Simone Engelender, MD, PhD
Associate Professor of Molecular Pharmacology
MD, 1993 - Federal University of Rio de Janeiro
PhD, 1996 - Federal University of Rio de Janeiro
Molecular mechanisms of Parkinson's disease
Parkinson disease (PD) is a common neurodegenerative disease. The accumulation of α-synuclein plays a central role in PD. α-Synuclein is monoubiquitinated by the E3 ubiquitin-ligase SIAH and its accumulation leads to formation of toxic inclusions. In the absence of proteolytic impairment, monoubiquitinated α-synuclein is degraded by the proteasome, while deubiquitinated α-synuclein is degraded by autophagy. This process is modulated by the deubiquitinase USP9X, supporting that monoubiquitination is not a spurious process but rather is key for α-synuclein fate.
Mitochondrial dysfunction also plays a role in PD. We identified PINK1-synphilin-1 as a novel mitochondrial pathway. Synphilin-1 is recruited to the mitochondria by PINK1 and together these proteins promote mitophagy (degradation of mitochondria by autophagy). Synphilin-1 fails to promote mitophagy when PINK1 bears disease mutations, supporting the importance of synphilin-1 in PD. Finding ways to drive the PINK1-synphilin-1 pathway may represent a strategy to promote the clearance of damaged mitochondria in the disease.
Based on our findings, we anticipate that the search for modulators of α-synuclein degradation and mitophagy may provide future treatments for PD.
Safory H, Neame S, Shulman Y, Zubedat S, Radzishevsky I, Rosenberg D, Sason H, Engelender S, Avital A, Hulsmann S, Schiller J and Wolosker H. 2015. The alanine-serine-cysteine-1 (Asc-1) transporter is a regulator of glycine metabolism and glycinergic inhibitory transmission: Potential relevance to hyperekplexia. EMBO Rep. 16, 590-598.
Norris KL, Hao R, Chen LF, Lai CH, Kapur M, Shaughnessy PJ, Chou D, Yan J, Taylor JP, Engelender S, West AE, Lim KL, and Yao TP. 2015. Convergence of parkin, PINK1 and α-synuclein on stress-induced mitochondrial morphological remodelling. J. Biol. Chem. 290, 13862-13874.
Haskin J, Szargel R, Shani V, Mekies LN, Rott R, Lim GG, Lim KL, Bandopadhyay R, Wolosker H and Engelender S. 2013. AF-6 is a positive modulator of the PINK1/parkin pathway and is deficient in Parkinson's disease. Hum. Mol. Genet. 22, 2083-96.
Abeywardana T, Lin YH, Rott R, Engelender S and Pratt MR. 2013. Site-specific differences in proteasome-dependent degradation of monoubiquitinated α-Synuclein. Chem. Biol. 20, 1207-1213.
Rott R, Szargel R, Haskin Y, Bandopadhyay R, Lees AJ, Shani V and Engelender S. 2011. α -Synuclein fate is determined by USP9X-regulated monoubiquitination. Proc. Natl. Acad. Sci. USA 108, 18666-71.
Figure 1. Monoubiquitination partitions α-synuclein between different proteolytic pathways. (A) SH-SY5Y cells were transfected as indicated and treated for 16 hours with DMSO, 10 µM Lactacystin (proteasomal inhibitor), 10 mM ammonium chloride (lysosomal inhibitor) or 10 mM 3-MA (autophagy inhibitor). The levels of α-synuclein and USP9X were revealed with anti-HA and anti-USP9X antibodies, respectively. (B) Monoubiquitination determines α-synuclein fate. USP9X deubiquitinates α-synuclein, and then non-ubiquitinated α-synuclein is mostly degraded by the autophagy pathway. SIAH monoubiquitinates α-synuclein, leading to its degradation by the proteasome.
Figure 2. Synphilin-1 translocates to the mitochondria and promotes PINK1-dependent mitophagy.
(A) SH-SY5Y cells were transfected as indicated and lysates were fractionated into cytosolic and mitochondrial fractions. myc-Synphilin-1 was detected with anti-myc antibody (upper panels) and PINK1-HA with anti-HA antibody (middle panels). The purity of cytosolic and mitochondrial fractions was examined using anti-LDH and anti-VDAC antibodies, respectively. (B) SH-SY5Y cells were transfected with PINK1-Flag, GFP (as marker for transfection), in the presence of HA-synphilin-1 or myc-LacZ. Cells were processed for immunocytochemistry using anti-Tom20 antibody as a marker for mitochondria (in red). Mitophagy was determined by the presence of Tom20 staining in GFP-positive cells. Cells transfected with GFP were outlined to enable proper visualization and cells containing no mitochondria are indicated by arrows. Scale bar, 25 µm. (C) PINK1 disease-mutations are defective in PINK1-synphilin-1 pathway. SH-SY5Y cells were transfected as indicated. The presence of synphilin-1 and PINK1 in cytosolic and mitochondrial fractions and the purity of the fractions were determined as in (A).