Studying Myeloid Cell Heterogeneity After Spinal Cord Injury via Time-Resolved Single-Cell RNA Sequencing

Spinal cord injury (SCI) is a devastating pathology that affects thousands of individuals annually, resulting in the requirement for long-term physical and medical care and thus significant personal, societal, and economic burdens. The SCI pathology is characterised by an initial mechanical insult, followed by a spatiotemporally dynamic secondary injury. Decades of research have worked to assemble a general picture of this secondary pathology. We now understand that compared to the normal wound healing observed in the periphery, tissue recovery after SCI is dysregulated and results in a chronic wound state characterized by persistent inflammation and functional deficits. The primary drivers of this inflammation are central nervous system (CNS) resident microglia and infiltrating myeloid cells. However, the precise role of these myeloid cell subsets remains unclear as upon crossing the blood-spinal cord barrier (BSCB), infiltrating monocyte-derived macrophages may take on the morphology of microglia, and upregulate canonical microglia markers, making the two populations difficult to distinguish. In this PhD project, I employed single-cell RNA sequencing (scRNAseq) to deconvolute the complex heterogeneity of infiltrating and resident myeloid cells in mouse models of thoracic contusion SCI at an unprecedented resolution. To fully appreciate the temporal dynamics of the pathology, I collected samples across the acute, subacute, and early chronic phases of SCI, plus a sham-injured control. Recent experiments have demonstrated that CNS infiltrating macrophages also take on the transcriptional profiles of microglia, which led me to question whether I had accurately annotated infiltrating macrophages in the dataset. To address this, I repeated the experiment with a transgenic fate-mapping mouse line then integrated these two datasets to generate a time-resolved SCI myeloid cell atlas with definitive ontogeny labelling. With this dataset I generated a putative time resolved map of myeloid cell dynamics across the SCI pathology. Through collaboration, I was also able to verify the expression of select genes via single-molecule fluorescent in situ hybridization (smFISH) and immunofluorescence (IF). A key observation was the persistence of a pro-inflammatory foam cell-like state in both microglia and macrophages, which may contribute to the non-resolving chronic injury. Future studies might investigate the functional relevance of this population, and its suitability as a therapeutic target to reduce the long-term disabilities of SCI patients.Regan Hamel was supported by the Cambridge Trust and is the recipient of a Canadian Scholarship Trust Foundation, an MNI-Cambridge Douglas Avrith Graduate Studentship, and a Rosetrees Trust Studentship

Metabolic Control of Smoldering Neuroinflammation.

Compelling evidence exists that patients with chronic neurological conditions, which includes progressive multiple sclerosis, display pathological changes in neural metabolism and mitochondrial function. However, it is unknown if a similar degree of metabolic dysfunction occurs also in non-neural cells in the central nervous system. Specifically, it remains to be clarified (i) the full extent of metabolic changes in tissue-resident microglia and infiltrating macrophages after prolonged neuroinflammation (e.g., at the level of chronic active lesions), and (ii) whether these alterations underlie a unique pathogenic phenotype that is amenable for therapeutic targeting. Herein, we discuss how cell metabolism and mitochondrial function govern the function of chronic active microglia and macrophages brain infiltrates and identify new metabolic targets for therapeutic approaches aimed at reducing smoldering neuroinflammation

Harnessing the Neural Stem Cell Secretome for Regenerative Neuroimmunology.

Increasing evidence foresees the secretome of neural stem cells (NSCs) to confer superimposable beneficial properties as exogenous NSC transplants in experimental treatments of traumas and diseases of the central nervous system (CNS). Naturally produced secretome biologics include membrane-free signaling molecules and extracellular membrane vesicles (EVs) capable of regulating broad functional responses. The development of high-throughput screening pipelines for the identification and validation of NSC secretome targets is still in early development. Encouraging results from pre-clinical animal models of disease have highlighted secretome-based (acellular) therapeutics as providing significant improvements in biochemical and behavioral measurements. Most of these responses are being hypothesized to be the result of modulating and promoting the restoration of key inflammatory and regenerative programs in the CNS. Here, we will review the most recent findings regarding the identification of NSC-secreted factors capable of modulating the immune response to promote the regeneration of the CNS in animal models of CNS trauma and inflammatory disease and discuss the increased interest to refine the pro-regenerative features of the NSC secretome into a clinically available therapy in the emerging field of Regenerative Neuroimmunology

Stem Cell Therapies for Progressive Multiple Sclerosis.

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system characterized by demyelination and axonal degeneration. MS patients typically present with a relapsing-remitting (RR) disease course, manifesting as sporadic attacks of neurological symptoms including ataxia, fatigue, and sensory impairment. While there are several effective disease-modifying therapies able to address the inflammatory relapses associated with RRMS, most patients will inevitably advance to a progressive disease course marked by a gradual and irreversible accrual of disabilities. Therapeutic intervention in progressive MS (PMS) suffers from a lack of well-characterized biological targets and, hence, a dearth of successful drugs. The few medications approved for the treatment of PMS are typically limited in their efficacy to active forms of the disease, have little impact on slowing degeneration, and fail to promote repair. In looking to address these unmet needs, the multifactorial therapeutic benefits of stem cell therapies are particularly compelling. Ostensibly providing neurotrophic support, immunomodulation and cell replacement, stem cell transplantation holds substantial promise in combatting the complex pathology of chronic neuroinflammation. Herein, we explore the current state of preclinical and clinical evidence supporting the use of stem cells in treating PMS and we discuss prospective hurdles impeding their translation into revolutionary regenerative medicines

Anchors aweigh: the sources, variety, and challenges of mission drift

The growing number of studies which reference the concept of mission drift imply that such drift is an undesirable strategic outcome related to inconsistent organizational action, yet beyond such references little is known about how mission drift occurs, how it impacts organizations, and how organizations should respond. Existing management theory more broadly offers initial albeit equivocal insight for understanding mission drift. On the one hand, prior studies have argued that inconsistent or divergent action can lead to weakened stakeholder commitment and reputational damage. On the other hand, scholars have suggested that because environments are complex and dynamic, such action is necessary for ensuring organizational adaptation and thus survival. In this study, we offer a theory of mission drift that unpacks its origin, clarifies its variety, and specifies how organizations might respond to external perceptions of mission drift. The resulting conceptual model addresses the aforementioned theoretical tension and offers novel insight into the relationship between organizational actions and identity

Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure