Light stimuli control neuronal migration by altering of insulin-like growth factor 1 (IGF-1) signaling.

The role of genetic inheritance in brain development has been well characterized, but little is known about the contributions of natural environmental stimuli, such as the effect of light-dark cycles, to brain development. In this study, we determined the role of light stimuli in neuronal cell migration to elucidate how environmental factors regulate brain development. We show that in early postnatal mouse cerebella, granule cell migration accelerates during light cycles and decelerates during dark cycles. Furthermore, cerebellar levels of insulin-like growth factor 1 (IGF-1) are high during light cycles and low during dark cycles. There are causal relationships between light-dark cycles, speed of granule cell migration, and cerebellar IGF-1 levels. First, changes in light-dark cycles result in corresponding changes in the fluctuations of both speed of granule cell migration and cerebellar IGF-1 levels. Second, in vitro studies indicate that exogenous IGF-1 accelerates the migration of isolated granule cells through the activation of IGF-1 receptors. Third, in vivo studies reveal that inhibiting the IGF-1 receptors decelerates granule cell migration during light cycles (high IGF-1 levels) but does not alter migration during dark cycles (low IGF-1 levels). In contrast, stimulating the IGF-1 receptors accelerates granule cell migration during dark cycles (low IGF-1 levels) but does not alter migration during light cycles (high IGF-1 levels). These results suggest that during early postnatal development light stimuli control granule cell migration by altering the activity of IGF-1 receptors through modification of cerebellar IGF-1 levels.

Myelin repair is accelerated by inactivating CXCR2 on nonhematopoietic cells.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS and remyelination in MS ultimately fails. Although strategies to promote myelin repair are eagerly sought, mechanisms underlying remyelination in vivo have been elusive. CXCR2 is expressed on neutrophils and oligodendrocyte lineage cells in the CNS. CXCR2-positive neutrophils facilitate inflammatory demyelination in demyelination models such as experimental autoimmune encephalomyelitis (EAE) and cuprizone intoxication. Systemic injection of a small molecule CXCR2 antagonist at the onset of EAE decreased demyelinated lesions. These results left the cellular target of the CXCR2 antagonist uncertain and did not clarify whether CXCR2 blockade prevented demyelination or promoted remyelination. Here, we show that the actions of CXCR2 on nonhematopoietic cells unexpectedly delay myelin repair. Bone marrow chimeric mice (Cxcr2(+/-)-->Cxcr2(-/-) and Cxcr2(+/-)-->Cxcr2(+/+)) were subjected to two distinct models of myelin injury. In all cases, myelin repair was more efficient in Cxcr2(+/-)-->Cxcr2(-/-) animals. Oligodendrocyte progenitor cells (OPCs) in demyelinated lesions of Cxcr2(+/-)-->Cxcr2(-/-) mice proliferated earlier and more vigorously than in tissues from Cxcr2(+/-)--> Cxcr2(+/+) animals. In vitro demyelinated CNS slice cultures also showed better myelin repair when CXCR2 was blocked with neutralizing antibodies or was genetically deleted. Our results suggest that CXCR2 inactivation permits optimal spatiotemporal positioning of OPCs in demyelinating lesions to receive local proliferative and differentiating signals. Given that CXCR2 exerts dual functions that promote demyelination and decrease remyelination by actions toward hematopoietic cells and nonhematopoietic cells, respectively, our findings identify CXCR2 as a promising drug target for clinical demyelinating disorders.

Four distinct phases of basket/stellate cell migration after entering their final destination (the molecular layer) in the developing cerebellum.

In the adult cerebellum, basket/stellate cells are scattered throughout the ML, but little is known about the process underlying the cell dispersion. To determine the allocation of stellate/basket cells within the ML, we examined their migration in the early postnatal mouse cerebellum. We found that after entering the ML, basket/stellate cells sequentially exhibit four distinct phases of migration. First, the cells migrated radially from the bottom to the top while exhibiting saltatory movement with a single leading process (Phase I). Second, the cells turned at the top and migrated tangentially in a rostro-caudal direction, with an occasional reversal of the direction of migration (Phase II). Third, the cells turned and migrated radially within the ML at a significantly reduced speed while repeatedly extending and withdrawing the leading processes (Phase III). Fourth, the cells turned at the middle and migrated tangentially at their slowest speed, while extending several dendrite-like processes after having completely withdrawn the leading process (Phase IV). Finally, the cells stopped and completed their migration. These results suggest that the dispersion of basket/stellate cells in the ML is controlled by the orchestrated activity of external guidance cues, cell-cell contact and intrinsic programs in a position- and time-dependent manner.

Scavenging roles of chemokine receptors: chemokine receptor deficiency is associated with increased levels of ligand in circulation and tissues.

