Lee, V. M.- Y. | bioRxiv Science

bioRxiv2020

Poly(ADP-ribose) induces α-synuclein aggregation in neuronal-like cells andinteracts with phosphorylated α-synuclein in post mortem PD samples

BackgroundPoly (ADP-ribose) (PAR) is a negatively charged polymer that is biosynthesized by Poly (ADP-ribose) Polymerase-1 (PARP-1) and regulates various cellular processes. Alpha-synuclein (Syn) is an intrinsically disordered protein (IDP) that has been directly implicated with driving the onset and progression of Parkinsons disease (PD). The mechanisms by which Syn elicits its neurotoxic effects remain unclear. Recent findings indicate that one of the key processes driving PD pathology are oligomeric species of Syn. Furthermore, it is well established that the main components of Lewy bodies (LBs) and Lewy neurites (LNs) in PD patients are aggregated hyperphosphorylated (S129) forms of Syn (pSyn). MethodsWe used biochemical and immunofluorescence-based assays to explore if PARP-1 enzymatic product (PAR) drives the conversion of monomeric Syn into aggregated assemblies. We performed quantitative measurements using in situ proximity ligation assays (PLA) on a transgenic murine model of -synucleinopathy (M83-SNCA*A53T) and post-mortem PD/PDD patient samples to characterize PAR-pSyn interactions. Additionally, we used bioinformatic approaches and site-directed mutagenesis to identify PAR-binding regions on fibrillar Syn. ResultsOur studies show that elevated intracellular levels of PAR promote the transition of Syn into higher molecular weight forms. We report that PAR-pSyn interactions are predominant in pathological states. Moreover, we confirm that the interactions between PAR and Syn involve electrostatic forces between negatively charged PAR and lysine residues on the N-terminal region of Syn. ConclusionsPAR plays a critical role in the early stages of monomeric Syn aggregation, thereby attributing to PD pathogenesis. Based on our results, we report that PAR seeds monomeric Syn aggregation and directly interacts with phosphorylated Syn in conditions that are pathologically relevant to PD.

neuroscience↗

bioRxiv2020

The Sigma-2 Receptor/TMEM97, PGRMC1, and LDL Receptor complex are responsible for the cellular uptake of Aβ42 and its protein aggregates

BackgroundOur lab has recently shown that the Sigma-2 Receptor/Transmembrane Protein 97 (TMEM97) and Progesterone Receptor Membrane Component 1 (PGRMC1) form a complex with the Low Density Lipoprotein Receptor (LDLR), and this intact complex is required for efficient uptake of lipoproteins such as LDL and apolipoprotein E (apoE). These receptors are expressed in the nervous system where they have implications in neurodegenerative diseases such as Alzheimers Disease (AD), where apoE is involved in neuronal uptake and accumulation of A{beta}42, eventually cascading into neurodegeneration, synaptic dysfunction, and ultimately, dementia. HypothesisWe hypothesize that the intact Sigma-2 receptor complex -TMEM97, PGRMC1, and LDLR-- is necessary for internalization of apoE and A{beta}42 monomers (mA{beta}42) and oligomers (oA{beta}42), and the disruption of the receptor complex inhibits uptake. ResultsThe results of this study suggest that the intact Sigma-2 receptor complex is a binding site for mA{beta}42 and oA{beta}42, in the presence or absence of apoE2, apoE3, and apoE4. The loss or pharmacological inhibition of one or both of these proteins results in the disruption of the complex leading to decreased uptake of mA{beta}42 and oA{beta}42 and apoE in primary neurons. ConclusionThe TMEM97, PGRMC1, and LDLR complex is a pathway for the cellular uptake of A{beta}42 via apoE dependent and independent mechanisms. This study suggests that the complex may potentially be a novel pharmacological target to decrease neuronal A{beta}42 internalization and accumulation, which may represent a new strategy for inhibiting the rate of neurotoxicity, neurodegeneration, and progression of AD.

neuroscience↗