In vivo two-photon imaging reveals a role of progesterone in reducing axonal dieback after spinal cord injury in mice

In vivo imaging in mouse spinal cord reveals that microglia prevent degeneration of injured axons

Microglia, the primary immune cells in the central nervous system, play a critical role in regulating neuronal function and fate through their interaction with neurons. Despite extensive research, the specific functions and mechanisms of microglia-neuron interactions remain incompletely understood. In this study, we demonstrate that microglia establish direct contact with myelinated axons at Nodes of Ranvier in the spinal cord of mice. The contact associated with neuronal activity occurs in a random scanning pattern. In response to axonal injury, microglia rapidly transform their contact into a robust wrapping form, preventing acute axonal degeneration from extending beyond the nodes. This wrapping behavior is dependent on the function of microglial P2Y12 receptors, which may be activated by ATP released through axonal volume-activated anion channels at the nodes. Additionally, voltage-gated sodium channels (NaV) and two-pore-domain potassium (K2P) channels contribute to the interaction between nodes and glial cells following injury, and inhibition of NaV delays axonal degeneration. Through in vivo imaging, our findings reveal a neuroprotective role of microglia during the acute phase of single spinal cord axon injury, achieved through neuron-glia interaction.

Evaluating Sex Steroid Hormone Neuroprotection in Spinal Cord Injury in Animal Models: Is It Promising in the Clinic?

The primary mechanism of traumatic spinal cord injury (SCI) comprises the initial mechanical trauma due to the transmission of energy to the spinal cord, subsequent deformity, and persistent compression. The secondary mechanism of injury, which involves structures that remained undamaged after the initial trauma, triggers alterations in microvascular perfusion, the liberation of free radicals and neurotransmitters, lipid peroxidation, alteration in ionic concentrations, and the consequent cell death by necrosis and apoptosis. Research in the treatment of SCI has sought to develop early therapeutic interventions that mitigate the effects of these pathophysiological mechanisms. Clinical and experimental evidence has demonstrated the therapeutic benefits of sex-steroid hormone administration after traumatic brain injury and SCI. The administration of estradiol, progesterone, and testosterone has been associated with neuroprotective effects, better neurological recovery, and decreased mortality after SCI. This review evaluated evidence supporting hormone-related neuroprotection over SCI and the possible underlying mechanisms in animal models. As neuroprotection has been associated with signaling pathways, the effects of these hormones are observed on astrocytes and microglia, modulating the inflammatory response, cerebral blood flow, and metabolism, mediating glutamate excitotoxicity, and their antioxidant effects. Based on the current evidence, it is essential to analyze the benefit of sex steroid hormone therapy in the clinical management of patients with SCI.

Three-photon excited fluorescence microscopy enables imaging of blood flow, neural structure and inflammatory response deep into mouse spinal cord in vivo

Nonlinear optical microscopy enables non-invasive imaging in scattering samples with cellular resolution. The spinal cord connects the brain with the periphery and governs fundamental behaviors such as locomotion and somatosensation. Because of dense myelination on the dorsal surface, imaging to the spinal grey matter is challenging, even with two-photon microscopy. Here we show that three-photon excited fluorescence (3PEF) microscopy enables multicolor imaging at depths of up to ~550 μm into the mouse spinal cord, in vivo. We quantified blood flow across vessel types along the spinal vascular network. We then followed the response of neurites and microglia after occlusion of a surface venule, where we observed depth-dependent structural changes in neurites and interactions of perivascular microglia with vessel branches upstream from the clot. This work establishes that 3PEF imaging enables studies of functional dynamics and cell type interactions in the top 550 μm of the murine spinal cord, in vivo.

