Retinal microvascular and neuronal function in patients with multiple sclerosis: 2-year follow-up.

OBJECTIVE: To determine the longitudinal changes in retinal microstructure, microvasculature, microcirculation, and axonal and neuronal functions in patients with relapsing-remitting multiple sclerosis (RRMS) over the time course of about two years. METHODS: A total of 30 patients (60 eyes) with RRMS were followed for a period of 27 ± 6 months and evaluated with a battery of clinical tests including low contrast letter acuity (LCLA), intraretinal layer thicknesses by optical coherence tomography (OCT), ganglion cell function by steady-state pattern electroretinography (PERG), axonal function by polarization-sensitive OCT, volumetric vessel density (VVD) by OCT angiography, and retinal tissue perfusion (RTP) by retinal function imager. RESULTS: Axonal function measured as retinal nerve fiber layer birefringence in the temporal quadrant and vessel density in the deep vascular plexus were significantly decreased at 2-year follow-up (P < 0.05). Subgroup analyses showed that the increased retinal blood flow volume occurred in patients with no evidence of disease activity (NEDA), and with stable or improved visual function (P < 0.05). There was no significant difference in the expanded disability state scale, LCLA, RTP, VVD, or PERG measures between the two visits (P > 0.05). CONCLUSION: To our best knowledge, this is the first 2-year prospective comprehensive study with a detailed assessment of retinal microstructure and neuronal functions in patients with RRMS. The recovery of retinal microcirculation occurred in patients with NEDA, and stable or improved visual function, suggesting these measurements as potential imaging biomarkers for monitoring disease progression.

Effect of riluzole on weight in short-term and long-term survivors of amyotrophic lateral sclerosis.

INTRODUCTION: Riluzole is the first disease-modifying therapy for amyotrophic lateral sclerosis (ALS) approved in 1995 by the Food and Drug Administration in the USA, and is now available worldwide. It delays time to tracheostomy or death and prolongs survival. The precise mechanism of the survival prolonging effect is unknown. Malnutrition and ensuing weight loss are associated with shorter survival in ALS. Given the life-prolonging effects of riluzole and nutritional maintenance, we examined the relationship between riluzole and weight in ALS patients. Materials and Methods: Using data from the National ALS Center of Excellence clinic database at the University of Vermont Medical Center, we stratified 244 patients into cohorts based on riluzole use, and duration of survival from the baseline visit into short-term (≤3 years) and long-term (>3 years) survivors. We examined average monthly weight change in patients during the first year after the baseline visit, and the last year before death. Results and Discussion: In 156 short-term survivors taking riluzole compared to those not taking riluzole, there was a 37% attenuation of weight loss in the first year after baseline, and 46% attenuation of weight loss in the last year before death. Seventy-four n long-term survivors on riluzole showed reduced weight decline in the first year after the baseline visit. We speculate that one mechanism by which riluzole may affect survival is by attenuating weight loss and possibly maintaining nutritional status and body composition, although this warrants prospective study.

Thrombospondin-1 Mediates Axon Regeneration in Retinal Ganglion Cells.

Neuronal subtypes show diverse injury responses, but the molecular underpinnings remain elusive. Using transgenic mice that allow reliable visualization of axonal fate, we demonstrate that intrinsically photosensitive retinal ganglion cells (ipRGCs) are both resilient to cell death and highly regenerative. Using RNA sequencing (RNA-seq), we show genes that are differentially expressed in ipRGCs and that associate with their survival and axon regeneration. Strikingly, thrombospondin-1 (Thbs1) ranked as the most differentially expressed gene, along with the well-documented injury-response genes Atf3 and Jun. THBS1 knockdown in RGCs eliminated axon regeneration. Conversely, RGC overexpression of THBS1 enhanced regeneration in both ipRGCs and non-ipRGCs, an effect that was dependent on syndecan-1, a known THBS1-binding protein. All structural domains of the THBS1 were not equally effective; the trimerization and C-terminal domains promoted regeneration, while the THBS type-1 repeats were dispensable. Our results identify cell-type-specific induction of Thbs1 as a novel gene conferring high regenerative capacity.

