Simvastatin Promotes Neurite Outgrowth in the Presence of Inhibitory Molecules Found in Central Nervous System Injury

Srebf2 mediates successful optic nerve axon regeneration via the mevalonate synthesis pathway

BACKGROUND

Axon regeneration within the mammalian central nervous system is extremely limited. In optic neuropathy conditions like glaucoma, the inability of retinal ganglion cell (RGC) axons to regenerate is a major impediment to functional recovery. In contrast, adult teleost fish such as zebrafish can fully regenerate RGC axons enabling visual recovery from optic nerve (ON) injury making it an ideal model to probe the mechanisms of successful axon regeneration.

METHODS

Laser Capture Microdissection followed by RNA-sequencing (LCM-seq) was used to identify genes and pathways differentially expressed in RGCs during ON regeneration. We validate these findings by in situ hybridization and qRT-PCR. Using loss- and gain-of-function experiments we demonstrate the necessity of srebf2 for efficient ON regeneration and recovery of visual function. Finally, we use LCM-seq coupled with experimental manipulations to identify downstream srebf2 target genes and test the role of hmgcra/b and mevalonate in this process. Statistical analysis was performed using Student's t-test, two-way ANOVA, or repeated measures with appropriate post-hoc tests where applicable.

RESULTS

LCM-seq comparison of uninjured versus 3-day post ON injury RGCs identified significant upregulation of the cholesterol synthesis pathway during axon regeneration. The master regulator of this pathway, the transcription factor srebf2, is upregulated throughout the regeneration phase. Chemical inhibition or morpholino-based gene knockdown of srebf2 decreased axon regeneration into the ON and optic tectum and delayed recovery of visual behavior over the course of normal optic nerve regeneration without causing a significant loss of RGCs. Constitutively active srebf2 can fully rescue axon regeneration and visual behavior losses caused by inhibition of endogenous srebf2 but does not accelerate regeneration compared to the control group. LCM-seq confirms the expected regulation of predicted srebf2 target genes after loss- or gain-of-function in vivo. Downstream of srebf2, hmgcra/b knockdown or simvastatin treatment delayed axon regeneration and this effect was rescued by supplemental mevalonate. Mevalonate treatment alone was sufficient to accelerate ON regeneration.

CONCLUSIONS

These results demonstrate that srebf2 and the downstream mevalonate synthesis pathway plays an important role in regulating efficient axon regeneration in the zebrafish visual system. Involvement of this pathway should be closely examined in failed mammalian ON regeneration.

Immunomodulation by the combination of statin and matrix-bound nanovesicle enhances optic nerve regeneration

Modulating inflammation is critical to enhance nerve regeneration after injury. However, clinically applicable regenerative therapies that modulate inflammation have not yet been established. Here, we demonstrate synergistic effects of the combination of an HMG-CoA reductase inhibitor, statin/fluvastatin and critical components of the extracellular matrix, Matrix-Bound Nanovesicles (MBV) to enhance axon regeneration and neuroprotection after mouse optic nerve injury. Mechanistically, co-intravitreal injections of fluvastatin and MBV robustly promote infiltration of monocytes and neutrophils, which lead to RGC protection and axon regeneration. Furthermore, monocyte infiltration is triggered by elevated expression of CCL2, a chemokine, in the superficial layer of the retina after treatment with a combination of fluvastatin and MBV or IL-33, a cytokine contained within MBV. Finally, this therapy can be further combined with AAV-based gene therapy blocking anti-regenerative pathways in RGCs to extend regenerated axons. These data highlight novel molecular insights into the development of immunomodulatory regenerative therapy.

Impact of commonly administered drugs on the progression of spinal cord injury: a systematic review

BACKGROUND

Complications arising from acute traumatic spinal cord injury (SCI) are routinely managed by various pharmacological interventions. Despite decades of clinical application, the potential impact on neurological recovery has been largely overlooked. This study aims to highlight commonly administered drugs with potential disease-modifying effects.

METHODS

This systematic literature review included studies referenced in PubMed, Scopus and Web of Science from inception to March 31st, 2021, which assess disease-modifying properties on neurological and/or functional recovery of drugs routinely administered following spinal cord injury. Drug effects were classified as positive, negative, mixed, no effect, or not (statistically) reported. Risk of bias was assessed separately for animal, randomized clinical trials, and observational human studies.

RESULTS

We analyzed 394 studies conducting 486 experiments that evaluated 144 unique or combinations of drugs. 195 of the 464 experiments conducted on animals (42%) and one study in humans demonstrate positive disease-modifying properties on neurological and/or functional outcomes. Methylprednisolone, melatonin, estradiol, and atorvastatin are the most common drugs associated with positive effects. Two studies on morphine and ethanol report negative effects on recovery.

CONCLUSION

Despite a large heterogeneity observed in study protocols, research from bed to bench and back to bedside provides an alternative approach to identify new candidate drugs in the context of SCI. Future research in human populations is warranted to determine if introducing drugs like melatonin, estradiol, or atorvastatin would contribute to enhancing neurological outcomes after acute SCI.

Cholesterol synthesis inhibition or depletion in axon regeneration

Cholesterol is biosynthesized by all animal cells. Beyond its metabolic role in steroidogenesis, it is enriched in the plasma membrane where it has key structural and regulatory functions. Cholesterol is thus presumably important for post-injury axon regrowth, and this notion is supported by studies showing that impairment of local cholesterol reutilization impeded regeneration. However, several studies have also shown that statins, inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase, are enhancers of axon regeneration, presumably acting through an attenuation of the mevalonate isoprenoid pathway and consequent reduction in protein prenylation. Several recent reports have now shown that cholesterol depletion, as well as inhibition of cholesterol synthesis per se, enhances axon regeneration. Here, I discussed these findings and propose some possible underlying mechanisms. The latter would include possible disruptions to axon growth inhibitor signaling by lipid raft-localized receptors, as well as other yet unclear neuronal survival signaling process enhanced by cholesterol lowering or depletion.

