Effects of a Combination of Polynucleotide and Hyaluronic Acid for Treating Osteoarthritis.

Knee osteoarthritis (OA), an age-related degenerative disease characterized by severe pain and disability, is treated using polynucleotides (PNs) and hyaluronic acid (HA). The intra-articular (IA) injection of HA has been studied extensively in both animal models and in humans; however, the efficacy and mechanisms of action remain unclear. In addition, there has been a paucity of research regarding the use of PN alone or in combination with HA in OA. To investigate the effect of the combined injection of PN and HA in vivo, pathological and behavioral changes were assessed in an OA model. Anterior cruciate ligament transection and medial meniscectomy were performed in Sprague-Dawley rats to create the OA animal model. The locomotor activity improved following PNHA injection, while the OARSI grade improved in the medial tibia and femur. In mild OA, TNFα levels decreased histologically in the PN, HA, and PNHA groups but only the PNHA group showed behavioral improvement in terms of distance. In conclusion, PNHA exhibited anti-inflammatory effects during OA progression and improved locomotor activity regardless of the OARSI grade.

Crif1 deficiency in dopamine neurons triggers early-onset parkinsonism.

Mitochondrial dysfunction has been implicated in Parkinson's Disease (PD) progression; however, the mitochondrial factors underlying the development of PD symptoms remain unclear. One candidate is CR6-interacting factor1 (CRIF1), which controls translation and membrane insertion of 13 mitochondrial proteins involved in oxidative phosphorylation. Here, we found that CRIF1 mRNA and protein expression were significantly reduced in postmortem brains of elderly PD patients compared to normal controls. To evaluate the effect of Crif1 deficiency, we produced mice lacking the Crif1 gene in dopaminergic neurons (DAT-CRIF1-KO mice). From 5 weeks of age, DAT-CRIF1-KO mice began to show decreased dopamine production with progressive neuronal degeneration in the nigral area. At ~10 weeks of age, they developed PD-like behavioral deficits, including gait abnormalities, rigidity, and resting tremor. L-DOPA, a medication used to treat PD, ameliorated these defects at an early stage, although it was ineffective in older mice. Taken together, the observation that CRIF1 expression is reduced in human PD brains and deletion of CRIF1 in dopaminergic neurons leads to early-onset PD with stepwise PD progression support the conclusion that CRIF1-mediated mitochondrial function is important for the survival of dopaminergic neurons.

General anesthesia activates the mitochondrial unfolded protein response and induces age-dependent, long-lasting changes in mitochondrial function in the developing brain.

General anesthesia induces changes in dendritic spine number and synaptic transmission in developing mice. These changes are rather disturbing, as similar changes are seen in animal models of neurodevelopmental disorders. We previously suggested that mTor-dependent upregulation of mitochondrial function may be involved in such changes. To further understand the significance of mitochondrial changes after general anesthesia during neurodevelopment, we exposed young mice to 2.5 % sevoflurane for 2 h followed by injection of rotenone, a mitochondrial complex I inhibitor. In postnatal day 17 (PND17) mice, intraperitoneal injection of rotenone not only blocked sevoflurane-induced increases in mitochondrial function, it also prevented sevoflurane-induced changes in excitatory synaptic transmission. Interestingly, similar changes were not observed in younger, neonatal mice (PND7). We next assessed whether the mitochondrial unfolded protein response (UPRmt) acted as a link between anesthetic exposure and mitochondrial function. Expression of UPRmt proteins, which help maintain protein-folding homeostasis and increase mitochondrial function, was increased 6 h after sevoflurane exposure. Our results show that a single, brief sevoflurane exposure induces age-dependent changes in mitochondrial function that constitute an important mechanism for the increase in excitatory synaptic transmission in late postnatal mice, and also suggest mitochondria and UPRmt as potential targets for preventing anesthesia toxicity.

Schisandra Extract and Ascorbic Acid Synergistically Enhance Cognition in Mice Through Modulation of Mitochondrial Respiration.

