Development and Application of a Mitochondrial Genetically Encoded Voltage Indicator in Narcosis.

Mitochondrial membrane potential (MMP) plays a crucial role in the function of cells and organelles, involving various cellular physiological processes, including energy production, formation of reactive oxygen species (ROS), unfolded protein stress, and cell survival. Currently, there is a lack of genetically encoded fluorescence indicators (GEVIs) for MMP. In our screening of various GEVIs for their potential monitoring MMP, the Accelerated Sensor of Action Potentials (ASAP) demonstrated optimal performance in targeting mitochondria and sensitivity to depolarization in multiple cell types. However, mitochondrial ASAPs also displayed sensitivity to ROS in cardiomyocytes. Therefore, two ASAP mutants resistant to ROS were generated. A double mutant ASAP3-ST exhibited the highest voltage sensitivity but weaker fluorescence. Overall, four GEVIs capable of targeting mitochondria were obtained and named mitochondrial potential indicators 1-4 (MPI-1-4). In vivo, fiber photometry experiments utilizing MPI-2 revealed a mitochondrial depolarization during isoflurane-induced narcosis in the M2 cortex.

Neurotransmitter accumulation and Parkinson's disease-like phenotype caused by anion channelrhodopsin opto-controlled astrocytic mitochondrial depolarization in substantia nigra pars compacta.

Parkinson's disease (PD) is a mitochondria-related neurodegenerative disease characterized by locomotor deficits and loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc). Majority of PD research primarily focused on neuronal dysfunction, while the roles of astrocytes and their mitochondria remain largely unexplored. To bridge the gap and investigate the roles of astrocytic mitochondria in PD progression, we constructed a specialized optogenetic tool, mitochondrial-targeted anion channelrhodopsin, to manipulate mitochondrial membrane potential in astrocytes. Utilizing this tool, the depolarization of astrocytic mitochondria within the SNc in vivo led to the accumulation of γ-aminobutyric acid (GABA) and glutamate in SNc, subsequently resulting in excitatory/inhibitory imbalance and locomotor deficits. Consequently, in vivo calcium imaging and interventions of neurotransmitter antagonists demonstrated that GABA accumulation mediated movement deficits of mice. Furthermore, 1 h/day intermittent astrocytic mitochondrial depolarization for 2 weeks triggered spontaneous locomotor dysfunction, α-synuclein aggregation, and the loss of DA neurons, suggesting that astrocytic mitochondrial depolarization was sufficient to induce a PD-like phenotype. In summary, our findings suggest the maintenance of proper astrocytic mitochondrial function and the reinstatement of a balanced neurotransmitter profile may provide a new angle for mitigating neuronal dysfunction during the initial phases of PD.

A sensitive mitochondrial thermometry 2.0 and the availability of thermogenic capacity of brown adipocyte.

The temperature of a living cell is a crucial parameter for cellular events, such as cell division, gene expressions, enzyme activities and metabolism. We previously developed a quantifiable mitochondrial thermometry 1.0 based on rhodamine B methyl ester (RhB-ME) and rhodamine 800 (Rh800), and the theory for mitochondrial thermogenesis. Given that the synthesized RhB-ME is not readily available, thus, a convenient mitochondrial thermometry 2.0 based on tetra-methyl rhodamine methyl ester (TMRM) and Rh800 for the thermogenic study of brown adipocyte was further evolved. The fluorescence of TMRM is more sensitive (∼1.4 times) to temperature than that of RhB-ME, then the TMRM-based mito-thermometry 2.0 was validated and used for the qualitatively dynamic profiles for mitochondrial thermogenic responses and mitochondrial membrane potential in living cells simultaneously. Furthermore, our results demonstrated that the heterogenous thermogenesis evoked by ß3 adrenoceptor agonist only used overall up to ∼46% of the thermogenic capacity evoked by CCCP stimulation. On the other hand, the results demonstrated that the maximum thermogenesis evoked by NE and oligomycin A used up to ∼79% of the thermogenic capacity, which suggested the maximum thermogenic capacity under physiological conditions by inhibiting the proton-ATPase function of the mitochondrial complex V, such as under the cold activation of sympathetic nerve and the co-release of sympathetic transmitters.

