AMP-activated Protein Kinase In Brain Research Articles

Decreased Levels of Blood AMPKα1 but not AMPKα2 Isoform in Patients with Mild Cognitive Impairment and Alzheimer's Disease: A Pilot Study.

There is an urgent need to develop feasible biomarkers for diagnosis and prognosis of Alzheimer's disease (AD). Mounting evidence implicates that dysregulation of energy metabolism is a key and early event in AD pathogenesis. AMP-activated protein kinase (AMPK) is a central molecular sensor that plays a critical role in maintaining cellular energy homeostasis, and aberrant brain AMPK activities are linked to AD pathophysiology. We aimed to investigated protein levels of AMPKα isoforms, AMPKα1 and AMPKα2, in plasma samples from patients clinically diagnosed with mild cognitive impairment (MCI) or AD, along with age-matched healthy controls. 30 participants (10 MCI, 10 AD, and 10 controls) were included in our pilot study. Plasma levels of AMPKα1 and AMPKα2 were determined by ELISA. Receiver operating characteristic (ROC) analysis was used to assess sensitivity and specificity. Linear regression was used to assess the correlation between levels of AMPKα isoforms and other biomarkers. Plasma levels of AMPKα1 were decreased in MCI and AD patients, while levels of AMPKα2 were unaltered as compared to controls. ROC analysis showed relatively high sensitivity and specificity for AMPKα1 to distinguish MCI and AD from controls. Linear regression analysis showed that plasma levels of AMPKα1 were correlated with a brain imaging biomarker (AD signature cortical thicknesses). Plasma levels of AMPKα1 were decreased in MCI and AD patients. Future endeavor to explore whether blood AMPKα1 protein expression has the value as a potential biomarker for AD and MCI diagnosis shall be encouraged.

Expression of messenger RNA encoding two cellular metabolic regulators, AMP-activated protein kinase (AMPK) and O-GlcNAc transferase (OGT), in channel catfish: Their tissue distribution and relationship with changes in food intake

AMP-activated protein kinase (AMPK) is considered as the master cellular metabolism regulator that activates various proteins, including O-GlcNAc transferase (OGT). Physiological roles of AMPK and OGT, including the relationship between their mRNA expression and food intake, are poorly understood in channel catfish. This study examined the tissue distribution of AMPK and OGT mRNA and changes in their expression in response to changes in food intake in channel catfish. Expression of all AMPK subunit and OGT mRNA was detectable in the whole brain, liver, heart, spleen, white muscle, and kidney of channel catfish. The OGT mRNA was highly localized in the brain compared to other tissues. 28-day fasting increased hepatic expression of AMPK α1, β1, and OGT mRNA while refeeding fish for 14 days after the 14-day fast decreased their expression to the level similar to that of fish that were fed daily. No changes were noted in the expression of muscle and brain AMPK mRNA or OGT mRNA by fasting and refeeding. Hepatic AMPK α1, α2 and β1 mRNA decreased in response to increased feeding frequency, whereas no changes in the expression of AMPK or OGT mRNA were noted in the brain or the muscle. Results of the current study indicated that the hepatic expression of AMPK and OGT mRNA appeared to be more sensitive to changes in food intake in channel catfish. However, further studies are needed to clearly demonstrate if food intake influences the expression of AMPK and OGT mRNA in various tissues, including the hypothalamus.