Cognitive decline is observed in aging and neurodegenerative diseases, including Alzheimer's disease (AD) and dementia. Intracellular energy produced via mitochondrial respiration is used in the regulation of synaptic plasticity and structure, including dendritic spine length and density, as well as for the release of neurotrophic factors involved in learning and memory. To date, a few synthetic agents for improving mitochondrial function have been developed for overcoming cognitive impairment. However, no natural compounds that modulate synaptic plasticity by directly targeting mitochondria have been developed. Here, we demonstrate that a mixture of Schisandra chinensis extract (SCE) and ascorbic acid (AA) improved cognitive function and induced synaptic plasticity-regulating proteins by enhancing mitochondrial respiration. Treatment of embryonic mouse hippocampal mHippoE-14 cells with a 4:1 mixture of SCE and AA increased basal oxygen consumption rate. We found that mice injected with the SCE-AA mixture showed enhanced learning and memory and recognition ability. We further observed that injection of the SCE-AA mixture in mice significantly increased expression of postsynaptic density protein 95 (PSD95), an increase that was correlated with enhanced brain-derived neurotrophic factor (BDNF) expression. These results demonstrate that a mixture of SCE and AA improves mitochondrial function and memory, suggesting that this natural compound mixture could be used to alleviate AD and aging-associated memory decline.

The mTOR Inhibitor Rapamycin Prevents General Anesthesia-Induced Changes in Synaptic Transmission and Mitochondrial Respiration in Late Postnatal Mice.

Preclinical animal studies have continuously reported the possibility of long-lasting neurotoxic effects after general anesthesia in young animals. Such studies also show that the neurological changes induced by anesthesia in young animals differ by their neurodevelopmental stage. Exposure to anesthetic agents increase dendritic spines and induce sex-dependent changes of excitatory/inhibitory synaptic transmission in late postnatal mice, a critical synaptogenic period. However, the mechanisms underlying these changes remain unclear. Abnormal activation of the mammalian target of rapamycin (mTOR) signaling pathway, an important regulator of neurodevelopment, has also been shown to induce similar changes during neurodevelopment. Interestingly, previous studies show that exposure to general anesthetics during neurodevelopment can activate the mTOR signaling pathway. This study, therefore, evaluated the role of mTOR signaling after exposing postnatal day (PND) 16/17 mice to sevoflurane, a widely used inhalation agent in pediatric patients. We first confirmed that a 2-h exposure of 2.5% sevoflurane could induce widespread mTOR phosphorylation in both male and female mice. Pretreatment with the mTOR inhibitor rapamycin not only prevented anesthesia-induced mTOR phosphorylation, but also the increase in mitochondrial respiration and male-dependent enhancement of excitatory synaptic transmission. However, the changes in inhibitory synaptic transmission that appear after anesthesia in female mice were not affected by rapamycin pretreatment. Our results suggest that mTOR inhibitors may act as potential therapeutic agents for anesthesia-induced changes in the developing brain.

An adipocyte-specific defect in oxidative phosphorylation increases systemic energy expenditure and protects against diet-induced obesity in mouse models.

AIMS/HYPOTHESIS: Mitochondrial oxidative phosphorylation (OxPhos) is essential for energy production and survival. However, the tissue-specific and systemic metabolic effects of OxPhos function in adipocytes remain incompletely understood. METHODS: We used adipocyte-specific Crif1 (also known as Gadd45gip1) knockout (AdKO) mice with decreased adipocyte OxPhos function. AdKO mice fed a normal chow or high-fat diet were evaluated for glucose homeostasis, weight gain and energy expenditure (EE). RNA sequencing of adipose tissues was used to identify the key mitokines affected in AdKO mice, which included fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15). For in vitro analysis, doxycycline was used to pharmacologically decrease OxPhos in 3T3L1 adipocytes. To identify the effects of GDF15 and FGF21 on the metabolic phenotype of AdKO mice, we generated AdKO mice with global Gdf15 knockout (AdGKO) or global Fgf21 knockout (AdFKO). RESULTS: Under high-fat diet conditions, AdKO mice were resistant to weight gain and exhibited higher EE and improved glucose tolerance. In vitro pharmacological and in vivo genetic inhibition of OxPhos in adipocytes significantly upregulated mitochondrial unfolded protein response-related genes and secretion of mitokines such as GDF15 and FGF21. We evaluated the metabolic phenotypes of AdGKO and AdFKO mice, revealing that GDF15 and FGF21 differentially regulated energy homeostasis in AdKO mice. Both mitokines had beneficial effects on obesity and insulin resistance in the context of decreased adipocyte OxPhos, but only GDF15 regulated EE in AdKO mice. CONCLUSIONS/INTERPRETATION: The present study demonstrated that the adipose tissue adaptive mitochondrial stress response affected systemic energy homeostasis via cell-autonomous and non-cell-autonomous pathways. We identified novel roles for adipose OxPhos and adipo-mitokines in the regulation of systemic glucose homeostasis and EE, which facilitated adaptation of an organism to local mitochondrial stress.

