Cellular levels of growth factor receptor bound protein 2 (Grb2) and cytoskeleton stability are correlated in a neurodegenerative scenario

Abstract

Alzheimer's disease (AD) manifests as neuronal loss. On the premise of Grb2 overexpression in AD mouse brain and brain tissues of AD patients, our study primarily focuses on the stability of cytoskeletal proteins in the context of degenerative AD-like conditions. Two predominant molecular features of AD, extracellular accumulation of β-amyloid oligomers and intracellular elevation of amyloid precursor protein intracellular domain levels, have been used to closely inspect the series of signalling events. In their presence, multiple signalling pathways involving ROCK and PAK1 proteins lead to disassembly of the cytoskeleton, and Grb2 partially counterbalances the cytoskeletal loss. Increased Grb2-NOX4 interactions play a preventive role against cytoskeletal disassembly, in turn blocking the activity of nitrogen oxides and decreasing the expression of slingshot homolog 1 (SSH-1) protein, a potent inducer of cytoskeleton disassembly. This study unravels a unique role of Grb2 in protecting the cytoskeletal architecture in AD-like conditions and presents a potential new strategy for controlling neurodegeneration.

Transcriptional regulator PAX4 links Receptor Tyrosine Kinases (RTKs) and cytoskeleton stability in Alzheimer’s disease and type 2 diabetes

“…Grb2 happens to be a common downstream adapter for both (52). It was shown previously that Grb2 strengthened its interaction with NOX4 to rescue the cytoskeleton degradation in AD like situations (16). We postulated that the two RTKs, ALK and RYK, might act like non-canonical receptors with the potential to become a significant link between AD and T2D via Grb2 and NOX4.…”

“…The error bar represents standard error [(standard deviation/ √n); n= sample size]. To arrive at the statistically significant sample size for each experiment we did power analysis using the a priori model (45) as incorporated in the G*power 3.1 (46) software (16).…”

“…Protein concentration was determined by Bradford protein estimation assay. Western blots and quantification were done as per described protocol (16).…”

“…RNA was isolated from cells by TRIzol Reagent (Invitrogen,USA) extraction method following manufacturer's protocol which discussed in Majumder et al, 2017 (16). Real time RT-PCR reaction was carried out using Syber green 2X Universal PCR Master Mix (Applied Biosystems, USA) in ABI Prism 7500 sequence detection system.…”

“…A ROS producing NADPH oxidase, NOX4, is constitutively active with its regulatory protein tyrosine kinase substrate (Tsk4/5) with multiple SH3 domains (13) and interacts with Grb2 naturally (14,15). Reportedly, in AD post-mortem brain, in AD cell models as well as AD mouse model (APP/PS1 mouse) Grb2 transcript expression shows significant upregulation (16). In AD brain, the NOX4 expression is significantly increased with substantial correlation between its activity and age-dependent increases of Aβ and cognitive dysfunction (17,18).…”