Nanoparticle Delivery of Fidgetin siRNA as a Microtubule-based Therapy to Augment Nerve Regeneration

Downregulation of Fidgetin-Like 2 Increases Microglial Function: The Relationship Between Microtubules, Morphology, and Activity

The microtubule cytoskeleton regulates microglial morphology, motility, and effector functions. The microtubule-severing enzyme, fidgetin-like 2 (FL2), negatively regulates cell motility and nerve regeneration, making it a promising therapeutic target for central nervous system injury. Microglia perform important functions in response to inflammation and injury, but how FL2 affects microglia is unclear. In this study, we investigated the role of FL2 in microglial morphology and injury responses in vitro. We first determined that the pro-inflammatory stimulus, lipopolysaccharide (LPS), induced a dose- and time-dependent reduction in FL2 expression associated with reduced microglial ramification. We then administered nanoparticle-encapuslated FL2 siRNA to knockdown FL2 and assess microglial functions compared to negative control siRNA and vehicle controls. Time-lapse live-cell microscopy showed that FL2 knockdown increased the velocity of microglial motility. After incubation with fluorescently labeled IgG-opsonized beads, FL2 knockdown increased phagocytosis. Microglia were exposed to low-dose LPS after nanoparticle treatment to model injury-induced cytokine secretion. FL2 knockdown enhanced LPS-induced cytokine secretion of IL-1α, IL-1β, and TNFα. These results identify FL2 as a regulator of microglial morphology and suggest that FL2 can be targeted to increase or accelerate microglial injury responses.

Evolution and functional divergence of the Fidgetin family

The Fidgetin (FIGN) family, which comprises FIGN, Fidgetin-like 1 (FIGNL1), and Fidgetin-like 2 (FIGNL2), is a vital group of microtubule-severing proteins. These proteins feature a conserved AAA+ domain essential for ATPase activity and a hexameric assembly. This review provides an in-depth analysis of the evolution and functional divergence of the FIGN family members, highlighting their role in the dynamic organization of the cytoskeleton. We further explore their broader biological functions across various species, systems, and subcellular localization. Although the FIGN family is conserved, each member exhibits unique structural characteristics and functions that reflect their evolutionary adaptations. FIGNL1 is found across animal species, while FIGNL2 is specific to vertebrates, thereby indicating its more recent evolutionary origin. Moreover, synteny analysis has revealed that FIGN is located in a more conserved genomic region compared to FIGNL2, which has undergone substantial evolutionary changes. The expression patterns of the FIGN members also vary across organisms and tissues. For example, FIGNL2 shows a notably reduced expression in the mammalian nervous system compared to that in lower vertebrates. The FIGN family members have distinct roles in microtubule severing, cell division, and DNA repair. Specifically, FIGN is involved in cell division and neuronal regeneration, FIGNL1 in axonal growth and DNA repair, and FIGNL2 in cell migration and vascular development. Their involvement in these processes underscores their role as potential biomarkers for certain cancers as well as therapeutic targets for diseases affecting the nervous system and cardiovascular development. All these evolutionary insights and functional distinctions of the FIGN family offer a comprehensive framework for understanding cytoskeletal regulation and its implications in health and disease.

Comprehensive characterization of Fidgetin on tumor immune microenvironment evaluation and immunotherapy in human hepatocellular carcinoma

Most cancers have a downregulation of Fidgetin (FIGN), which has been linked to tumor growth. However, there aren't many papers that mention FIGN's connection to hepatocellular carcinoma (HCC). Here, FIGN expression in HCC tissues was markedly reduced as compared to nearby normal liver tissues. According to univariate and multivariate Cox regression, it served as an independent predictor of survival outcomes. Patients with high levels of FIGN expression had a worse outcome. FIGN was shown to be engaged in immune-related pathways and to have a positive correlation with immunological score and immune cells according to KEGG pathway analysis. In HCC patients, FIGN was substantially linked with immunological checkpoints and the hot tumor state. Additionally, immunotherapy and chemotherapy showed a significant therapeutic response in HCC patients with low FIGN expression. This research revealed that FIGN expression was tightly related to hepatoma immunity and might be employed as a biomarker to predict patient prognosis and guide medication.