Therapeutic potential of progesterone in spinal cord injury-induced neuropathic pain: At the crossroads between neuroinflammation and N-methyl-D-aspartate receptor

In recent decades, an area of active research has supported the notion that progesterone promotes a wide range of remarkable protective actions in experimental models of nervous system trauma or disease, and has also provided a strong basis for considering this steroid as a promising molecule for modulating the complex maladaptive changes that lead to neuropathic pain, especially after spinal cord injury. In this review, we intend to give the readers a brief appraisal of the main mechanisms underlying the increased excitability of the spinal circuit in the pain pathway after trauma, with particular emphasis on those mediated by the activation of resident glial cells, the subsequent release of proinflammatory cytokines and their impact on N-methyl-D-aspartate receptor function. We then summarize the available preclinical data pointing to progesterone as a valuable repurposing molecule for blocking critical cellular and molecular events that occur in the dorsal horn of the injured spinal cord and are related to the development of chronic pain. Since the treatment and management of neuropathic pain after spinal injury remains challenging, the potential therapeutic value of progesterone opens new traslational perspectives to prevent central pain.

Pathophysiology and Therapeutic Approaches for Spinal Cord Injury

Spinal cord injury (SCI) is a disabling condition that disrupts motor, sensory, and autonomic functions. Despite extensive research in the last decades, SCI continues to be a global health priority affecting thousands of individuals every year. The lack of effective therapeutic strategies for patients with SCI reflects its complex pathophysiology that leads to the point of no return in its function repair and regeneration capacity. Recently, however, several studies started to uncover the intricate network of mechanisms involved in SCI leading to the development of new therapeutic approaches. In this work, we present a detailed description of the physiology and anatomy of the spinal cord and the pathophysiology of SCI. Additionally, we provide an overview of different molecular strategies that demonstrate promising potential in the modulation of the secondary injury events that promote neuroprotection or neuroregeneration. We also briefly discuss other emerging therapies, including cell-based therapies, biomaterials, and epidural electric stimulation. A successful therapy might target different pathologic events to control the progression of secondary damage of SCI and promote regeneration leading to functional recovery.

Inflammation: A Target for Treatment in Spinal Cord Injury

Spinal cord injury (SCI) is a significant cause of disability, and treatment alternatives that generate beneficial outcomes and have no side effects are urgently needed. SCI may be treatable if intervention is initiated promptly. Therefore, several treatment proposals are currently being evaluated. Inflammation is part of a complex physiological response to injury or harmful stimuli induced by mechanical, chemical, or immunological agents. Neuroinflammation is one of the principal secondary changes following SCI and plays a crucial role in modulating the pathological progression of acute and chronic SCI. This review describes the main inflammatory events occurring after SCI and discusses recently proposed potential treatments and therapeutic agents that regulate inflammation after insult in animal models.

Progesterone attenuates neurological deficits and exerts a protective effect on damaged axons via the PI3K/AKT/mTOR-dependent pathway in a mouse model of intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating event with high disability and fatality rates. However, there is a lack of effective treatments for this condition. We aimed to investigate the neuroprotective and axonal regenerative effects of progesterone after ICH. For this purpose, an ICH model was established in adult mice by injecting type VII collagenase into the striatum; the mice were then treated with progesterone (8 mg/kg). Hematoma absorption, neurological scores, and brain water content were evaluated on days one, three, and seven after the ICH. The effect of progesterone on inflammation and axonal regeneration was examined on day three after the ICH using western blotting, immunohistochemistry, immunofluorescence, as well as hematoxylin-eosin, Nissl, and Luxol fast blue staining. In addition, we combined progesterone with the phosphoinositide 3-kinase/serine/threonine-specific protein kinase (PI3K/AKT) inhibitor, LY294002, to explore its potential neuroprotective mechanisms. Administration of progesterone attenuated the neurological deficits and expression of inflammatory cytokines and promoted axonal regeneration after ICH, this effect was blocked by LY294002. Collectively, these results suggest that progesterone could reduce axonal damage and produced partial neuroprotective effects after ICH through the PI3K/AKT/mTOR pathway, providing a new therapeutic target and basis for the treatment of ICH.

In vivo imaging in experimental spinal cord injury – Techniques and trends

Introduction

Traumatic Spinal Cord Injury (SCI) is one of the leading causes of disability in the world. Treatment is limited to supportive care and no curative therapy exists. Experimental research to understand the complex pathophysiology and potential mediators of spinal cord regeneration is essential to develop innovative translational therapies. A multitude of experimental imaging methods to monitor spinal cord regeneration in vivo have developed over the last years. However, little literature exists to deal with advanced imaging methods specifically available in SCI research.

