Idebenone Has Distinct Effects on Mitochondrial Respiration in Cortical Astrocytes Compared to Cortical Neurons Due to Differential NQO1 Activity.

Idebenone is a synthetic quinone that on reduction in cells can bypass mitochondrial Complex I defects by donating electrons to Complex III. The drug is used clinically to treat the Complex I disease Leber's hereditary optic neuropathy (LHON), but has been less successful in clinical trials for other neurodegenerative diseases. NAD(P)H:quinone oxidoreductase 1 (NQO1) appears to be the main intracellular enzyme catalyzing idebenone reduction. However, NQO1 is not universally expressed by cells of the brain. Using primary rat cortical cells pooled from both sexes, we tested the hypotheses that the level of endogenous NQO1 activity limits the ability of neurons, but not astrocytes, to use idebenone as an electron donor to support mitochondrial respiration. We then tested the prediction that NQO1 induction by pharmacological activation of the transcription factor nuclear erythroid 2-related factor 2 (Nrf2) enables idebenone to bypass Complex I in cells with poor NQO1 expression. We found that idebenone stimulated respiration by astrocytes but reduced the respiratory capacity of neurons. Importantly, idebenone supported mitochondrial oxygen consumption in the presence of a Complex I inhibitor in astrocytes but not neurons, and this ability was reversed by inhibiting NQO1. Conversely, recombinant NQO1 delivery to neurons prevented respiratory impairment and conferred Complex I bypass activity. Nrf2 activators failed to increase NQO1 in neurons, but carnosic acid induced NQO1 in COS-7 cells that expressed little endogenous enzyme. Carnosic acid-idebenone combination treatment promoted NQO1-dependent Complex I bypass activity in these cells. Thus, combination drug strategies targeting NQO1 may promote the repurposing of idebenone for additional disorders.SIGNIFICANCE STATEMENT Idebenone is used clinically to treat loss of visual acuity in Leber's hereditary optic neuropathy. Clinical trials for several additional diseases have failed. This study demonstrates a fundamental difference in the way idebenone affects mitochondrial respiration in cortical neurons compared with cortical astrocytes. Cortical neurons are unable to use idebenone as a direct mitochondrial electron donor due to NQO1 deficiency. Our results suggest that idebenone behaves as an NQO1-dependent prodrug, raising the possibility that lack of neuronal NQO1 activity has contributed to the limited efficacy of idebenone in neurodegenerative disease treatment. Combination therapy with drugs able to safely induce NQO1 in neurons, as well as other brain cell types, may be able to unlock the neuroprotective therapeutic potential of idebenone or related quinones.

Inceptor as a regulator of brain insulin sensitivity.

While historically viewed as an insulin insensitive organ, it is now accepted that insulin has a role in brain physiology. Changes in brain insulin and IGF1 signaling have been associated with neurological diseases, however the molecular factors regulating brain insulin sensitivity remain uncertain. In this study, we proposed that a recently described protein, termed Inceptor, may play a role in brain insulin and IGF1 resistance. We studied Inceptor in healthy and diseased nervous tissue to understand the distribution of the protein and examine how it may change in states of insulin resistance. We found that Inceptor is in fact present in cerebellum, hippocampus, hypothalamus, and cortex of the brain in neurons, with higher levels in cortex of female compared to male mice. We also confirmed that Inceptor colocalized with IR and IGF1R in brain. We saw little difference in insulin receptor signaling following Inceptor knockdown in neuron cultures, or in Inceptor levels with high-fat diet in mouse or Alzheimer's disease in mouse or human tissue. These results all provide significant advancements to our understanding of Inceptor in the brain. PROTOCOL REGISTRATION: The Stage 1 registered report manuscript was accepted-in-principle on 9 August 2022. This manuscript was registered through Open Science Forum (OSF) on 24 August 2022 and is available here: https://osf.io/9q8sw .

Drug library screen identifies inhibitors of toxic astrogliosis.

