Low-Molecular-Weight Compound GSB-106 Mimics the Cellular Effects of BDNF after Serum Deprivation

Analysis of Antidepressant-like Effects and Action Mechanisms of GSB-106, a Small Molecule, Affecting the TrkB Signaling

Induction of BDNF-TrkB signaling is associated with the action mechanisms of conventional and fast-acting antidepressants. GSB-106, developed as a small dimeric dipeptide mimetic of BDNF, was previously shown to produce antidepressant-like effects in the mouse Porsolt test, tail suspension test, Nomura water wheel test, in the chronic social defeat stress model and in the inflammation-induced model of depression. In the present study, we evaluated the effect of chronic per os administration of GSB-106 to Balb/c mice under unpredictable chronic mild stress (UCMS). It was observed for the first time that long term GSB-106 treatment (1 mg/kg, 26 days) during ongoing UCMS procedure ameliorated the depressive-like behaviors in mice as indicated by the Porsolt test. In addition, chronic per os administration of GSB-106 resulted in an increase in BDNF levels, which were found to be decreased in the prefrontal cortex and hippocampus of mice after UCMS. Furthermore, prolonged GSB-106 treatment was accompanied by an increase in the content of pTrkB^706/707 in the prefrontal cortex and by a pronounced increase in the level of pTrkB⁸¹⁶ in both studied brain structures of mice subjected to UCMS procedure. In summary, the present data show that chronic GSB-106 treatment produces an antidepressant-like effect in the unpredictable chronic mild stress model, which is likely to be associated with the regulation of the BDNF-TrkB signaling.

Dimeric mimetic of BDNF loop 4 promotes survival of serum-deprived cell through TrkB-dependent apoptosis suppression

Brain-derived neurotrophic factor (BDNF) is involved in the regulation of neuronal cell growth, differentiation, neuroprotection and synaptic plasticity. Although aberrant BDNF/TrkB signaling is implicated in several neurological, neurodegenerative and psychiatric disorders, neurotrophin-based therapy is challenging and is limited by improper pharmacokinetic properties of BDNF. Dimeric dipeptide compound GSB-106 (bis-(N-monosuccinyl-L-seryl-L-lysine) hexamethylenediamide) has earlier been designed to mimic the TrkB-interaction 4 loop of BDNF. It displayed protective effect in various cell-damaging models in vitro. Animal studies uncovered antidepressive and neuroprotective properties upon GSB-106 per os administration. Current study shows that GSB-106 acts similarly to BDNF, promoting survival of serum-deprived neuronal-like SH-SY5Y cells. 100 nmol concentration of GSB-106 provided maximum neurotrophic effect, which corresponds to about 37% of the maximum effect provided by BDNF. Protective properties of GSB-106 arise from its ability to counteract cell apoptosis via activation of TrkB-dependent pro-survival mechanisms, including inactivation of pro-apoptotic BAD protein and suppression of caspases 9 and 3/7. Thus, our study has characterized neurotrophic activity of small dimeric compound GSB-106, which mimics certain biological functions of BDNF and neurotrophin-specific protective mechanisms. GSB-106 also displays similarities to some known low weight peptide and non-peptide TrkB ligands.

The Effects of Serum Removal on Gene Expression and Morphological Plasticity Markers in Differentiated SH-SY5Y Cells

Despite the widespread use of the SH-SY5Y human neuroblastoma cell line in modeling human neurons in vitro, protocols for growth, differentiation and experimentation differ considerably across the literature. Many studies fully differentiate SH-SY5Y cells before experimentation, to investigate plasticity measures in a mature, human neuronal-like cell model. Prior to experimentation, serum is often removed from cell culture media, to arrest the cell growth cycle and synchronize cells. However, the exact effect of this serum removal before experimentation on mature, differentiated SH-SY5Y cells has not yet been described. In studies using differentiated SH-SY5Y cells, any effect of serum removal on plasticity markers may influence results. The aim of the current study was to systematically characterize, in differentiated, neuronal-like SH-SY5Y cells, the potentially confounding effects of complete serum removal in terms of morphological and gene expression markers of plasticity. We measured changes in commonly used morphological markers and in genes related to neuroplasticity and synaptogenesis, particularly in the BDNF-TrkB signaling pathway. We found that complete serum removal from already differentiated SH-SY5Y cells increases neurite length, neurite branching, and the proportion of cells with a primary neurite, as well as proportion of βIII-Tubulin and MAP2 expressing cells. Gene expression results also indicate increased expression of PSD95 and NTRK2 expression 24 h after serum removal. We conclude that serum deprivation in differentiated SH-SY5Y cells affects morphology and gene expression and can potentially confound plasticity-related outcome measures, having significant implications for experimental design in studies using differentiated SH-SY5Y cells as a model of human neurons.