Bor Luen Tang

Regulation of Nogo and Nogo receptor during the development of the entorhino-hippocampal pathway and after adult hippocampal lesions.

Axonal regeneration in the adult CNS is limited by the presence of several inhibitory proteins associated with myelin. Nogo-A, a myelin-associated inhibitor, is responsible for axonal outgrowth inhibition in vivo and in vitro. Here we study the onset and maturation of Nogo-A and Nogo receptor in the entorhino-hippocampal formation of developing and adult mice. We also provide evidence that Nogo-A does not inhibit embryonic hippocampal neurons, in contrast to other cell types such as cerebellar granule cells. Our results also show that Nogo and Nogo receptor mRNA are expressed in the adult by both principal and local-circuit hippocampal neurons, and that after lesion, Nogo-A is also transiently expressed by a subset of reactive astrocytes. Furthermore, we analyzed their regulation after kainic acid (KA) treatment and in response to the transection of the entorhino-hippocampal connection. We found that Nogo-A and Nogo receptor are differentially regulated after kainic acid or perforant pathway lesions. Lastly, we show that the regenerative potential of lesioned entorhino-hippocampal organotypic slice co-cultures is increased after blockage of Nogo-A with two IN-1 blocking antibodies. In conclusion, our results show that Nogo and its receptor might play key roles during development of hippocampal connections and that they are implicated in neuronal plasticity in the adult.

Coaxing bone marrow stromal mesenchymal stem cells towards neuronal differentiation: progress and uncertainties

Abstract.Multipotent adult stem cells capable of developing into particular neuronal cell types have great potential for autologous cell replacement therapy for central nervous system neurodegenerative disorders and traumatic injury. Bone marrow-derived stromal mesenchymal stem cells (BMSCs) appear to be attractive starting materials. One question is whether BMSCs could be coaxed to differentiate in vitro along neuronal or glial lineages that would aid their functional integration post-transplantation, while reducing the risk of malignant transformation. Recent works suggest that BMSCs could indeed be differentiated in vitro to exhibit some cellular and physiological characteristics of neural cell lineages, but it is not likely to be achievable with simple chemical treatments. We discussed recent findings pertaining to efforts in neuronal differentiation of BMSCs in vitro, and results obtained when these were transplanted in vivo.

Cell Autonomous Function of Nogo and Reticulons : The Emerging Story at the Endoplasmic Reticulum

The myelin‐associated membrane protein reticulon‐4 (RTN4)/Nogo has been extensively studied with regards to its neurite outgrowth inhibitory function, both in limiting plasticity in the healthy adult brain and regeneration during central nervous system injury. These activities are presumably associated with Nogo splice isoforms expressed on the cell surface and function largely in trans, exerting an influence as an intercellular membrane‐bound ligand. Nogo, and other reticulon paralogues and orthologues, are however mainly localized to the endoplasmic reticulum (ER), and are likely to have cell autonomous functions that are not yet clear. Emerging evidence suggests that Nogo may have a role in modulating the morphology and functions of the ER. This role is apparently not essential for cell viability under normal growth conditions, but may be manifested under certain stress conditions. J. Cell. Physiol. 216: 303–308, 2008.

Neural differentiation and potential use of stem cells from the human umbilical cord for central nervous system transplantation therapy

The human umbilical cord is a rich source of autologous stem and progenitor cells. Interestingly, subpopulations of these, particularly mesenchymal‐like cells from both cord blood and the cord stroma, exhibited a potential to be differentiated into neuron‐like cells in culture. Umbilical cord blood stem cells have demonstrated efficacy in reducing lesion sizes and enhancing behavioral recovery in animal models of ischemic and traumatic central nervous system (CNS) injury. Recent findings also suggest that neurons derived from cord stroma mesenchymal cells could alleviate movement disorders in hemiparkinsonian animal models. We review here the neurogenic potential of umbilical cord stem cells and discuss possibilities of their exploitation as an alternative to human embryonic stem cells or neural stem cells for transplantation therapy of traumatic CNS injury and neurodegenerative diseases.

Sirt1’s Complex Roles in Neuroprotection

The nicotinamide adenine dinucleotide (NAD)-activated protein deacetylase Sir2p/Sirt1 has been strongly implicated in the modulation of replicative lifespan and promotion of longevity. Part of Sirt1’s capacity for lifespan extension in complex organisms may be attributed to its protective activity against neuronal degeneration. Manipulation of Sirt1’s activity or levels by pharmacological and genetic means in several models of neurodegenerative diseases demonstrated its neuroprotective credentials. However, recent data have indicated that under certain contexts, Sirt1 inhibition, rather than activation, is neuroprotective. These inconsistencies highlight the complex nature of Sirt1-mediated effects. The enzyme has both histone and nonhistone targets, and could potentially act in both nuclear and cytoplasmic compartments. These activities intertwine in a manner depending on the context of a system under investigation. One needs to be cautious in extrapolating results derived from short-term observations to a longer-term context, and in assessing efficacies of Sirt1-based therapeutic approaches in treating neurodegenerative diseases.

