Energy status determines hindbrain signal transduction pathway transcriptional reactivity to AMPK in the estradiol-treated ovariectomized female rat

Advances in the study of mitophagy in osteoarthritis

Osteoarthritis (OA), characterized by cartilage degeneration, synovial inflammation, and subchondral bone remodeling, is among the most common musculoskeletal disorders globally in people over 60 years of age. The initiation and progression of OA involves the abnormal metabolism of chondrocytes as an important pathogenic process. Cartilage degeneration features mitochondrial dysfunction as one of the important causative factors of abnormal chondrocyte metabolism. Therefore, maintaining mitochondrial homeostasis is an important strategy to mitigate OA. Mitophagy is a vital process for autophagosomes to target, engulf, and remove damaged and dysfunctional mitochondria, thereby maintaining mitochondrial homeostasis. Cumulative studies have revealed a strong association between mitophagy and OA, suggesting that the regulation of mitophagy may be a novel therapeutic direction for OA. By reviewing the literature on mitophagy and OA published in recent years, this paper elaborates the potential mechanism of mitophagy regulating OA, thus providing a theoretical basis for studies related to mitophagy to develop new treatment options for OA.

The effect of inhibiting hindbrain A2 noradrenergic neurons by 6-Hydroxydopamine on lipopolysaccharide-treated male rats autistic animal model

Autism spectrum disorder (ASD) is a complex neurodevelopmental illness that often emerges in early childhood. The incidence of ASD has shown a notable rise in recent years. ASD is defined by deficits in social communication, and presence of rigid and repetitive behaviors and interests. The underlying mechanisms of ASD remain elusive. Multiple studies have documented the presence of neuroinflammation and increased levels of inflammatory cytokines, specifically, IL-6, TNF, and NF-κB, in various brain regions, including the prefrontal cortex (PFC) and hippocampus in individuals with ASD. Noradrenergic neurons play a crucial role in brain development and the regulation of motor, behavioral, and memory functions. This study sought to examine the impact of intracerebroventricular (icv.) injection of the neurotoxin, 6-hydroxydopamine (6-OHDA), in the caudal dorsal vagal complex A2 neurons on various neuroinflammatory pathways at the hippocampus and PFC in valproic acid (VPA) autistic animal model. This was done in conjunction with an intraperitoneal (i.p.) injection of Lipopolysaccharides (LPS) in animal models with VPA-induced autism. We specifically examined the impact of the caudal fourth ventricle 6-OHDA icv. injection and LPS (i.p.) injection on self-grooming behavior. We measured the mRNA expression of IL-6, TNF-a, and NF-κB using qRT-PCR, and the protein expression of COX-2, GPX-1, p-AMPK, and AMPK using western blot analysis. The self-grooming activity was considerably higher in the combined treatment group (6-OHDA icv. + LPS i.p.) compared to the control group. A substantial increase observed in the expression of IL-6, TNF-α, and NF-κB genes in the PFC of the treatment group that received icv. Administration of 6-OHDA, compared to the control group. The VPA-autism rats that received the combo treatment exhibited a slight increase in the expression level of NF-κB gene in the hippocampus, compared to the control group. At the PFC, we noticed a substantial drop in the expression of the antioxidant protein GPX-1 in the group that received the combo treatment compared to the control group. Our data investigates a novel aspect that the 6-OHDA-induced inhibition of hindbrain A2 neurons could be influencing the neuroinflammatory pathways in the PFC and hippocampus of autistic animal models.

Mitophagy—A New Target of Bone Disease

Bone diseases are usually caused by abnormal metabolism and death of cells in bones, including osteoblasts, osteoclasts, osteocytes, chondrocytes, and bone marrow mesenchymal stem cells. Mitochondrial dysfunction, as an important cause of abnormal cell metabolism, is widely involved in the occurrence and progression of multiple bone diseases, including osteoarthritis, intervertebral disc degeneration, osteoporosis, and osteosarcoma. As selective mitochondrial autophagy for damaged or dysfunctional mitochondria, mitophagy is closely related to mitochondrial quality control and homeostasis. Accumulating evidence suggests that mitophagy plays an important regulatory role in bone disease, indicating that regulating the level of mitophagy may be a new strategy for bone-related diseases. Therefore, by reviewing the relevant literature in recent years, this paper reviews the potential mechanism of mitophagy in bone-related diseases, including osteoarthritis, intervertebral disc degeneration, osteoporosis, and osteosarcoma, to provide a theoretical basis for the related research of mitophagy in bone diseases.