Endothelial-specific Crif1 deletion induces BBB maturation and disruption via the alteration of actin dynamics by impaired mitochondrial respiration.

Cerebral endothelial cells (ECs) require junctional proteins to maintain blood-brain barrier (BBB) integrity, restricting toxic substances and controlling peripheral immune cells with a higher concentration of mitochondria than ECs of peripheral capillaries. The mechanism underlying BBB disruption by defective mitochondrial oxidative phosphorylation (OxPhos) is unclear in a mitochondria-related gene-targeted animal model. To assess the role of EC mitochondrial OxPhos function in the maintenance of the BBB, we developed an EC-specific CR6-interactin factor1 (Crif1) deletion mouse. We clearly observed defects in motor behavior, uncompacted myelin and leukocyte infiltration caused by BBB maturation and disruption in this mice. Furthermore, we investigated the alteration in the actin cytoskeleton, which interacts with junctional proteins to support BBB integrity. Loss of Crif1 led to reorganization of the actin cytoskeleton and a decrease in tight junction-associated protein expression through an ATP production defect in vitro and in vivo. Based on these results, we suggest that mitochondrial OxPhos is important for the maturation and maintenance of BBB integrity by supplying ATP to cerebral ECs.

Chloramphenicol Mitigates Oxidative Stress by Inhibiting Translation of Mitochondrial Complex I in Dopaminergic Neurons of Toxin-Induced Parkinson's Disease Model.

Paraquat (PQ), an herbicide considered an environmental contributor to the development of Parkinson's disease (PD), induces dopaminergic neuronal loss through reactive oxygen species (ROS) production and oxidative stress by mitochondrial complex I. Most patients with PQ-induced PD are affected by chronic exposure and require a preventive strategy for modulation of disease progression. To identify drugs that are effective in preventing PD, we screened more than 1000 drugs that are currently used in clinics and in studies employing PQ-treated cells. Of these, chloramphenicol (CP) showed the most powerful inhibitory effect. Pretreatment with CP increased the viability of PQ-treated SN4741 dopaminergic neuronal cells and rat primary cultured dopaminergic neurons compared with control cells treated with PQ only. CP pretreatment also reduced PQ-induced ROS production, implying that mitochondrial complex I is a target of CP. This effect of CP reflected downregulation of the mitochondrial complex I subunit ND1 and diminished PQ recycling, a major mechanism of ROS production, and resulted in the prevention of cell loss. Notably, these effects of CP were not observed in rotenone-pretreated SN4741 cells and Rho-negative cells, in which mitochondrial function is defective. Consistent with these results, CP pretreatment of MPTP-treated PD model mice also ameliorated dopaminergic neuronal cell loss. Our findings indicate that the inhibition of mitochondrial complex I with CP protects dopaminergic neurons and may provide a strategy for preventing neurotoxin-induced PD.

Synergistic Neuroprotective Effect of Schisandra chinensis and Ribes fasciculatum on Neuronal Cell Death and Scopolamine-Induced Cognitive Impairment in Rats.