Dietary restriction of amino acids for Cancer therapy.

Biosyntheses of proteins, nucleotides and fatty acids, are essential for the malignant proliferation and survival of cancer cells. Cumulating research findings show that amino acid restrictions are potential strategies for cancer interventions. Meanwhile, dietary strategies are popular among cancer patients. However, there is still lacking solid rationale to clarify what is the best strategy, why and how it is. Here, integrated analyses and comprehensive summaries for the abundances, signalling and functions of amino acids in proteomes, metabolism, immunity and food compositions, suggest that, intermittent dietary lysine restriction with normal maize as an intermittent staple food for days or weeks, might have the value and potential for cancer prevention or therapy. Moreover, dietary supplements were also discussed for cancer cachexia including dietary immunomodulatory.

Changes of Metabolites in Acute Ischemic Stroke and Its Subtypes.

Existing techniques have many limitations in the diagnosis and classification of ischemic stroke (IS). Considering this, we used metabolomics to screen for potential biomarkers of IS and its subtypes and to explore the underlying related pathophysiological mechanisms. Serum samples from 99 patients with acute ischemic stroke (AIS) [the AIS subtypes included 49 patients with large artery atherosclerosis (LAA) and 50 patients with small artery occlusion (SAO)] and 50 matched healthy controls (HCs) were analyzed by non-targeted metabolomics based on liquid chromatography-mass spectrometry. A multivariate statistical analysis was performed to identify potential biomarkers. There were 18 significantly different metabolites, such as oleic acid, linoleic acid, arachidonic acid, L-glutamine, L-arginine, and L-proline, between patients with AIS and HCs. These different metabolites are closely related to many metabolic pathways, such as fatty acid metabolism and amino acid metabolism. There were also differences in metabolic profiling between the LAA and SAO groups. There were eight different metabolites, including L-pipecolic acid, 1-Methylhistidine, PE, LysoPE, and LysoPC, which affected glycerophospholipid metabolism, glycosylphosphatidylinositol-anchor biosynthesis, histidine metabolism, and lysine degradation. Our study effectively identified the metabolic profiles of IS and its subtypes. The different metabolites between LAA and SAO may be potential biomarkers in the context of clinical diagnosis. These results highlight the potential of metabolomics to reveal new pathways for IS subtypes and provide a new avenue to explore the pathophysiological mechanisms underlying IS and its subtypes.

History and progress of hypotheses and clinical trials for Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive memory loss along with neuropsychiatric symptoms and a decline in activities of daily life. Its main pathological features are cerebral atrophy, amyloid plaques, and neurofibrillary tangles in the brains of patients. There are various descriptive hypotheses regarding the causes of AD, including the cholinergic hypothesis, amyloid hypothesis, tau propagation hypothesis, mitochondrial cascade hypothesis, calcium homeostasis hypothesis, neurovascular hypothesis, inflammatory hypothesis, metal ion hypothesis, and lymphatic system hypothesis. However, the ultimate etiology of AD remains obscure. In this review, we discuss the main hypotheses of AD and related clinical trials. Wealthy puzzles and lessons have made it possible to develop explanatory theories and identify potential strategies for therapeutic interventions for AD. The combination of hypometabolism and autophagy deficiency is likely to be a causative factor for AD. We further propose that fluoxetine, a selective serotonin reuptake inhibitor, has the potential to treat AD.

Erratum: Author Correction: History and progress of hypotheses and clinical trials for Alzheimer's disease.

[This corrects the article DOI: 10.1038/s41392-019-0063-8.].

Modelling liver cancer initiation with organoids derived from directly reprogrammed human hepatocytes.

