Mutation of mitochondrial ATP8 gene improves hepatic energy status in a murine model of acute endotoxemic liver failure

Effect of Pseudostellaria heterophylla polysaccharide on the growth and liver metabolism of chicks

In this study, the effects of Pseudostellaria heterophylla polysaccharide (PHP) on the growth, development, and liver metabolism of chicks were investigated by feeding chicks diets. Four hundred 7-d-old Gushi roosters were selected and randomly divided into four groups, labeled A, B, C, and D. Group A was fed the basal diet, and Groups B, C, and D were fed 100, 200, and 400 mg PHP per kilogram of basal diet, respectively. At 14, 21, 28 and 35 d of age, five chicks were randomly selected from each group to collect samples for index detection. The results showed that compared with Group A, there were significant reduction in average daily feed intake (ADFI) and feed-to-weight ratio (F/G) at 14, 21, and 28 d (P < 0.05), significant increase in average daily gain (ADG) at 21, 28 d (P < 0.05), significantly increased levels of total protein (TP), albumin (ALB), insulin (INS), thyroxine (T3), growth hormone (GH) at 14, 28 d (P < 0.05), significantly decreased levels of glucose (GLU), total cholesterol (TC), glucagon (GC), and triglyceride (TG) at 28 d in Group C (P < 0.05). There were significantly increased levels of TP, ALB at 14, 21 d (P < 0.05), significantly increased level of TP at 35 d (P < 0.05), significantly increased level of GH at 28 d (P < 0.05), significantly decreased levels of GLU, GC at 28 d (P < 0.05), significant reduction in F/G at 14, 21 d in Groups B and D (P < 0.05). Based on the above results, the livers from chicks in Groups A and C at 28 d were selected for transcriptome sequencing. The sequencing results showed that significantly differentially expressed genes (SDEGs) were enriched in growth and development, oxidative phosphorylation, the PPAR signaling pathway and the lipid metabolism pathway. All these results revealed that the addition of 200 mg/kg PHP in the diet promoted the growth and development, lipid metabolism and energy metabolism of chicks, inhibit inflammation and tumor development, and improve the function of the liver.

Mitochondrial genome variations, mitochondrial-nuclear compatibility, and their association with metabolic diseases

Two genomes regulate the energy metabolism of eukaryotic cells: the nuclear genome, which codes for most cellular proteins, and the mitochondrial genome, which, together with the nuclear genome, coregulates cellular bioenergetics. Therefore, mitochondrial genome variations can affect, directly or indirectly, all energy-dependent cellular processes and shape the metabolic state of the organism. This review provides a current and up-to-date overview on how codependent these two genomes are, how they appear to have coevolved, and how variations within the mitochondrial genome might be associated with the manifestation of metabolic diseases. This review summarizes and structures results obtained from epidemiological studies that identified links between mitochondrial haplogroups and individual risks for developing obesity and diabetes. This is complemented by findings on the compatibility of mitochondrial and nuclear genomes and cellular bioenergetic fitness, which have been acquired from well-controlled studies in conplastic animal models. These elucidate, more mechanistically, how single-nucleotide variants can influence cellular metabolism and physiology. Overall, it seems that certain mitochondrial genome variations negatively affect mitochondrial-nuclear compatibility and are statistically linked with the onset of metabolic diseases, whereas, for others, greater uncertainty exists, and additional research into this exciting field is required.

The role of mitochondrial ATP synthase in cancer

The mitochondrial ATP synthase is a multi-subunit enzyme complex located in the inner mitochondrial membrane which is essential for oxidative phosphorylation under physiological conditions. In this review, we analyse the enzyme functions involved in cancer progression by dissecting specific conditions in which ATP synthase contributes to cancer development or metastasis. Moreover, we propose the role of ATP synthase in the formation of the permeability transition pore (PTP) as an additional mechanism which controls tumour cell death. We further describe transcriptional and translational modifications of the enzyme subunits and of the inhibitor protein IF1 that may promote adaptations leading to cancer metabolism. Finally, we outline ATP synthase gene mutations and epigenetic modifications associated with cancer development or drug resistance, with the aim of highlighting this enzyme complex as a potential novel target for future anti-cancer therapy.

