Fully human agonist antibodies to TrkB using autocrine cell-based selection from a combinatorial antibody library.

The diverse physiological roles of the neurotrophin family have long prompted exploration of their potential as therapeutic agents for nerve injury and neurodegenerative diseases. To date, clinical trials of one family member, brain-derived neurotrophic factor (BDNF), have disappointingly failed to meet desired endpoints. Contributing to these failures is the fact that BDNF is pharmaceutically a nonideal biologic drug candidate. It is a highly charged, yet is a net hydrophobic molecule with a low molecular weight that confers a short t1/2 in man. To circumvent these shortcomings of BDNF as a drug candidate, we have employed a function-based cellular screening assay to select activating antibodies of the BDNF receptor TrkB from a combinatorial human short-chain variable fragment antibody library. We report here the successful selection of several potent TrkB agonist antibodies and detailed biochemical and physiological characterization of one such antibody, ZEB85. By using a human TrkB reporter cell line and BDNF-responsive GABAergic neurons derived from human ES cells, we demonstrate that ZEB85 is a full agonist of TrkB, comparable in potency to BDNF toward human neurons in activation of TrkB phosphorylation, canonical signal transduction, and mRNA transcriptional regulation.

Brain-derived neurotrophic factor prevents dendritic retraction of adult mouse retinal ganglion cells.

We used cultured adult mouse retinae as a model system to follow and quantify the retraction of dendrites using diolistic labelling of retinal ganglion cells (RGCs) following explantation. Cell death was monitored in parallel by nuclear staining as 'labelling' with RGC and apoptotic markers was inconsistent and exceedingly difficult to quantify reliably. Nuclear staining allowed us to delineate a lengthy time window during which dendrite retraction can be monitored in the absence of RGC death. The addition of brain-derived neurotrophic factor (BDNF) produced a marked reduction in dendritic degeneration, even when application was delayed for 3 days after retinal explantation. These results suggest that the delayed addition of trophic factors may be functionally beneficial before the loss of cell bodies in the course of conditions such as glaucoma.

Sholl analysis: a quantitative comparison of semi-automated methods.

BACKGROUND: Sholl analysis remains one of the most commonly used methods to quantify neuronal dendritic complexity and is therefore a key analysis tool in neurobiology. While initially proposed when the quantification of neuronal structure was undertaken manually, the advent of software packages allowing automated analysis has resulted in the introduction of several semi and fully automated methods to quantify dendritic complexity. Unfortunately results from these methods have not in all cases been consistent. We therefore compared the results of five commonly used methods (Simple Neurite Tracer, manual, Fast Sholl, Bitmap, and Ghosh lab) using manual analysis as a ground truth. NEW METHOD: Comparison of four semi-automated methods to the manual method using diolistically labelled mouse retinal ganglion cells. RESULTS: We report consistency across a range of published techniques. While the majority perform well (Simple Neurite Tracer and Fast Sholl profiles have areas under the curve within 4.5% of the profile derived using the manual method), we highlight two areas in two of the methods (Bitmap and Ghosh lab methods) where errors may occur, namely undercounting (>20% relative to the manual profile) and a second peak. COMPARISON WITH EXISTING METHODS: Our results support published validation of the Fast Sholl method. CONCLUSIONS: Our study highlights the importance of manual calibration of automated analysis software.