The association between statins exposure and peripheral neuropathy risk: A meta-analysis

WHAT IS KNOWN AND OBJECTIVE

Statins are widely used lipid-lowering drugs and play an important role in the treatment of many cardiovascular diseases. With the increase in the scope of use and the number of users, peripheral neuropathy caused by statins has been frequently reported. There are no randomized controlled trials comparing the relationship between statins and the risk of peripheral neuropathy. Therefore, we systematically reviewed and meta-analysed observational studies evaluating the impact of statins on the risk of peripheral neuropathy.

METHODS

PubMed, Embase, the Cochrane Library databases and Web of Science were used to search the effects of statins on polyneuropathy from inception to 3 December 2020. We included studies that met the following criteria: (i) A randomized controlled trial, prospective or retrospective cohort study examining the relationship between statins and peripheral neuropathy (PN). Exclusion criteria included the following: Reviews and research related to other diseases or subjects; and studies without data on the prevalence of PN were excluded. Newcastle-Ottawa scale (NOS) was used for quality assessment of included studies. Meta-analysis was used to estimate the risk of disease. We conducted a subgroup analysis of duration of follow-up, adjusted (adjusted RR vs. unadjusted RR), sample size, study design and region.

RESULTS AND DISCUSSION

A total of 9 independent studies assessing 150 556 patients were included in this analysis. In this meta-analysis, we found that there was a nonsignificant increase of PN with statins exposure (RR 1.26, 95% CI (0.92-1.74)). Our results revealed that there was no significant association between statins exposure and peripheral neuropathy risk.

WHAT IS NEW AND CONCLUSION

Statins exposure does not influence the risk of developing peripheral neuropathy. The quality of the evidence included in this study is low, but it can provide useful information for clinicians.

Comparative benefits of simvastatin and exercise in a mouse model of vascular cognitive impairment and dementia

Aerobic physical exercise (EX) and controlling cardiovascular risk factors in midlife can improve and protect cognitive function in healthy individuals and are considered to be effective at reducing late-onset dementia incidence. By investigating commonalities between these preventative approaches, we sought to identify possible targets for effective interventions. We compared the efficacy of EX and simvastatin (SV) pharmacotherapy to counteract cognitive deficits induced by a high-cholesterol diet (2%, HCD) in mice overexpressing TGF-β1 (TGF mice), a model of vascular cognitive impairment and dementia. Cognitive deficits were found in hypercholesterolemic mice for object recognition memory, and both SV and EX prevented this decline. EX improved stimulus-evoked cerebral blood flow responses and was as effective as SV in normalizing endothelium-dependent vasodilatory responses in cerebral arteries. The up-regulation of galectin-3-positive microglial cells in white matter (WM) of HCD-fed TGF mice with cognitive deficits was significantly reduced by both SV and EX concurrently with cognitive recovery. Altered hippocampal neurogenesis, gray matter astrogliosis, or microgliosis did not correlate with cognitive deficits or benefits. Overall, results indicate that SV and EX prevented cognitive decline in hypercholesterolemic mice and that they share common sites of action in preventing endothelial cell dysfunction and reducing WM inflammation.-Trigiani, L. J., Royea, J., Tong, X.-K., Hamel, E. Comparative benefits of simvastatin and exercise in a mouse model of vascular cognitive impairment and dementia.

Effects of Atorvastatin in Patients with Acute Spinal Cord Injury

Study Design

Clinical trial study.

Purpose

The aim of this study was to evaluate the effect of atorvastatin on sensory and motor function in patients with acute spinal cord injury.

Overview of Literature

The prevalence and incidence of traumatic spinal cord injury are increasing. Statins are well established for use in hypercholesterolemia as well as during anti-inflammatory events.

Methods

This clinical trial study included 60 patients with acute spinal cord injury. These were randomly divided into two groups: the case group which received atorvastatin and also underwent surgical therapy and the control group which only underwent surgical therapy.

Results

The severity of spinal cord lesions was evaluated based on the Frankel grade at three periods; this showed no significant difference between the two groups. Comparisons of the levels of pain between the groups based on a Visual Analog Scale system showed no significant difference at the three periods.

Conclusions

We observed no improvement at the 3- and 6-month follow-up in patients who were administered atorvastatin. However, a comparison of the two groups based on pain severity demonstrated a significant difference, suggesting that atorvastatin had a positive effect on patients with spinal cord injury.

The mevalonate pathway in neurons: It's not just about cholesterol

Cholesterol homeostasis greatly impacts neuronal function due to the essential role of this sterol in the brain. The mevalonate (MVA) pathway leads to the synthesis of cholesterol, but also supplies cells with many other intermediary molecules crucial for neuronal function. Compelling evidence point to a model in which neurons shutdown cholesterol synthesis, and rely on a shuttle derived from astrocytes to meet their cholesterol needs. Nevertheless, several reports suggest that neurons maintain the MVA pathway active, even with sustained cholesterol supply by astrocytes. Hence, in this review we focus not on cholesterol production, but rather on the role of the MVA pathway in the synthesis of particular intermediaries, namely isoprenoids, and on their role on neuronal function. Isoprenoids act as anchors for membrane association, after being covalently bound to proteins, such as most of the small guanosine triphosphate-binding proteins, which are critical to neuronal cell function. Based on literature, on our own results, and on the analysis of public transcriptomics databases, we raise the idea that in neurons there is a shift of the MVA pathway towards the non-sterol branch, responsible for isoprenoid synthesis, in detriment to post-squalene branch, and that this is ultimately essential for synaptic activity. Nevertheless new tools that facilitate imaging and the biochemical characterization and quantification of the prenylome in neurons and astrocytes are needed to understand the regulation of isoprenoid production and protein prenylation in the brain, and to analyze its differences on diverse physiological or pathological conditions, such as aging and neurodegenerative states.

