Omics profile of iPSC-derived astrocytes from Progressive Supranuclear Palsy (PSP) patients

INTRODUCTION

Progressive Supranuclear Palsy (PSP) is a neurodegenerative tauopathy and, to date, the pathophysiological mechanisms in PSP that lead to Tau hyperphosphorylation and neurodegeneration are not clear. In some brain areas, Tau pathology in glial cells appears to precede Tau aggregation in neurons. The development of a model using astrocyte cell lines derived from patients has the potential to identify molecules and pathways that contribute to early events of neurodegeneration. We developed a model of induced pluripotent stem cells (iPSC)-derived astrocytes to investigate the pathophysiology of PSP, particularly early events that might contribute to Tau hyperphosphorylation, applying omics approach to detect differentially expressed genes, metabolites, and proteins, including those from the secretome.

METHODS

Skin fibroblasts from PSP patients (without MAPT mutations) and controls were reprogrammed to iPSCs, further differentiated into neuroprogenitor cells (NPCs) and astrocytes. In the 5th passage, astrocytes were harvested for total RNA sequencing. Intracellular and secreted proteins were processed for proteomics experiments. Metabolomics profiling was obtained from supernatants only.

RESULTS

We identified hundreds of differentially expressed genes. The main networks were related to cell cycle re-activation in PSP. Several proteins were found exclusively secreted by the PSP group. The cellular processes related to the cell cycle and mitotic proteins, TriC/CCT pathway, and redox signaling were enriched in the secretome of PSP. Moreover, we found distinct sets of metabolites between PSP and controls.

CONCLUSION

Our iPSC-derived astrocyte model can provide distinct molecular signatures for PSP patients and it is useful to elucidate the initial stages of PSP pathogenesis.

A spontaneous mutation in the nicotinamide nucleotide transhydrogenase gene of C57BL/6J mice results in mitochondrial redox abnormalities

NADPH is the reducing agent for mitochondrial H2O2 detoxification systems. Nicotinamide nucleotide transhydrogenase (NNT), an integral protein located in the inner mitochondrial membrane, contributes to an elevated mitochondrial NADPH/NADP(+) ratio. This enzyme catalyzes the reduction of NADP(+) at the expense of NADH oxidation and H(+) reentry to the mitochondrial matrix. A spontaneous Nnt mutation in C57BL/6J (B6J-Nnt(MUT)) mice arose nearly 3 decades ago but was only discovered in 2005. Here, we characterize the consequences of the Nnt mutation on the mitochondrial redox functions of B6J-Nnt(MUT) mice. Liver mitochondria were isolated both from an Nnt wild-type C57BL/6 substrain (B6JUnib-Nnt(W)) and from B6J-Nnt(MUT) mice. The functional evaluation of respiring mitochondria revealed major redox alterations in B6J-Nnt(MUT) mice, including an absence of transhydrogenation between NAD and NADP, higher rates of H2O2 release, the spontaneous oxidation of NADPH, the poor ability to metabolize organic peroxide, and a higher susceptibility to undergo Ca(2+)-induced mitochondrial permeability transition. In addition, the mitochondria of B6J-Nnt(MUT) mice exhibited increased oxidized/reduced glutathione ratios as compared to B6JUnib-Nnt(W) mice. Nonetheless, the maximal activity of NADP-dependent isocitrate dehydrogenase, which is a coexisting source of mitochondrial NADPH, was similar between both groups. Altogether, our data suggest that NNT functions as a high-capacity source of mitochondrial NADPH and that its functional loss due to the Nnt mutation results in mitochondrial redox abnormalities, most notably a poor ability to sustain NADP and glutathione in their reduced states. In light of these alterations, the potential drawbacks of using B6J-Nnt(MUT) mice in biomedical research should not be overlooked.

Protection of rat skeletal muscle fibers by either L-carnitine or coenzyme Q10 against statins toxicity mediated by mitochondrial reactive oxygen generation

Mitochondrial redox imbalance has been implicated in mechanisms of aging, various degenerative diseases and drug-induced toxicity. Statins are safe and well-tolerated therapeutic drugs that occasionally induce myotoxicity such as myopathy and rhabdomyolysis. Previous studies indicate that myotoxicity caused by statins may be linked to impairment of mitochondrial functions. Here, we report that 1-h incubation of permeabilized rat soleus muscle fiber biopsies with increasing concentrations of simvastatin (1–40 μM) slowed the rates of ADP-or FCCP-stimulated respiration supported by glutamate/malate in a dose-dependent manner, but caused no changes in resting respiration rates. Simvastatin (1 μM) also inhibited the ADP-stimulated mitochondrial respiration supported by succinate by 24% but not by TMPD/ascorbate. Compatible with inhibition of respiration, 1 μM simvastatin stimulated lactate release from soleus muscle samples by 26%. Co-incubation of muscle samples with 1 mM L-carnitine, 100 μM mevalonate or 10 μM coenzyme Q10 (Co-Q10) abolished simvastatin effects on both mitochondrial glutamate/malate-supported respiration and lactate release. Simvastatin (1 μM) also caused a 2-fold increase in the rate of hydrogen peroxide generation and a decrease in Co-Q10 content by 44%. Mevalonate, Co-Q10 or L-carnitine protected against stimulation of hydrogen peroxide generation but only mevalonate prevented the decrease in Co-Q10 content. Thus, independently of Co-Q10 levels, L-carnitine prevented the toxic effects of simvastatin. This suggests that mitochondrial respiratory dysfunction induced by simvastatin, is associated with increased generation of superoxide, at the levels of complexes-I and II of the respiratory chain. In all cases the damage to these complexes, presumably at the level of 4Fe-4S clusters, is prevented by L-carnitine.