Mild cognitive impairment (MCI) is considered as a transitional stage between aging and Alzheimer's disease. In the present study, we examined the protective effect of Schisandra chinensis (SC) and Ribes fasciculatum (RF) on neuronal cell death in vitro and scopolamine-induced cognitive impairment in Sprague Dawley® rats in vivo. A mixture of SC and RF extracts (SC+RF) significantly protected against hydrogen peroxide-induced PC12 neuronal cell death. The neuroprotective effect of SC+RF on scopolamine-induced memory impairment in rats was evaluated using the passive avoidance test and the Morris water maze test. In the passive avoidance test, SC+RF-treated rats showed an increased latency to escape, compared to the scopolamine-treated rats. Moreover, SC+RF treatment significantly reduced escape latency in water maze test, compared to treatment with scopolamine alone. To verify the long-term memory, we performed probe test of water maze test. As a result, rat treated with SC+RF spent more time in the target quadrant. Consistent with enhancement of memory function, the brain derived neurotrophic factor (BDNF) and its downstream molecules (pERK, pATK, and pCREB) are increased in SC+RF treatment in hippocampal area compared with scopolamine treated group. These results suggest that a mixture of SC and RF extracts may be a good therapeutic candidate for preventing mild cognitive impairment.

PTEN/AKT signaling mediates chemoresistance in refractory acute myeloid leukemia through enhanced glycolysis.

Primary refractory acute myeloid leukemia (AML) and early recurrence of leukemic cells are among the most difficult hurdles to overcome in the treatment of AML. Moreover, uncertainties surrounding the molecular mechanism underlying refractory AML pose a challenge when it comes to developing novel therapeutic drugs. However, accumulating evidence suggests a contribution of phosphatase and tensin homolog (PTEN)/protein kinase B (AKT) signaling to the development of refractory AML. To assess PTEN/AKT signaling in AML, two types of AML cell lines were evaluated, namely control HL60 cells and KG1α cells, a refractory AML cell line that is resistant to idarubicin and cytarabine (AraC) treatment. Changes in the expression level of glycolysis­ and mitochondrial oxidative phosphorylation­related genes and proteins were evaluated by reverse transcription­quantitative polymerase chain reaction and western blot analyses, respectively. The mitochondrial oxygen consumption and extracellular acidification rates were measured using an XF24 analyzer. CCK8 assay and Annexin V/PI staining were used to analyze cell viability and cellular apoptosis, respectively. The PTEN protein was found to be depleted, whereas AKT phosphorylation levels were elevated in KG1α cells compared with HL60 cells. These changes were associated with increased expression of glucose transporter 1 and hexokinase 2, and increased lactate production. AKT inhibition decreased the proliferation of KG1α cells and decreased extracellular acidification without affecting HL60 cells. Notably, AKT inhibition increased the susceptibility of KG1α cells to chemotherapy with idarubicin and AraC. Taken together, the findings of the present study indicate that activation of AKT by PTEN deficiency sustains the refractory AML status through enhancement of glycolysis and mitochondrial respiration, effects that may be rescued by inhibiting AKT activity.

Auraptene Mitigates Parkinson's Disease-Like Behavior by Protecting Inhibition of Mitochondrial Respiration and Scavenging Reactive Oxygen Species.

Current therapeutics for Parkinson's disease (PD) are only effective in providing relief of symptoms such as rigidity, tremors and bradykinesia, and do not exert disease-modifying effects by directly modulating mitochondrial function. Here, we investigated auraptene (AUR) as a potent therapeutic reagent that specifically protects neurotoxin-induced reduction of mitochondrial respiration and inhibits reactive oxygen species (ROS) generation. Further, we explored the mechanism and potency of AUR in protecting dopaminergic neurons. Treatment with AUR significantly increased the viability of substantia nigra (SN)-derived SN4741 embryonic dopaminergic neuronal cells and reduced rotenone-induced mitochondrial ROS production. By inducing antioxidant enzymes AUR treatment also increased oxygen consumption rate. These results indicate that AUR exerts a protective effect against rotenone-induced mitochondrial oxidative damage. We further assessed AUR effects in vivo, investigating tyrosine hydroxylase (TH) expression in the striatum and substantia nigra of MPTP-induced PD model mice and behavioral changes after injection of AUR. AUR treatment improved movement, consistent with the observed increase in the number of dopaminergic neurons in the substantia nigra. These results demonstrate that AUR targets dual pathogenic mechanisms, enhancing mitochondrial respiration and attenuating ROS production, suggesting that the preventative potential of this natural compound could lead to improvement in PD-related neurobiological changes.