The fidgetin family: Shaking things up among the microtubule-severing enzymes

The microtubule cytoskeleton is required for several crucial cellular processes, including chromosome segregation, cell polarity and orientation, and intracellular transport. These functions rely on microtubule stability and dynamics, which are regulated by microtubule-binding proteins (MTBPs). One such type of regulator is the microtubule-severing enzymes (MSEs), which are ATPases Associated with Diverse Cellular Activities (AAA+ ATPases). The most recently identified family are the fidgetins, which contain three members: fidgetin, fidgetin-like 1 (FL1), and fidgetin-like 2 (FL2). Of the three known MSE families, the fidgetins have the most diverse range of functions in the cell, spanning mitosis/meiosis, development, cell migration, DNA repair, and neuronal function. Furthermore, they offer intriguing novel therapeutic targets for cancer, cardiovascular disease, and wound healing. In the two decades since their first report, there has been great progress in our understanding of the fidgetins; however, there is still much left unknown about this unusual family. This review aims to consolidate the present body of knowledge of the fidgetin family of MSEs and to inspire deeper exploration into the fidgetins and the MSEs as a whole.

Fidgetin interacting with microtubule end binding protein EB3 affects axonal regrowth in spinal cord injury

Fidgetin, a microtubule-severing enzyme, regulates neurite outgrowth, axonal regeneration, and cell migration by trimming off the labile domain of microtubule polymers. Because maintenance of the microtubule labile domain is essential for axon initiation, elongation, and navigation, it is of interest to determine whether augmenting the microtubule labile domain via depletion of fidgetin serves as a therapeutic approach to promote axonal regrowth in spinal cord injury. In this study, we constructed rat models of spinal cord injury and sciatic nerve injury. Compared with spinal cord injury, we found that expression level of tyrosinated microtubules in the labile portion of microtubules continuously increased, whereas fidgetin decreased after peripheral nerve injury. Depletion of fidgetin enhanced axon regeneration after spinal cord injury, whereas expression level of end binding protein 3 (EB3) markedly increased. Next, we performed RNA interference to knockdown EB3 or fidgetin. We found that deletion of EB3 did not change fidgetin expression. Conversely, deletion of fidgetin markedly increased expression of tyrosinated microtubules and EB3. Deletion of fidgetin increased the amount of EB3 at the end of neurites and thereby increased the level of tyrosinated microtubules. Finally, we deleted EB3 and overexpressed fidgetin. We found that fidgetin trimmed tyrosinated tubulins by interacting with EB3. When fidgetin was deleted, the labile portion of microtubules was elongated, and as a result the length of axons and number of axon branches were increased. These findings suggest that fidgetin can be used as a novel therapeutic target to promote axonal regeneration after spinal cord injury. Furthermore, they reveal an innovative mechanism by which fidgetin preferentially severs labile microtubules.

Nano-encapsulated anandamide reduces inflammatory cytokines in vitro and lesion severity in a murine model of cutaneous lupus erythematosus

Cutaneous lupus erythematosus (CLE) is a heterogeneous autoimmune skin disease which occurs independently and in conjunction with systemic lupus erythematosus. Drug development for CLE is severely lacking. Anandamide (AEA) is a primary endocannabinoid which exhibits immunomodulatory effects through mixed cannabinoid receptor agonism. We evaluated AEA as topical treatment for CLE and assessed benefits of nanoparticle encapsulation (AEA-NP) on cutaneous drug penetration, delivery and biological activity. Compared to untreated controls, AEA-NP decreased IL-6 and MCP-1 in UVB-stimulated keratinocytes (p < 0.05) in vitro. In BALB/c mice, AEA-NP displayed improved cutaneous penetration, extended release and persistence of AEA in the follicular unit extending to the base after 24 h. Utilizing the MRL-lpr lupus murine model, twice weekly treatment of lesions with topical AEA-NP for 10 weeks led to decreased clinical and histologic lesion scores compared to unencapsulated AEA and untreated controls (p < 0.05). Prophylactic application of AEA-NP to commonly involved areas on MRL-lpr mice similarly resulted in decreased clinical and histologic scores when compared to controls (p < 0.05), and reduced C3 and IBA-1 in lesional tissue (p < 0.05). The demonstrated clinical and immunomodulatory effects of treatment with AEA support its potential as therapy for CLE. This work also suggests that encapsulation of AEA improves penetration and treatment efficacy. Future studies will be conducted to assess full therapeutic potential.