Metabolic regulation of female puberty via hypothalamic AMPK–kisspeptin signaling

Conditions of metabolic distress, from malnutrition to obesity, impact, via as yet ill-defined mechanisms, the timing of puberty, whose alterations can hamper later cardiometabolic health and even life expectancy. AMP-activated protein kinase (AMPK), the master cellular energy sensor activated in conditions of energy insufficiency, has a major central role in whole-body energy homeostasis. However, whether brain AMPK metabolically modulates puberty onset remains unknown. We report here that central AMPK interplays with the puberty-activating gene, Kiss1, to control puberty onset. Pubertal subnutrition, which delayed puberty, enhanced hypothalamic pAMPK levels, while activation of brain AMPK in immature female rats substantially deferred puberty. Virogenetic overexpression of a constitutively active form of AMPK, selectively in the hypothalamic arcuate nucleus (ARC), which holds a key population of Kiss1 neurons, partially delayed puberty onset and reduced luteinizing hormone levels. ARC Kiss1 neurons were found to express pAMPK, and activation of AMPK reduced ARC Kiss1 expression. The physiological relevance of this pathway was attested by conditional ablation of the AMPKα1 subunit in Kiss1 cells, which largely prevented the delay in puberty onset caused by chronic subnutrition. Our data demonstrate that hypothalamic AMPK signaling plays a key role in the metabolic control of puberty, acting via a repressive modulation of ARC Kiss1 neurons in conditions of negative energy balance.

Long-term caloric restriction in ApoE-deficient mice results in neuroprotection via Fgf21-induced AMPK/mTOR pathway.

Caloric restriction (CR) decelerates the aging process, extends lifespan and exerts neuroprotective effects in diverse species by so far unknown mechanisms. Based on known neuroprotective effects of fibroblastic growth factor 21 (Fgf21) we speculate that CR upregulates Fgf21, which phosphorylates neuronal AMP-activated protein kinase (AMPK), leading to a decrease of mammalian target of rapamycin (mTOR) signaling activity and an inhibition of tau-hyperphosphorylation. This in turn reduces the formation of neurofibrillary tangles, a neuropathological hallmark of Alzheimer's disease. ApoE-deficient mice (ApoE−/−), serving as a model of neurodegeneration, showed upon CR vs. ad libitum feeding increased Fgf21 levels in both, plasma and brain as well as higher phosphorylation of fibroblastic growth factor receptor 1c (Fgfr1c), extracellular signal-regulated kinases 1/2 (ERK1/2) and AMPK in brain, lower activity of mTOR and decreased Tau-phosphorylation. Finally, CR in ApoE−/− mice caused neuroprotection as indicated by a higher synaptic plasticity shown by immunohistochemical analysis with increased numbers of PSD95-positive neurons and a better cognitive performance as analyzed with Morris water maze test. These data provide substantial evidence that neuroprotection upon CR seems to be Fgf21-dependent. Further experiments are necessary to evaluate Fgf21 as a therapeutic tool to treat tauopathy for improvement of cognitive performance.

Molecular mechanisms of appetite and obesity: a role for brain AMPK.

Feeding behaviour and energy storage are both crucial aspects of survival. Thus, it is of fundamental importance to understand the molecular mechanisms regulating these basic processes. The AMP-activated protein kinase (AMPK) has been revealed as one of the key molecules modulating energy homoeostasis. Indeed, AMPK appears to be essential for translating nutritional and energy requirements into generation of an adequate neuronal response, particularly in two areas of the brain, the hypothalamus and the hindbrain. Failure of this physiological response can lead to energy imbalance, ultimately with extreme consequences, such as leanness or obesity. Here, we will review the data that put brain AMPK in the spotlight as a regulator of appetite.

Telmisartan prevention of LPS-induced microglia activation involves M2 microglia polarization via CaMKKβ-dependent AMPK activation