Non-cell autonomous modulation of tyrosine hydroxylase by HMGB1 released from astrocytes in an acute MPTP-induced Parkinsonian mouse model.

High-mobility group box 1 (HMGB1) is actively secreted from inflammatory cells and acts via a non-cell-autonomous mechanism to play an important role in mediating cell proliferation and migration. The HMGB1-RAGE (receptor for advanced glycation end products) axis upregulates tyrosine hydroxylase (TH) expression in response to extracellular insults in dopaminergic neurons in vitro, but little is known about HMGB1 in modulation of dopaminergic neurons in vivo. Here, using immunohistochemistry, we show that HMGB1 and RAGE expression are higher in the nigral area of MPTP (methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-treated mice, a toxin-induced Parkinsonian mouse model, compared with saline-treated controls. HMGB1 was predominantly localized to astrocytes and may affect neighboring dopaminergic neurons in the MPTP mouse model, owing to co-localization of RAGE in these TH-positive cells. In addition, MPTP induced a decrease in TH expression, an effect that was potentiated by inhibition of c-Jun N-terminal kinase (JNK) or RAGE. Moreover, stereotaxic injection of recombinant HMGB1 attenuated the MPTP-induced reduction of TH in a Parkinsonian mouse model. Collectively, our results suggest that an increase of HMGB1, released from astrocytes, upregulates TH expression in an acute MPTP-induced Parkinsonian mouse model, thereby maintaining dopaminergic neuronal functions.

L­Deprenyl exerts cytotoxicity towards acute myeloid leukemia through inhibition of mitochondrial respiration.

The identification of large numbers of genetic mutations in immature myeloid cells has made it difficult to identify specific targets for acute myeloid leukemia (AML) therapy. Although current pharmacological targets for controlling cancer are focused on identifying genetic mutations, it is hard to develop the specific drugs to achieve complete remission due to complex and variable genetic mutations. To overcome the failure of the genetic mutation theory, the present study targeted mitochondrial metabolism as a strategy for inducing anti­leukemic activity, based on evidence that AML cells have an abnormally high amount of mitochondria and that somatic mutations can alter metabolic flux in cancer. It was found that L­deprenyl, which is clinically available for the treatment of Parkinson's disease, exerts anti­mitochondria activity in KG­1α cells, as assessed by detection of oxygen consumption rate (OCR) and extracellular acidification (ECAR) using XF analyzer, respectively. Using a luciferase assay for detecting adenosine triphosphate (ATP) content, it was found that suppression of mitochondrial activity led to ATP depletion and was associated with potent cytotoxic activity. L­deprenyl is known to target monoamine oxidase­B (MAO­B) on the outer membrane of mitochondria, therefore, the activity of MAO­A and ­B was measured based on the fluorometric detection of H2O2 produced by the enzyme reaction. Notably, MAO­A and -B activity was low in AML cells and the present findings suggested that the anticancer effect of L­deprenyl was independent of MAO­B. Change of mitochondrial respiration­ and glycolysis­related gene expression levels were measured by reverse transcription­quantitative polymerase chain reaction. Consistent with the aforementioned results, treatment with L­deprenyl reduced the mRNA level of mitochondrial respiration­ and glycolysis­related genes. Collectively, the present results identify L­deprenyl as a novel candidate for the treatment of AML through inhibition of mitochondrial respiration.

Rho-kinase/AMPK axis regulates hepatic lipogenesis during overnutrition.