Fidgetin impacts axonal growth and branching in a local mTOR signal dependent manner

Neurons require a constant increase in protein synthesis during axonal growth and regeneration. AKT-mTOR is a central pathway for mammalian cell survival and regeneration. Fidgetin (Fign) is an ATP-dependent microtubule (MT)-severing enzyme whose functions are associated with neurite outgrowth, axon regeneration and cell migration. Although most previous studies have indicated that depletion of Fign is involved in those biological activities by increasing labile MT mass, it remains unknown whether mTOR activation contributes to this process. Here, we showed that depletion of Fign enhanced p-mTOR/p-S6K activation, and the mTOR inhibitor Rapamycin inhibited axon outgrowth and p-rpS6 activation. We then investigated the effects of neuronal-specific Fign deletion in a rat spinal cord hemisection model by injecting syn-GFP Fign shRNA virus. BBB values revealed an improvement in functional recovery. The p-mTOR was activated along with neuronal Fign depletion. The syn-mCherry virus showed more sprouting neurites entering the injury region, which was confirmed by immunostaining GAP43 protein. Further, we showed that Fign siRNA treatment promoted axon outgrowth and branching, whose underlying mechanism was firstly attributed to local activation of the mTOR pathway, and increased MT dynamicity. Finally, considering L-leucine, promotes axonal growth and neuronal survival, we applied L-leucine with Fign depletion after spinal cord injury or in chondroitin sulfate proteoglycan inhibitory molecules. The phenomenon of synergistically augmented axon regeneration was observed. In summary, our results indicated a novel local mTOR pathway for fidgetin to impact axon growth and provided a combined strategy in SCI.

Bridging the gap of axonal regeneration in the central nervous system: A state of the art review on central axonal regeneration

Neuronal regeneration in the central nervous system (CNS) is an important field of research with relevance to all types of neuronal injuries, including neurodegenerative diseases. The glial scar is a result of the astrocyte response to CNS injury. It is made up of many components creating a complex environment in which astrocytes play various key roles. The glial scar is heterogeneous, diverse and its composition depends upon the injury type and location. The heterogeneity of the glial scar observed in different situations of CNS damage and the consequent implications for axon regeneration have not been reviewed in depth. The gap in this knowledge will be addressed in this review which will also focus on our current understanding of central axonal regeneration and the molecular mechanisms involved. The multifactorial context of CNS regeneration is discussed, and we review newly identified roles for components previously thought to solely play an inhibitory role in central regeneration: astrocytes and p75NTR and discuss their potential and relevance for deciding therapeutic interventions. The article ends with a comprehensive review of promising new therapeutic targets identified for axonal regeneration in CNS and a discussion of novel ways of looking at therapeutic interventions for several brain diseases and injuries.

The Role of Spastin in Axon Biology

Neurons are highly polarized cells with elaborate shapes that allow them to perform their function. In neurons, microtubule organization—length, density, and dynamics—are essential for the establishment of polarity, growth, and transport. A mounting body of evidence shows that modulation of the microtubule cytoskeleton by microtubule-associated proteins fine tunes key aspects of neuronal cell biology. In this respect, microtubule severing enzymes—spastin, katanin and fidgetin—a group of microtubule-associated proteins that bind to and generate internal breaks in the microtubule lattice, are emerging as key modulators of the microtubule cytoskeleton in different model systems. In this review, we provide an integrative view on the latest research demonstrating the key role of spastin in neurons, specifically in the context of axonal cell biology. We focus on the function of spastin in the regulation of microtubule organization, and axonal transport, that underlie its importance in the intricate control of axon growth, branching and regeneration.

