SH-SY5Y cells, a neuroblastoma cell line that is a well-established model system to study the initial phases of neuronal differentiation, have been used in studies to elucidate the mechanisms of neuronal differentiation. In the present study, we investigated alterations of gene expression in SH-SY5Y cells during neuronal differentiation mediated by retinoic acid (RA) treatment. We evaluated important pathways involving nuclear factor kappa B (NF-κB), nuclear E2-related factor 2 (Nrf2), glycolytic, and p53 during neuronal differentiation. We also investigated the involvement of reactive oxygen species (ROS) in modulating the gene expression profile of those pathways by antioxidant co-treatment with Trolox®, a hydrophilic analogue of α-tocopherol. We found that RA treatment increases levels of gene expression of NF-κB, glycolytic, and antioxidant pathway genes during neuronal differentiation of SH-SY5Y cells. We also found that ROS production induced by RA treatment in SH-SY5Y cells is involved in gene expression profile alterations, chiefly in NF-κB, and glycolytic pathways. Antioxidant co-treatment with Trolox® reversed the effects mediated by RA NF-κB, and glycolytic pathways gene expression. Interestingly, co-treatment with Trolox® did not reverse the effects in antioxidant gene expression mediated by RA in SH-SY5Y. To confirm neuronal differentiation, we quantified endogenous levels of tyrosine hydroxylase, a recognized marker of neuronal differentiation. Our data suggest that during neuronal differentiation mediated by RA, changes in profile gene expression of important pathways occur. These alterations are in part mediated by ROS production. Therefore, our results reinforce the importance in understanding the mechanism by which RA induces neuronal differentiation in SH-SY5Y cells, principally due this model being commonly used as a neuronal cell model in studies of neuronal pathologies.

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Maple syrup urine disease (MSUD) is an inborn error of metabolism caused by a severe deficiency in the activity of the branched-chain α-keto acid dehydrogenase complex, leading to accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine, and valine. Infections have a significant role in precipitating acute metabolic decompensation in patients with MSUD; however, the mechanisms underlying the neurotoxicity in this disorder are poorly understood. In this study, we subjected rats to the coadministration of lipopolysaccharide (LPS), which is a major component of gram-negative bacteria cell walls, and high concentrations of BCAA (H-BCAA) to determine their effects on the permeability of the blood-brain barrier (BBB) and on the levels of matrix metalloproteinases (MMP-2 and MMP-9). Our results demonstrated that the coadministration of H-BCAA and LPS causes breakdown of the BBB and increases the levels of MMP-2 and MMP-9 in the hippocampus of these rats. On the other hand, examination of the cerebral cortex of the 10- and 30-day-old rats revealed a significant difference in Evan's Blue content after coadministration of H-BCAA and LPS, as MMP-9 levels only increased in the cerebral cortex of the 10-day-old rats. In conclusion, these results suggest that the inflammatory process associated with high levels of BCAA causes BBB breakdown. Thus, we suggest that BBB breakdown is relevant to the perpetuation of brain inflammation and may be related to the brain dysfunction observed in MSUD patients.

Cellular and molecular mechanisms related to lung cancer have been extensively studied in recent years, but the availability of effective treatments is still scarce. Hecogenin acetate, a natural saponin presenting a wide spectrum of reported pharmacological activities, has been previously evaluated for its anticancer/antiproliferative activity in some in vivo and in vitro models. Here, we investigated the effects of hecogenin acetate in a human lung cancer cell line. A549 non-small lung cancer cells were exposed to different concentrations of hecogenin acetate and reactive species production, ERK1/2 activation, matrix metalloproteinase expression, cell cycle arrest and cell senescence parameters were evaluated. Hecogenin acetate significantly inhibited increase in intracellular reactive species production induced by H2O2. In addition, hecogenin acetate blocked ERK1/2 phosphorylation and inhibited the increase in MMP-2 caused by H2O2. Treatment with hecogenin acetate induced G0/G1-phase arrest at two concentrations (75 and 100 µM, 74% and 84.3% respectively), and increased the staining of senescence-associated β -galactosidase positive cells. These data indicate that hecogenin acetate is able to exert anti-cancer effects by modulating reactive species production, inducing cell cycle arrest and senescence and also modulating ERK1/2 phosphorylation and MMP-2 production.