Human liver cancers, including hepatocellular carcinomas and intra-hepatic cholangiocarcinomas, are often diagnosed late with poor prognosis. A better understanding of cancer initiation could provide potential preventive therapies and increase survival. Models for studying human liver cancer initiation are largely missing. Here, using directly reprogrammed human hepatocytes (hiHeps) and inactivation of p53 and RB, we established organoids possessing liver architecture and function. HiHep organoids were genetically engineered to model the initial alterations in human liver cancers. Bona fide hepatocellular carcinomas were developed by overexpressing c-Myc. Excessive mitochondrion-endoplasmic reticulum coupling induced by c-Myc facilitated hepatocellular carcinoma initiation and seemed to be a target of preventive treatment. Furthermore, through the analysis of human intra-hepatic cholangiocarcinoma-enriched mutations, we demonstrate that the RAS-induced lineage conversion from hepatocytes to intra-hepatic cholangiocarcinoma cells can be prevented by the combined inhibition of Notch and JAK-STAT. Together, hiHep organoids represent a system that can be genetically manipulated to model cancer initiation and identify potential preventive therapies.

Application of a dye-based mitochondrion-thermometry to determine the receptor downstream of prostaglandin E2 involved in the regulation of hepatocyte metabolism.

Temperature distributions inside a living cell reflect the thermodynamics and functions of cellular components. We used a newly-developed method of mitochondrial thermometry based on Rhodamine B methyl ester, which equilibrates as a thermosensitive mixture of nonfluorescent and fluorescent resonance forms. Prostaglandin E2 (PGE2) is released from hepatic non-parenchymal Kupffer cells and acts as an inflammatory factor to impact various functions of hepatocytes. The activity of PGE2 on energy mechanism of hepatocytes has not been fully elucidated and in particular, which PGE2 receptor mediates the functions has been elusive. We identified EP4 as the major receptor of PGE2 via our mitochondrion-thermometry approach and then substantiated this receptor's role in hepatic metabolism. We discovered that PGE2 is able to decrease intracellular temperature of hepatocytes, via increasing some lipogenic genes' expressions, hampering lipolysis and mitochondrial ß-oxidation, reducing intracellular ATP level and elevating cAMP level through EP4 receptor. The redox status of hepatocytes represented by FAD vs FAD + NADH ratio is influenced by PGE2 in an EP4 receptor-dependent manner. Collectively, these data demonstrate that PGE2 regulates metabolism of hepatocytes mainly through EP4 receptor.

Theoretical model and characteristics of mitochondrial thermogenesis.

Based on the first law of thermodynamics and the thermal diffusion equation, the deduced theoretical model of mitochondrial thermogenesis satisfies the Laplace equation and is a special case of the thermal diffusion equation. The model settles the long-standing question of the ability to increase cellular temperature by endogenous thermogenesis and explains the thermogenic characteristics of brown adipocytes. The model and calculations also suggest that the number of free available protons is the major limiting factor for endogenous thermogenesis and its speed.

Dye-based mito-thermometry and its application in thermogenesis of brown adipocytes.

Mitochondrion is the main intracellular site for thermogenesis and attractive energy expenditure targeting for obesity therapy. Here, we develop a method of mitochondrial thermometry based on Rhodamine B methyl ester, which equilibrates as a thermosensitive mixture of nonfluorescent and fluorescent resonance forms. Using this approach, we are able to demonstrate that the efficacy of norepinephrine-induced thermogenesis is low, and measure the maximum transient rate of temperature increase in brown adipocytes. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s41048-017-0039-6) contains supplementary material, which is available to authorized users.

Sympathetic transmitters control thermogenic efficacy of brown adipocytes by modulating mitochondrial complex V.

Obesity is a worldwide epidemic and results from excessive energy intake or inefficient energy expenditure. It is promising to utilize the thermogenic function of brown adipose tissue for obesity intervention. However, the mechanisms controlling the efficacy of norepinephrine-induced thermogenesis in brown adipocytes remain elusive. Here we demonstrate that norepinephrine (NE) induces low-efficacy thermogenesis, evoking both heterogeneous changes (ΔΨm and ΔpH) and homogenous responses, one of which is that NE stimulation causes large amounts of ATP consumption in brown adipocytes. We reveal that the proton-ATPase activity of mitochondrial complex V is a key factor that antagonizes proton leakage by UCP1 and determines the efficacy of NE-induced thermogenesis in brown adipocytes. Furthermore, to avoid unnecessary and undesired heat production, we reveal that ATP is a necessary sympathetic cotransmitter for the high efficacy and specificity of NE-induced thermogenesis in brown adipocytes as it increases intracellular calcium concentrations and upregulates the ATP synthase activity of complex V. Thus, we demonstrate the modulation mechanism of thermogenic efficacy in brown adipocytes. These findings imply new strategies to partially or fully utilize the thermogenic capacity of brown adipocytes to identify therapeutic targets for the treatment of obesity and diabetes.

