Yunhua Peng

Hydroxytyrosol improves mitochondrial function and reduces oxidative stress in the brain of db/db mice: role of AMP-activated protein kinase activation.

Hydroxytyrosol (HT) is a major polyphenolic compound found in olive oil with reported anti-cancer and anti-inflammatory activities. However, the neuroprotective effect of HT on type 2 diabetes remains unknown. In the present study, db/db mice and SH-SY-5Y neuroblastoma cells were used to evaluate the neuroprotective effects of HT. After 8 weeks of HT administration at doses of 10 and 50 mg/kg, expression levels of the mitochondrial respiratory chain complexes I/II/IV and the activity of complex I were significantly elevated in the brain of db/db mice. Likewise, targets of the antioxidative transcription factor nuclear factor erythroid 2 related factor 2 including p62 (sequestosome-1), haeme oxygenase 1 (HO-1), and superoxide dismutases 1 and 2 increased, and protein oxidation significantly decreased. HT treatment was also found to activate AMP-activated protein kinase (AMPK), sirtuin 1 and PPARγ coactivator-1α, which constitute an energy-sensing protein network known to regulate mitochondrial function and oxidative stress responses. Meanwhile, neuronal survival indicated by neuron marker expression levels including activity-regulated cytoskeleton-associated protein, N-methyl-d-aspartate receptor and nerve growth factor was significantly improved by HT administration. Additionally, in a high glucose-induced neuronal cell damage model, HT effectively increased mitochondrial complex IV and HO-1 expression through activating AMPK pathway, followed by the prevention of high glucose-induced production of reactive oxygen species and declines of cell viability and VO2 capacity. Our observations suggest that HT improves mitochondrial function and reduces oxidative stress potentially through activation of the AMPK pathway in the brain of db/db mice.

AMPK activation prevents prenatal stress-induced cognitive impairment: Modulation of mitochondrial content and oxidative stress

Prenatal stress induces cognitive functional impairment in offspring, an eventuality in which mitochondrial dysfunction and oxidative stress are believed to be closely involved. In this study, the involvement of the AMP-activated protein kinase (AMPK) pathway was investigated. A well-known activator, resveratrol (Res), was used to induce AMPK activation in SH-SY-5Y cells. Significant mitochondrial biogenesis and phase II enzyme activation, accompanied by decreased protein oxidation and GSSG content, were observed after Res treatment, and inhibition of AMPK with Compound c abolished the induction effects of Res. Further study utilizing a prenatal restraint stress (PRS) animal model indicated that maternal supplementation of Res may activate AMPK in the hippocampi of both male and female offspring, and that PRS-induced mitochondrial loss in the offspring hippocampus was inhibited by Res maternal supplementation. In addition, Res activated Nrf2-mediated phase II enzymes and reduced PRS-induced oxidative damage in both male and female offspring. Moreover, PRS markedly decreased mRNA levels of various neuron markers, as well as resultant offspring cognitive function, based on spontaneous alternation performance and Morris water maze tests, the results of which were significantly improved by maternal Res supplementation. Our results provide evidence indicating that AMPK may modulate mitochondrial content and phase II enzymes in neuronal cells, a process which may play an essential role in preventing PRS-induced cognitive impairment. Through the coupling of mitochondrial biogenesis and the Nrf2 pathway, AMPK may modulate oxidative stress and be a promising target against neurological disorders.

Depressed mitochondrial biogenesis and dynamic remodeling in mouse tibialis anterior and gastrocnemius induced by 4‐week hindlimb unloading

Mitochondrial dynamics is highly involved in muscle atrophy, the slow twitch muscle as soleus, preferentially affected by hindlimb unloading (HU), was well characterized by mitochondrial dysfunction in biogenesis. However, the fast twitch muscles like tibialis anterior (TA) and gastrocnemius (GAS), which are the most massive parts of the hindlimb muscles, are less elucidated on mitochondrial adaptations responding to HU. To investigate the mitochondrial dynamic responses and the involved molecules mediating atrophy in TA and GAS, we studied a 4‐week HU mouse model. We found GAS was preferentially affected to atrophy by unloading compared with TA. Furthermore, the depressed mitochondrial biogenesis occurred, accounting for mitochondrial loss in GAS by unloading. PGC‐1α, as well as its transcriptional/post‐translational modification regulators, such as p‐CREB, SIRT1, and p‐AMPK, were consistently reduced in response to unloading in GAS. Molecules relevant to autophagy, mitochondrial fusion, and fission, were compromised following unloading both in TA and GAS. These results suggested that TA exhibited resistance to unloading induced muscle atrophy while GAS presented significant mitochondrial loss, which might be due to the mitochondrial biogenesis suppressed by the inactivation of PGC‐1α. However, both in TA and GAS muscles, a similar sedentary mitochondrial dynamics of mitochondrial fusion and fission was induced by unloading though TA exhibited little muscle atrophy.