Microtubule Dynamics Following Central and Peripheral Nervous System Axotomy

Disturbance in the neuronal network leads to instability in the microtubule (MT) railroad of axons, causing hindrance in the intra-axonal transport and making it difficult to re-establish the broken network. Peripheral nervous system (PNS) neurons can stabilize their MTs, leading to the formation of regeneration-promoting structures called "growth cones". However, central nervous system (CNS) neurons lack this intrinsic reparative capability and, instead, form growth-incompetent structures called "retraction bulbs", which have a disarrayed MT network. It is evident from various studies that although axonal regeneration depends on both cell-extrinsic and cell-intrinsic factors, any therapy that aims at axonal regeneration ultimately converges onto MTs. Understanding the neuronal MT dynamics will help develop effective therapeutic strategies in diseases where the MT network gets disrupted, such as spinal cord injury, traumatic brain injury, multiple sclerosis, and amyotrophic lateral sclerosis. It is also essential to know the factors that aid or inhibit MT stabilization. In this review, we have discussed the MT dynamics postaxotomy in the CNS and PNS, and factors that can directly influence MT stability in various diseases.

Role of microtubule dynamics in Wallerian degeneration and nerve regeneration after peripheral nerve injury

Wallerian degeneration, the progressive disintegration of distal axons and myelin that occurs after peripheral nerve injury, is essential for creating a permissive microenvironment for nerve regeneration, and involves cytoskeletal reconstruction. However, it is unclear whether microtubule dynamics play a role in this process. To address this, we treated cultured sciatic nerve explants, an in vitro model of Wallerian degeneration, with the microtubule-targeting agents paclitaxel and nocodazole. We found that paclitaxel-induced microtubule stabilization promoted axon and myelin degeneration and Schwann cell dedifferentiation, whereas nocodazole-induced microtubule destabilization inhibited these processes. Evaluation of an in vivo model of peripheral nerve injury showed that treatment with paclitaxel or nocodazole accelerated or attenuated axonal regeneration, as well as functional recovery of nerve conduction and target muscle and motor behavior, respectively. These results suggest that microtubule dynamics participate in peripheral nerve regeneration after injury by affecting Wallerian degeneration. This study was approved by the Animal Care and Use Committee of Southern Medical University, China (approval No. SMU-L2015081) on October 15, 2015.

Dorsal Root Injury-A Model for Exploring Pathophysiology and Therapeutic Strategies in Spinal Cord Injury

Unraveling the cellular and molecular mechanisms of spinal cord injury is fundamental for our possibility to develop successful therapeutic approaches. These approaches need to address the issues of the emergence of a non-permissive environment for axonal growth in the spinal cord, in combination with a failure of injured neurons to mount an effective regeneration program. Experimental in vivo models are of critical importance for exploring the potential clinical relevance of mechanistic findings and therapeutic innovations. However, the highly complex organization of the spinal cord, comprising multiple types of neurons, which form local neural networks, as well as short and long-ranging ascending or descending pathways, complicates detailed dissection of mechanistic processes, as well as identification/verification of therapeutic targets. Inducing different types of dorsal root injury at specific proximo-distal locations provide opportunities to distinguish key components underlying spinal cord regeneration failure. Crushing or cutting the dorsal root allows detailed analysis of the regeneration program of the sensory neurons, as well as of the glial response at the dorsal root-spinal cord interface without direct trauma to the spinal cord. At the same time, a lesion at this interface creates a localized injury of the spinal cord itself, but with an initial neuronal injury affecting only the axons of dorsal root ganglion neurons, and still a glial cell response closely resembling the one seen after direct spinal cord injury. In this review, we provide examples of previous research on dorsal root injury models and how these models can help future exploration of mechanisms and potential therapies for spinal cord injury repair.

Expression of Microtubule Associated Protein Tau in Mouse Pancreatic Islets Is Restricted to Autonomic Nerve Fibers

BACKGROUND

Evidence from clinical studies and basic research has shown a strong correlation between Alzheimer's disease (AD) and type 2 diabetes. Tau, a neuronal microtubule-associated protein, is hyperphosphorylated and aggregated into neurofibrillary tangles in the AD brain. However, the expression of tau in pancreas is under debate.

OBJECTIVE

We determined the expression of tau in mouse pancreas.

METHODS

We used western blots, immunoprecipitation, and immunohistochemical staining to analyze pancreatic expression of tau in mice.

