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Antibody Mediated Transdifferentiation

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Original article from PNAS

"Autocrine signaling based selection of combinatorial antibodies that transdifferentiate human stem cells"

The group of Richard A. Lerner at The Scripps Research Institute, La Jolla, CA have previously described a means of expressing antibodies through lentiviral infection of cells and studying how the cells are affected in an autocrine manner (Zhang et al) through interactions with membrane bound co-expressed receptors.   In a recent report in PNAS they now describe a co-expression system of an antibody library with the granulocyte colony-stimulating factor receptor (G-CSFR), and have isolated agonist antibodies which can transdifferentiate human CD34+ haematopoietic stem cells (HSCs) into neural progenitor cells (NPCs) (Xie et al).

The group used what they term a "near neighbour" approach in which the various antibodies, which are phenocopies of natural receptor agonists, and the receptor of choice is co-expressed on the plasma membrane, which favours unusual or rare interactions and also an autocrine function.   This principle, assessed through fluorescence resonance energy transfer (FRET) analysis and stimulation of cell growth, was next used to identify antibodies which induced both downstream G-CSFR signaling and growth in the reporter cell lines.    Their ability of identified antibodies to activate human CD34+ HSCs was then assessed, in the hope that HSCs would become more potent or drive differentiation along the myeloid lineage.   Fascinatingly, however, the antibodies in fact stimulated neurogenesis, the resultant cells being mobile with long neurites, exhibiting multiple morphologies including bipolar configurations and extensive development of pyramidal shaped growth cones.   Scanning electron microscopy further demonstrated that growth cones on the neurite tips had a classical morphology with extensive formation of filopodia and lamellipodia.   Additionally, cells were positive for neuronal tubulin (Tuj1) (neuronal marker), nestin (NPC marker) and F-actin (growth cone marker).   Analysis of known downstream events of G-CSF stimulation (activation of STAT5, Protein Kinase B (AKT), and ERK) in the antibody treated CD34+ HSCs found only phosphorylation of AKT which is known to be important in neurogenesis (Torroglosa et al, Wang et al and Zhang et al).   Gene expression analysis also found that genes associated with neurogenesis were upregulated in response to the antibodies, suggesting that the effect of these antibodies on this receptor may be a unique interaction causing specific downstream events.

Overall, this paper not only suggests that a simple combination of antibody agonists has the ability to transdifferentiate a haematopoietic cell into a neuronal cell, but also creates a platform from where additional transdifferentiation-inducing antibodies combinations can be identified.   Antibodies also have advantages such as their long life in vivo and their lack or requirement to enter a cell to elicit a response, such as the generation of a clinically relevant cell type, although further functional analysis is required to ascertain the potential usefulness of these cells.

References

Torroglosa A, et al. (2007)
Nitric oxide decreases subventricular zone stem cell proliferation by inhibition of epidermal growth factor receptor and phosphoinositide-3-kinase/Akt pathway.
Stem Cells 25(1):88–97

Wang L et al (2005)
Activation of the PI3-K/Akt pathway mediates cGMP enhanced-neurogenesis in the adult progenitor cells derived from the subventricular zone.
J Cereb Blood Flow Metab 25(9):1150–1158

Zhang H et al (2012)
Selection of antibodies that regulate phenotype from intracellular combinatorial antibody libraries.
Proc Natl Acad Sci USA 109(39):15728–15733

Zhang L, et al. (2002)
Dehydroepiandrosterone (DHEA) and its sulfated derivative (DHEAS) regulate apoptosis during neurogenesis by triggering the Akt signaling pathway in opposing ways.
Brain Res Mol Brain Res 98(1-2):58–66

From PNAS.

Stem Cell Correspondent Stuart P Atkinson reports on those studies appearing in current journals that are destined to make an impact on stem cell research and clinical studies.