Tissue-Specificity of Antibodies Raised Against TrkB and p75NTR Receptors; Implications for Platelets as Models of Neurodegenerative Diseases

Abstract

Platelets and neurons share many similarities including comparable secretory granule types with homologous calcium-dependent secretory mechanisms as well as internalization, sequestration and secretion of many neurotransmitters. Thus, platelets present a high potential to be used as peripheral biomarkers to reflect neuronal pathologies. The brain-derived neurotrophic factor (BDNF) acts as a neuronal growth factor involved in learning and memory through the binding of two receptors, the tropomyosin receptor kinase B (TrkB) and the 75 kDa pan-neurotrophic receptor (p75NTR). In addition to its expression in the central nervous system, BDNF is found in much greater quantities in blood circulation, where it is largely stored within platelets. Levels 100- to 1,000-fold those of neurons make platelets the most important peripheral reservoir of BDNF. This led us to hypothesize that platelets would express canonical BDNF receptors, i.e., TrkB and p75NTR, and that the receptors on platelets would bear significant resemblance to the ones found in the brain. However, herein we report discrepancies regarding detection of these receptors using antibody-based assays, with antibodies displaying important tissue-specificity. The currently available antibodies raised against TrkB and p75NTR should therefore be used with caution to study platelets as models for neurological disorders. Rigorous characterization of antibodies and bioassays appears critical to understand the interplay between platelet and neuronal biology of BDNF.

Design, synthesis and evaluation of 1-(1,5-bis(4-substituted phenyl)-2-methyl-1H-pyrrol-3-yl)-N-methylmethanamines as SERT inhibitors with potential antidepressant action

“…Platelets are more easily accessible than other cells that need to be cultured using laborious and expensive equipment and protocols. [34][35][36][37][38] Platelets were used as the model to study the effect of the target compounds on serotonin reuptake by the enzymelinked immunoassay (ELISA) method. 39 The standard curve constructed using serotonin standard solutions from 25 ng mL −1 to 400 ng mL −1 showed an r value of 0.97 and an r 2 value of 0.94.…”

“…Platelets are more easily accessible than other cells that need to be cultured using laborious and expensive equipment and protocols. 34–38…”

Clinical Correlates Identify ProBDNF and Thrombo-Inflammatory Markers as Key Predictors of Circulating p75NTR Extracellular Domain Levels in Older Adults

“…In addition to the nervous system, p75 NTR is also expressed in the vascular system. Notably, p75 NTR is weakly expressed by endothelial cells, where its expression can be induced under ischemic conditions ( Caporali et al, 2008 ), as well as in peripheral blood mononuclear cells ( Fauchais et al, 2008 ; Brunelli et al, 2012 ) and platelets ( Fleury et al, 2021 ). Of interest, our data highlight a weak yet significant negative correlation between p75 NTR ECD and platelet activation marker P-selectin ( Table 2 ), suggesting that platelet activation could modulate circulating p75 NTR ECD levels, and thus sets the basis for future studies regarding platelets as contributors to plasma p75 NTR ECD.…”

“…However, p75 NTR expression can be induced during adulthood in conditions involving damage to neurons, where it is believed to be involved in neuronal apoptosis of injured cells. The p75 NTR receptor is also expressed outside the central nervous system and found on peripheral blood mononuclear cells, on endothelial cells where its expression is increased by ischemia, and on platelets ( Salis et al, 2004 ; Brunelli et al, 2012 ; Minnone et al, 2017 ; Fleury et al, 2021 ). Upon activation, the p75 NTR receptor undergoes shedding, causing its extracellular domain (ECD) to be released into circulation ( Bergmeier et al, 2004 ; Weskamp et al, 2004 ; Duerschmied et al, 2009 ; Skeldal et al, 2011 ).…”

Modulation of neurotrophic factors in the treatment of dementia, stroke and TBI: Effects of Cerebrolysin

“…BDNF and NGF can both bind the p75NTR receptor. P75NTR is a 75 kDa 43 transmembrane receptor containing extracellular cysteine‐rich domains, a single transmembrane domain and an intracellular region comprising a juxtamembrane domain (Chopper‐domain) and a death‐domain (DD) 44 . Although p75NTR's DD is lacking catalytic activity it is still forming an intracellular signaling hub 45,46 .…”