Down syndrome (DS) is associated with significant perturbances in mitochondrial function. Here we tested the hypothesis that the suppression of mitochondrial electron transport in DS cells is due to high expression of cystathionine-β-synthase (CBS) and subsequent overproduction of the gaseous transmitter hydrogen sulfide (H2S). Fibroblasts from DS individuals showed higher CBS expression than control cells; CBS localization was both cytosolic and mitochondrial. DS cells produced significantly more H2S and polysulfide and exhibited a profound suppression of mitochondrial electron transport, oxygen consumption, and ATP generation. DS cells also exhibited slower proliferation rates. In DS cells, pharmacological inhibition of CBS activity with aminooxyacetate or siRNA-mediated silencing of CBS normalized cellular H2S levels, restored Complex IV activity, improved mitochondrial electron transport and ATP synthesis, and restored cell proliferation. Thus, CBS-derived H2S is responsible for the suppression of mitochondrial function in DS cells. When H2S overproduction is corrected, the tonic suppression of Complex IV is lifted, and mitochondrial electron transport is restored. CBS inhibition offers a potential approach for the pharmacological correction of DS-associated mitochondrial dysfunction.

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Growing evidence suggests that agonists of glucagon-like peptide (GLP-1) receptor exert neuroprotective and neurorestorative effects across a range of experimental models of neuronal degeneration, and, recently, a pilot clinical trial of Liraglutide in Alzheimer’s disease patients showed improvements in cerebral glucose consumption that signifies disease progression. However, the exact underlying mechanism of action remains unclear. Chronic endoplasmic reticulum (ER) stress has recently emerged as a mechanism for neuronal injury, rendering it a potent therapeutic target for acute and chronic neurodegenerative disorders. Here, we investigate the neuroprotective effects of Liraglutide along with the signalling network against prolong ER stress and autophagy impairments induced by the non-competitive inhibitor of sarco/ER Ca2+-ATPase, thapsigargin. We show that Liraglutide modulates the ER stress response and elicits ER proteostasis and autophagy machinery homeostasis in human SH-SY5Y neuroblastoma cell line. These effects correlate with resolution of hyper-activity of the antioxidant Nrf2 factor and restoration of the impaired cell viability and proliferation. Mechanistically, Liraglutide engages Akt and signal transducer and activator of transcription 3 (STAT3) signalling to favour adaptive responses and shift cell fate from apoptosis to survival under chronic stress conditions in SH-SY5Y cells.

Alzheimer's disease (AD) afflicts more than 46.8 million people worldwide, with a newly diagnosed case every 3 seconds and no remission in the disease progression. The discovery of disease-modifying drugs is now on the summit of the neuropharmacological research priorities. The long-lasting derivatives of the insulinotropic incretin hormones-glucagonlike peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP)-have repeatedly been shown to cross the blood-brain barrier and counteract an array of deleterious effects across a range of experimental models of neuronal degeneration. Clinical trials for the efficacy of GLP-1 agonists in Alzheimer's and Parkinson's diseases have revealed beneficial effects of these anti-diabetic agents in halting neuronal degeneration progression. Herein, we examine whether the chronic treatment with the novel dual GLP-1/GIP receptor agonist DA-CH3 can restore the cognitive decline and AD-like cerebral pathology of the APP SWE /PS1 E9 mouse model at the age of 10 months old. We report that once-a-daily, eight-week intraperitoneal administration of 25 nmol/kg of the novel DA-CH3 dual-incretin analog rescues the spatial acquisition and memory impairments of this murine model that corresponds to the attenuation of the excessive plaque deposition, gliosis and synaptic damage in the APP SWE /PS1 E9 brain. The amelioration of the AD-related pathology reflects the resolution of the endoplasmic-reticulum stress and derailed autophagy that both lay downstream of the rectified Akt signaling. Collectively, our findings endorse the beneficial effects of the incretin-based therapeutic approaches for the neurotrophic support of the AD brain and for the first time associate the incretin-induced neuroprotection with the proteostasis machinery in vivo.

In mammalian cells, cyanide is viewed as a cytotoxic agent, which exerts its effects through inhibition of mitochondrial Complex IV (Cytochrome C oxidase [CCOx]). However, the current report demonstrates that cyanide’s effect on CCOx is biphasic; low (nanomolar to low-micromolar) concentrations stimulate CCOx activity, while higher (high-micromolar) concentrations produce the “classic” inhibitory effect. Low concentrations of cyanide stimulated mitochondrial electron transport and elevated intracellular adenosine triphosphate (ATP), resulting in the stimulation of cell proliferation. The stimulatory effect of cyanide on CCOx was associated with the removal of the constitutive, inhibitory glutathionylation on its catalytic 30- and 57-kDa subunits. Transfer of diluted Pseudomonas aeruginosa (a cyanide-producing bacterium) supernatants to mammalian cells stimulated cellular bioenergetics, while concentrated supernatants were inhibitory. These effects were absent with supernatants from mutant Pseudomonas lacking its cyanide-producing enzyme. These results raise the possibility that cyanide at low, endogenous levels serves regulatory purposes in mammals. Indeed, the expression of six putative mammalian cyanide-producing and/or -metabolizing enzymes was confirmed in HepG2 cells; one of them (myeloperoxidase) showed a biphasic regulation after cyanide exposure. Cyanide shares features with “classical” mammalian gasotransmitters NO, CO, and H2S and may be considered the fourth mammalian gasotransmitter.