Codon optimization is an essential parameter for the efficient allotopic expression of mtDNA genes

Mutations in mitochondrial DNA can be inherited or occur de novo leading to several debilitating myopathies with no curative option and few or no effective treatments. Allotopic expression of recoded mitochondrial genes from the nucleus has potential as a gene therapy strategy for such conditions, however progress in this field has been hampered by technical challenges. Here we employed codon optimization as a tool to re-engineer the protein-coding genes of the human mitochondrial genome for robust, efficient expression from the nucleus. All 13 codon-optimized constructs exhibited substantially higher protein expression than minimally-recoded genes when expressed transiently, and steady-state mRNA levels for optimized gene constructs were 5-180 fold enriched over recoded versions in stably-selected wildtype cells. Eight of thirteen mitochondria-encoded oxidative phosphorylation (OxPhos) proteins maintained protein expression following stable selection, with mitochondrial localization of expression products. We also assessed the utility of this strategy in rescuing mitochondrial disease cell models and found the rescue capacity of allotopic expression constructs to be gene specific. Allotopic expression of codon optimized ATP8 in disease models could restore protein levels and respiratory function, however, rescue of the pathogenic phenotype for another gene, ND1 was only partially successful. These results imply that though codon-optimization alone is not sufficient for functional allotopic expression of most mitochondrial genes, it is an essential consideration in their design.

The potential mechanism of mitochondrial dysfunction in septic cardiomyopathy

Septic cardiomyopathy is one of the most serious complications of sepsis or septic shock. Basic and clinical research has studied the mechanism of cardiac dysfunction for more than five decades. It has become clear that myocardial depression is not related to hypoperfusion. As the heart is highly dependent on abundant adenosine triphosphate (ATP) levels to maintain its contraction and diastolic function, impaired mitochondrial function is lethally detrimental to the heart. Research has shown that mitochondria play an important role in organ damage during sepsis. The mitochondria-related mechanisms in septic cardiomyopathy have been discussed in terms of restoring mitochondrial function. Mitochondrial uncoupling proteins located in the mitochondrial inner membrane can promote proton leakage across the mitochondrial inner membrane. Recent studies have demonstrated that proton leakage is the essential regulator of mitochondrial membrane potential and the generation of reactive oxygen species (ROS) and ATP. Other mechanisms involved in septic cardiomyopathy include mitochondrial ROS production and oxidative stress, mitochondria Ca²⁺ handling, mitochondrial DNA in sepsis, mitochondrial fission and fusion, mitochondrial biogenesis, mitochondrial gene regulation and mitochondria autophagy. This review will provide an overview of recent insights into the factors contributing to septic cardiomyopathy.

Genetic diversity of ATP8 and ATP6 genes is associated with high-altitude adaptation in yak

ATP synthase 8 (ATP8) and ATPase synthase 6 (ATP6) play an important role in mitochondrial ATPase assembly. Mutations in either of these units could affect the ATP processing and the respiration chain in mitochondria. To find out if there were differences in gene diversity between Tibetan yaks and domestic cattle, we sequenced the ATP8 and ATP6 genes in 66 Tibetan yaks and 81 domestic cattle. We identified 20 SNPs in the ATP8 gene and 60 SNPs in the ATP6 gene. Ten SNPs detected in ATP8 were probably positively associated with high-altitude adaptation, of which SNPs m.8164 G > A, m.8210 G > A, m.8231 C > T and m. 8249 C > T resulted in amino acid changes. Similarly, SNPs m.8308A > G, m.8370A > C, m.8514G > A of ATP6 also appeared to be associated with high-altitude adaptability. Specifically, m.8308 A > G, located in the overlap region, might bring in a conserved region found in cytochrome b561 which play an important role in iron regulation, thus it might help the Tibetan yaks with this mutation to utilize rare oxygen efficiently. Considering all mutations, three of eight haplotypes identified in gene ATP8 were present only in Tibetan yaks, and six (H3 to H8) out of 21 haplotypes (H1 to H21) in gene ATP6 were restricted to Tibetan yaks. Haplotypes present only in Tibetan yaks could be positively associated with high-altitude adaptation.

Anti-apoptotic therapeutic approaches in liver diseases: do they really make sense?