Atorvastatin activates autophagy and promotes neurological function recovery after spinal cord injury

Atorvastatin, a lipid-lowering medication, provides neuroprotective effects, although the precise mechanisms of action remain unclear. Our previous studies confirmed activated autophagy following spinal cord injury, which was conducive to recovery of neurological functions. We hypothesized that atorvastatin could also activate autophagy after spinal cord injury, and subsequently improve recovery of neurological functions. A rat model of spinal cord injury was established based on the Allen method. Atorvastatin (5 mg/kg) was intraperitoneally injected at 1 and 2 days after spinal cord injury. At 7 days post-injury, western blot assay, reverse transcription-polymerase chain reaction, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining results showed increased Beclin-1 and light chain 3B gene and protein expressions in the spinal cord injury + atorvastatin group. Additionally, caspase-9 and caspase-3 expression was decreased, and the number of TUNEL-positive cells was reduced. Compared with the spinal cord injury + saline group, Basso, Beattie, and Bresnahan locomotor rating scale scores significantly increased in the spinal cord injury + atorvastatin group at 14-42 days post-injury. These findings suggest that atorvastatin activated autophagy after spinal cord injury, inhibited apoptosis, and promoted recovery of neurological function.

Protein Prenylation Constitutes an Endogenous Brake on Axonal Growth

Suboptimal axonal regeneration contributes to the consequences of nervous system trauma and neurodegenerative disease, but the intrinsic mechanisms that regulate axon growth remain unclear. We screened 50,400 small molecules for their ability to promote axon outgrowth on inhibitory substrata. The most potent hits were the statins, which stimulated growth of all mouse- and human-patient-derived neurons tested, both in vitro and in vivo, as did combined inhibition of the protein prenylation enzymes farnesyltransferase (PFT) and geranylgeranyl transferase I (PGGT-1). Compensatory sprouting of motor axons may delay clinical onset of amyotrophic lateral sclerosis (ALS). Accordingly, elevated levels of PGGT1B, which would be predicted to reduce sprouting, were found in motor neurons of early- versus late-onset ALS patients postmortem. The mevalonate-prenylation pathway therefore constitutes an endogenous brake on axonal growth, and its inhibition provides a potential therapeutic approach to accelerate neuronal regeneration in humans.

Simvastatin inhibits neural cell apoptosis and promotes locomotor recovery via activation of Wnt/β-catenin signaling pathway after spinal cord injury

Statins exhibit neuroprotective effects after spinal cord injury (SCI). However, the molecular mechanism underlying these effects remains unknown. This study demonstrates that the hydroxymethylglutaryl coenzyme A reductase inhibitor simvastatin (Simv) exhibits neuroprotective effects on neuronal apoptosis and supports functional recovery in a rat SCI model by activating the Wnt/β‐catenin signaling pathway. In specific, Simv administration after SCI significantly up‐regulated the expression of low density lipoprotein receptor‐related protein 6 phosphorylation and β‐catenin protein, increased the mRNA expression of lymphoid enhancer factor‐1 and T‐cell factor‐1, and suppressed the expression of β‐catenin phosphorylation in the spinal cord neurons. Simv enhanced motor neuronal survival in the spinal cord anterior horn and decreased the lesion of spinal cord tissues after SCI. Simv administration after SCI also evidently reduced the expression levels of Bax, active caspase‐3, and active caspase‐9 in the spinal cord neurons and the proportion of transferase UTP nick end labeling (TUNEL)‐positive neuron cells, but increased the expression level of Bcl‐2 in the spinal cord neurons. However, the anti‐apoptotic effects of Simv were reduced in cultured spinal cord nerve cells when the Wnt/β‐catenin signaling pathway was suppressed in the lipopolysaccharide‐induced model. Furthermore, the Basso, Beattie, and Bresnahan scores indicated that Simv treatment significantly improved the locomotor functions of rats after SCI. This study is the first to report that Simv exerts neuroprotective effects by reducing neuronal apoptosis, and promoting functional and pathological recovery after SCI by activating the Wnt/β‐catenin signaling pathway.

We verified the neuroprotective properties associated with simvastatin following spinal cord injury (SCI). Simvastatin reduced neuronal apoptosis, improved the functional and pathological recovery via activating Wnt/β‐catenin signal pathway, however, the anti‐apoptosis effects of simvastatin were reversed following suppressing Wnt/β‐catenin signaling pathway in primary spinal cord neurons. The significant findings may provide clinical therapeutic value of simvastatin for treating SCI.

