[show abstract][hide abstract] ABSTRACT: Nogo-A is the largest isoform of the Nogo/RTN4 proteins and has been characterized as a major myelin associated inhibitor of regenerative nerve growth in the adult central nervous system (CNS). Apart from the myelin sheath, Nogo-A is expressed at high levels in principal neurons of the CNS. The specificity of Nogo-A resides in its central domain, NiG. We identified Apg-1, a member of the stress induced Hsp110 family, as a novel interactor of NiG/Nogo-A. The interaction is selective because Apg-1 interacts with Nogo-A/RTN4-A but not with RTN1-A, the closest paralog of Nogo-A. Conversely, Nogo-A binds to Apg-1 but not to Apg-2 or Hsp105, two other members of the Hsp110 family. We characterized the Nogo-A / Apg-1 interaction by affinity precipitation, co-immunoprecipitation, and proximity ligation assay, using primary hippocampal neurons derived from nogo deficient mice. Under conditions of hypoxic and oxidative stress we found that Nogo-A and Apg-1 were tightly co-regulated in hippocampal neurons. While both proteins were up-regulated under hypoxic conditions, their expression levels were reduced on the addition of hydrogen peroxide. Taken together, our data suggest that Nogo-A is closely involved in the neuronal response to hypoxic and oxidative stress, an observation that may be of relevance not only in stroke induced ischemia, but also in neuroblastoma formation.
[show abstract][hide abstract] ABSTRACT: Members of the Nogo66 receptor family (NgR) are closely associated with nerve growth inhibition and plasticity in the CNS. All three members, NgR1, NgR2 and NgR3, are GPI anchored and highly glycosylated proteins. The binding and signaling properties of NgR1 are well described, but largely unknown for NgR2. At present the only known ligands are myelin associated glycoprotein (MAG) and amyloid beta precursor protein (APP). Despite the requirement of co-receptors for signaling no other binding partner has been uncovered. To learn more about the interactome of NgR2 we performed pull down experiments and were able to identify F-box protein that recognizes sugar chain 1 (Fbs1) as binding partner. We confirmed this finding with co-immunoprecipitations and in vitro binding assays and showed that the binding is mediated by the substrate recognition domain of Fbs1. As a substrate recognition protein of the SCF complex, Fbs1 binding leads to polyubiquitination and finally degradation of its substrates. This is the first time a member of the Nogo receptor family has been connected with an intracellular degradation pathway, which has not only implications for its production, but also for amyloid deposition in Alzheimer's disease.
Biochemical and Biophysical Research Communications 12/2011; 417(3):977-81. · 2.41 Impact Factor
[show abstract][hide abstract] ABSTRACT: Nogo-66 receptor NgR1 and its structural homologue NgR2 are binding proteins for a number of myelin-associated inhibitory factors. After neuronal injury, these inhibitory factors are responsible for preventing axonal outgrowth via their interactions with NgR1 and NgR2 expressed on neurons. In vitro, cells expressing NgR1/2 are inhibited from adhering to and spreading on a myelin substrate. Neuronal injury also results in the presence of dendritic cells (DCs) in the central nervous system, where they can come into contact with myelin debris. The exact mechanisms of interaction of immune cells with CNS myelin are, however, poorly understood.
Human DCs were differentiated from peripheral blood monocytes and mouse DCs were differentiated from wild type and NgR1/NgR2 double knockout bone marrow precursors. NgR1 and NgR2 expression were determined with quantitative real time PCR and immunoblot, and adhesion of cells to myelin was quantified.
We demonstrate that human immature myeloid DCs express NgR1 and NgR2, which are then down-regulated upon maturation. Human mature DCs also adhere to a much higher extent to a myelin substrate than immature DCs. We observe the same effect when the cells are plated on Nogo-66-His (binding peptide for NgR1), but not on control proteins. Mature DCs taken from Ngr1/2 knockout mice adhere to a much higher extent to myelin compared to wild type mouse DCs. In addition, Ngr1/2 knockout had no effect on in vitro DC differentiation or phenotype.
These results indicate that a lack of NgR1/2 expression promotes the adhesion of DCs to myelin. This interaction could be important in neuroinflammatory disorders such as multiple sclerosis in which peripheral immune cells come into contact with myelin debris.
Journal of Neuroinflammation 09/2011; 8:113. · 4.35 Impact Factor