Effect of oral contraceptives on energy balance in women: A review of current knowledge and potential cellular mechanisms

Body weight management is currently of major concern as the obesity epidemic is still a worldwide challenge. As women face more difficulties to lose weight than men, there is an urgent need to better understand the underlying reasons and mechanisms. Recent data have suggested that the use of oral contraceptive (OC) could be involved. The necessity of utilization and development of contraceptive strategies for birth regulation is undeniable and contraceptive pills appear as a quite easy approach. Moreover, OC also represent a strategy for the management of premenstrual symptoms, acne or bulimia nervosa. The exact impact of OC on body weight remains not clearly established. Thus, after exploring the potential underlying mechanisms by which OC could influence the two side of energy balance, we then provide an overview of the available evidence regarding the effects of OC on energy balance (i.e. energy expenditure and energy intake). Finally, we highlight the necessity for future research to clarify the cellular effects of OC and how the individualization of OC prescriptions can improve long-term weight loss management.

17β-Estradiol Induces Mitophagy Upregulation to Protect Chondrocytes via the SIRT1-Mediated AMPK/mTOR Signaling Pathway

Increasing evidence reveals that estrogen, especially 17β-estradiol (17β-E2), is associated with articular cartilage metabolism disorder and postmenopausal osteoarthritis (OA). SIRT1, AMPK, and mTOR are regarded as critical mitophagy regulators. Recent studies have shown that mitophagy displays a protective effect against OA, but the molecular mechanism is not well known. This study aimed to investigate the effect of 17β-E2 on Sirtuin-1 (SIRT1) expression and the induction of mitophagy upregulation by 17β-E2 via the SIRT1-mediated AMP-activated protein kinase (AMPK)/mammalian target of the rapamycin (mTOR) signaling pathway to protect chondrocytes. ATDC5 chondrocytes were treated with different concentrations of 17β-E2 (0 M, 1 × 10^-9 M, 1 × 10^-8 M, and 1 × 10^-7 M) for 24 h or pretreatment with or without NAM (SIRT1 inhibitor), Compound C (AMPK inhibitor) and S1842 (mTOR inhibitor) for 30 min prior to treatment with 17β-E2 (1 × 10^-7 M) for 24 in each groups. Expression of SIRT1 was evaluated by real-time PCR, Western blotting and confocal immunofluorescence staining. Then, the mitophagosomes in cells were observed under a transmission electron microscopy (TEM), and the AMPK/mTOR signaling pathway was detected by Western blotting. The mitophagy-related proteins, p-AMPK, p-mTOR, p-JNK, and p-p38 were also identified by Western blot analysis. The chondrocytes viability and proliferation were determined by MTT and 5-Bromo-2'-deoxyuridine (BrdU) assay. These experiments were independently repeated 3 times The study found that 17β-E2 increased the expression level of SIRT1, p-AMPK, and mitophagy-related proteins but decreased p-mTOR expression, and then induced mitophagy upregulation in chondrocytes. More mitochondrial autophagosomes were observed in 17β-E2-treated chondrocytes under a transmission electron microscope. Also, 17β-E2 improved cell viability and proliferation with the higher expression of SIRT1 and activation of the AMPK/mTOR signaling pathway. However, SIRT1 inhibitor nicotinamide (NAM) and AMPK inhibitor Compound C blocked the beneficial effect of 17β-E2. In summary, this study was novel in demonstrating that 17β-E2 induced mitophagy upregulation to protect chondrocytes via the SIRT1-mediated AMPK/mTOR signaling pathway.