Neurovascular and Cognitive failure in Alzheimer's Disease: Benefits of Cardiovascular Therapy

Alzheimer's disease (AD) is a multifactorial and multifaceted disease for which we currently have very little to offer since there is no curative therapy, with only limited disease-modifying drugs. Recent studies in AD mouse models that recapitulate the amyloid-β (Aβ) pathology converge to demonstrate that it is possible to salvage cerebrovascular function with a variety of drugs and, particularly, therapies used to treat cardiovascular diseases such as hypercholesterolemia and hypertension. These drugs can reestablish dilatory function mediated by various endothelial and smooth muscle ion channels as well as nitric oxide availability, benefits that result in normalized brain perfusion. These cerebrovascular benefits would favor brain perfusion, which may help maintain neuronal function and, possibly, delay cognitive failure. However, restoring cerebrovascular function in AD mouse models was not necessarily accompanied by rescue of cognitive deficits related to spatial learning and memory. The results with cardiovascular therapies rather suggest that drugs originally designed to treat cardiovascular diseases that concurrently restore cerebrovascular and cognitive function do so through their pleiotropic effects. Specifically, recent findings suggest that these drugs act directly on brain cells and neuronal pathways involved in memory formation, hence, working simultaneously albeit independently on neuronal and vascular targets. These findings may help select medications for patients with cardiovascular diseases at risk of developing AD with increasing age. Further, they may identify molecular targets for recovering memory pathways that bear potential for new therapeutic avenues.

Modulation of the Isoprenoid/Cholesterol Biosynthetic Pathway During Neuronal Differentiation In Vitro

During differentiation, neurons acquire their typical shape and functional properties. At present, it is unclear, whether this important developmental step involves metabolic changes. Here, we studied the contribution of the mevalonate (MVA) pathway to neuronal differentiation using the mouse neuroblastoma cell line N1E-115 as experimental model. Our results show that during differentiation, the activity of 3-hydroxy 3-methylglutaryl Coenzyme A reductase (HMGR), a key enzyme of MVA pathway, and the level of Low Density Lipoprotein receptor (LDLr) decrease, whereas the level of LDLr-related protein-1 (LRP1) and the dimerization of Scavanger Receptor B1 (SRB-1) rise. Pharmacologic inhibition of HMGR by simvastatin accelerated neuronal differentiation by modulating geranylated proteins. Collectively, our data suggest that during neuronal differentiation, the activity of the MVA pathway decreases and we postulate that any interference with this process impacts neuronal morphology and function. Therefore, the MVA pathway appears as an attractive pharmacological target to modulate neurological and metabolic symptoms of developmental neuropathologies. J. Cell. Biochem. 117: 2036-2044, 2016. © 2016 Wiley Periodicals, Inc.

Neuroprotective Effect of Simvastatin via Inducing the Autophagy on Spinal Cord Injury in the Rat Model

Simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, is invariably used to treat cardiovascular diseases. Simvastatin has been recently demonstrated to have a neuroprotective effect in nervous system diseases. The present study aimed to further verify the neuroprotection and molecular mechanism of simvastatin on rats after spinal cord injury (SCI). The expression of Beclin-1 and LC3-B was evidently enhanced at postoperation days 3 and 5, respectively. However, the reduction of the mTOR protein and ribosomal protein S6 kinase p70 subtype (p70S6K) phosphorylation level occurred at the same time after SCI. Simvastatin significantly increased the expression of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF). Meanwhile, immunofluorescence results indicated that the expression of chondroitin sulfate proteoglycan (CSPG) and caspase-3 protein was obviously reduced by simvastatin. Furthermore, Nissl staining and Basso, Beattie, and Bresnahan (BBB) scores showed that the quantity and function of motor neurons were visibly preserved by simvastatin after SCI. The findings of this study showed that simvastatin induced autophagy by inhibiting the mTOR signaling pathway and contributed to neuroprotection after SCI.

Non-prenylatable, cytosolic Rac1 alters neurite outgrowth while retaining the ability to be activated

Rac1 is an important regulator of axon extension, cell migration and actin reorganization. Like all Rho guanine triphosphatases (GTPases), Rac1 is targeted to the membrane by the addition of a geranylgeranyl moiety, an action thought to result in Rac1 guanosine triphosphate (GTP) binding. However, the role that Rac1 localization plays in its activation (GTP loading) and subsequent activation of effectors is not completely clear. To address this, we developed a non-prenylatable emerald green fluorescent protein (EmGFP)-Rac1 fusion protein (EmGFP-Rac1(C189A)) and assessed how expressing this construct affected neurite outgrowth, Rac1 localization and activation in neuroblastoma cells. Expression of EmGFP-Rac1(C189A) increased localization to the cytosol and induced cell clustering while increasing neurite initiation. EmGFP-Rac1(C189A) expression also increased Rac1 activation in the cytosol, compared to cells expressing wild-type Rac1 (EmGFP-Rac1). These results suggest that activation of Rac1 may not require plasma membrane localization, potentially leading to differential activation of cytosolic signaling pathways that alter cell morphology. Understanding the consequences of differential localization and activation of Rho GTPases, including Rac1, could lead to new therapeutic targets for treating neurological disorders.

Inhibiting geranylgeranylation increases neurite branching and differentially activates cofilin in cell bodies and growth cones