RESULTS

We found that neither total tau nor phosphorylated tau was detectable in the mouse pancreas by western blots. Immunostaining with pan tau antibodies R134d and Tau-5 revealed bright and dense varicosities in the pancreatic islets and the exocrine pancreas. These varicosities were immunoreactive to synapsin 1, a presynaptic marker which can outline autonomic nerve profiles in pancreas, exhibiting complete colocalization with tau. Importantly, endocrine cells in islets did not exhibit specific immunoreactivity to any of pan tau antibodies tested, nor did the exocrine cells.

CONCLUSION

In the mouse pancreas, we found that tau is exclusively expressed in autonomic nerve fibers, but there is no detectable expression in endocrine cells in the islet.

Fidgetin-like 2 negatively regulates axonal growth and can be targeted to promote functional nerve regeneration

The microtubule (MT) cytoskeleton plays a critical role in axon growth and guidance. Here, we identify the MT-severing enzyme fidgetin-like 2 (FL2) as a negative regulator of axon regeneration and a therapeutic target for promoting nerve regeneration after injury. Genetic knockout of FL2 in cultured adult dorsal root ganglion neurons resulted in longer axons and attenuated growth cone retraction in response to inhibitory molecules. Given the axonal growth-promoting effects of FL2 depletion in vitro, we tested whether FL2 could be targeted to promote regeneration in a rodent model of cavernous nerve (CN) injury. The CNs are parasympathetic nerves that regulate blood flow to the penis, which are commonly damaged during radical prostatectomy (RP), resulting in erectile dysfunction (ED). Application of FL2-siRNA after CN injury significantly enhanced functional nerve recovery. Remarkably, following bilateral nerve transection, visible and functional nerve regeneration was observed in 7 out of 8 animals treated with FL2-siRNA, while no control-treated animals exhibited regeneration. These studies identify FL2 as a promising therapeutic target for enhancing regeneration after peripheral nerve injury and for mitigating neurogenic ED after RP - a condition for which, at present, only poor treatment options exist.

FIGNL1 promotes non‑small cell lung cancer cell proliferation

Lung cancer is the most frequently diagnosed cancer and the leading cause of cancer‑associated mortality worldwide. In the present study, a novel molecular therapeutic target for lung cancer was investigated. The protein expression level of fidgetin‑like 1 (FIGNL1) in human lung cancer tissues was determined and its potential functions in the H1299 and A549 lung cancer cell lines was subsequently studied. In addition, the protein expression level of FIGNL1 in 109 lung cancer samples and corresponding para‑cancerous tissues was investigated, using immunohistochemical staining. RNA interference and overexpression of FIGNL1 was used to determine the role of FIGNL1 in regulating cell proliferation, and cDNA microarray analysis was performed to identify the potential regulatory pathways. Lastly, the potential role of FIGNL1 in regulating tumorigenesis in lungs and also the proliferation of lung cancer cells was investigated. Firstly, lung cancer tissues were found to express higher protein levels of FIGNL1 and was significantly associated with decreased cell proliferation, migration and invasion abilities, and enhanced cell death. Overexpression of FIGNL1 significantly promoted cell proliferation, including decreased arrest at the G1 phase of the cell cycle and apoptosis, as well as increased ability for fission and migration. These in vitro findings were consistent with the results of the cell‑line derived xenografts in BALB/c nude mice, where tumor growth was decreased when injected with cells transfected with shFIGNL1. Collectively, these results provide suggest that FIGNL1 is involved in cell growth and tumorigenesis.

Chronic neuronal activation increases dynamic microtubules to enhance functional axon regeneration after dorsal root crush injury

After a dorsal root crush injury, centrally-projecting sensory axons fail to regenerate across the dorsal root entry zone (DREZ) to extend into the spinal cord. We find that chemogenetic activation of adult dorsal root ganglion (DRG) neurons improves axon growth on an in vitro model of the inhibitory environment after injury. Moreover, repeated bouts of daily chemogenetic activation of adult DRG neurons for 12 weeks post-crush in vivo enhances axon regeneration across a chondroitinase-digested DREZ into spinal gray matter, where the regenerating axons form functional synapses and mediate behavioral recovery in a sensorimotor task. Neuronal activation-mediated axon extension is dependent upon changes in the status of tubulin post-translational modifications indicative of highly dynamic microtubules (as opposed to stable microtubules) within the distal axon, illuminating a novel mechanism underlying stimulation-mediated axon growth. We have identified an effective combinatory strategy to promote functionally-relevant axon regeneration of adult neurons into the CNS after injury.