Sonic hedgehog as a chemoattractant for adult NPCs

The developmental morphogen Sonic hedgehog (Shh) is well known for its role in modulating the proliferation and survival of neural progenitor cells in the developing mouse brain. A recent report now showed that Shh could regulate the migration of neuroblast in the adult subventricular zone (SVZ) along the rostral migratory stream (RMS) to the olfactory bulb, by functioning as a chemoattractant. Functions of Shh in regulating the migration and survival of neural progenitor cells in the adult central nervous system are suggestive of its potential roles in neural regeneration and CNS oncogenesis.

AMIGO is expressed in multiple brain cell types and may regulate dendritic growth and neuronal survival.

Amphoterin‐induced gene and ORF (AMIGO) is a brain‐enriched transmembrane immunoglobulin (Ig) superfamily protein with six extracellular leucine‐rich repeats (LRR) and a single immunoglobulin‐like (Ig) domain. We report here that AMIGO is a glycosylated protein widely expressed in the central nervous system (CNS), and can be found in neurons, astrocytes as well as oligodendrocytes. In morphologically mature primary neurons, endogenous AMIGO, and transfected full length AMIGO (AMIGO‐FL) are largely dendritic, while AMIGO with its LRR domain deleted (AMIGO‐Ig) is predominantly axonal. In line with AMIGOs dendritic localization, siRNA‐mediated silencing of AMIGO resulted in reduced dendritic growth of cortical neurons in culture. SH‐SY5Y cells stably over‐expressing AMIGO are more resistant to apoptosis induced by staurosporine and H2O2 compared to vector controls. AMIGO therefore likely plays important roles in dendritic outgrowth during development, and could modulate the survival of developing and adult neurons. J. Cell. Physiol. 227: 2217–2229, 2012.

Rab GTPases regulating receptor trafficking at the late endosome–lysosome membranes

Lysosomes serve key degradative functions for the turnover of membrane lipids and protein components. Its biogenesis is principally dependent on exocytic traffic from the late endosome via the trans‐Golgi network, and it also receives cargo to be degraded from the endocytic pathway. Membrane trafficking to the late endosome–lysosome is tightly regulated to maintain the amplitude of signalling events and cellular homeostasis. Key coordinators of lysosomal traffic include members of the Rab small GTPase family. Amongst these, Rab7, Rab9 and the more recently studied Rab22B/31 have all been reported to regulate membrane trafficking processed at the late endosome–lysosome system. We discuss what is known about the roles of these Rab proteins and their interacting partners on the regulation of traffic of important receptor proteins such as the epidermal growth factor receptor (EGFR) and the mannose 6‐phosphate receptor (M6PR), in association with the late endosome–lysosome system. Better knowledge of EGFR and M6PR traffic in this regard may aid in understanding the pathological processes, such as oncogenic transformations associated with these receptors. Copyright

Rab22B is expressed in the CNS astroglia lineage and plays a role in epidermal growth factor receptor trafficking in A431 cells.

The expression profile and functions of the brain‐enriched Rab22B/Rab31 small GTPase had remained uncharacterized. Using specific antibodies against Rab22B, we found the protein to be exceptionally enriched in nestin and RC2‐positive radial glia of the embryonic mouse brain. In the adult brain, Rab22B is rather specifically expressed in glial fibrillary acidic protein (GFAP)‐positive mature astrocytes, but is not clearly detectable in either 2′,3′‐cyclic nucleotide 3′‐phosphodiesterase (CNPase)‐positive mature oligodendrocytes or βIII‐tubulin (TuJ)‐positive neurons. In probing for specific functions of Rab22B, we found that Rab22B silencing in A431 cells resulted in abnormal trafficking of the epidermal growth factor receptor (EGFR), Texas‐red‐labeled EGF, and the cation‐independent mannose 6‐phosphate receptor (M6PR). Affinity pull‐down assays and co‐immunoprecipitation analysis indicated that Rab22B could associate with EGFR in a GTP‐dependent manner. Rab22B is thus a Rab protein specifically expressed in the astroglia lineage and may have a role in regulating EGFR trafficking in some cell types. Given that EGFR signaling modulates astrocyte development and oncogenesis of multiple cell types, Rab22B may thus have specific developmental or pathophysiological roles in cell types which it is enriched in. J. Cell. Physiol. 221: 716–728, 2009.

Genetic Manipulation of Neural Stem Cells for Transplantation into the Injured Spinal Cord

The injured adult spinal cord is not conducive for neuronal regeneration and neurogenesis. Engrafted neural precursor cells (NPCs) differentiate largely into astroglia, with only a very small percentage becoming neurons (which might replace injured neurons) or oligodendroglia (which might improve injury induced demyelination of spared neurons). Several recent attempts have been made to enhanced neurogenesis or oligodendroglia differentiation of transplanted NPCs by genetic manipulation. These include exogenous expression of noggin, with the idea of antagonizing the astroglia differentiation promoting Bone Morphogenetic Proteins (BMPs). Direct attempts to enhance neurogenesis have also been made in transgenic over-expression of neurogenic basic helix-loop-helix transcription factors. These experiments resulted in some interesting observations, which we discuss here in the light of recent advances in development of cell-based engraftment therapy for spinal cord injuries.