Obesity is a major risk factor for developing nonalcoholic fatty liver disease (NAFLD). NAFLD is the most common form of chronic liver disease and is closely associated with insulin resistance, ultimately leading to cirrhosis and hepatocellular carcinoma. However, knowledge of the intracellular regulators of obesity-linked fatty liver disease remains incomplete. Here we showed that hepatic Rho-kinase 1 (ROCK1) drives obesity-induced steatosis in mice through stimulation of de novo lipogenesis. Mice lacking ROCK1 in the liver were resistant to diet-induced obesity owing to increased energy expenditure and thermogenic gene expression. Constitutive expression of hepatic ROCK1 was sufficient to promote adiposity, insulin resistance, and hepatic lipid accumulation in mice fed a high-fat diet. Correspondingly, liver-specific ROCK1 deletion prevented the development of severe hepatic steatosis and reduced hyperglycemia in obese diabetic (ob/ob) mice. Of pathophysiological significance, hepatic ROCK1 was markedly upregulated in humans with fatty liver disease and correlated with risk factors clustering around NAFLD and insulin resistance. Mechanistically, we found that hepatic ROCK1 suppresses AMPK activity and a ROCK1/AMPK pathway is necessary to mediate cannabinoid-induced lipogenesis in the liver. Furthermore, treatment with metformin, the most widely used antidiabetes drug, reduced hepatic lipid accumulation by inactivating ROCK1, resulting in activation of AMPK downstream signaling. Taken together, our findings establish a ROCK1/AMPK signaling axis that regulates de novo lipogenesis, providing a unique target for treating obesity-related metabolic disorders such as NAFLD.

Activation of the HMGB1-RAGE axis upregulates TH expression in dopaminergic neurons via JNK phosphorylation.

The derangement of tyrosine hydroxylase (TH) activity reduces dopamine synthesis and is implicated in the pathogenesis of Parkinson's disease. However, the extracellular modulator and intracellular regulatory mechanisms of TH have yet to be identified. Recently, high-mobility group box 1 (HMGB1) was reported to be actively secreted from glial cells and is regarded as a mediator of dopaminergic neuronal loss. However, the mechanism for how HMGB1 affects TH expression, particularly through the receptor for advanced glycation endproducts (RAGE), has not yet been investigated. We found that recombinant HMGB1 (rHMGB1) upregulates TH mRNA expression via simultaneous activation of JNK phosphorylation, and this induction of TH expression is blocked by inhibitors of RAGE and JNK. To investigate how TH expression levels change through the HMGB1-RAGE axis as a result of MPP+ toxicity, we co-treated SN4741 dopaminergic cells with MPP+ and rHMGB1. rHMGB1 blocked the reduction of TH mRNA following MPP+ treatment without altering cell survival rates. Our results suggest that HMGB1 upregulates TH expression to maintain dopaminergic neuronal function via activating RAGE, which is dependent on JNK phosphorylation.

Growth Differentiation Factor 15 Mediates Systemic Glucose Regulatory Action of T-Helper Type 2 Cytokines.

T-helper type 2 (Th2) cytokines, including interleukin (IL)-13 and IL-4, produced in adipose tissue, are critical regulators of intra-adipose and systemic lipid and glucose metabolism. Furthermore, IL-13 is a potential therapy for insulin resistance in obese mouse models. Here, we examined mediators produced by adipocytes that are responsible for regulating systemic glucose homeostasis in response to Th2 cytokines. We used RNA sequencing data analysis of cultured adipocytes to screen factors secreted in response to recombinant IL-13. Recombinant IL-13 induced expression of growth differentiation factor 15 (GDF15) via the Janus kinase-activated STAT6 pathway. In vivo administration of α-galactosylceramide or IL-33 increased IL-4 and IL-13 production, thereby increasing GDF15 levels in adipose tissue and in plasma of mice; however, these responses were abrogated in STAT6 knockout mice. Moreover, administration of recombinant IL-13 to wild-type mice fed a high-fat diet (HFD) improved glucose intolerance; this was not the case for GDF15 knockout mice fed the HFD. Taken together, these data suggest that GDF15 is required for IL-13-induced improvement of glucose intolerance in mice fed an HFD. Thus, beneficial effects of Th2 cytokines on systemic glucose metabolism and insulin sensitivity are mediated by GDF15. These findings open up a potential pharmacological route for reversing insulin resistance associated with obesity.

A High-fat Diet Induces a Loss of Midbrain Dopaminergic Neuronal Function That Underlies Motor Abnormalities.

