Identification of the growth cone as a probe and driver of neuronal migration in the injured brain.

Axonal growth cones mediate axonal guidance and growth regulation. We show that migrating neurons in mice possess a growth cone at the tip of their leading process, similar to that of axons, in terms of the cytoskeletal dynamics and functional responsivity through protein tyrosine phosphatase receptor type sigma (PTPσ). Migrating-neuron growth cones respond to chondroitin sulfate (CS) through PTPσ and collapse, which leads to inhibition of neuronal migration. In the presence of CS, the growth cones can revert to their extended morphology when their leading filopodia interact with heparan sulfate (HS), thus re-enabling neuronal migration. Implantation of an HS-containing biomaterial in the CS-rich injured cortex promotes the extension of the growth cone and improve the migration and regeneration of neurons, thereby enabling functional recovery. Thus, the growth cone of migrating neurons is responsive to extracellular environments and acts as a primary regulator of neuronal migration.

Amphiphilic peptide-tagged N-cadherin forms radial glial-like fibers that enhance neuronal migration in injured brain and promote sensorimotor recovery.

The mammalian brain has very limited ability to regenerate lost neurons and recover function after injury. Promoting the migration of young neurons (neuroblasts) derived from endogenous neural stem cells using biomaterials is a new and promising approach to aid recovery of the brain after injury. However, the delivery of sufficient neuroblasts to distant injured sites is a major challenge because of the limited number of scaffold cells that are available to guide neuroblast migration. To address this issue, we have developed an amphiphilic peptide [(RADA)3-(RADG)] (mRADA)-tagged N-cadherin extracellular domain (Ncad-mRADA), which can remain in mRADA hydrogels and be injected into deep brain tissue to facilitate neuroblast migration. Migrating neuroblasts directly contacted the fiber-like Ncad-mRADA hydrogel and efficiently migrated toward an injured site in the striatum, a deep brain area. Furthermore, application of Ncad-mRADA to neonatal cortical brain injury efficiently promoted neuronal regeneration and functional recovery. These results demonstrate that self-assembling Ncad-mRADA peptides mimic both the function and structure of endogenous scaffold cells and provide a novel strategy for regenerative therapy.

Postnatal neuronal migration in health and disease.

Postnatal neuronal migration modulates neuronal circuit formation and function throughout life and is conserved among species. Pathological conditions activate the generation of neuroblasts in the ventricular-subventricular zone (V-SVZ) and promote their migration towards a lesion. However, the neuroblasts generally terminate their migration before reaching the lesion site unless their intrinsic capacity is modified or the environment is improved. It is important to understand which factors impede neuronal migration for functional recovery of the brain. We highlight similarities and differences in the mechanisms of neuroblast migration under physiological and pathological conditions to provide novel insights into endogenous neuronal regeneration.

Insulin degludec requires lower bolus insulin doses than does insulin glargine in Japanese diabetic patients with insulin-dependent state.

BACKGROUND: The study presents a comparison of the glucose-lowering effects, glycemic variability, and insulin doses during treatment with insulin degludec or insulin glargine. METHODS: In this open-label, single-center, 2-way crossover study, 13 Japanese diabetic outpatients in the insulin-dependent state on basal-bolus therapy were assigned to receive either insulin glargine followed by insulin degludec, or insulin degludec followed by insulin glargine. Basal insulin doses were fixed in principle, and patients self-adjusted their bolus insulin doses. Seventy-two-hour continuous glucose monitoring was performed 2 weeks after switching the basal insulin. RESULTS: Mean blood glucose (mg/dL) was not significantly different between insulin degludec and insulin glargine over 48 hours (141.8 ± 35.2 vs 151.8 ± 43.3), at nighttime (125.6 ± 40.0 vs 124.7 ± 50.4), or at daytime (149.3 ± 37.1 vs 163.3 ± 44.5). The standard deviation (mg/dL) was also similar (for 48 hours: 48.9 ± 19.4 vs 50.3 ± 17.3; nighttime: 18.7 ± 14.3 vs 13.7 ± 6.7; daytime: 49.3 ± 20.0 vs 44.3 ± 17.7). Other indices of glycemic control, glycemic variability, and hypoglycemia were similar for both insulin analogs. Total daily insulin dose (TDD) and total daily bolus insulin dose (TDBD) were significantly lower with insulin degludec than with insulin glargine (TDD: 0.42 ± 0.20 vs 0.46 ± 0.22 U/kg/day, P = .028; TDBD: 0.27 ± 0.13 vs 0.30 ± 0.14 U/kg/day, P = .036). CONCLUSIONS: Insulin degludec and insulin glargine provided effective and stable glycemic control. Insulin degludec required lower TDD and TDBD in this population of patients.

The lipoprotein receptor LRP1 modulates sphingosine-1-phosphate signaling and is essential for vascular development.