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Calcium (Ca2+) is a key regulator in diverse intracellular signaling pathways, and has long been implicated in metabolic control and mitochondrial function. Mitochondria can actively take up large amounts of Ca2+, thereby acting as important intracellular Ca2+ buffers and affecting cytosolic Ca2+ transients. Excessive mitochondrial matrix Ca2+ is known to be deleterious due to opening of the mitochondrial permeability transition pore (mPTP) and consequent membrane potential dissipation, leading to mitochondrial swelling, rupture and cell death. But moderate Ca2+ within the organelle can directly or indirectly activate mitochondrial matrix enzymes, possibly impacting on ATP production. However, in vitro studies involving the regulation of mitochondrial enzymes by Ca2+ may not uncover its full effects on oxidative phosphorylation. Here, we aimed to determine if extra or intramitochondrial Ca2+ modulate oxidative phosphorylation in mouse liver mitochondria and intact hepatocytes. We found that isolated mitochondria present increased respiratory control ratios (a measure of oxidative phosphorylation efficiency) when incubated with low and medium Ca2+ concentrations in the presence of complex I-linked substrates pyruvate plus malate and a-ketoglutarate, respectively, but not complex II-linked succinate. In intact hepatocytes, both low and high cytosolic Ca2+ led to decreased respiratory rates, while ideal rates were present under physiological conditions. High Ca2+ decreased mitochondrial respiration in cells in a substrate-dependent manner, mediated by mPTP. Overall, our results uncover a Goldilocks effect of Ca2+ on liver mitochondria, with specific 'just right' concentrations that activate oxidative phosphorylation.

Autophagy is an essential cellular process regulated by intracellular calcium signals, which play an important role in autophagic activation during metabolic changes. Calcium transporters are present in mitochondria, an organelle able to uptake and release calcium ions, thus participating in cellular calcium signaling. Uptake by mitochondria is mediated by the mitochondrial calcium uniporter (MCU), while extrusion occurs through the mitochondrial sodium/lithium/calcium exchanger (NCLX). The aim of this work was to investigate how MCU and NCLX affect autophagy. To do so, we evaluated makers of autophagic activity in murine Aml‐12 hepatic cells transfected with siRNAs targeting either MCU or NCLX expression, leading to genetic knockdown (KD). Additionally, we investigated the autophagic response to serum/amino acid starvation and rapamycin (mTORC1 inhibitor) treatment in Aml‐12 cells with NCLX KD or pharmacological inhibition by CGP37157 (CGP). Using a cell line stably expressing the autophagic probe LC3‐GFP‐mCherry, we observed that NCLX KD leads to impaired autophagosome formation under basal conditions. Curiously, this effect was associated with a significant decrease in mRNA expression of LC3A and LC3B genes, while the expression of other autophagy‐related genes, such as TFEB, ATG5, ATG12, and ATG7, was upregulated or unchanged. Conversely, MCU KD led to an apparent increase in autophagosome and autolysosome numbers, indicating enhanced autophagic activity. Interestingly, MCU KD also led to decreased expression of LC3A, but not LC3B. The expression of TFEB, ATG12, ATG5, and ATG7 were decreased or unchanged by MCU KD. After autophagic stimulation by serum/amino acid starvation, the levels of LC3 II were lower in NCLX KD cells compared to negative control in the presence or absence of bafilomycin A1, which indicates a reduction of autophagic flux. The levels of LC3 I were significantly lower in NCLX KD cells under basal and stimulated conditions, corroborating the decreased LC3 mRNA levels observed. Importantly, these effects were also observed using CGP to inhibit NCLX. The reduction of autophagic flux by NCLX KD or CGP was not observed in cells treated with rapamycin. We also measured the levels of phosphorylated 4E‐BP1 as an indication of mTORC1 activity. As expected, serum/amino acid starvation and rapamycin decreased the levels of p‐4E‐BP1; however, this decrease was modulated by CGP only in starved cells, indicating that NCLX may affect mTORC1 activity in an upstream pathway. In conclusion, we show that mitochondrial calcium transporters are novel autophagy‐regulating pathways: MCU modulates autophagic activation under basal conditions, while NCLX maintains autophagic activity under basal and stimulated conditions.