An Endogenous Serine/Threonine Protein Phosphatase Inhibitor, G-Substrate, Reduces Vulnerability in Models of Parkinson's Disease

Abstract

Relative neuronal vulnerability is a universal yet poorly understood feature of neurodegenerative diseases. In Parkinson's disease, dopaminergic (DA) neurons in the substantia nigra (SN) (A9) are particularly vulnerable, whereas adjacent DA neurons within the ventral tegmental area (A10) are essentially spared. Our previous laser capture microdissection and microarray study (Chung et al., 2005) demonstrated that molecular differences between these DA neurons may underlie their differential vulnerability. Here we show that G-substrate, an endogenous inhibitor of Ser/Thr protein phosphatases, exhibits higher expression in A10 compared with A9 DA neurons in both rodent and human midbrain. Overexpression of G-substrate protected dopaminergic BE(2)-M17 cells against toxins, including 6-OHDA and MG-132 (carbobenzoxy-L-leucyl-L-leucyl-L-leucinal), whereas RNA interference (RNAi)-mediated knockdown of endogenous G-substrate increased their vulnerability to these toxins. G-substrate reduced 6-OHDA-mediated protein phosphatase 2A (PP2A) activation in vitro and increased phosphorylated levels of PP2A targets including Akt, glycogen synthase kinase 3␤, and extracellular signal-regulated kinase 2 but not p38. RNAi to Akt diminished the protective effect of G-substrate against 6-OHDA. In vivo, lentiviral delivery of G-substrate to the rat SN increased baseline levels of phosphorylated Akt and protected A9 DA neurons from 6-OHDA-induced toxicity. These results suggest that inherent differences in the levels of G-substrate contribute to the differential vulnerability of DA neurons and that enhancing G-substrate levels may be a neuroprotective strategy for the vulnerable A9 (SN) DA neurons in Parkinson's disease.

Dynamic Changes in Presynaptic and Axonal Transport Proteins Combined with Striatal Neuroinflammation Precede Dopaminergic Neuronal Loss in a Rat Model of AAV α-Synucleinopathy

“…Quantification of TH-positive neuronal number within the SN was performed using Stereo Investigator software (MBF Bioscience) and stereologic principles as previously described (Chung et al, 2007). Briefly, the anterior and posterior boundaries of the SN included in the analysis were defined according to the area transduced by the rAAV-eGFP in preliminary experiments [~−4.80 mm through −6.00 mm from bregma (according to the rat brain atlas of Paxinos and Watson, 1986)].…”

The Toll-Like Receptor-3 Agonist Polyinosinic:Polycytidylic Acid Triggers Nigrostriatal Dopaminergic Degeneration

“…Quantification of TH-positive neuronal number within the SN and VTA was performed by investigators blind to group treatments using an integrated Axioskop 2 microscope (Carl Zeiss, Thornwood, NY) and Stereo Investigator software (MBF Bioscience) and stereological principles as previously described (Chung et al, 2007) (Koprich et al, 2008). Briefly, SN and VTA were outlined by using the third cranial nerve as a landmark to define the vertical border between SN and VTA and by using the medial lemniscus as their dorsal border.…”

Unregulated mitochondrial GSK3β activity results in NADH:Ubiquinone oxidoreductase deficiency

“…Glycogen synthase kinase-3ß (GSK3β) has emerged as a major therapeutic target due to its involvement in several neurodegenerative diseases, including Parkinson's disease (King et al ., 2001; Chen et al ., 2004; Jope and Johnson, 2004; Avraham et al ., 2005; Chung et al ., 2007; Wang et al ., 2007; Yuan et al ., 2008). GSK3β was originally discovered as a regulator of glycogen synthesis (Parker et al ., 1982).…”