BACKGROUND: Multiple sclerosis (MS) is a chronic neuroinflammatory disorder, in which activated immune cells directly or indirectly induce demyelination and axonal degradation. Inflammatory stimuli also change the phenotype of astrocytes, making them neurotoxic. The resulting 'toxic astrocyte' phenotype has been observed in animal models of neuroinflammation and in MS lesions. Proteins secreted by toxic astrocytes are elevated in the cerebrospinal fluid (CSF) of MS patients and reproducibly correlate with the rates of accumulation of neurological disability and brain atrophy. This suggests a pathogenic role for neurotoxic astrocytes in MS. METHODS: Here, we applied a commercially available library of small molecules that are either Food and Drug Administration-approved or in clinical development to an in vitro model of toxic astrogliosis to identify drugs and signaling pathways that inhibit inflammatory transformation of astrocytes to a neurotoxic phenotype. RESULTS: Inhibitors of three pathways related to the endoplasmic reticulum stress: (1) proteasome, (2) heat shock protein 90 and (3) mammalian target of rapamycin reproducibly decreased inflammation-induced conversion of astrocytes to toxic phenotype. Dantrolene, an anti-spasticity drug that inhibits calcium release through ryanodine receptors expressed in the endoplasmic reticulum of central nervous system cells, also exerted inhibitory effect at in vivo achievable concentrations. Finally, we established CSF SERPINA3 as a relevant pharmacodynamic marker for inhibiting toxic astrocytes in clinical trials. CONCLUSION: Drug library screening provides mechanistic insight into the generation of toxic astrocytes and identifies candidates for immediate proof-of-principle clinical trial(s).

The brain as an insulin-sensitive metabolic organ.

BACKGROUND: The brain was once thought of as an insulin-insensitive organ. We now know that the insulin receptor is present throughout the brain and serves important functions in whole-body metabolism and brain function. Brain insulin signaling is involved not only in brain homeostatic processes but also neuropathological processes such as cognitive decline and Alzheimer's disease. SCOPE OF REVIEW: In this review, we provide an overview of insulin signaling within the brain and the metabolic impact of brain insulin resistance and discuss Alzheimer's disease, one of the neurologic diseases most closely associated with brain insulin resistance. MAJOR CONCLUSIONS: While brain insulin signaling plays only a small role in central nervous system glucose regulation, it has a significant impact on the brain's metabolic health. Normal insulin signaling is important for mitochondrial functioning and normal food intake. Brain insulin resistance contributes to obesity and may also play an important role in neurodegeneration.

Intrathecal, Not Systemic Inflammation Is Correlated With Multiple Sclerosis Severity, Especially in Progressive Multiple Sclerosis.

Objective: To test the hypothesis that Multiple Sclerosis (MS) patients have increased peripheral inflammation compared to healthy donors and that this systemic activation of the immune system, reflected by acute phase reactants (APRs) measured in the blood, contributes to intrathecal inflammation, which in turn contributes to the development of disability in MS. Methods: Eight serum APRs measured in a prospectively-collected cross-sectional cohort with a total of 51 healthy donors and 291 untreated MS patients were standardized and assembled into related biomarker clusters to derive global measures of systemic inflammation. The resulting APR clusters were compared between diagnostic categories and correlated to equivalently-derived cerebrospinal fluid (CSF) biomarkers of innate and adaptive immunity. Finally, correlations were calculated between biomarkers of systemic and intrathecal inflammation and MS severity measures, which predict future rates of disability progression. Results: While two blood APR clusters were elevated in MS patients, only one exhibited a weak correlation with MS severity. All CSF inflammation clusters, except CSF albumin, correlated with at least one measure of MS severity, with biomarkers of humoral adaptive immunity exhibiting the strongest correlations, especially in Progressive MS. Conclusion: Systemic inflammation does not appear to be strongly associated with intrathecal inflammation in MS. Positive correlations between markers of intrathecal inflammation, especially of humoral immunity, with MS severity measures support a pathogenic role of intrathecal (compartmentalized) inflammation in central nervous system tissue destruction, including in Progressive MS.