Loss of pdr-1/parkin influences Mn homeostasis through altered ferroportin expression in C. elegans

Abstract

Overexposure to the essential metal manganese (Mn) can result in an irreversible condition known as manganism that shares similar pathophysiology with Parkinson's disease (PD), including dopaminergic (DAergic) cell loss that leads to motor and cognitive impairments. However, the mechanisms behind this neurotoxicity and its relationship with PD remain unclear. Many genes confer risk for autosomal recessive, early-onset PD, including the parkin/PARK2 gene that encodes for the E3 ubiquitin ligase Parkin. Using Caenorhabditis elegans (C. elegans) as an invertebrate model that conserves the DAergic system, we previously reported significantly increased Mn accumulation in pdr-1/parkin mutants compared to wildtype (WT) animals. For the current study, we hypothesize that this enhanced accumulation is due to alterations in Mn transport in the pdr-1 mutants. While no change in mRNA expression of the major Mn importer proteins (smf-1-3) was found in pdr-1 mutants, significant downregulation in mRNA levels of the putative Mn exporter ferroportin (fpn-1.1) was observed. Using a strain overexpressing fpn-1.1 in worms lacking pdr-1, we show evidence for attenuation of several endpoints of Mn-induced toxicity, including survival, metal accumulation, mitochondrial copy number and DAergic integrity, compared to pdr-1 mutants alone. These changes suggest a novel role of pdr-1 in modulating Mn export through altered transporter expression, and provides further support of metal dyshomeostasis as a component of Parkinsonism pathophysiology.

Involvement of heat shock proteins on Mn-induced toxicity in Caenorhabditis elegans

“…Hence, we hypothesized that the absence of hsp-70 would alter the expression of these genes. First, we verified for the first time that Mn increases mRNA levels of all these genes in wild type worms, which is in agreement with the hypothesis that these proteins are required to protect cells against Mn-induced toxicity [19, 20, 41]. While in the hsp-70 mutants mRNA levels of pdr-1 and djr-1.1 increased dose-dependently in a manner indistinguishable from N2 worms, the pink1 expression failed to increase and was not significantly different compared to non-treated mutants.…”

“…Recently, our group demonstrated that pdr-1 and djr-1.1 loss in C. elegans increased their susceptibility to Mn in comparison to wild type worms and that the observed enhanced oxidative stress is related to increased Mn accumulation [19]. In addition, the higher Mn accumulation caused by loss of pdr-1/parkin gene was due to reduction of ferroportin (a Mn cell exporter) expression in worms [20]. Furthermore, Chen et al demonstrated that worms overexpressing DJR-1.2 are not subject to lifespan reduction caused by Mn exposure, in contrary to djr-1.2 mutants [41].…”

“…The mutation of dj-1, pink-1, parkin, for example, have been strongly linked to the early-onset of PD neurodegenerative disease in humans. In addition, it has been demonstrated that mutation in these genes also relate to onset of manganism [18–20]. As a putative treatment, recently, studies provided evidence on the important role of HSP70 in recovering DAergic neurons or degrading misfolded proteins in PD models [21, 22].…”

“Manganese-induced neurotoxicity: a review of its behavioral consequences and neuroprotective strategies”

“…Among these behaviors, basal slowing response is DA-specific, and other behaviors are usually controlled by DA along with other neurotransmitters, such as serotonin, glutamate or GABA, etc. To date, basal slowing response and dauer movement have been studied with Mn exposure [175, 177, 178]. Levya-Illades, Chen et al (2014), have shown that Mn exposure resulted in decreased basal slowing response, while expression of Mn exporter SLC30A10 exclusively in DAergic neurons rescued this behavioral defect together with decreased DAergic neurodegeneration [67].…”

Caenorhabditis elegans as a model system to study post-translational modifications of human transthyretin

“…Total RNA was isolated using the Trizol method as described before50. Briefly 1 mL Trizol (Life Technologies) was added to each tube containing about 60 000 eggs, 20 000 L1 stage or 4 000 L4 stage worms, followed by three cycles of freezing in liquid nitrogen and thawing.…”