Mechanisms of Axon Elongation Following CNS Injury: What Is Happening at the Axon Tip?

After an injury to the central nervous system (CNS), functional recovery is limited by the inability of severed axons to regenerate and form functional connections with appropriate target neurons beyond the injury. Despite tremendous advances in our understanding of the mechanisms of axon growth, and of the inhibitory factors in the injured CNS that prevent it, disappointingly little progress has been made in restoring function to human patients with CNS injuries, such as spinal cord injury (SCI), through regenerative therapies. Clearly, the large number of overlapping neuron-intrinsic and -extrinsic growth-inhibitory factors attenuates the benefit of neutralizing any one target. More daunting is the distances human axons would have to regenerate to reach some threshold number of target neurons, e.g., those that occupy one complete spinal segment, compared to the distances required in most experimental models, such as mice and rats. However, the difficulties inherent in studying mechanisms of axon regeneration in the mature CNS in vivo have caused researchers to rely heavily on extrapolation from studies of axon regeneration in peripheral nerve, or of growth cone-mediated axon development in vitro and in vivo. Unfortunately, evidence from several animal models, including the transected lamprey spinal cord, has suggested important differences between regeneration of mature CNS axons and growth of axons in peripheral nerve, or during embryonic development. Specifically, long-distance regeneration of severed axons may not involve the actin-myosin molecular motors that guide embryonic growth cones in developing axons. Rather, non-growth cone-mediated axon elongation may be required to propel injured axons in the mature CNS. If so, it may be necessary to use other experimental models to promote regeneration that is sufficient to contact a critical number of target neurons distal to a CNS lesion. This review examines the cytoskeletal underpinnings of axon growth, focusing on the elongating axon tip, to gain insights into how CNS axons respond to injury, and how this might affect the development of regenerative therapies for SCI and other CNS injuries.

Microtubule dynamics in healthy and injured neurons

Most neurons must last a lifetime and their microtubule cytoskeleton is an important contributor to their longevity. Neurons have some of the most stable microtubules of all cells, but the tip of every microtubule remains dynamic and, although requiring constant GTP consumption, microtubules are always being rebuilt. While some ongoing level of rebuilding always occurs, overall microtubule stability can be modulated in response to injury and stress as well as the normal developmental process of pruning. Specific microtubule severing proteins act in different contexts to increase microtubule dynamicity and promote degeneration and pruning. After axon injury, complex changes in dynamics occur and these are important for both neuroprotection induced by injury and subsequent outgrowth of a new axon. Understanding how microtubule dynamics is modulated in different scenarios, as well as the impact of the changes in stability, is an important avenue to explore for development of strategies to promote neuroprotection and regeneration.

Anti-biofilm activity of garlic extract loaded nanoparticles

The emergence and widespread distribution of multi-drug resistant bacteria are considered as a major public health concern. The inabilities to curb severe infections due to antibiotic resistance have increased healthcare costs as well as patient morbidity and mortality. Bacterial biofilms formed by drug-resistant bacteria add additional challenges to treatment. This study describes a solgel based nanoparticle system loaded with garlic extract (GE-np) that exhibits: i) slow and sustained release of garlic components; ii) stabilization of the active components; and iii) significant enhancement of antimicrobial and antibiofilm activity relative to the free garlic extract. Also, GE-np were efficient in penetrating and disrupting the well-established methicillin-resistant Staphylococcus aureus (MRSA) biofilms. Overall, the study suggests that GE-np might be a promising candidate for the treatment of chronic infections due to biofilm forming drug-resistant bacteria.