Brain inflammation plays an important role in the pathophysiology of many psychiatric and neurological diseases. During brain inflammation, microglia cells are activated, producing neurotoxic molecules and neurotrophic factors depending on their pro-inflammatory M1 and anti-inflammatory M2 phenotypes. It has been demonstrated that Angiotensin II type 1 receptor blockers (ARBs) ameliorate brain inflammation and reduce M1 microglia activation. The ARB telmisartan suppresses glutamate-induced upregulation of inflammatory genes in cultured primary neurons. We wished to clarify whether telmisartan, in addition, prevents microglia activation through polarization to an anti-inflammatory M2 phenotype. We found that telmisartan promoted M2 polarization and reduced M1 polarization in LPS-stimulated BV2 and primary microglia cells, effects partially dependent on PPARγ activation. The promoting effects of telmisartan on M2 polarization, were attenuated by an AMP-activated protein kinase (AMPK) inhibitor or AMPK knockdown, indicating that AMPK activation participates on telmisartan effects. Moreover, in LPS-stimulated BV2 cells, telmisartan enhancement of M2 gene expression was prevented by the inhibitor STO-609 and siRNA of calmodulin-dependent protein kinase kinase β (CaMKKβ), an upstream kinase of AMPK. Furthermore, telmisartan enhanced brain AMPK activation and M2 gene expression in a mouse model of LPS-induced neuroinflammation. In addition, telmisartan reduced the LPS-induced sickness behavior in this in vivo model, and this effect was prevented by prior administration of an AMPK inhibitor. Our results indicate that telmisartan can be considered as a novel AMPK activator, suppressing microglia activation by promoting M2 polarization. Telmisartan may provide a novel, safe therapeutic approach to treat brain disorders associated with enhanced inflammation.

Acute metformin preconditioning confers neuroprotection against focal cerebral ischaemia by pre‐activation of AMPK‐dependent autophagy

Recent clinical trials report that metformin, an activator of AMP-activated protein kinase (AMPK) used to treat type 2 diabetes, significantly reduces the risk of stroke by actions that are independent of its glucose-lowering effects. However, the underlying molecular mechanisms are not known. Here, we tested the possibility that acute metformin preconditioning confers neuroprotection by pre-activation of AMPK-dependent autophagy in a rat model of permanent middle cerebral artery occlusion (pMCAO). Male Sprague-Dawley rats were pretreated with either vehicle, an AMPK inhibitor, Compound C, or an autophagy inhibitor, 3-methyladenine, and were injected with a single dose of metformin (10 mg kg(-1), i.p.). Then, AMPK activity and autophagy biomarkers in the brain were assessed. At 24 h after metformin treatment, rats were subjected to pMCAO; infarct volume, neurological deficits and cell apoptosis were evaluated 24 and 96 h later. A single dose of metformin significantly activated AMPK and induced autophagy in the brain. The enhanced autophagic activity was inhibited by Compound C pretreatment. Furthermore, acute metformin preconditioning significantly reduced infarct volume, neurological deficits and cell apoptosis during a subsequent focal cerebral ischaemia. The neuroprotection mediated by metformin preconditioning was fully abolished by Compound C and partially inhibited by 3-methyladenine. These results provide the first evidence that acute metformin preconditioning induces autophagy by activation of brain AMPK, which confers neuroprotection against subsequent cerebral ischaemia. This suggests that metformin, a well-known hypoglycaemic drug, may have a practical clinical use for stroke prevention.

Ischemic preconditioning provides neuroprotection by induction of AMP-activated protein kinase-dependent autophagy in a rat model of ischemic stroke.

Accumulating evidence suggests that ischemic preconditioning (IPC) increases cerebral tolerance to the subsequent ischemic exposure. However, the underlying mechanisms are still not fully understood. In the present study, we tested the hypothesis that AMP-activated protein kinase (AMPK)-dependent autophagy contributed to the neuroprotection of IPC in rats with permanent cerebral ischemia. Male Sprague-Dawley rats were pretreated with vehicle, compound C (an AMPK inhibitor), or 3-methyladenine (3-MA, an autophagy inhibitor) and then were subjected to IPC induced by a 10-min middle cerebral artery occlusion. Afterward, the brain AMPK activity and autophagy biomarkers were measured. At 24 h after IPC, permanent cerebral ischemia was induced in these rats, and infarct volume, neurological deficits as well as cell apoptosis were evaluated 24 h later. We demonstrated that IPC activated AMPK and induced autophagy in the brain, which was accompanied by a reduction of infract volume, neurological deficits, and cell apoptosis after cerebral ischemia. Meanwhile, the IPC-induced autophagy was inhibited by compound C while the neuroprotection of IPC was abolished by compound C or 3-MA. These findings suggest that AMPK-mediated autophagy contributes to the neuroprotection of IPC, highlighting AMPK as a therapeutic target for stroke prevention and treatment.