Low density lipoprotein receptor-related protein 1 (LRP1) is indispensable for embryonic development. Comparing different genetically engineered mouse models, we found that expression of Lrp1 is essential in the embryo proper. Loss of LRP1 leads to lethal vascular defects with lack of proper investment with mural cells of both large and small vessels. We further demonstrate that LRP1 modulates Gi-dependent sphingosine-1-phosphate (S1P) signaling and integrates S1P and PDGF-BB signaling pathways, which are both crucial for mural cell recruitment, via its intracellular domain. Loss of LRP1 leads to a lack of S1P-dependent inhibition of RAC1 and loss of constraint of PDGF-BB-induced cell migration. Our studies thus identify LRP1 as a novel player in angiogenesis and in the recruitment and maintenance of mural cells. Moreover, they reveal an unexpected link between lipoprotein receptor and sphingolipid signaling that, in addition to angiogenesis during embryonic development, is of potential importance for other targets of these pathways, such as tumor angiogenesis and inflammatory processes.

Low density lipoprotein receptor-related protein 1 (LRP1) modulates N-methyl-D-aspartate (NMDA) receptor-dependent intracellular signaling and NMDA-induced regulation of postsynaptic protein complexes.

The lipoprotein receptor LRP1 is essential in neurons of the central nervous system, as was revealed by the analysis of conditional Lrp1-deficient mouse models. The molecular basis of its neuronal functions, however, is still incompletely understood. Here we show by immunocytochemistry, electron microscopy, and postsynaptic density preparation that LRP1 is located postsynaptically. Basal and NMDA-induced phosphorylation of the transcription factor cAMP-response element-binding protein (CREB) as well as NMDA target gene transcription are reduced in LRP1-deficient neurons. In control neurons, NMDA promotes γ-secretase-dependent release of the LRP1 intracellular domain (LRP1-ICD). However, pull-down and chromatin immunoprecipitation (ChIP) assays showed no direct interaction between the LRP1-ICD and either CREB or target gene promoters. On the other hand, NMDA-induced degradation of the postsynaptic scaffold protein PSD-95 was impaired in the absence of LRP1, whereas its ubiquitination was increased, indicating that LRP1 influences the composition of postsynaptic protein complexes. Accordingly, NMDA-induced internalization of the AMPA receptor subunit GluA1 was impaired in LRP1-deficient neurons. These results show a role of LRP1 in the regulation and turnover of synaptic proteins, which may contribute to the reduced dendritic branching and to the neurological phenotype observed in the absence of LRP1.

Quantitative regional and ultrastructural localization of the Ca(v)2.3 subunit of R-type calcium channel in mouse brain.

R-type calcium channels (RTCCs) are well known for their role in synaptic plasticity, but little is known about their subcellular distribution across various neuronal compartments. Using subtype-specific antibodies, we characterized the regional and subcellular localization of Ca(v)2.3 in mice and rats at both light and electron microscopic levels. Ca(v)2.3 immunogold particles were found to be predominantly presynaptic in the interpeduncular nucleus, but postsynaptic in other brain regions. Serial section analysis of electron microscopic images from the hippocampal CA1 revealed a higher density of immunogold particles in the dendritic shaft plasma membrane compared with the pyramidal cell somata. However, the labeling densities were not significantly different among the apical, oblique, or basal dendrites. Immunogold particles were also observed over the plasma membrane of dendritic spines, including both synaptic and extrasynaptic sites. Individual spine heads contained <20 immunogold particles, with an average density of ∼260 immunoparticles per µm(3) spine head volume, in accordance with the density of RTCCs estimated using calcium imaging (Sabatini and Svoboda, 2000). The Ca(v)2.3 density was variable among similar-sized spine heads and did not correlate with the density in the parent dendrite, implying that spines are individual calcium compartments operating autonomously from their parent dendrites.

Gamma-secretase limits the inflammatory response through the processing of LRP1.

Inflammation is a potentially self-destructive process that needs tight control. We have identified a nuclear signaling mechanism through which the low-density lipoprotein receptor-related protein 1 (LRP1) limits transcription of lipopolysaccharide (LPS)-inducible genes. LPS increases the proteolytic processing of the ectodomain of LRP1, which results in the gamma-secretase-dependent release of the LRP1 intracellular domain (ICD) from the plasma membrane and its translocation to the nucleus, where it binds to and represses the interferon-gamma promoter. Basal transcription of LPS target genes and LPS-induced secretion of proinflammatory cytokines are increased in the absence of LRP1. The interaction between LRP1-ICD and interferon regulatory factor 3 (IRF-3) promotes the nuclear export and proteasomal degradation of IRF-3. Feedback inhibition of the inflammatory response through intramembranous processing of LRP1 thus defines a physiological role for gamma-secretase.