Knockdown of Fidgetin Improves Regeneration of Injured Axons by a Microtubule-Based Mechanism

Fidgetin is a microtubule-severing protein that pares back the labile domains of microtubules in the axon. Experimental depletion of fidgetin results in elongation of the labile domains of microtubules and faster axonal growth. To test whether fidgetin knockdown assists axonal regeneration, we plated dissociated adult rat DRGs transduced using AAV5-shRNA-fidgetin on a laminin substrate with spots of aggrecan, a growth-inhibitory chondroitin sulfate proteoglycan. This cell culture assay mimics the glial scar formed after CNS injury. Aggrecan is more concentrated at the edge of the spot, such that axons growing from within the spot toward the edge encounter a concentration gradient that causes growth cones to become dystrophic and axons to retract or curve back on themselves. Fidgetin knockdown resulted in faster-growing axons on both laminin and aggrecan and enhanced crossing of axons from laminin onto aggrecan. Strikingly, axons from within the spot grew more avidly against the inhibitory aggrecan concentration gradient to cross onto laminin, without retracting or curving back. We also tested whether depleting fidgetin improves axonal regeneration in vivo after a dorsal root crush in adult female rats. Whereas control DRG neurons failed to extend axons across the dorsal root entry zone after injury, DRG neurons in which fidgetin was knocked down displayed enhanced regeneration of axons across the dorsal root entry zone into the spinal cord. Collectively, these results establish fidgetin as a novel therapeutic target to augment nerve regeneration and provide a workflow template by which microtubule-related targets can be compared in the future.SIGNIFICANCE STATEMENT Here we establish a workflow template from cell culture to animals in which microtubule-based treatments can be tested and compared with one another for their effectiveness in augmenting regeneration of injured axons relevant to spinal cord injury. The present work uses a viral transduction approach to knock down fidgetin from rat neurons, which coaxes nerve regeneration by elevating microtubule mass in their axons. Unlike previous strategies using microtubule-stabilizing drugs, fidgetin knockdown adds microtubule mass that is labile (rather than stable), thereby better recapitulating the growth status of a developing axon.

Microtubule Hyperacetylation Enhances KL1-Dependent Micronucleation under a Tau Deficiency in Mammary Epithelial Cells

Enhanced microtubule acetylation has been identified as a negative prognostic indicator in breast cancer. We reported previously that primary cultured human mammary epithelial cells manifest breast cancer-related aneuploidization via the activation of severing protein katanin-like (KL)1 when tau is deficient. To address in this current study whether microtubule hyperacetylation is involved in breast carcinogenesis through mitosis, the effects of tubacin on human mammary epithelial cells were tested using immunofluorescence techniques. Tau-knockdown cells showed enhancement of KL1-dependent events, chromosome-bridging and micronucleation in response to tubacin. These enhancements were suppressed by further expression of an acetylation-deficient tubulin mutant. Consistently, using a rat fibroblast-based microtubule sensitivity test, it was confirmed that KL1 also shows enhanced activity in response to microtubule hyperacetylation as well as katanin. It was further observed in rat fibroblasts that exogenously expressed KL1 results in more micronucleation under microtubule hyperacetylation conditions. These data suggest that microtubule acetylation upregulates KL1 and induces more aneuploidy if tau is deficient. It is thus plausible that microtubule hyperacetylation promotes tumor progression by enhancing microtubule sensitivity to KL1, thereby disrupting spindle microtubules and this process could be reversed by the microtubule-binding and microtubule protective octapeptide NAPVSIPQ (NAP) which recruits tau to the microtubules.

Tau Does Not Stabilize Axonal Microtubules but Rather Enables Them to Have Long Labile Domains

It is widely believed that tau stabilizes microtubules in the axon [1-3] and, hence, that disease-induced loss of tau from axonal microtubules leads to their destabilization [3-5]. An individual microtubule in the axon has a stable domain and a labile domain [6-8]. We found that tau is more abundant on the labile domain, which is inconsistent with tau's proposed role as a microtubule stabilizer. When tau is experimentally depleted from cultured rat neurons, the labile microtubule mass of the axon drops considerably, the remaining labile microtubule mass becomes less labile, and the stable microtubule mass increases. MAP6 (also called stable tubule-only polypeptide), which is normally enriched on the stable domain [9], acquires a broader distribution across the microtubule when tau is depleted, providing a potential explanation for the increase in stable microtubule mass. When MAP6 is depleted, the labile microtubule mass becomes even more labile, indicating that, unlike tau, MAP6 is a genuine stabilizer of axonal microtubules. We conclude that tau is not a stabilizer of axonal microtubules but is enriched on the labile domain of the microtubule to promote its assembly while limiting the binding to it of genuine stabilizers, such as MAP6. This enables the labile domain to achieve great lengths without being stabilized. These conclusions are contrary to tau dogma.