A variety of data suggesting apoptotic cell death as a key feature of liver injury stimulated researchers to investigate the therapeutic potential of anti-apoptotic strategies in experimental models. However, the overestimated role of apoptotic cell death in liver injury has tempered the clinical translation of the protection afforded by anti-apoptotic regimes in experimental models. Thus, the hope for apoptosis modulation as potential treatment strategy for injured liver in humans could not be confirmed. Herein, we evaluated the degree of apoptosis in different hepatic stress models which are relevant for the human pathophysiology. Using morphological criteria of apoptosis, caspase-3 activation as well as TUNEL assay in combination with a positive control of apoptosis in liver injury, we quantified apoptotic cell death discriminating between parenchymal and non-parenchymal cells and confirmed these results by cleaved caspase-3 and PARP-1 protein expression. Discussing our findings and relating them to the existing literature on the potential role of apoptotic cell death, we strongly recommend reconsidering anti-apoptotic strategies to ameliorate liver injury efficiently.

The mtDNA nt7778 G/T polymorphism augments formation of lymphocytic foci but does not aggravate cerulein-induced acute pancreatitis in mice

A polymorphism in the ATP synthase 8 (ATP8) gene of the murine mitochondrial genome, G-to-T transversion at position 7778, has been suggested to increase susceptibility to multiple autoimmune diseases, including autoimmune pancreatitis (AIP). The polymorphism also induces mitochondrial reactive oxygen species generation, secretory dysfunction and β-cell mass adaptation. Here, we have used two conplastic mouse strains, C57BL/6N-mtAKR/J (B6-mtAKR; nt7778 G; control) and C57BL/6N-mtFVB/N (B6-mtFVB; nt7778 T), to address the question if the polymorphism also affects the course of cerulein-induced acute pancreatitis in mice. Therefore, two age groups of mice (3 and 12-month-old, respectively) were subjected to up to 7 injections of the secretagogue cerulein (50 µg/kg body weight) at hourly intervals. Disease severity was assessed at time points from 3 hours to 7 days based on pancreatic histopathology, serum levels of α-amylase and activities of myeloperoxidase (MPO) in lung tissue. A comparison of cerulein-induced pancreatic tissue damage and increases of α-amylase and MPO activities showed no differences between the age-matched groups of both strains. Interestingly, histological evaluation of pancreatic tissue of both untreated and cerulein-treated B6-mtAKR and B6-mtFVB mice also revealed the presence of infiltrates of immune cells surrounding ducts and vessels; a finding that is compatible with an early stage of AIP. After recovery from cerulein-induced pancreatitis (day 7 after the injections), 12-month-old B6-mtFVB mice but not B6-mtAKR mice displayed aggravated lymphocytic lesions. A comparison of 12-month-old mice with other age groups of both strains revealed that lymphocytic foci were largely absent in 3-month-old mice, while 24-month-old mice were more affected. Together, our data suggest that the mtDNA nt7778 G/T polymorphism does not aggravate cerulein-induced acute pancreatitis. Autoimmune-like lesions, however, may progress faster if additional tissue damage occurs.

Late recognition and illness severity are determinants of early death in severe septic patients

OBJECTIVE

To identify the independent variables associated with death within 4 days after the first sepsis-induced organ dysfunction.

METHODS

In this prospective observational study, severe sepsis and septic shock patients were classified into 3 groups: Group 1, survivors; Group 2, late non-survivors; and Group 3, early non-survivors. Early death was defined as death occurring within 4 days after the first sepsis-induced organ dysfunction. Demographic, clinical and laboratory data were collected and submitted to univariate and multinomial analyses.

RESULTS

The study included 414 patients: 218 (52.7%) in Group 1, 165 (39.8%) in Group 2, and 31 (7.5%) in Group 3. A multinomial logistic regression analysis showed that age, Acute Physiology and Chronic Health Evaluation II score, Sepsis-related Organ Failure Assessment score after the first 24 hours, nosocomial infection, hepatic dysfunction, and the time elapsed between the onset of organ dysfunction and the sepsis diagnosis were associated with early mortality. In contrast, Black race and a source of infection other than the urinary tract were associated with late death. Among the non-survivors, early death was associated with Acute Physiology and Chronic Health Evaluation II score, chronic renal failure, hepatic dysfunction Sepsis-related Organ Failure Assessment score after 24 hours, and the duration of organ dysfunction.

CONCLUSION

Factors related to patients' intrinsic characteristics and disease severity as well as the promptness of sepsis recognition are associated with early death among severe septic patients.