Glial Dysfunction in Parkin Null Mice: Effects of Aging

Abstract

Parkin mutations in humans produce parkinsonism whose pathogenesis is related to impaired protein degradation, increased free radicals, and abnormal neurotransmitter release. The role of glia in parkin deficiency is little known. We cultured midbrain glia from wild-type (WT) and parkin knock-out (PK-KO) mice. After 18 -20 d in vitro, PK-KO glial cultures had less astrocytes, more microglia, reduced proliferation, and increased proapoptotic protein expression.PK-KO glia had greater levels of intracellular glutathione (GSH), increased mRNA expression of the GSH-synthesizing enzyme ␥-glutamylcysteine synthetase, and greater glutathione S-transferase and lower glutathione peroxidase activities than WT. The reverse happened in glia cultured in serum-free defined medium (EF12) or in old cultures. PK-KO glia was more susceptible than WT to transference to EF12 or neurotoxins (1-methyl-4-phenylpyridinium, blockers of GSH synthesis or catalase, inhibitors of extracellular signal-regulated kinase 1/2 and phosphatidylinositol 3 kinases), aging of the culture, or combination of these insults. PK-KO glia was less susceptible than WT to Fe 2ϩ plus H 2 O 2 and less responsive to protection by deferoxamine. Old WT glia increased the expression of heat shock protein 70, but PK-KO did not. Glia conditioned medium (GCM) from PK-KO was less neuroprotective and had lower levels of GSH than WT. GCM from WT increased the levels of dopamine markers in midbrain neuronal cultures transferred to EF12 more efficiently than GCM from PK-KO, and the difference was corrected by supplementation with GSH. PK-KO-GCM was a less powerful suppressor of apoptosis and microglia in neuronal cultures. Our data prove that abnormal glial function is critical in parkin mutations, and its role increases with aging.

Different Mechanisms Underlying the Antiepileptic and Antiparkinsonian Effects of Zonisamide

“…Glutathione synthesis in neurons is dependent on the expression of the cystine/glutamate exchange transporter on astrocytes (Shih et al, 2006;Wang & Cynader, 2000). Other studies demonstrated that glutathione and its synthesis-related molecules provide protection for astrocytes against age-dependent nigrostriatal dopaminergic neuro-degeneration (Chinta et al, 2007;Solano et al, 2008). ZNS markedly increased glutathione levels by enhancing the astroglial cystine/glutamate exchange transporter and astroglial proliferation via S100β production or secretion.…”

The multiple mechanisms of amyloid deposition: The role of parkin

“…51,52 The elevated levels of free radicals in absence of parkin could contribute to the amyloidosis. Other mechanisms though parkin could be involved in amyloid deposition, are the altered inflammatory response and elevated microglial levels observed in absence of parkin [82][83][84] which have been extensively implied in AD 85 and are also observed in the PK -/-/Tau VLW mice model. 51 This model suggests that parkin could be a link between tau and amyloid deposition, the two most important pathogenic mechanisms in AD.…”

NP7 protects from cell death induced by oxidative stress in neuronal and glial midbrain cultures from parkin null mice

“…Apoptosis was measured by light microscopy, DNA staining with bis-benzimide (Hoechst 33342) and the TUNEL assay [16,28,29]. Necrosis was measured according to lactate dehydrogenase activity [30] in the culture medium and by trypan blue dye exclusion in cells [29].…”

“…But parkin null cells are more susceptible to additional insults such as treatment with rotenone, a mitochondrial toxin [14], calcium channel antagonists, such as cinnarizine [15] or to the effects of aging, when the supportive function of glia is reduced and the increased production of GSH collapses [16].…”

“…Furthermore, a reduction in parkin levels renders the rat glial-like cell line RG-6 more susceptible to dopamine (DA)-and H 2 O 2 -induced cell death [23]. In PK-KO aging midbrain glia, low H 2 O 2 concentration induced cell death [16].…”