Andrew Ferree

MKK6 binds and regulates expression of Parkinson's disease-related protein LRRK2.

J. Neurochem. (2010) 112, 1593–1604.

Investigating Convergent Actions of Genes Linked to Familial Parkinson's Disease

Background: Mutations in LRRK2 are among the most frequent genetic changes identified in Parkinson’s disease (PD), but how LRRK2 contributes to the pathophysiology of PD is not known. Objectives: To investigate how expressing wild-type or G2019S LRRK2 modifies cellular responses to rotenone, a mitochondrial toxin. Methods: We investigated the vulnerability to mitochondrial toxins in Caenorhabditis elegans expressing wild-type or G2019S LRRK2. Results: We observed a powerful role for LRRK2 in mitochondrial biology. Overexpressing LRRK2 strongly protects C. elegans against rotenone toxicity. The G2019S LRRK2 construct also protected LRRK2 against rotenone, but to a lesser degree than wild-type LRRK2. Knockdown of lrk-1 potentiated rotenone toxicity. Conclusions: These data suggest that LRRK1/2 regulate mitochondrial physiology.

MitoTimer probe reveals the impact of autophagy, fusion, and motility on subcellular distribution of young and old mitochondrial protein and on relative mitochondrial protein age

To study mitochondrial protein age dynamics, we targeted a time-sensitive fluorescent protein, MitoTimer, to the mitochondrial matrix. Mitochondrial age was revealed by the integrated portions of young (green) and old (red) MitoTimer protein. Mitochondrial protein age was dependent on turnover rates as pulsed synthesis, decreased import, or autophagic inhibition all increased the proportion of aged MitoTimer protein. Mitochondrial fusion promotes the distribution of young mitochondrial protein across the mitochondrial network as cells lacking essential fusion genes Mfn1 and Mfn2 displayed increased heterogeneity in mitochondrial protein age. Experiments in hippocampal neurons illustrate that the distribution of older and younger mitochondrial protein within the cell is determined by subcellular spatial organization and compartmentalization of mitochondria into neurites and soma. This effect was altered by overexpression of mitochondrial transport protein, RHOT1/MIRO1. Collectively our data show that distribution of young and old protein in the mitochondrial network is dependent on turnover, fusion, and transport.

Regulation of physiologic actions of LRRK2: focus on autophagy.

Background: Mutations in LRRK2 are associated with familial and sporadic Parkinson’s disease (PD). Subjects with PD caused by LRRK2 mutations show pleiotropic pathology that can involve inclusions containing α-synuclein, tau or neither protein. The mechanisms by which mutations in LRRK2 lead to this pleiotropic pathology remain unknown. Objectives: To investigate mechanisms by which LRRK2 might cause PD. Methods: We used systems biology to investigate the transcriptomes from human brains, human blood cells and Caenorhabditis elegans expressing wild-type LRRK2. The role of autophagy was tested in lines of C. elegans expressing LRRK2, V337M tau or both proteins. Neuronal function was measured by quantifying thrashing. Results: Genes regulating autophagy were coordinately regulated with LRRK2. C. elegans expressing V337M tau showed reduced thrashing, as has been noted previously. Coexpressing mutant LRRK2 (R1441C or G2019S) with V337M tau increased the motor deficits. Treating the lines of C. elegans with an mTOR inhibitor that enhances autophagic flux, ridaforolimus, increased the thrashing behavior to the same level as nontransgenic nematodes. Conclusion: These data support a role for LRRK2 in autophagy, raise the possibility that deficits in autophagy contribute to the pathophysiology of LRRK2, and point to a potential therapeutic approach addressing the pathophysiology of LRRK2 in PD.

Watching Worms Whither: Modeling Neurodegeneration in C. elegans

Caenorhabditis elegans is increasingly being used to study neurodegenerative diseases. Nematodes are translucent, which facilitates study of particular neurons in the living animal, and easy to manipulate genetically. Despite vast evolutionary divergence, human proteins are functionally active when expressed in C. elegans, and disease-linked mutations in these proteins also cause phenotypic changes in the nematode. In this chapter, we review use of C. elegans to investigate the pathophysiology of Alzheimers disease, Parkinsons disease, and axonal degeneration. Studies of presenilin, β-amyloid, tau, α-synuclein, and LRRK2 all produce strong phenotypic effects in C. elegans, and in many cases reproduce selective neuronal vulnerability observed in humans. Disease-linked mutations enhance degeneration in the C. elegans models. These studies are increasingly leading to high-throughput screens that identify novel genes and novel pharmaceuticals that modify the disease course.

Mitochondrial Dynamics: The Intersection of Form and Function

Mitochondria within a cell exist as a population in a dynamic -morphological continuum. The balance of mitochondrial fusion and fission dictates a spectrum of shapes from interconnected networks to fragmented individual units. This plasticity bestows the adaptive flexibility needed to adjust to changing cellular stresses and metabolic demands. The mechanisms that regulate mitochondrial dynamics, their importance in normal cell biology, and the roles they play in disease conditions are only beginning to be understood. Dysfunction of mitochondrial dynamics has been identified as a possible disease mechanism in Parkinsons disease. This chapter will introduce the budding field of mitochondrial dynamics and explore unique characteristics of affected neurons in Parkinsons disease that increase susceptibility to disruptions in mitochondrial dynamics.

Mitochondrial Dynamics and Autophagy

Efficient mitochondrial quality control is critical for maintenance of a healthy mitochondrial population. Both mitochondrial dynamics and selective mitochondrial autophagy, termed mitophagy, contribute to mitochondrial turnover and quality control. Mitochondrial fusion and fission allow for complementation of mitochondrial solutes, proteins, and DNA but also for generation of unequal daughter organelles. Selective fusion is utilized for incorporation of polarized mitochondria back into the network, while a depolarized mitochondrion will not fuse, but instead will be targeted for elimination by mitophagy. Mitophagy is dependent on mitochondrial dysfunction, such as depolarization, and a number of proteins are required for core autophagic machinery, signaling, and mitochondrial segregation and targeting. The relationship between mitochondrial dynamics and autophagy and how they may contribute to both mitochondrial and cellular quality control is beginning to be elucidated. Even with the questions that remain in regards to the regulation and interdependence of mitochondrial dynamics and mitophagy, it is clear that alterations in these processes lead to mitochondrial dysfunction and pathological states such as neurodegeneration.

Cefepime induced neurotoxicity: A case series and review of the literature

Cefepime is a fourth generation cephalosporin which is bactericidal for broad spectrum of organisms. This is a case-series of three patients who presented to our hospital with confusion secondary to cefepime use to treat urinary tract infection (UTI) and health care associated pneumonia (HCAP), after excluding other common etiologies of altered mental status (AMS). Of these three patients, one had progressive expressive aphasia and the other two demonstrated asynchronous myoclonic activity of the limbs. The symptoms were seen within four to five days of initiating the treatment and resolved within three days of discontinuation of cefepime. Acute structural abnormalities were excluded by computed tomography (CT) and magnetic resonance imaging (MRI) of the brain. Electroencephalogram (EEG) showed diffuse slowing activity with triphasic waves consistent with encephalopathy. In one patient, renal function was within normal limits, whereas it was abnormal in two patients. To our knowledge, this is the first report of cefepime induced asynchronous myoclonus and expressive aphasia in a patient with normal kidney function.