Ginkgo biloba Extract (GbE) Stimulates the Hypothalamic Serotonergic System and Attenuates Obesity in Ovariectomized Rats

Menopause is associated with increased risk to develop obesity but the mechanisms involved are not fully understood. We have shown that Ginkgo biloba extract (GbE) improved diet-induced obesity. Since GbE might be effective in the treatment of obesity related to menopause, avoiding the side effects of hormone replacement therapy, we investigated the effect of GbE on hypothalamic systems controlling energy homeostasis. Wistar rats were either ovariectomized (OVX) or Sham-operated. After 2 months, either 500 mg.kg^-1 of GbE or vehicle were administered daily by gavage for 14 days. A subset of animals received an intracerebroventricular (i.c.v.) injection of serotonin (300 μg) or vehicle and food intake was measured after 12 and 24 h. Another subset was submitted to in vivo microdialysis and 5-HT levels of the medial hypothalamus were measured by high performance liquid chromatography, before and up to 2 h after the administration of 500 mg.kg^-1 of GbE. Additional animals were used for quantification of 5-HT_1A, 5-HT_1B, 5-HT_2C, 5-HTT, and pro-opiomelanocortin hypothalamic protein levels by Western blotting. OVX increased food intake and body weight and adiposity while GbE attenuated these alterations. i.c.v. serotonin significantly reduced food intake in Sham, Sham + GbE, and OVX + GbE groups while it failed to do so in the OVX group. In the OVX rats, GbE stimulated 5-HT microdialysate levels while it reduced hypothalamic 5-HTT protein levels. The results indicate that GbE improved the ovariectomy-induced resistance to serotonin hypophagia, at least in part through stimulation of the hypothalamic serotonergic activity. Since body weight gain is one of the most important consequences of menopause, the stimulation of the serotonergic transmission by GbE may represent a potential alternative therapy for menopause-related obesity.

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.

SIRT1-dependent AMPK pathway in the protection of estrogen against ischemic brain injury

AIMS

Stroke is a major cause of mortality and disability, especially for postmenopausal women. In view of the protective action of estrogen, hormone therapy remains the only effective way to limit this risk. The objective of this study was to investigate the efficiency and underlying mechanisms of estrogen neuroprotection.

METHODS

Subcutaneous injection of 17β-estradiol in rats after ovariectomy (OVX) was used to manipulate estrogen level and explore the effects of estrogen in cerebral ischemic damage both in vivo and in vitro. Silent mating type information regulation 2 homolog 1 (SIRT1) knockout mice and adenosine monophosphate (AMP)-activated kinase (AMPK) inhibitor Compound C were also used to investigate the underlying pathway of estrogen.

RESULTS

Estrogen deficiency induced by OVX aggravated brain infarction in experimentally induced cerebral ischemia rats, whereas estrogen pretreatment reduced ischemia-induced cerebral injuries. Neurons of estrogen deficiency models were susceptible to apoptosis under oxygen-glucose deprivation (OGD). In contrast, neurons with estrogen-supplemented serum exhibited restored resistance to cell apoptosis. In OGD neurons, estrogen promoted AMPK activation through estrogen receptor α, and neuroprotection of estrogen was prevented by AMPK inhibition. Estrogen increased SIRT1 expression and activation, and estrogen-induced AMPK activation disappeared in SIRT1 knockout neurons. Moreover, estrogen-induced neuroprotection was abolished in SIRT1 knockout mice and AMPK-inhibited rats.

CONCLUSION

Our data support that estrogen protects against ischemic stroke through preventing neuron death via the SIRT1-dependent AMPK pathway.