Movement defects in obesity are associated with peripheral muscle defects, arthritis, and dysfunction of motor control by the brain. Although movement functionality is negatively correlated with obesity, the brain regions and downstream signaling pathways associated with movement defects in obesity are unclear. A dopaminergic neuronal pathway from the substantia nigra (SN) to the striatum is responsible for regulating grip strength and motor initiation through tyrosine hydroxylase (TH) activity-dependent dopamine release. We found that mice fed a high-fat diet exhibited decreased movement in open-field tests and an increase in missteps in a vertical grid test compared with normally fed mice. This motor abnormality was associated with a significant reduction of TH in the SN and striatum. We further found that phosphorylation of c-Jun N-terminal kinase (JNK), which modulates TH expression in the SN and striatum, was decreased under excess-energy conditions. Our findings suggest that high calorie intake impairs motor function through JNK-dependent dysregulation of TH in the SN and striatum.

ANGPTL6 expression is coupled with mitochondrial OXPHOS function to regulate adipose FGF21.

Recent studies revealed that the inhibition of mitochondrial oxidative phosphorylation (OXPHOS) is coupled with the mitochondrial unfolded protein response, thereby stimulating the secretion of non-cell autonomous factors, which may control systemic energy metabolism and longevity. However, the nature and roles of non-cell autonomous factors induced in adipose tissue in response to reduced OXPHOS function remain to be clarified in mammals. CR6-interacting factor 1 (CRIF1) is an essential mitoribosomal protein for the intramitochondrial production of mtDNA-encoded OXPHOS subunits. Deficiency of CRIF1 impairs the proper formation of the OXPHOS complex, resulting in reduced function. To determine which secretory factors are induced in response to reduced mitochondrial OXPHOS function, we analyzed gene expression datasets in Crif1-depleted mouse embryonic fibroblasts. Crif1 deficiency preferentially increased the expression of angiopoietin-like 6 (Angptl6) and did not affect other members of the ANGPTL family. Moreover, treatment with mitochondrial OXPHOS inhibitors increased the expression of Angptl6 in cultured adipocytes. To confirm Angptl6 induction in vivo, we generated a murine model of reduced mitochondrial OXPHOS function using adipose tissue-specific Crif1-deficient mice and verified the upregulation of Angptl6 and fibroblast growth factor 21 (Fgf21) in white adipose tissue. Treatment with recombinant ANGPTL6 protein increased oxygen consumption and Pparα expression through the extracellular signal-regulated kinase/mitogen-activated protein kinase pathway in cultured adipocytes. Furthermore, the ANGPTL6-mediated increase in Pparα expression resulted in increased FGF21 expression, thereby promoting ß-oxidation. In conclusion, mitochondrial OXPHOS function governs the expression of ANGPTL6, which is an essential factor for FGF21 production in adipose tissue and cultured adipocytes.

CR6-Interacting Factor 1 Deficiency Impairs Vascular Function by Inhibiting the Sirt1-Endothelial Nitric Oxide Synthase Pathway.

AIMS: Mitochondrial dysfunction has emerged as a major contributing factor to endothelial dysfunction and vascular disease, but the key mechanisms underlying mitochondrial dysfunction-induced endothelial dysfunction remain to be elucidated. In this study, we aim at determining whether mitochondrial dysfunction in endothelial cells plays a key role in vascular disease, by examining the phenotype of endothelial-specific CR6-interacting factor 1 (CRIF1) knockout mice. We also used siRNA-mediated downregulation of CRIF1 gene in the endothelial cells to study about the in vitro pathophysiological underlying mechanisms. RESULTS: Downregulation of CRIF1 in endothelial cells caused disturbances of mitochondrial oxidative phosphorylation complexes and membrane potential, leading to enhanced mitochondrial reactive oxygen species production. Gene silencing of CRIF1 results in decreased SIRT1 expression along with increased endothelial nitric oxide synthase (eNOS) acetylation, leading to reduced nitric oxide production both in vitro and in vivo. Endothelium-dependent vasorelaxation of aortic rings from CRIF1 knockout (KO) mice was considerably less than in wild-type mice, and it was partially recovered by Sirt1 overexpression in CRIF1 KO mice. INNOVATION: Our results show for the first time a relationship between mitochondrial dysfunction and impaired vascular function induced in CRIF1 deficiency conditions and also the possible underlying pathway involved. CONCLUSION: These findings indicate that CRIF1 plays an important role in maintaining mitochondrial and endothelial function through its effects on the SIRT1-eNOS pathway. Antioxid. Redox Signal. 27, 234-249.