Cellular model of neuronal atrophy induced by DYNC1I1 deficiency reveals protective roles of RAS-RAF-MEK signaling.

Neuronal atrophy is a common pathological feature occurred in aging and neurodegenerative diseases. A variety of abnormalities including motor protein malfunction and mitochondrial dysfunction contribute to the loss of neuronal architecture; however, less is known about the intracellular signaling pathways that can protect against or delay this pathogenic process. Here, we show that the DYNC1I1 deficiency, a neuron-specific dynein intermediate chain, causes neuronal atrophy in primary hippocampal neurons. With this cellular model, we are able to find that activation of RAS-RAF-MEK signaling protects against neuronal atrophy induced by DYNC1I1 deficiency, which relies on MEK-dependent autophagy in neuron. Moreover, we further reveal that BRAF also protects against neuronal atrophy induced by mitochondrial impairment. These findings demonstrate protective roles of the RAS-RAF-MEK axis against neuronal atrophy, and imply a new therapeutic target for clinical intervention.

Glycine site of NMDA receptor serves as a spatiotemporal detector of synaptic activity patterns.

Calcium influx associated with the opening of N-methyl-D-aspartate (NMDA) receptor channels is the major signal triggering synaptic and developmental plasticity. Controlling the NMDA receptor function is therefore critical for many functions of the brain. We explored the mechanisms of synaptic activation of the NMDAR glycine site by endogenous coagonist using whole cell voltage-clamp recordings from hippocampal neurons in mixed cultures, containing both neurons and glial cells, and, under more physiological conditions, in hippocampal slices. Here we show that the glycine site of the NMDA receptor at hippocampal synapses, both in culture and acute brain slices, is not saturated by the ambient coagonist concentration and is modulated through activity-dependent coagonist release. Augmentation of the NMDA receptor-mediated synaptic responses by local glutamate-induced coagonist release is spatially restricted and determined by spatiotemporal summation of synaptic events at neighboring synaptic inputs on a single dendritic branch. Therefore different spatiotemporal patterns of presynaptic activity could be translated into different levels of the NMDAR activation in specific afferent projections. These results suggest that the NMDA receptor glycine site may serve as a detector of the spatiotemporal characteristics of presynaptic activity patterns.

Docking of axonal mitochondria by syntaphilin controls their mobility and affects short-term facilitation.

Proper distribution of mitochondria within axons and at synapses is critical for neuronal function. While one-third of axonal mitochondria are mobile, a large proportion remains in a stationary phase. However, the mechanisms controlling mitochondrial docking within axons remain elusive. Here, we report a role for axon-targeted syntaphilin (SNPH) in mitochondrial docking through its interaction with microtubules. Axonal mitochondria that contain exogenously or endogenously expressed SNPH lose mobility. Deletion of the mouse snph gene results in a substantially higher proportion of axonal mitochondria in the mobile state and reduces the density of mitochondria in axons. The snph mutant neurons exhibit enhanced short-term facilitation during prolonged stimulation, probably by affecting calcium signaling at presynaptic boutons. This phenotype is fully rescued by reintroducing the snph gene into the mutant neurons. These findings demonstrate a molecular mechanism for controlling mitochondrial docking in axons that has a physiological impact on synaptic function.

Cloning and Distribution of rRP58, A Novel Neuronal Gene.

EST (AW055733) is a 3'-cDNA fragment specially expressed in rat brain. It is homologous to human and mouse RP58 gene, which is a transcriptional repressor gene. Primers were designed based on these two genes, and then two transcripts of rRP58 gene were got from male SD rat using RT-PCR method. The rRP58 protein is a C(2)H(2) type zinc finger protein, containing POZ domain at N-terminal and zinc finger domain (ZFD) at C-terminal. In addition, there is a highly acidic region between POZ and ZFD. POZ and ZFD were cloned, expressed and purified. Then, the antibodies to POZ and ZFD were prepared, and used to analyze distribution of alternative transcripts of rRP58.