Research Question

This systematic literature review examines the current standards in experimental imaging in SCI allowing for in vivo imaging of spinal cord regeneration on a neuronal, vascular, and cellular basis.

Material and Methods

Articles were included meeting the following criteria: experimental research, original studies, rodent subjects, and intravital imaging. Reviewed in detail are microstructural and functional Magnetic Resonance Imaging, Micro-Computed Tomography, Laser Speckle Imaging, Very High Resolution Ultrasound, and in vivo microscopy techniques.

Results

Following the PRISMA guidelines for systematic reviews, 689 articles were identified for review, of which 492 were sorted out after screening and an additional 104 after detailed review. For qualitative synthesis 93 articles were included in this publication.

Discussion and Conclusion

With this study we give an up-to-date overview about modern experimental imaging techniques with the potential to advance the knowledge on spinal cord regeneration following SCI. A thorough knowledge of the strengths and limitations of the reviewed techniques will help to optimally exploit our current experimental armamentarium in the field.

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In vivo imaging is essential to enhance the understanding of SCI pathophysiology.

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Multiple experimental imaging methods have evolved over the past years.

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Detailed review of in vivo (f)MRI, μCT, VHRUS, and Microcopy in experimental SCI.

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Experimental imaging allows for longitudinal examination to the cellular level.

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Knowledge of the strengths and limitations is essential for future research.

Protective effect of melatonin against chronic cadmium-induced hepatotoxicity by suppressing oxidative stress, inflammation, and apoptosis in mice

Cadmium (Cd) is a widespread environmental heavy metal pollutant that has high toxicity to human health. Cd accumulates in the liver and results in oxidative stress and inflammatory reactions. Melatonin (MT), a hormone exhibiting strong antioxidative properties, has been proved to have hepatoprotective effect against both acute and chronic liver injury. However, the molecular mechanism underlying MT's hepatoprotective effect against Cd-induced liver injury remain not fully understood. In this study, the potential protective effect of MT on Cd-induced hepatic injury was investigated. Adult male C57BL/6 mice were randomly divided into four groups: control, CdCl2, MT, and CdCl2 plus MT groups. Animals were daily treated with either CdCl2 (5 mg/kg) or MT (10 mg/kg) or both through intragastric administration for 30 consecutive days. Serum enzymatic analysis indicated that treatment mice with Cd significantly increased AST, ALT, LDH and ALP levels, by contrast, MT treatment resulted in significant decreases of AST, ALT, LDH and ALP levels in the serum of Cd treated mice. By biochemical analysis, it was found that MT treatment significantly increased the activities of SOD, GSH, GST, CAT and GR, while significantly decreased the contents of MDA in the liver tissue of Cd treated mice. Moreover, MT treatment also suppressed the Cd-induced inflammation by reducing the inflammatory mediators, including IL-1β, IL-6, TNF-α and iNOS. Furthermore, MT treatment ameliorated the Cd-induced histopathological variations of liver tissue, which was confirmed by the biochemical and molecular data. It is clear from the results of this study that MT exerts hepatoprotective effect by improving the redox state, suppressing inflammatory reaction and cell apoptosis as well as ameliorating the performance of liver tissue histopathology, which is eventually reflected by the improvement of liver function in mice.

Progesterone alters the activation and typing of the microglia in the optic nerve crush model