Hindbrain A2 noradrenergic neuron adenosine 5'-monophosphate-activated protein kinase activation, upstream kinase/phosphorylase protein expression, and receptivity to hormone and fuel reporters of short-term food deprivation are regulated by estradiol

Estradiol (E) mitigates acute and postacute adverse effects of 12 hr-food deprivation (FD) on energy balance. Hindbrain 5'-monophosphate-activated protein kinase (AMPK) regulates hyperphagic and hypothalamic metabolic neuropeptide and norepinephrine responses to FD in an E-dependent manner. Energy-state information from AMPK-expressing hindbrain A2 noradrenergic neurons shapes neural responses to metabolic imbalance. Here we investigate the hypothesis that FD causes divergent changes in A2 AMPK activity in E- vs. oil (O)-implanted ovariectomized female rats, alongside dissimilar adjustments in circulating metabolic fuel (glucose, free fatty acids [FFA]) and energy deficit-sensitive hormone (corticosterone, glucagon, leptin) levels. FD decreased blood glucose in oil (O)- but not E-implanted ovariectomized female rats and elevated and reduced glucagon levels in O and E, respectively. FD decreased circulating leptin in O and E, but increased corticosterone and FFA concentrations in E only. Western blot analysis of laser-microdissected A2 neurons showed that glucocorticoid receptor type II and very-long-chain acyl-CoA synthetase 3 protein profiles were amplified in FD/E vs. FD/O. A2 total AMPK protein was elevated without change in activity in FD/O, whereas FD/E exhibited increased AMPK activation along with decreased upstream phosphatase expression. The catecholamine biosynthetic enzyme dopamine-β-hydroxylase (DβH) was increased in FD/O but not FD/E A2 cells. The data show discordance between A2 AMPK activation and glycemic responses to FD; sensor activity was refractory to glucose decrements in FD/O but augmented in FD/E despite stabilized glucose and elevated FFA levels. E-dependent amplification of AMPK activity may reflect adaptive conversion to fatty acid oxidation and/or glucocorticoid stimulation. FD augmentation of A2 DβH protein profiles in FD/O but not FD/E animals suggests that FD may correspondingly regulate NE synthesis vs. metabolism/release in the absence vs. presence of E. Mechanisms underlying translation of E-contingent A2 neuron responses to FD into regulatory signaling remain to be determined. © 2016 Wiley Periodicals, Inc.

Hindbrain estrogen receptor-beta antagonism normalizes reproductive and counter-regulatory hormone secretion in hypoglycemic steroid-primed ovariectomized female rats

Hindbrain dorsal vagal complex A2 noradrenergic signaling represses the pre-ovulatory luteinizing hormone (LH) surge in response to energy deficiency. Insulin-induced hypoglycemia augments A2 neuron adenosine 5'-monophosphate-activated protein kinase (AMPK) activity and estrogen receptor-beta (ERβ) expression, coincident with LH surge suppression. We hypothesized that ERβ is critical for hypoglycemia-associated patterns of LH secretion and norepinephrine (NE) activity in key reproduction-relevant forebrain structures. The neural mechanisms responsible for tight coupling of systemic energy balance and procreation remain unclear; here, we investigated whether ERβ-dependent hindbrain signals also control glucose counter-regulatory responses to hypoglycemia. Gonadal steroid-primed ovariectomized female rats were pretreated by caudal fourth ventricular administration of the ERβ antagonist 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP) or vehicle before insulin injection at LH surge onset. Western blot analysis of laser-microdissected A2 neurons revealed hypoglycemic intensification of AMPK activity and dopamine-β-hydroxylase protein expression; the latter response was attenuated by PHTPP pretreatment. PHTPP regularized LH release, but not preoptic GnRH-I precursor protein expression in insulin-injected rats, and reversed hypoglycemic stimulation of glucagon and corticosterone secretion. Hypoglycemia caused PHTPP-reversible changes in NE and prepro-kisspeptin protein content in the hypothalamic arcuate (ARH), but not anteroventral periventricular nucleus. Results provide novel evidence for ERβ-dependent caudal hindbrain regulation of LH and counter-regulatory hormone secretion during hypoglycemia. Observed inhibition of LH likely involves mechanisms at the axon terminal that impede GnRH neurotransmission. Data also show that caudal hindbrain ERβ exerts site-specific control of NE activity in forebrain projection sites during hypoglycemia, including the ARH where prepro-kisspeptin may be a target of that signaling.

