Remdesivir triphosphate blocks DNA synthesis and increases exonucleolysis by the replicative mitochondrial DNA polymerase, Pol γ.

The COVID-19 pandemic prompted the FDA to authorize a new nucleoside analogue, remdesivir, for emergency use in affected individuals. We examined the effects of its active metabolite, remdesivir triphosphate (RTP), on the activity of the replicative mitochondrial DNA polymerase, Pol γ. We found that while RTP is not incorporated by Pol γ into a nascent DNA strand, it remains associated with the enzyme impeding its synthetic activity and stimulating exonucleolysis. In spite of that, we found no evidence for deleterious effects of remdesivir treatment on the integrity of the mitochondrial genome in human cells in culture.

Physical and Functional Interaction of Mitochondrial Single-Stranded DNA-Binding Protein and the Catalytic Subunit of DNA Polymerase Gamma.

The maintenance of the mitochondrial genome depends on a suite of nucleus-encoded proteins, among which the catalytic subunit of the mitochondrial replicative DNA polymerase, Pol γα, plays a pivotal role. Mutations in the Pol γα-encoding gene, POLG, are a major cause of human mitochondrial disorders. Here we present a study of direct and functional interactions of Pol γα with the mitochondrial single-stranded DNA-binding protein (mtSSB). mtSSB coordinates the activity of the enzymes at the DNA replication fork. However, the mechanism of this functional relationship is elusive, and no direct interactions between the replicative factors have been identified to date. This contrasts strikingly with the extensive interactomes of SSB proteins identified in other homologous replication systems. Here we show for the first time that mtSSB binds Pol γα directly, in a DNA-independent manner. This interaction is strengthened in the absence of the loop 2.3 structure in mtSSB, and is abolished upon preincubation with Pol γß. Together, our findings suggest that the interaction between mtSSB and polymerase gamma holoenzyme (Pol γ) involves a balance between attractive and repulsive affinities, which have distinct effects on DNA synthesis and exonucleolysis.

Impact of regional striatal dopaminergic function on kinematic parameters of Parkinson's disease.

Among the cardinal parkinsonian motor deficits, the severity of bradykinesia correlates with striatal dopamine loss. However, the impact of regional striatal dopamine loss on specific components of bradykinesia remains unknown. Using gyroscopes, we measured the amplitude, speed, and frequency of finger tapping in 24 untreated patients with Parkinson's disease (PD) and 28 healthy controls. Using positron emission tomography (PET) studies and [(18)F]-N-3-fluoropropyl-2-beta-carboxymethoxy-3-beta-(4-iodophenyl) nortropane (FP-CIT) in PD patients, we investigated the relationship between the mean values, variability and decrements of various kinematic parameters of finger tapping on one side (e.g. the mean, variability and decrement) and contralateral striatal FP-CIT binding. Compared with controls, PD patients had reduced amplitudes and speeds of tapping and showed greater decrement in those parameters. PD patients also exhibited greater irregularity in amplitude, speed, and frequency. Putaminal FP-CIT uptake levels correlated with the mean speed and amplitude, and caudate uptake levels correlated with mean amplitude. The variability of amplitude and speed correlated only with the caudate uptake levels. Neither caudate nor putaminal uptake correlated with frequency-related parameters or decrement in amplitude or speed. Reduced amplitude and speed of repetitive movement may be related to striatal dopaminergic deficit. Dopaminergic action in the caudate nucleus is required to maintain consistency of amplitude and speed. Although decrement of amplitude and speed is known to be specific for PD, we found that it did not mirror the degree of striatal dopamine depletion.

Cognitive dysfunction associated with falls in progressive supranuclear palsy.

BACKGROUND: Attentional and executive dysfunctions are associated with falls in community-dwelling elderly individuals and patients with PD. Frontal cognitive dysfunction and falls are frequent symptoms of PSP. We studied to identify the cognitive domains associated with recurrent falls in patients with PSP. METHODS: We performed a battery of neuropsychological tests in 59 individuals with probable PSP. We categorized patients into infrequent fall (≤one fall during the last 12 months, n=29) or recurrent fall (≥two falls during the last 12 months, n=30) groups. RESULTS: UPDRS subscores for axial deficits were significantly higher in the recurrent fall group than the infrequent fall group, but there were no significant differences in UPDRS total motor scores or subscores for bradykinesia, rigidity, and tremor. There was no difference between groups in MMSE scores. ANCOVA with adjustment for confounding factors showed that, recurrent falls were associated with abnormalities in alternating hand movement, alternating square and triangle, RCFT copying task, and ideomotor apraxia. Group difference of abnormalities in Stroop test was marginal (p=0.054). However, there were no group differences in the frequency of abnormalities in forward or backward digit span, motor impersistence, fist-edge-palm, contrast programming, go-no-go, Luria loop drawing, or Controlled Oral Word Association Tests. Recurrent falls were not associated with memory or language dysfunction. CONCLUSIONS: Recurrent falls in patients with PSP were associated mainly with executive and visuospatial dysfunctions, including (1) impaired coordinated alternating uni- and bimanual motor programming and execution, (2) deficit of attention and decision making in the presence of interference, (3) visuospatial misperception and (4) ideomotor apraxia.