Inhibitors of the mevalonate pathway, including the highly prescribed statins, reduce the production of cholesterol and isoprenoids such as geranylgeranyl pyrophosphates. The Rho family of small guanine triphosphatases (GTPases) requires isoprenylation, specifically geranylgeranylation, for activation. Because Rho GTPases are primary regulators of actin filament rearrangements required for process extension, neurite arborization, and synaptic plasticity, statins may affect cognition or recovery from nervous system injury. Here, we assessed how manipulating geranylgeranylation affects neurite initiation, elongation, and branching in neuroblastoma growth cones. Treatment with the statin, lovastatin (20 μM), decreased measures of neurite initiation by 17.0 to 19.0 % when a source of cholesterol was present and increased neurite branching by 4.03- to 9.54-fold (regardless of exogenous cholesterol). Neurite elongation was increased by treatment with lovastatin only in cholesterol-free culture conditions. Treatment with lovastatin decreased growth cone actin filament content by up to 24.3 %. In all cases, co-treatment with the prenylation precursor, geranylgeraniol (10 μM), reversed the effect of lovastatin. In a prior work, statin effects on outgrowth were linked to modulating the actin depolymerizing factor, cofilin. In our assays, treatment with lovastatin or geranylgeraniol decreased cofilin phosphorylation in whole cell lysates. However, lovastatin increased cofilin phosphorylation in cell bodies and decreased it in growth cones, indicating differential regulation in specific cell regions. Together, we interpret these data to suggest that protein geranylgeranylation likely regulates growth cone actin filament content and subsequent neurite outgrowth through mechanisms that also affect actin nucleation and polymerization.

Simvastatin induced neurite outgrowth unveils role of cell surface cholesterol and acetyl CoA carboxylase in SH-SY5Y cells

Statins are known to modulate cell surface cholesterol (CSC) and AMP-activated protein kinase (AMPK) in non-neural cells; however no study demonstrates whether CSC and AMPK may regulate simvastatin induced neuritogenesis (SIN). We found that simvastatin (SIM) maintains CSC as shown by Fillipin III staining, Flotillin-2 protein expression / localization and phosphorylation of various receptor tyrosine kinases (RTKs) in the plasma membrane. Modulation of CSC revealed that SIN is critically dependent on this CSC. Simultaneously, phospho array for mitogen activated protein kinases (MAPKs) revealed PI3K / Akt as intracellular pathway which modulates lipid pathway by inhibiting AMPK activation. Though, SIM led to a transient increase in AMPK phosphorylation followed by a sudden decline; the effect was independent of PI3K. Strikingly, AMPK phosphorylation was regulated by protein phosphatase 2A (PP2A) activity which was enhanced upon SIM treatment as evidenced by increase in threonine phosphorylation. Moreover, it was observed that addition of AMP analogue and PP2A inhibitor inhibited SIN. Bio-composition of neurites shows that lipids form a major part of neurites and AMPK is known to regulate lipid metabolism majorly through acetyl CoA carboxylase (ACC). AMPK activity is negative regulator of ACC activity and we found that phosphorylation of ACC started to decrease after 6 hrs which becomes more pronounced at 12 hrs. Addition of ACC inhibitor showed that SIN is dependent on ACC activity. Simultaneously, addition of Fatty acid synthase (FAS) inhibitor confirmed that endogenous lipid pathway is important for SIN. We further investigated SREBP-1 pathway activation which controls ACC and FAS at transcriptional level. However, SIM did not affect SREBP-1 processing and transcription of its target genes likes ACC1 and FAS. In conclusion, this study highlights a distinct role of CSC and ACC in SIN which might have implication in process of neuronal differentiation induced by other agents.

Atorvastatin requires geranylgeranyl transferase-I and Rac1 activation to exert neuronal protection and induce plasticity

Statins are widely used cholesterol-lowering drugs that may reduce the incidence of stroke and the progression of Alzheimer's disease (AD). However, how statins exert these beneficial effects remains poorly understood. Thus, this study evaluated the roles of Rac1 geranylgeranylation and the relationship between Rac1 and αN-catenin in the protective activity of atorvastatin (ATV) in a cortical neuronal culture model of glutamate (GLU) excitotoxicity. We found that ATV-induced neuroprotection and plasticity were blocked by isoprenoids, such as farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP), inhibition of farnesylation (FTI-277) and geranylgeranylation (GGTI-286), down-regulation of GGTase-Iβ and Rac activity and promotion of active RhoA. Additionally, ATV rescued the distribution of dendritic αN-catenin and increased the number and length of dendritic branches; these effects were reversed by GGTI-286, GGTase-Iβ shRNA, Rac1 shRNA and a dominant-negative version of Rac1 (T17N). In summary, our findings suggest that ATV requires GGTase-Iβ, prenylation and active Rac1 to induce protection and plasticity. In this regard, αN-catenin is a marker for stable interactions between adhesion proteins and the actin cytoskeleton and is necessary for the neuroprotective action of ATV.

Atorvastatin enhances neurite outgrowth in cortical neurons in vitro via up-regulating the Akt/mTOR and Akt/GSK-3β signaling pathways

AIM

To investigate whether atorvastatin can promote formation of neurites in cultured cortical neurons and the signaling mechanisms responsible for this effect.

METHODS

Cultured rat cerebral cortical neurons were incubated with atorvastatin (0.05-10 μmol/L) for various lengths of time. For pharmacological experiments, inhibitors were added 30 min prior to addition of atorvastatin. Control cultures received a similar amount of DMSO. Following the treatment period, phase-contrast digital images were taken. Digital images of neurons were analyzed for total neurite branch length (TNBL), neurite number, terminal branch number, and soma area by SPOT Advanced Imaging software. After incubation with atorvastatin for 48 h, the levels of phosphorylated 3-phosphoinoside-dependent protein kinase-1 (PDK1), phospho-Akt, phosphorylated mammalian target of rapamycin (mTOR), phosphorylated 4E-binding protein 1 (4E-BP1), p70S6 kinase (p70S6K), and glycogen synthase kinase-3β (GSK-3β) in the cortical neurons were evaluated using Western blotting analyses.

