Cerebrospinal fluid flow extends to peripheral nerves further unifying the nervous system.

Cerebrospinal fluid (CSF) is responsible for maintaining brain homeostasis through nutrient delivery and waste removal for the central nervous system (CNS). Here, we demonstrate extensive CSF flow throughout the peripheral nervous system (PNS) by tracing distribution of multimodal 1.9-nanometer gold nanoparticles, roughly the size of CSF circulating proteins, infused within the lateral cerebral ventricle (a primary site of CSF production). CSF-infused 1.9-nanometer gold transitions from CNS to PNS at root attachment/transition zones and distributes through the perineurium and endoneurium, with ultimate delivery to axoplasm of distal peripheral nerves. Larger 15-nanometer gold fails to transit from CNS to PNS and instead forms "dye-cuffs," as predicted by current dogma of CSF restriction within CNS, identifying size limitations in central to peripheral flow. Intravenous 1.9-nanometer gold is unable to cross the blood-brain/nerve barrier. Our findings suggest that CSF plays a consistent role in maintaining homeostasis throughout the nervous system with implications for CNS and PNS therapy and neural drug delivery.

Cerebrospinal Fluid Flow Extends to Peripheral Nerves.

Cerebrospinal fluid (CSF) is an aqueous solution responsible for nutrient delivery and waste removal for the central nervous system (CNS). The three-layer meningeal coverings of the CNS support CSF flow. Peripheral nerves have an analogous three-layer covering consisting of the epineurium, perineurium, and endoneurium. Peripheral axons, located in the inner endoneurium, are bathed in "endoneurial fluid" similar to CSF but of undefined origin. CSF flow in the peripheral nervous system has not been demonstrated. Here we show CSF flow extends beyond the CNS to peripheral nerves in a contiguous flowing system. Utilizing gold nanoparticles, we identified that CSF is continuous with the endoneurial fluid and reveal the endoneurial space as the likely site of CSF flow in the periphery. Nanogold distribution along entire peripheral nerves and within their axoplasm suggests CSF plays a role in nutrient delivery and waste clearance, fundamental aspects of peripheral nerve health and disease. One Sentence Summary: Cerebrospinal fluid unites the nervous system by extending beyond the central nervous system into peripheral nerves.

Bone marrow-derived cells home to and regenerate retinal pigment epithelium after injury.

PURPOSE: To determine whether hematopoietic stem and progenitor cells (HSCs/HPCs) can home to and regenerate the retinal pigment epithelium (RPE) after induced injury. METHODS: Enriched HSCs/HPCs from green fluorescent protein (gfp) transgenic mice were transplanted into irradiated recipient mice to track bone marrow-derived cells. Physical damage was induced by breaching Bruch's membrane and inducing vascular endothelial growth factor A (VEGFa) expression to promote neovascularization. RPE damage was also induced by sodium iodate injection (40 mg/kg) into wild-type or albino C57Bl/6 mice. Cell morphology, gfp expression, the presence of the Y chromosome, and the presence of melanosomes were used to determine whether the injured RPE was being repaired by the donor bone marrow. RESULTS: Injury to the RPE recruits HSC/HPC-derived cells to incorporate into the RPE layer and differentiate into an RPE phenotype. A portion of the HSCs/HPCs adopt RPE morphology, express melanosomes, and integrate into the RPE without cell fusion. CONCLUSIONS: HSCs/HPCs can migrate to the RPE layer after physical or chemical injury and regenerate a portion of the damaged cell layer.

Cone cell survival and downregulation of GCAP1 protein in the retinas of GC1 knockout mice.

PURPOSE: To examine the spatial and temporal characteristics of cone cell survival and the expression of guanylate cyclase-activating proteins (GCAPs) in the guanylate cyclase (GC)-1 knockout (KO) mouse retina. METHODS: Immunohistochemical analyses with peanut agglutinin and an antibody specific for cone transducin were used to examine cone cell survival in the GC1 KO retina at 4, 5, 9, 16, and 24 weeks of age. Immunohistochemical and Northern and Western blot analyses were used to examine the expression of GCAP1 and GCAP2 in 4- to 5-week-old mice. RESULTS: The number of cone cells appeared normal throughout the superior and inferior retinal regions in 4- and 5-week-old GC1 KO mice but gradually decreased by 6 months. Cone cell loss was exacerbated in the inferior retinal region, with only 2% to 8% remaining by 6 months of age; however, 40% to 70% of the cone cells survived in the superior region at this age. GCAP1 and GCAP2 protein levels were downregulated in GC1 KO retinas at 4 weeks of age and GCAP1 immunostaining was absent from the photoreceptor outer segments. CONCLUSIONS: The results of this study show that the rate of cone cell loss in the GC1 KO mouse is comparable to that previously described in the GUCY1*B chicken and in humans with Leber congenital amaurosis (LCA)-1. The GCAP expression data, when combined with those of previous electrophysiological studies of the GC1 KO mouse retina, provide evidence that GC1-GCAP1 interactions are essential for cone cell function in mice and that GC2 and GCAP2 activities contribute to the rod cell response in the absence of GC1.

Adult hematopoietic stem cells provide functional hemangioblast activity during retinal neovascularization.

Adults maintain a reservoir of hematopoietic stem cells that can enter the circulation to reach organs in need of regeneration. We developed a novel model of retinal neovascularization in adult mice to examine the role of hematopoietic stem cells in revascularizing ischemic retinas. Adult mice were durably engrafted with hematopoietic stem cells isolated from transgenic mice expressing green fluorescent protein. We performed serial long-term transplants, to ensure activity arose from self-renewing stem cells, and single hematopoietic stem-cell transplants to show clonality. After durable hematopoietic engraftment was established, retinal ischemia was induced to promote neovascularization. Our results indicate that self-renewing adult hematopoietic stem cells have functional hemangioblast activity, that is, they can clonally differentiate into all hematopoietic cell lineages as well as endothelial cells that revascularize adult retina. We also show that recruitment of endothelial precursors to sites of ischemic injury has a significant role in neovascularization.