Mitochondrial Dysfunction Launches Dexamethasone-Induced Skeletal Muscle Atrophy via AMPK/FOXO3 Signaling

Muscle atrophy occurs in several pathologic conditions such as diabetes and chronic obstructive pulmonary disease (COPD), as well as after long-term clinical administration of synthesized glucocorticoid, where increased circulating glucocorticoid accounts for the pathogenesis of muscle atrophy. Others and we previously reported mitochondrial dysfunction in muscle atrophy-related conditions and that mitochondria-targeting nutrients efficiently prevent kinds of muscle atrophy. However, whether and how mitochondrial dysfunction involves glucocorticoid-induced muscle atrophy remains unclear. Therefore, in the present study, we measured mitochondrial function in dexamethasone-induced muscle atrophy in vivo and in vitro, and we found that mitochondrial respiration was compromised on the 3rd day following after dexamethasone administration, earlier than the increases of MuRF1 and Fbx32, and dexamethasone-induced loss of mitochondrial components and key mitochondrial dynamics proteins. Furthermore, dexamethasone treatment caused intracellular ATP deprivation and robust AMPK activation, which further activated the FOXO3/Atrogenes pathway. By directly impairing mitochondrial respiration, FCCP leads to similar readouts in C2C12 myotubes as dexamethasone does. On the contrary, resveratrol, a mitochondrial nutrient, efficiently reversed dexamethasone-induced mitochondrial dysfunction and muscle atrophy in both C2C12 myotubes and mice, by improving mitochondrial function and blocking AMPK/FOXO3 signaling. These results indicate that mitochondrial dysfunction acts as a central role in dexamethasone-induced skeletal muscle atrophy and that nutrients or drugs targeting mitochondria might be beneficial in preventing or curing muscle atrophy.

Mitochondrial dysfunction precedes depression of AMPK/AKT signaling in insulin resistance induced by high glucose in primary cortical neurons

Recent studies have demonstrated brain insulin signaling impairment and mitochondrial dysfunction in diabetes. Hyperinsulinemia and hyperlipidemia arising from diabetes have been linked to neuronal insulin resistance, and hyperglycemia induces peripheral sensory neuronal impairment and mitochondrial dysfunction. However, how brain glucose at diabetic conditions elicits cortical neuronal insulin signaling impairment and mitochondrial dysfunction remains unknown. In the present study, we cultured primary cortical neurons with high glucose levels and investigated the neuronal mitochondrial function and insulin response. We found that mitochondrial function was declined in presence of 10 mmol/L glucose, prior to the depression of AKT signaling in primary cortical neurons. We further demonstrated that the cerebral cortex of db/db mice exhibited both insulin resistance and loss of mitochondrial complex components. Moreover, we found that adenosine monophosphate‐activated protein kinase (AMPK) inactivation is involved in high glucose‐induced mitochondrial dysfunction and insulin resistance in primary cortical neurons and neuroblastoma cells, as well as in cerebral cortex of db/db mice, and all these impairments can be rescued by mitochondrial activator, resveratrol. Taken together, our results extend the finding that high glucose (≥10 mmol/L) comparable to diabetic brain extracellular glucose level leads to neuronal mitochondrial dysfunction and resultant insulin resistance, and targeting mitochondria‐AMPK signaling might be a promising strategy to protect against diabetes‐related neuronal impairment in central nerves system.

High-Fat-Diet-Induced Weight Gain Ameliorates Bone Loss without Exacerbating AβPP Processing and Cognition in Female APP/PS1 Mice.

Osteoporosis is negatively correlated with body mass, whereas both osteoporosis and weight loss occur at higher incidence during the progression of Alzheimer’s disease (AD) than the age-matched non-dementia individuals. Given that there is no evidence that being overweight is associated with AD-type cognitive dysfunction, we hypothesized that moderate weight gain might have a protective effect on the bone loss in AD without exacerbating cognitive dysfunction. In this study, feeding a high-fat diet (HFD, 45% calorie from fat) to female APP/PS1 transgenic mice, an AD animal model, induced weight gain. The bone mineral density, microarchitecture, and biomechanical properties of the femurs were then evaluated. The results showed that the middle-aged female APP/PS1 transgenic mice were susceptible to osteoporosis of the femoral bones and that weight gain significantly enhanced bone mass and mechanical properties. Notably, HFD was not detrimental to brain insulin signaling and AβPP processing, as well as to exploration ability and working, learning, and memory performance of the transgenic mice measured by T maze and Morris water maze, compared with the mice fed a normal-fat diet (10% calorie from fat). In addition, the circulating levels of leptin but not estradiol were remarkably elevated in HFD-treated mice. These results suggest that a body weight gain induced by the HFD feeding regimen significantly improved bone mass in female APP/PS1 mice with no detriments to exploration ability and spatial memory, most likely via the action of elevated circulating leptin.

Reloading functionally ameliorates disuse-induced muscle atrophy by reversing mitochondrial dysfunction, and similar benefits are gained by administering a combination of mitochondrial nutrients.