RESULTS

Atorvastatin (0.05-10 μmol/L) resulted in dose-dependent increase in neurite number and length in these neurons. Pretreatment of the cortical neurons with phosphatidylinositol 3-kinase (PI3K) inhibitors LY294002 (30 μmol/L) and wortmannin (5 μmol/L), Akt inhibitor tricribine (1 μmol/L) or mTOR inhibitor rapamycin (100 nmol/L) blocked the atorvastatin-induced increase in neurite outgrowth, suggesting that atorvastatin promoted neurite outgrowth via activating the PI3K/Akt/mTOR signaling pathway. Atorvastatin (10 μmol/L) significantly increased the levels of phosphorylated PDK1, Akt and mTOR in the cortical neurons, which were prevented by LY294002 (30 μmol/L). Moreover, atorvastatin (10 μmol/L) stimulated the phosphorylation of 4E-BP1 and p70S6K, the substrates of mTOR, in the cortical neurons. In addition, atorvastatin (10 μmol/L) significantly increased the phosphorylated GSK-3β level in the cortical neurons, which was prevented by both LY294002 and tricribine.

CONCLUSION

These results suggest that activation of both the PI3K/Akt/mTOR and Akt/GSK-3β signaling pathways is responsible for the atorvastatin-induced neurite outgrowth in cultured cortical neurons.

Isoprenoids and related pharmacological interventions: potential application in Alzheimer's disease

Two major isoprenoids, farnesyl pyrophosphate and geranylgeranyl pyrophosphate, serve as lipid donors for the posttranslational modification (known as prenylation) of proteins that possess a characteristic C-terminal motif. The prenylation reaction is catalyzed by prenyltransferases. The lipid prenyl group facilitates to anchor the proteins in cell membranes and mediates protein-protein interactions. A variety of important intracellular proteins undergo prenylation, including almost all members of small GTPase superfamilies as well as heterotrimeric G protein subunits and nuclear lamins. These prenylated proteins are involved in regulating a wide range of cellular processes and functions, such as cell growth, differentiation, cytoskeletal organization, and vesicle trafficking. Prenylated proteins are also implicated in the pathogenesis of different types of diseases. Consequently, isoprenoids and/or prenyltransferases have emerged as attractive therapeutic targets for combating various disorders. This review attempts to summarize the pharmacological agents currently available or under development that control isoprenoid availability and/or the process of prenylation, mainly focusing on statins, bisphosphonates, and prenyltransferase inhibitors. Whereas statins and bisphosphonates deplete the production of isoprenoids by inhibiting the activity of upstream enzymes, prenyltransferase inhibitors directly block the prenylation of proteins. As the importance of isoprenoids and prenylated proteins in health and disease continues to emerge, the therapeutic potential of these pharmacological agents has expanded across multiple disciplines. This review mainly discusses their potential application in Alzheimer's disease.

Simvastatin improves morphological and functional recovery of sciatic nerve injury in Wistar rats

AIM

The purpose of this work is to investigate the effects of simvastatin on sciatic nerve regeneration in male Wistar Rats.

MATERIALS AND METHODS

Forty animals were allocated into four groups: (1) control (C); (2) control+simvastatin (CS); (3) lesioned animals+sterile PBS (LC) and (4) lesioned animals+simvastatin (LS). Lesioned animals were submitted to crushing lesion of right sciatic nerve. Simvastatin (20mg/kg/day, i.p.) was administered for five days. Footprints were obtained weekly for evaluation of functional locomotor recovery by means of the Sciatic Function Index (SFI). Blood samples were obtained weekly for quantifying circulating leukocytes. Animals were sacrificed after 21 days for histological analyses of sciatic nerve and spleen.

RESULTS

LS Animals presented increased SFI scores, decreased areas of oedema and mononuclear cell infiltration during Wallerian degeneration and nerve regeneration (7,14 and 21 days; P<0.05). Spleen weight and white pulp areas was increased in LC animals after 21 days. Increased numbers of circulating neutrophils were observed in simvastatin treated animals (CS e LS) at seven, 14 and 21 days, compared to non-treated groups (C and LC).

CONCLUSION

The study suggests that simvastatin accelerates the morphological and functional recovery process of the peripheral nervous system interfering with innate and acquired immunity.

Chemical priming for spinal cord injury: a review of the literature part II-potential therapeutics

INTRODUCTION

Spinal cord injury is a complex cascade of reactions secondary to the initial mechanical trauma that puts into action the innate properties of the injured cells, the circulatory, inflammatory, and chemical status around them, into a non-permissive and destructive environment for neuronal function and regeneration. Priming means putting a cell, in a state of "arousal" towards better function. Priming can be mechanical as trauma is known to enhance activity in cells.

MATERIALS AND METHODS

A comprehensive review of the literature was performed to better understand the possible chemical primers used for spinal cord injuries.

CONCLUSIONS

Taken together, many studies have shown various promising results using the substances outlined herein for treating SCI.

The effects of potential neuroprotective agents on rat facial function recovery following facial nerve injury

OBJECTIVE

To evaluate whether a series of pharmacologic agents with potential neuroprotective effects accelerate and/or improve facial function recovery after facial nerve crush injury.

STUDY DESIGN

Randomized animal study.

SETTING

Tertiary care facility.

METHODS

Eighty female Wistar-Hannover rats underwent head restraint implantation and daily conditioning. Animals then underwent unilateral crush injury to the main trunk of the facial nerve and were randomized to receive treatment with atorvastatin (n = 10), sildenafil (n = 10), darbepoetin (n = 20), or a corresponding control agent (n = 40). The return of whisking function was tracked throughout the recovery period.