Microglia have a protective effect on the central nervous system (CNS), but their over-proliferation can cause secondary injury to the retina following optic nerve crush (ONC). Progesterone as a steroid gonadal hormone has been used in some experimental animal models for its neuroprotective effect. However, there is limited attention on the interactions between progesterone and microglia in retinal diseases. This study investigated the proliferation, morphology changes, and cell types of microglia at 3 days and 7 days after ONC. We found that progesterone treatment in unilateral optic nerve injury mice significantly reduced densities and morphological change of microglia at 7 days in the ganglion cell layer (GCL), especially in the retinal central. Inhibition of the microglia proliferation and transformation of ramified microglia into ameboid macrophages also appeared in the inner plexiform layer (IPL). Moreover, progesterone also regulated the TNF signal pathway, which was similar to the specific elimination of the M1 phenotype. M1 marks such as tumor necrosis factor alpha (TNF-α), inducible NOS(iNOS), interleukin-6 (IL-6), and Fc receptor (CD16 and CD32) significantly downregulated by progesterone treatment whether at 3 days or 7 days after ONC. On the other hand, progesterone continuously increased the expression of the M2 marks, including interleukin-4 (IL-4), arginase 1 (Arg1), and mannose receptor (CD206) since the third day, while the expression levels of transforming growth factor (TGF-β) only increased at 7 days. In general, this study elucidated the mechanism that progesterone prevented further damage on the retina by inhibiting proliferation, activation, and changing the type of microglia.

Methods for calculating the stereotaxic coordinates of rat brain structures by pixel coordinates of the image obtained by confocal and two-photon laser scanning microscopy

BACKGROUND

There is a challenge to determine stereotaxic coordinates of a target structure with the accuracy, comparable to their size, when imaging the rat brain through cranial windows using confocal (multiphoton) microscopy in vivo. Some methods based on the estimation of the linear displacement from the intersections of the cerebral vessels are most often used for these purposes, but their accuracy can be improved.

NEW METHOD

A new method for converting pixel coordinates of points of interest on an image obtained in two-photon microscopy into stereotaxic ones using quadratic approximation with L₂ regularization has been developed. A comparative analysis of several methods for converting pixel coordinates into stereotaxic ones was carried out. The current study is aimed to select a method which minimizes the error of coordinate conversion within the a priori specified threshold value.

RESULTS

A method for determining the stereotaxic coordinates of each pixel in an image obtained by laser scanning in two-photon and / or confocal modes with an accuracy of several tens of microns is proposed.

COMPARISON WITH EXISTING METHOD(S)

It is shown that the error probability of the most common method based on calculating the points of interest coordinates as displacements relative to the selected vessels intersections can be reduced by using the quadratic approximation with L₂ regularization. Our proposed method allows us to improve the accuracy of determining the coordinates of points of interest on 10-30 µm.

CONCLUSIONS

The proposed approach will be useful in research where precise positioning of microelectrodes, sensors, etc. for implantation in specified brain structures or groups of neurons determined by functional mapping is required.

Progress in progestin-based therapies for neurological disorders

Hormone therapy, primarily progesterone and progestins, for central nervous system (CNS) disorders represents an emerging field of regenerative medicine. Following a failed clinical trial of progesterone for traumatic brain injury treatment, attention has shifted to the progestin Nestorone for its ability to potently and selectively transactivate progesterone receptors at relatively low doses, resulting in robust neurogenetic, remyelinating, and anti-inflammatory effects. That CNS disorders, including multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), spinal cord injury (SCI), and stroke, develop via demyelinating, cell death, and/or inflammatory pathological pathways advances Nestorone as an auspicious candidate for these disorders. Here, we assess the scientific and clinical progress over decades of research into progesterone, progestins, and Nestorone as neuroprotective agents in MS, ALS, SCI, and stroke. We also offer recommendations for optimizing timing, dosage, and route of the drug regimen, and identifying candidate patient populations, in advancing Nestorone to the clinic.

Microglia Dynamics and Interactions with Motoneurons Axotomized After Nerve Injuries Revealed By Two-Photon Imaging

