable Rac1 activators (GEFs) and inhibitors (GAPs) to act in concert to regulate Rac1 signaling. Here, we identify a regulatory complex composed of a Rac-GEF (Tiam1) and a Rac-GAP (Bcr) that cooperate to control excitatory synapse development. Disruption of Bcr function within this complex increases Rac1 activity and dendritic spine remodeling, resulting in excessive synaptic growth that is rescued by Tiam1 inhibition. Notably, EphB receptors utilize the Tiam1-Bcr complex to control synaptogenesis. Following EphB activation, Tiam1 induces Rac1-dependent spine formation, whereas Bcr prevents Rac1-mediated receptor internalization, promoting spine growth over retraction. The finding that a Rac-specific GEF/GAP complex is required to maintain optimal levels of Rac1 signaling provides an important insight into the regulation of small GTPases.
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•The Rac-GAP Bcr is a critical regulator of synapse and spine development•Tiam1 and Bcr form a GEF/GAP complex, which precisely regulates Rac1 signaling•EphB receptors utilize this GEF/GAP complex to promote excitatory synaptogenesis•Bcr restricts Rac1-mediated EphB endocytosis, enabling Tiam1-induced spine growth
Um et al. identify a Rac1 GTPase regulatory complex composed of a GEF (Tiam1) and GAP (Bcr) that cooperate to control Rac1 activity and excitatory synapse development. In response to EphB receptor activation, Tiam1 induces Rac1-dependent dendritic spine formation, whereas Bcr prevents Rac1-mediated EphB internalization, promoting spine growth over retraction.
The small GTPases RhoA and Rac1 are key cytoskeletal regulators that function in a mutually antagonistic manner to control the migration and morphogenesis of a broad range of cell types. However, ...their role in shaping the cerebellum, a unique brain structure composed of an elaborate set of folia separated by fissures of different lengths, remains largely unexplored. Here we show that dysregulation of both RhoA and Rac1 signaling results in abnormal cerebellar ontogenesis. Ablation of RhoA from neuroprogenitor cells drastically alters the timing and placement of fissure formation, the migration and positioning of granule and Purkinje cells, the alignment of Bergmann glia, and the integrity of the basement membrane, primarily in the anterior lobules. Furthermore, in the absence of RhoA, granule cell precursors located at the base of fissures fail to undergo cell shape changes required for fissure initiation. Many of these abnormalities can be recapitulated by deleting RhoA specifically from granule cell precursors but not postnatal glia, indicating that RhoA functions in granule cell precursors to control cerebellar morphogenesis. Notably, mice with elevated Rac1 activity due to loss of the Rac1 inhibitors Bcr and Abr show similar anterior cerebellar deficits, including ectopic neurons and defects in fissure formation, Bergmann glia organization and basement membrane integrity. Together, our results suggest that RhoA and Rac1 play indispensable roles in patterning cerebellar morphology.
Dendritic arbor architecture profoundly impacts neuronal connectivity and function, and aberrant dendritic morphology characterizes neuropsychiatric disorders. Here, we identify the adhesion-GPCR ...BAI1 as an important regulator of dendritic arborization. BAI1 loss from mouse or rat hippocampal neurons causes dendritic hypertrophy, whereas BAI1 overexpression precipitates dendrite retraction. These defects specifically manifest as dendrites transition from growth to stability. BAI1-mediated growth arrest is independent of its Rac1-dependent synaptogenic function. Instead, BAI1 couples to the small GTPase RhoA, driving late RhoA activation in dendrites coincident with growth arrest. BAI1 loss lowers RhoA activation and uncouples it from dendrite dynamics, causing overgrowth. None of BAI1's known downstream effectors mediates BAI1-dependent growth arrest. Rather, BAI1 associates with the Rho-GTPase regulatory protein Bcr late in development and stimulates its cryptic RhoA-GEF activity, which functions together with its Rac1-GAP activity to terminate arborization. Our results reveal a late-acting signaling pathway mediating a key transition in dendrite development.
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