Role of estradiol in intrinsic hindbrain AMPK regulation of hypothalamic AMPK, metabolic neuropeptide, and norepinephrine activity and food intake in the female rat

This study addressed the hypothesis that dorsomedial hindbrain adenosine 5'-monophosphate-activated protein kinase (AMPK) imposes inherent estradiol-dependent control of hypothalamic AMPK, neuropeptide, and norepinephrine (NE) activity and feeding in the female rat. Estradiol (E)- or oil (O)-implanted ovariectomized rats were injected with the AMPK inhibitor compound c (Cc) or vehicle into the caudal fourth ventricle (CV4) prior to micropunch-dissection of individual hypothalamic metabolic loci or assessment of food intake. Cc decreased hindbrain dorsal vagal complex phosphoAMPK (pAMPK) in both E and O; tissue ATP levels were reduced by this treatment in O only. In E/Cc, pAMPK expression was diminished in the lateral hypothalamic area (LHA) and ventromedial (VMH) and paraventricular (PVH) nuclei; only PVH pAMPK was suppressed by this treatment in O/Cc. Cc decreased PVH corticotropin-releasing hormone and arcuate (ARH) proopiomelanocortin (POMC) and neuropeptide Y in O, but suppressed only POMC in E. O/Cc exhibited both augmented (PVH, VMH) and decreased (LHA, ARH) hypothalamic NE content, whereas Cc treatment of E elevated preoptic and dorsomedial hypothalamic nucleus NE. Cc completely or incompletely repressed feeding in E versus O, respectively. Results implicate dorsomedial hindbrain AMPK in physiological stimulus-induced feeding in females. Excepting POMC, hypothalamic neuropeptide responses to this sensor may be contingent on estrogen. Estradiol likely designates hypothalamic targets of altered NE signaling due to hindbrain AMPK activation. Divergent changes in NE content of hypothalamic loci in O/Cc uniquely demonstrate sensor-induced bimodal catecholamine signaling to those sites.

Estradiol Regulates Dorsal Vagal Complex Signal Transduction Pathway Transcriptional Reactivity to the AMPK Activator 5-Aminoimidazole-4-Carboxamide-Riboside (AICAR)

The ovarian hormone estradiol (E) regulates effects of hindbrain adenosine 5'-monophosphate-activated protein kinase (AMPK) on caudal dorsal vagal complex (cDVC) neuron genomic activation and systemic glucostasis. The present study examined the hypothesis that cDVC signal transduction pathways exhibit distinctive E-dependent reactivity to activation of this sensor. RT-PCR microarray analysis was performed on RNA extracted from the cDVC of E- or oil (O)-implanted ovariectomized (OVX) adult female rats injected into the caudal fourth ventricle with the AMP mimetic 5-aminoimidazole-4-carboxamide-riboside (AICAR) (A) or saline (S). Microarray results show that the majority of marker genes differentially expressed in the E/S versus O/S cDVC were upregulated, as only myc (TGFβ; WNT pathways), bcl2 (Hedgehog pathway), and serpine (hypoxia pathway) mRNA profiles were downregulated by E. Several JAK/STAT and NFκB signaling pathway marker gene profiles were upregulated in O/A but unchanged in E/A; additional NFκB genes were inhibited by A in E but not O. Hypoxia and p53 pathways contain genes that were inhibited or stimulated in O/A, but unaltered in E/A. Conversely, TGFβ, p53, and NOTCH pathways each contained marker genes that were correspondingly modified or maintained in E/A versus O/A. Moreover, several oxidative stress pathway genes were suppressed in O/A while elevated or unchanged in E/A. Hedgehog, PPAR, and WNT signaling pathways were characterized by numerous examples of A-induced reversal of E augmentation of marker gene expression coinciding with opposite or no drug effects in O. Data presented here demonstrate that E exerts distinctive effects on cDVC signal transduction pathway marker gene reactivity to activated AMPK. Further research is needed to determine if observed changes in signal pathway marker gene transcription correlate with adjustments in gene product protein expression, and to characterize the role of aforementioned signaling pathways in E-sensitive cellular and systemic responses to hindbrain AMPK activation.