The significance of activated microglia around motoneurons axotomized after nerve injuries has been intensely debated. In particular, whether microglia become phagocytic is controversial. To resolve these issues we directly observed microglia behaviors with two-photon microscopy in ex vivo spinal cord slices from CX3CR1-GFP mice complemented with confocal analyses of CD68 protein. Axotomized motoneurons were retrogradely-labeled from muscle before nerve injuries. Microglia behaviors close to axotomized motoneurons greatly differ from those within uninjured motor pools. They develop a phagocytic phenotype as early as 3 days after injury, characterized by frequent phagocytic cups, high phagosome content and CD68 upregulation. Interactions between microglia and motoneurons changed with time after axotomy. Microglia first extend processes that end in phagocytic cups at the motoneuron surface, then they closely attach to the motoneuron while extending filopodia over the cell body. Confocal 3D analyses revealed increased microglia coverage of the motoneuron cell body surface with time after injury and the presence of CD68 granules in microglia surfaces opposed to motoneurons. Some microglia formed macroclusters associated with dying motoneurons. Microglia in these clusters display the highest CD68 expression and associate with cytotoxic T-cells. These observations are discussed in relation to current theories on microglia function around axotomized motoneurons.

Targeting CARD6 attenuates spinal cord injury (SCI) in mice through inhibiting apoptosis, inflammation and oxidative stress associated ROS production

Spinal cord injury (SCI) causes long-term and severe disability, influencing the quality of life and triggering serious socioeconomic consequences. Lack of effective pharmacotherapies for SCI is largely attributable to an incomplete understanding of its pathogenesis. Caspase recruitment domain family member 6 (CARD6) was initially suggested to be a protein playing significant role in NF-κB activation. However, the effects of CARD6 on SCI progression remain unknown. In this study, the wild type (CARD6+/+), CARD6 knockout (CARD6-/-) and CARD6 transgenic (TG) mice were subjected to a SCI model in vivo, and in vitro experiments were conducted by treating microglia cells with lipopolysaccharide (LPS). Here, we identified CARD6 as a suppressor of SCI in mice. CARD6 knockout significantly accelerated functional deficits, neuron death and glia activation, whereas CARD6 overexpression resulted in the opposite effects. Both in vivo and in vitro SCI models suggested that CARD6 knockout markedly promoted apoptosis by increasing Cyto-c release to cytosol from mitochondria and activating Caspase-3 signaling. In addition, CARD6 knockout mice exhibited stronger inflammatory response after SCI, as evidenced by the significantly elevated expression of pro-inflammatory cytokines TNF-α, IL-1β and IL-6, which was largely through enhancing the activation of NF-κB signaling.

Comprehensive therapeutics targeting the corticospinal tract following spinal cord injury

Spinal cord injury (SCI), which is much in the public eye, is still a refractory disease compromising the well-being of both patients and society. In spite of there being many methods dealing with the lesion, there is still a deficiency in comprehensive strategies covering all facets of this damage. Further, we should also mention the structure called the corticospinal tract (CST) which plays a crucial role in the motor responses of organisms, and it will be the focal point of our attention. In this review, we discuss a variety of strategies targeting different dimensions following SCI and some treatments that are especially efficacious to the CST are emphasized. Over recent decades, researchers have developed many effective tactics involving five approaches: (1) tackle more extensive regions; (2) provide a regenerative microenvironment; (3) provide a glial microenvironment; (4) transplantation; and (5) other auxiliary methods, for instance, rehabilitation training and electrical stimulation. We review the basic knowledge on this disease and correlative treatments. In addition, some well-formulated perspectives and hypotheses have been delineated. We emphasize that such a multifaceted problem needs combinatorial approaches, and we analyze some discrepancies in past studies. Finally, for the future, we present numerous brand-new latent tactics which have great promise for curbing SCI.

Surgical preparations, labeling strategies, and optical techniques for cell-resolved, in vivo imaging in the mouse spinal cord

In vivo optical imaging has enabled detailed studies of cellular dynamics in the brain of rodents in both healthy and diseased states. Such studies were made possible by three advances: surgical preparations that give optical access to the brain; strategies for in vivo labeling of cells with structural and functional fluorescent indicators; and optical imaging techniques that are relatively insensitive to light scattering by tissue. In vivo imaging in the rodent spinal cord has lagged behind than that in the brain, largely due to the anatomy around the spinal cord that complicates the surgical preparation, and to the strong optical scattering of the dorsal white matter that limits the ability to image deep into the spinal cord. Here, we review recent advances in surgical methods, labeling strategies, and optical tools that have enabled in vivo, high-resolution imaging of the dynamic behaviors of cells in the spinal cord in mice. Surgical preparations that enable long-term optical access and robust stabilization of the spinal cord are now available. Labeling strategies that have been used in the spinal cord tend to follow those that have been used in the brain, and some recent advances in genetically-encoded labeling strategies remain to be capitalized on. The optical imaging methods used to date, including two photon excited fluorescence microscopy, are largely limited to imaging the superficial layers of the spinal cord by the optical scattering of the white matter. Finally, we show preliminary data that points to the use of higher-order nonlinear optical processes, such as three photon excited fluorescence, as a means to image deeper into the mouse spinal cord.