In vitro studies have implicated chemokine receptors in consumption and clearance of specific ligands. We studied the role that various signaling chemokine receptors play during ligand homeostasis in vivo. We examined the levels of ligands in serum and CNS tissue in mice lacking chemokine receptors. Compared with receptor-sufficient controls, Cx3cr1(-/-) mice exhibited augmented levels of CX3CL1 both in serum and brain, and circulating levels of CXCL1 and CXCL2 were increased in Cxcr2(-/-) mice. CCR2-deficient mice showed significantly increased amounts of circulating CCL2 compared with wild-type mice. Cxcr3(-/-) mice revealed increased levels of circulating and brain CXCL10 after experimental autoimmune encephalomyelitis (EAE) induction. CCR2-deficient peripheral blood and resident peritoneal cells exhibited reduced binding capacity and biologic responses to the CCR1 ligand CCL3, suggesting that elevated levels of CCR2 ligands had down-regulated CCR1. The results indicate that signaling chemokine receptors clear chemokines from circulation and tissues. These homeostatic functions of signaling chemokine receptors need to be integrated into safety and efficacy calculations when considering therapeutic receptor blockade.

Role of PACAP in controlling granule cell migration.

Pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide, regulates a wide variety of cellular functions, but little is known about its role in neuronal cell migration. Recent studies revealed that PACAP has short-term, cortical layer-specific effects on neuronal cell migration. In this article, we focus on the role of PACAP in controlling the migration of cerebellar granule cells.

CXCR2-positive neutrophils are essential for cuprizone-induced demyelination: relevance to multiple sclerosis.

Multiple sclerosis is an inflammatory demyelinating disorder of the CNS. Recent studies have suggested diverse mechanisms as underlying demyelination, including a subset of lesions induced by an interaction between metabolic insult to oligodendrocytes and inflammatory mediators. For mice of susceptible strains, cuprizone feeding results in oligodendrocyte cell loss and demyelination of the corpus callosum. Remyelination ensues and has been extensively studied. Cuprizone-induced demyelination remains incompletely characterized. We found that mice lacking the type 2 CXC chemokine receptor (CXCR2) were relatively resistant to cuprizone-induced demyelination and that circulating CXCR2-positive neutrophils were important for cuprizone-induced demyelination. Our findings support a two-hit process of cuprizone-induced demyelination, supporting the idea that multiple sclerosis pathogenesis features extensive oligodendrocyte cell loss. These data suggest that cuprizone-induced demyelination is useful for modeling certain aspects of multiple sclerosis pathogenesis.

Severe disease, unaltered leukocyte migration, and reduced IFN-gamma production in CXCR3-/- mice with experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is a CD4(+) Th1 T cell-mediated disease of the CNS, used to study certain aspects of multiple sclerosis. CXCR3, the receptor for CXCL10, CXCL9, and CXCL11, is preferentially expressed on activated Th1 T cells and has been proposed to govern the migration of lymphocytes into the inflamed CNS during multiple sclerosis and EAE. Unexpectedly, CXCL10-deficient mice were susceptible to EAE, leaving uncertain what the role of CXCR3 and its ligands might play in this disease model. In this study, we report that CXCR3(-/-) mice exhibit exaggerated severity of EAE compared with wild-type (CXCR3(+/+)) littermate mice. Surprisingly, there were neither quantitative nor qualitative differences in CNS-infiltrating leukocytes between CXCR3(+/+) and CXCR3(-/-) mice with EAE. Despite these equivalent inflammatory infiltrates, CNS tissues from CXCR3(-/-) mice with EAE showed worsened blood-brain barrier disruption and more von Willebrand factor-immunoreactive vessels within inflamed spinal cords, as compared with CXCR3(+/+) mice. Spinal cords of CXCR3(-/-) mice with EAE demonstrated decreased levels of IFN-gamma, associated with reduced inducible NO synthase immunoreactivity, and lymph node T cells from CXCR3(-/-) mice primed with MOG(35-55) secreted less IFN-gamma in Ag-driven recall responses than cells from CXCR3(+/+) animals. CXCR3(-/-) lymph node T cells also showed enhanced Ag-driven proliferation, which was reduced by addition of IFN-gamma. Taken with prior findings, our data show that CXCL10 is the most relevant ligand for CXCR3 in EAE. CXCR3 does not govern leukocyte trafficking in EAE but modulates T cell IFN-gamma production and downstream events that affect disease severity.

Cutting edge: the silent chemokine receptor D6 is required for generating T cell responses that mediate experimental autoimmune encephalomyelitis.

D6, a promiscuous nonsignaling chemokine binding molecule expressed on the lymphatic endothelium, internalizes and degrades CC chemokines, and D6(-/-) mice demonstrated increased cutaneous inflammation following topical phorbol ester or CFA injection. We report that D6(-/-) mice were unexpectedly resistant to the induction of experimental autoimmune encephalomyelitis due to impaired encephalitogenic responses. Following induction with myelin oligodendroglial glycoprotein (MOG) peptide 35-55 in CFA, D6(-/-) mice showed reduced spinal cord inflammation and demyelination with lower incidence and severity of experimental autoimmune encephalomyelitis attacks as compared with D6(+/+) littermates. In adoptive transfer studies, MOG-primed D6(+/-) T cells equally mediated disease in D6(+/+) or D6(-/-) mice, whereas cells from D6(-/-) mice transferred disease poorly to D6(+/-) recipients. Lymph node cells from MOG-primed D6(-/-) mice showed weak proliferative responses and made reduced IFN-gamma but normal IL-5. CD11c(+) dendritic cells accumulated abnormally in cutaneous immunization sites of D6(-/-) mice. Surprisingly, D6, a "silent" chemokine receptor, supports immune response generation.