RESULTS

All rats initiated the return of whisking function from nerve crush by day 12. Darbepoetin-treated rats (n = 20) showed significantly improved whisking amplitude and velocity across the recovery period, with several days of significant pairwise differences vs comparable control rats (n = 16) across the first 2 weeks of whisking function return. In contrast, rats treated with sildenafil (n = 10) and atorvastatin (n = 10) did not show significant improvement in whisking function recovery after facial nerve crush compared to controls. By week 8, all darbepoetin-treated animals and comparable nerve crush control animals fully recovered whisking function and were statistically indistinguishable.

CONCLUSION

Among the 3 potentially neuroprotective agents evaluated, only darbepoetin administration resulted in accelerated recovery of whisking parameters after facial nerve crush injury. Further efforts to define the mechanism of action and translate these findings to the use of darbepoetin in the care of patients with traumatic facial paralysis are needed.

RHO GTPase signaling for axon extension: is prenylation important?

Many lines of evidence indicate the importance of the Rho family guanine nucleotide triphosphatases (GTPases) in directing axon extension and guidance. The signaling networks that involve these proteins regulate actin cytoskeletal dynamics in navigating neuronal growth cones. However, the intricate patterns that regulate Rho GTPase activation and signaling are not yet fully defined. Activity and subcellular localization of the Rho GTPases are regulated by post-translational modification. The addition of a geranylgeranyl group to the carboxy (C-) terminus targets Rho GTPases to the plasma membrane and promotes their activation by facilitating interaction with guanine nucleotide exchange factors and allowing sequestering by association with guanine dissociation inhibitors. However, it is unclear how these modifications affect neurite extension or how subcellular localization alters signaling from the classical Rho GTPases (RhoA, Rac1, and Cdc42). Here, we review recent data addressing this issue and propose that Rho GTPase geranylgeranylation regulates outgrowth.

Simvastatin attenuates hypomyelination induced by hypoxia-ischemia in neonatal rats

OBJECTIVES

Simvastatin, the most widely used cholesterol-lowering drug, has been reported to protect the adult brain from ischemia. Nevertheless, little is known about its action on developing brain after stroke. Although a few reports have found recently that simvastatin displays anti-inflammation and anti-apoptosis properties and improves the cognitive and morphological consequences in the neonatal rats after hypoxia-ischemia (HI) damage, to our best knowledge, there has been no study of the effect of it on myelin formation after neonatal brain damage. Therefore, we investigated whether simvastatin could promote the myelination of oligodendrocytes in the neonatal rats after HI and explored the possible role of microglial responses in this process.

METHODS

Postnatal day 7 Sprague-Dawley rats were subjected to HI. White matter integrity and myelination were evaluated by the densitometry of myelin basic protein (MBP) immunostaining. OX-42 immunoreactivity and nissl staining were used for identifying microglial responses and the structure changes of white matter and adjacent gray matter after HI. Simvastatin was administrated prophylactically to rats.

RESULTS

HI induced serious hypomyelination especially in external and internal capsules 3 and 7 days after HI, accompanying with microglial activation remarkably. Simvastatin treatment greatly increased the densities of MBP immunostaining, inhibited microglial activation and reduced the numbers of pyknotic cells and neuronal loss.

DISCUSSION

The present study shows that simvastatin treatment in neonatal rats attenuates HI-induced developing oligodendrocytes injury and hypomyelination. Its anti-inflammatory properties via suppression of microglial activation are likely to contribute to this action. It provides experimental evidence to support the neuroprotective effects of statins in neonatal ischemic stroke.

Statins decrease dendritic arborization in rat sympathetic neurons by blocking RhoA activation

Clinical and experimental evidence suggest that statins decrease sympathetic activity, but whether peripheral mechanisms involving direct actions on post-ganglionic sympathetic neurons contribute to this effect is not known. Because tonic activity of these neurons is directly correlated with the size of their dendritic arbor, we tested the hypothesis that statins decrease dendritic arborization in sympathetic neurons. Oral administration of atorvastatin (20 mg/kg/day for 7 days) significantly reduced dendritic arborization in vivo in sympathetic ganglia of adult male rats. In cultured sympathetic neurons, statins caused dendrite retraction and reversibly blocked bone morphogenetic protein-induced dendritic growth without altering cell survival or axonal growth. Supplementation with mevalonate or isoprenoids, but not cholesterol, attenuated the inhibitory effects of statins on dendritic growth, whereas specific inhibition of isoprenoid synthesis mimicked these statin effects. Statins blocked RhoA translocation to the membrane, an event that requires isoprenylation, and constitutively active RhoA reversed statin effects on dendrites. These observations that statins decrease dendritic arborization in sympathetic neurons by blocking RhoA activation suggest a novel mechanism by which statins decrease sympathetic activity and protect against cardiovascular and cerebrovascular disease.

Combination therapy of lovastatin and rolipram provides neuroprotection and promotes neurorepair in inflammatory demyelination model of multiple sclerosis

Drug combination therapies for central nervous system (CNS) demyelinating diseases including multiple sclerosis (MS) are gaining momentum over monotherapy. Over the past decade, both in vitro and in vivo studies established that statins (HMG-CoA reductase inhibitors) and rolipram (phosphodiesterase-4 inhibitor; blocks the degradation of intracellular cyclic AMP) can prevent the progression of MS in affected individuals via different mechanisms of action. In this study, we evaluated the effectiveness of lovastatin (LOV) and rolipram (RLP) in combination therapy to promote neurorepair in an inflammatory CNS demyelination model of MS, experimental autoimmune encephalomyelitis (EAE). Combination treatment with suboptimal doses of these drugs in an established case of EAE (clinical disease score > or = 2.0) significantly attenuated the infiltration of inflammatory cells and protected myelin sheath and axonal integrity in the CNS. It was accompanied with elevated level of cyclic AMP and activation of its associated protein kinase A. Interestingly, combination treatment with these drugs impeded neurodegeneration and promoted neurorepair in established EAE animals (clinical disease score > or = 3.5) as verified by quantitative real-time polymerase chain reaction, immunohistochemistry and electron microscopic analyses. These effects of combination therapy were minimal and/or absent with either drug alone in these settings. Together, these data suggest that combination therapy with LOV and RLP has the potential to provide neuroprotection and promote neurorepair in MS, and may have uses in other related CNS demyelinating diseases.