Genetic selection for body weight in chickens has altered responses of the brain's AMPK system to food intake regulation effect of ghrelin, but not obestatin

The effects of ghrelin and obestatin regulation of food intake are different in mammals and chickens. We investigated central effects of ghrelin and obestatin in lines of chickens selected 50 generations for high (HWS) or low (LWS) body weight. We hypothesized that the effect of ghrelin and obestatin on food intake in 5-day-old chicks is mediated by the AMP-activated protein kinase (AMPK) system and selection for body weight alters the brain's response to ghrelin and obestatin by changing the neuronal AMPK system. Although intracerebroventricular (ICV) ghrelin injection decreased food intake in both lines, the threshold for the anorexigenic effect of central ghrelin was lower in LWS than HWS chicks. Obestatin caused a linear dose-dependent increase in food intake in HWS but not LWS chicks. ICV injection of 0.4 nmol ghrelin inhibited hypothalamic AMPK related gene expression and phosphorylation of AMPK α and acetyl-CoA carboxylase (ACC) with the magnitude of inhibition different in the two lines. In contrast, ICV injection of 4 nmol obestatin did not affect mRNA expression of AMPK system or phosphorylation of AMPK and ACC in either line. These data support the premise of a lower threshold for anorexigenic effect of central ghrelin in LWS than HWS chicks, and this difference may be associated with differential hypothalamic AMPK signaling. Additionally, the hypothalamic mRNA level of ghrelin was significantly higher in LWS than HWS, which may have also contributed to the different threshold response to ghrelin in these two lines. The expression of the ghrelin receptor was also higher in the LWS line, but not until 56 days of age. In summary, selection for body weight has resulted in differences in the central ghrelin and obestatin system, and an altered brain AMPK system may contribute to the different neuronal response to ghrelin, but not obestatin.

New Candidate Targets of AMP-Activated Protein Kinase in Murine Brain Revealed by a Novel Multidimensional Substrate-Screen for Protein Kinases

AMP-activated protein kinase (AMPK) is a heterotrimeric serine/threonine kinase that is involved in the maintenance of energy homeostasis and recovery from metabolic stresses both at the cellular and whole body level. AMPK is found in all tissues examined so far, and a number of downstream targets have been identified. Recent work suggests that AMPK has specialized functions in the brain, such as involvement in appetite control. Nevertheless, brain-specific substrates of AMPK are unknown. Here, we performed a proteomic in vitro screen to identify new putative AMPK targets in brain. Prefractionation of murine brain lysates by liquid chromatography, utilizing four different, serially connected columns with different chemistries was found to be superior to a single column method. A pilot screen involving incubation of small volumes of individual fractions with radiolabeled ATP in the presence or absence of active AMPK, followed by one-dimensional SDS-PAGE and autoradiography, revealed the presence of potential AMPK substrates in a number of different fractions. On the basis of these results, several kinase assays were repeated with selected fractions on a preparative scale. Following separation of the radiolabeled proteins by two-dimensional electrophoresis and comparison of samples with or without added AMPK by differential autoradiography, 53 AMPK-specific phospho-spots were detected and excised. Thereof, 26 unique proteins were identified by mass spectrometry and were considered as new potential downstream targets of AMPK. Kinase assays with 14 highly purified candidate substrate proteins confirmed that at least 12 were direct targets of AMPK in vitro. Although the physiological consequences of these phosphorylation events remain to be established, hypotheses concerning the most intriguing potential targets of AMPK that have been identified by this search are discussed herein. Our data suggests that signaling by AMPK in brain is likely to be involved in the regulation of pathways that have not yet been linked to this kinase.