3D Visualization of Individual Regenerating Retinal Ganglion Cell Axons Reveals Surprisingly Complex Growth Paths.

Retinal ganglion cells (RGCs), the sole output cells of the retina, are a heterogeneous population of neurons that project axons to visual targets in the brain. Like most CNS neurons, RGCs are considered incapable of mounting long distance axon regeneration. Using immunolabeling-enabled 3D imaging of solvent-cleared organs (iDISCO) in transgenic mice, we tracked the entire paths of individual RGC axons and show that adult RGCs are highly capable of spontaneous long-distance regeneration, even without any treatment. Our results show that the Thy1-H-YFP mouse sparsely labels RGCs, consisting predominantly of regeneration-competent α-type RGCs (αRGCs). Following optic nerve crush, many of the YFP-labeled RGC axons extend considerable distances proximal to the injury site with only a few penetrating through the lesion. This tortuous axon growth proximal to the lesion site is even more striking with intravitreal ciliary neurotrophic factor (CNTF) treatment. We further demonstrate that despite traveling more than 5 mm (i.e., a distance equal to the length of mouse optic nerve), many of these circuitous axons are confined to the injury area and fail to reach the brain. Our results re-evaluate the view that RGCs are naturally incapable of re-extending long axons, and shift the focus from promoting axon elongation, to understanding factors that prevent direct growth of axons through the lesion and the injured nerve.

Enhanced Transcriptional Activity and Mitochondrial Localization of STAT3 Co-induce Axon Regrowth in the Adult Central Nervous System.

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor central to axon regrowth with an enigmatic ability to act in different subcellular regions independently of its transcriptional roles. However, its roles in mature CNS neurons remain unclear. Here, we show that along with nuclear translocation, STAT3 translocates to mitochondria in mature CNS neurons upon cytokine stimulation. Loss- and gain-of-function studies using knockout mice and viral expression of various STAT3 mutants demonstrate that STAT3's transcriptional function is indispensable for CNS axon regrowth, whereas mitochondrial STAT3 enhances bioenergetics and further potentiates regrowth. STAT3's localization, functions, and growth-promoting effects are regulated by mitogen-activated protein kinase kinase (MEK), an effect further enhanced by Pten deletion, leading to extensive axon regrowth in the mouse optic pathway and spinal cord. These results highlight CNS neuronal dependence on STAT3 transcriptional activity, with mitochondrial STAT3 providing ancillary roles, and illustrate a critical contribution for MEK in enhancing diverse STAT3 functions and axon regrowth.

Promoting filopodial elongation in neurons by membrane-bound magnetic nanoparticles.

Filopodia are 5-10 µm long processes that elongate by actin polymerization, and promote axon growth and guidance by exerting mechanical tension and by molecular signaling. Although axons elongate in response to mechanical tension, the structural and functional effects of tension specifically applied to growth cone filopodia are unknown. Here we developed a strategy to apply tension specifically to retinal ganglion cell (RGC) growth cone filopodia through surface-functionalized, membrane-targeted superparamagnetic iron oxide nanoparticles (SPIONs). When magnetic fields were applied to surface-bound SPIONs, RGC filopodia elongated directionally, contained polymerized actin filaments, and generated retrograde forces, behaving as bona fide filopodia. Data presented here support the premise that mechanical tension induces filopodia growth but counter the hypothesis that filopodial tension directly promotes growth cone advance. Future applications of these approaches may be used to induce sustained forces on multiple filopodia or other subcellular microstructures to study axon growth or cell migration. From the clinical editor: Mechanical tension to the tip of filopodia is known to promote axonal growth. In this article, the authors used superparamagnetic iron oxide nanoparticles (SPIONs) targeted specifically to membrane molecules, then applied external magnetic field to elicit filopodial elongation, which provided a tool to study the role of mechanical forces in filopodia dynamics and function.