Mutations in LRRK2 underlie an autosomal-dominant, inherited form of Parkinson's disease (PD) that mimics the clinical features of the common "sporadic" form of PD. The LRRK2 protein includes putative GTPase, protein kinase, WD40 repeat, and leucine-rich repeat (LRR) domains of unknown function. Here we show that PD-associated LRRK2 mutations display disinhibited kinase activity and induce a progressive reduction in neurite length and branching both in primary neuronal cultures and in the intact rodent CNS. In contrast, LRRK2 deficiency leads to increased neurite length and branching. Neurons that express PD-associated LRRK2 mutations additionally harbor prominent phospho-tau-positive inclusions with lysosomal characteristics and ultimately undergo apoptosis.

Parkinson's disease (PD) pathology is characterized by the degeneration of midbrain dopamine neurons (DNs) ultimately leading to a progressive movement disorder in patients. The etiology of DN loss in sporadic PD is unknown, although it is hypothesized that aberrant protein aggregation and cellular oxidative stress may promote DN degeneration. Homozygous mutations in DJ-1 were recently described in two families with autosomal recessive inherited PD (Bonifati et al. 2003). In a companion article (Martinat et al. 2004), we show that mutations in DJ-1 alter the cellular response to oxidative stress and proteasomal inhibition. Here we show that DJ-1 functions as a redox-sensitive molecular chaperone that is activated in an oxidative cytoplasmic environment. We further demonstrate that DJ-1 chaperone activity in vivo extends to α-synuclein, a protein implicated in PD pathogenesis.

The lipocalins are secreted proteins that bind small organic molecules. Scn-Ngal [known as Neutrophil Gelatinase Associated Lipocalin, Siderocalin, Lipocalin 2] sequesters bacterial iron chelators, called siderophores, and consequently blocks bacterial growth. However, Scn-Ngal is also prominently expressed in aseptic diseases, implying that it binds additional ligands and serves additional functions. Using chemical screens, crystallography, and fluorescence methods, we report that Scn-Ngal binds iron together with a small metabolic product called catechol. The formation of the complex blocked the reactivity of iron and permitted its transport once introduced into circulation in vivo. Scn-Ngal then recycled its iron in endosomes by a pH sensitive mechanism. Since catechols derive from bacterial and mammalian metabolism of dietary compounds, the Scn-Ngal:catechol:iron complex represents an unforeseen microbial-host interaction, which mimics Scn-Ngal:siderophore interactions, but instead traffics iron in aseptic tissues. These results identify an endogenous siderophore, which may link the disparate roles of Scn-Ngal in different diseases.

Summary Developing organs require iron for a myriad of functions, but embryos deleted of the major adult transport protein, transferrin or its receptor transferrin receptor1 (TfR1−/−) initiate organogenesis, suggesting that non-transferrin pathways are important. To examine these pathways, we developed chimeras composed of fluorescence-tagged TfR1−/− cells and untagged wild type cells. In the kidney, TfR1−/− cells populated capsule and stroma, mesenchyme and nephron, but were underrepresented in ureteric bud tips. Consistently, TfR1 provided transferrin to the ureteric bud, but not to the capsule or the stroma. Instead of transferrin, we found that the capsule internalized ferritin. Since the capsule expressed a novel receptor called Scara5, we tested its role in ferritin uptake and found that Scara5 bound serum ferritin and stimulated its endocytosis from the cell surface with consequent iron delivery. These data implicate cell type-specific mechanisms of iron traffic in organogenesis, which alternatively utilize transferrin or non-transferrin iron delivery pathways.

The hallmark of Parkinson's disease (PD) is the selective loss of dopamine neurons in the ventral midbrain. Although the cause of neurodegeneration in PD is unknown, a Mendelian inheritance pattern is observed in rare cases, indicating a genetic factor. Furthermore, pathological analyses of PD substantia nigra have correlated cellular oxidative stress and altered proteasomal function with PD. Homozygous mutations in DJ-1 were recently described in two families with autosomal recessive Parkinsonism, one of which is a large deletion that is likely to lead to loss of function. Here we show that embryonic stem cells deficient in DJ-1 display increased sensitivity to oxidative stress and proteasomal inhibition. The accumulation of reactive oxygen species in toxin-treated DJ-1-deficient cells initially appears normal, but these cells are unable to cope with the consequent damage that ultimately leads to apoptotic death. Furthermore, we find that dopamine neurons derived from in vitro–differentiated DJ-1-deficient embryonic stem cells display decreased survival and increased sensitivity to oxidative stress. These data are consistent with a protective role for DJ-1, and demonstrate the utility of genetically modified embryonic stem cell–derived neurons as cellular models of neuronal disorders.