Bioluminescence imaging and two-photon microscopy guided laser ablation of GBM decreases tumor burden

Brain tumor delineation and treatment are the main concerns of neurosurgeons in neurosurgical operations. Bridging the gap between imaging/diagnosis and treatment will provide great convenience for neurosurgeons. Here, we developed an optical theranostics platform that helps to delineate the boundary and quantitatively analyze glioblastoma multiforms (GBMs) with bioluminescence imaging (BLI) to guide laser ablation, and we imaged the GBM cells with two-photon microscopy (TPM) to visualize the laser ablation zone in vivo.

Methods: Laser ablation, using the method of coupled ablated path planning with the guidance of BLI, was implemented in vivo for mouse brain tumors. The mapping relationship between semi-quantitative BLI and the laser ablation path was built through the quantitative tumor burden. The mapping was reflected through coupled ablated path planning. The BLI quantitatively and qualitatively evaluated treatment using laser ablation with the appropriate laser parameters and laser-tissue parameters. These parameters were measured after treatment. Furthermore, histopathological analysis of the brain tissue was conducted to compare the TPM images before and after laser ablation and to evaluate the results of in vivo laser ablation. The local recurrences were measured with three separate cohorts. The weights of all of the mice were measured during the experiment.

Results: Our in vivo BLI data show that the tumor cell numbers were significantly attenuated after treatment with the optical theranostics platform, and the delineation of GBM margins had clear views to guide the laser resection; the fluorescence intensity in vivo of GBMs quantitatively analyzed the rapid progression of GBMs. The laser-tissue parameters under guidance of multimodality imaging ranged between 1.0 mm and 0.1 mm. The accuracy of the laser ablation reached a submillimeter level, and the resection ratio reached more than 99% under the guidance of BLI. The histopathological sections were compared to TPM images, and the results demonstrated that these images highly coincided. The weight index and local recurrence results demonstrated that the therapeutic effect of the optical theranostics platform was significant.

Conclusion: We propose an optical multimodality imaging-guided laser ablation theranostics platform for the treatment of GBMs in an intravital mouse model. The experimental results demonstrated that the integration of multimodality imaging can precisely guide laser ablation for the treatment of GBMs. This preclinical research provides a possibility for the precision treatment of GBMs. The study also provides some theoretical support for clinical research.

Molecular mobility and activity in an intravital imaging setting - implications for cancer progression and targeting

Molecular mobility, localisation and spatiotemporal activity are at the core of cell biological processes and deregulation of these dynamic events can underpin disease development and progression. Recent advances in intravital imaging techniques in mice are providing new avenues to study real-time molecular behaviour in intact tissues within a live organism and to gain exciting insights into the intricate regulation of live cell biology at the microscale level. The monitoring of fluorescently labelled proteins and agents can be combined with autofluorescent properties of the microenvironment to provide a comprehensive snapshot of in vivo cell biology. In this Review, we summarise recent intravital microscopy approaches in mice, in processes ranging from normal development and homeostasis to disease progression and treatment in cancer, where we emphasise the utility of intravital imaging to observe dynamic and transient events in vivo We also highlight the recent integration of advanced subcellular imaging techniques into the intravital imaging pipeline, which can provide in-depth biological information beyond the single-cell level. We conclude with an outlook of ongoing developments in intravital microscopy towards imaging in humans, as well as provide an overview of the challenges the intravital imaging community currently faces and outline potential ways for overcoming these hurdles.