We previously found that mitochondrial dysfunction occurs in disuse-induced muscle atrophy. However, the mitochondrial remodeling that occurs during reloading, an effective approach for rescuing unloading-induced atrophy, remains to be investigated. In this study, using a rat model of 3-week hindlimb unloading plus 7-day reloading, we found that reloading protected mitochondria against dysfunction, including mitochondrial loss, abnormal mitochondrial morphology, inhibited biogenesis, and activation of mitochondria-associated apoptotic signaling. Interestingly, a combination of nutrients, including α-lipoic acid, acetyl-L-carnitine, hydroxytyrosol, and CoQ10, which we designed to target mitochondria, was able to efficiently rescue muscle atrophy via a reloading-like action. It is suggested that reloading ameliorates skeletal muscle atrophy through the activation of mitochondrial biogenesis and the amelioration of oxidative stress. Nutrient administration acted similarly in unloaded rats. Here, the study of mitochondrial remodeling in rats during unloading and reloading provides a more detailed picture of the pathology of muscle atrophy.

Hydroxytyrosol mildly improve cognitive function independent of APP processing in APP/PS1 mice.

SCOPE Olive products, the hallmark of Mediterranean diet, are associated with reduced risk of mild cognitive impairment and Alzheimers disease (AD). We and other groups have shown that hydroxytyrosol (HT), a bioactive compound of olive products, ameliorates oxidative stress, mitochondrial dysfunction, and neural toxicity. However, whether HT in Mediterranean diet acts as a functional ingredient in delaying AD pathogenesis remains unclear. METHODS AND RESULTS In the present study, APP/PS1 mice, an animal model of AD, were administrated for 6 months with 5 mg/kg/day of HT, a comparable level of HT in daily Mediterranean diet. HT improved electroencephalography activity and marginally benefited cognitive behavior of transgenic mice. In addition, HT treatment ameliorated mitochondrial dysfunction, reduced mitochondrial carbonyl protein, enhanced superoxide dismutase 2 expression, reversed the phase 2 enzyme system and reduced the levels of brain inflammatory markers, but had no effect on brain β-amyloid (Aβ) accumulation in APP/PS1 mice. CONCLUSIONS These results suggest that HT may represent as a functional ingredient in Mediterranean diet in ameliorating AD-involved neuronal impairment via modulating mitochondrial oxidative stress, neuronal inflammation, and apoptosis without affecting APP processing.

Early inflammation–associated factors blunt sterol regulatory element-binding proteins-1-mediated lipogenesis in high-fat diet-fed APPSWE/PSEN1dE9 mouse model of Alzheimer's disease

Alzheimers disease (AD) patients have an increased incidence of Type 2 diabetes (T2D); however, the underlying mechanisms are not well understood. Since AD is considered a multifactorial disease that affects both the central nerves system and periphery and the dysregulation of hepatic lipid and glucose metabolism play critical roles in T2D, we, therefore, aim to explore the influence of AD genotype on the liver during the progress of high‐fat diet (HFD)‐induced T2D. Fourteen‐week‐old female APPSWE/PSEN1dE9 (AD) mice and age‐, gender‐matched wild‐type controls C57BL/6J (WT) mice were fed a HFD (45% kcal fat content) or a standard chow diet (chow, 12% kcal fat content) for 22 weeks. The effects of diet and genotype were analyzed. Mouse primary hepatocytes were used to decipher the underlying mechanisms. HFD induced significantly higher body weight gain, more severe hyperglycemia, glucose intolerance and hepatic insulin resistance in AD mice than in WT mice. However, AD mice showed reduced HFD‐induced hepatic steatosis, and SREBP‐1‐mediated lipogenic signaling was activated by HFD in WT mice but not in AD mice. In addition, 14‐week‐old AD mice exhibited higher expression of NF‐κB p65, p‐JNK and p‐p38MAPK, as well as higher hepatic and serum contents of IL‐6 and TNFα. In mouse primary hepatocyte cultures, IL‐6 and TNFα inhibited high‐glucose plus insulin‐induced activation of SREBP‐1‐mediated lipogenic signaling and biosynthesis of non‐esterified fatty acid and triglyceride. Early inflammation–associated factors most likely diminish HFD‐induced hepatic lipid deposition by inhibiting SREBP‐1‐mediated de novo lipogenesis, thus driving substrate flux to glucose production for hyperglycemia and hepatic insulin resistance in T2D development.

Endogenously generated amyloid-β increases stiffness in human neuroblastoma cells

Amyloid-β (Aβ) is widely recognized as toxic to neuronal cells. Its deposition on plasma and intracellular membranes and aggregation into amyloid plaques can disturb the composition and physiological function of neurons. Whether a physical property of cells, such as stiffness, is altered by endogenously overexpressed Aβ has not yet been investigated. In this study, we used human neuroblastoma cells stably overexpressing amyloid precursor protein (APP) and its Swedish mutant form (APPswe) to measure the changes in cell stiffness. Our results showed that the stiffness of cells overexpressing APP or APPswe was higher than that of control SH-SY5Y cells. Either reducing levels of Aβ with the γ secretase inhibitor DAPT or blocking the membrane calcium channel formed by Aβ with tromethamine decreased cell stiffness to a level close to the control SH-SY5Y cells. Our results suggested that Aβ, not APP, contributed to increased cell stiffness and that closure of calcium channels formed by Aβ can alleviate the effects of Aβ on membrane stiffness.