Simvastatin treatment induces morphology alterations and apoptosis in murine cochlear neuronal cells

CONCLUSION

Simvastatin presented neurodegenerative morphological changes and cell death via its specific inhibition of mevalonate pathway induced apoptosis in cultured cochlear neuronal cells. These findings might contribute to understanding the auditory neurobiological effects of HMG-CoA reductase inhibitors.

OBJECTIVES

The statins are 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors that are widely used as anti-hypercholesterol drugs because of their beneficial cardiovascular effects. However, the effects of statins in neuronal cells are controversial, and no studies have examined the effect of statins in cochlear neuronal cells. The objective of this study was to evaluate the direct effect of simvastatin on cochlear neuronal cells and examine the mechanisms underlying these effects.

MATERIALS AND METHODS

Cultured mouse cochlear neuroblasts (VOT-33) and primary rat cochlear explants containing spiral ganglion neurons were treated with simvastatin in the absence or presence of mevalonate.

RESULTS

Simvastatin caused a loss of the cytoplasmic projections in VOT-33. In primary rat cochlear nerve cells, simvastatin decreased staining for NF200, a neuro-cytoskeletal protein. We also found that simvastatin-induced VOT-33 apoptosis, as indicated by accumulation of the sub G0/G1 fraction, DNA-ladder formation, and caspase-3 activation. The above-mentioned effects were abolished by mevalonate treatment.

Decorin promotes robust axon growth on inhibitory CSPGs and myelin via a direct effect on neurons

Inhibitory chondroitin sulfate proteoglycans (CSPGs) and myelin-associated molecules are major impediments to axon regeneration within the adult central nervous system (CNS). Decorin infusion can however suppress the levels of multiple inhibitory CSPGs and promote axon growth across spinal cord injuries [Davies, J.E., Tang, X., Denning, J.W., Archibald, S.J., and Davies, S.J., 2004. Decorin suppresses neurocan, brevican, phosphacan and NG2 expression and promotes axon growth across adult rat spinal cord injuries. Eur. J. Neurosci. 19, 1226-1242]. A question remained as to whether decorin can also increase axon growth on inhibitory CSPGs and myelin via a direct effect on neurons. We have therefore conducted an in vitro analysis of neurite extension by decorin-treated adult dorsal root ganglion (DRG) neurons cultured on substrates of inhibitory CSPGs or myelin membranes mixed with laminin. Decorin treatment promoted 14.5 and 5-fold increases in average neurite length/neuron over untreated controls on CSPGs or myelin membranes respectively. In addition to suppressing inhibitory scar formation, our present data shows that decorin can directly boost the ability of neurons to extend axons within CSPG or myelin rich environments.

Comparison of biochemical effects of statins and fish oil in brain: the battle of the titans

Neural membranes are composed of glycerophospholipids, sphingolipids, cholesterol and proteins. The distribution of these lipids within the neural membrane is not random but organized. Neural membranes contain lipid rafts or microdomains that are enriched in sphingolipids and cholesterol. These rafts act as platforms for the generation of glycerophospholipid-, sphingolipid-, and cholesterol-derived second messengers, lipid mediators that are necessary for normal cellular function. Glycerophospholipid-derived lipid mediators include eicosanoids, docosanoids, lipoxins, and platelet-activating factor. Sphingolipid-derived lipid mediators include ceramides, ceramide 1-phosphates, and sphingosine 1-phosphate. Cholesterol-derived lipid mediators include 24-hydroxycholesterol, 25-hydroxycholesterol, and 7-ketocholesterol. Abnormal signal transduction processes and enhanced production of lipid mediators cause oxidative stress and inflammation. These processes are closely associated with the pathogenesis of acute neural trauma (stroke, spinal cord injury, and head injury) and neurodegenerative diseases such as Alzheimer disease. Statins, the HMG-CoA reductase inhibitors, are effective lipid lowering agents that significantly reduce risk for cardiovascular and cerebrovascular diseases. Beneficial effects of statins in neurological diseases are due to their anti-excitotoxic, antioxidant, and anti-inflammatory properties. Fish oil omega-3 fatty acids, eicosapentaenoic acid and docosahexaenoic acid, have similar anti-excitotoxic, antioxidant and anti-inflammatory effects in brain tissue. Thus the lipid mediators, resolvins, protectins, and neuroprotectins, derived from eicosapentaenoic acid and docosahexaenoic acid retard neuroinflammation, oxidative stress, and apoptotic cell death in brain tissue. Like statins, ingredients of fish oil inhibit generation of beta-amyloid and provide protection from oxidative stress and inflammatory processes. Collective evidence suggests that antioxidant, anti-inflammatory, and anti-apoptotic properties of statins and fish oil contribute to the clinical efficacy of treating neurological disorders with statins and fish oil. We speculate that there is an overlap between neurochemical events associated with neural cell injury in stroke and neurodegenerative diseases. This commentary compares the neurochemical effects of statins with those of fish oil.