Sensitivity and specificity of phospho-Ser129 α-synuclein monoclonal antibodies.

α-Synuclein (α-syn) is an abundant presynaptic protein that is the primary constituent of inclusions that define Lewy body diseases (LBDs). In these inclusions, α-syn is phosphorylated at the serine-129 residue. Antibodies directed to this phosphorylation site are used to measure inclusion abundance and stage disease progression in preclinical models as well as in postmortem tissues in LBDs. While it is critical to reliably identify inclusions, phospho-specific antibodies often cross-react with nonspecific antigens. Four commercially available monoclonal antibodies, two from rabbits (clones EP1536Y and MJF-R13) and two from mice (81a and pSyn#64), have been the most widely used in detecting pS129-α-syn inclusions. Here, we systematically evaluated these antibodies in brain sections and protein lysates from rats and mice. All antibodies detected pS129-α-syn inclusions in the brain that were induced by preformed α-syn fibrils in wild-type rats and mice. Antibody titrations revealed that clones EP1536Y and 81a comparably labeled inclusions in both the perikarya and neuronal processes in contrast to clones MJF-R13 and pSyn#64 that incompletely labeled inclusions at various antibody concentrations. Except for EP1536Y, the clones produced nonspecific diffuse neuropil labeling in α-syn knockout mice as well as mice and rats injected with monomeric α-syn, with some nonspecific staining titrating with pS129-α-syn inclusions. By immunoblot, all the clones cross-reacted with proteins other than α-syn, warranting caution in interpretations of specificity. Clone EP1536Y uniquely and robustly detected endogenous pS129-α-syn in highly soluble protein fractions from the mouse brain. In summary, EP1536Y had the highest sensitivity and specificity for detecting pS129-α-syn.

Elevated LRRK2 autophosphorylation in brain-derived and peripheral exosomes in LRRK2 mutation carriers.

Missense mutations in the leucine-rich repeat kinase 2 (LRRK2) gene can cause late-onset Parkinson disease (PD). LRRK2 mutations increase LRRK2 kinase activities that may increase levels of LRRK2 autophosphorylation at serine 1292 (pS1292) and neurotoxicity in model systems. pS1292-LRRK2 protein can be packaged into exosomes and measured in biobanked urine. Herein we provide evidence that pS1292-LRRK2 protein is robustly expressed in cerebral spinal fluid (CSF) exosomes. In a novel cohort of Norwegian subjects with and without the G2019S-LRRK2 mutation, with and without PD, we quantified levels of pS1292-LRRK2, total LRRK2, and other exosome proteins in urine from 132 subjects and in CSF from 82 subjects. CSF and urine were collected from the same morning clinic visit in 55 of the participants. We found that total LRRK2 protein concentration was similar in exosomes purified from either CSF or urine but the levels did not correlate. pS1292-LRRK2 levels were higher in urinary exosomes from male and female subjects with a LRRK2 mutation. Male LRRK2 mutation carriers without PD had intermediate pS1292-LRRK2 levels compared to male carriers with PD and controls. However, female LRRK2 mutation carriers without PD had the same pS1292-LRRK2 levels compared to female carriers with PD. pS1292-LRRK2 levels in CSF exosomes were near saturated in most subjects, ten-fold higher on average than pS1292-LRRK2 levels in urinary exosomes, irrespective of LRRK2 mutation status or PD diagnosis. These results provide insights into the effects of LRRK2 mutations in both the periphery and brain in a well-characterized clinical population and show that LRRK2 protein in brain exosomes may be much more active than in the periphery in most subjects.

α-Synuclein fibril-induced inclusion spread in rats and mice correlates with dopaminergic Neurodegeneration.

Proteinaceous inclusions in neurons, composed primarily of α-synuclein, define the pathology in several neurodegenerative disorders. Neurons can internalize α-synuclein fibrils that can seed new inclusions from endogenously expressed α-synuclein. The factors contributing to the spread of pathology and subsequent neurodegeneration are not fully understood, and different compositions and concentrations of fibrils have been used in different hosts. Here, we systematically vary the concentration and length of well-characterized α-synuclein fibrils and determine their relative ability to induce inclusions and neurodegeneration in different hosts (primary neurons, C57BL/6J and C3H/HeJ mice, and Sprague Dawley rats). Using dynamic-light scattering profiles and other measurements to determine fibril length and concentration, we find that femptomolar concentrations of fibrils are sufficient to induce robust inclusions in primary neurons. However, a narrow and non-linear dynamic range characterizes fibril-mediated inclusion induction in axons and the soma. In mice, the C3H/HeJ strain is more sensitive to fibril exposures than C57BL/6J counterparts, with more inclusions and dopaminergic neurodegeneration. In rats, injection of fibrils into the substantia nigra pars compacta (SNpc) results in similar inclusion spread and dopaminergic neurodegeneration as injection of the fibrils into the dorsal striatum, with prominent inclusion spread to the amygdala and several other brain areas. Inclusion spread, particularly from the SNpc to the striatum, positively correlates with dopaminergic neurodegeneration. These results define biophysical characteristics of α-synuclein fibrils that induce inclusions and neurodegeneration both in vitro and in vivo, and suggest that inclusion spread in the brain may be promoted by a loss of neurons.