ROS and Sympathetically Mediated Mitochondria Activation in Brown Adipose Tissue Contribute to Methamphetamine-Induced Hyperthermia

Methamphetamine signals transcription of IL1β and TNFα in a reactive oxygen species-dependent manner and interacts with HIV-1 Tat to decrease antioxidant defense mechanisms

Methamphetamine (Meth) abuse is a common HIV co-morbidity that is linked to aggravated Central Nervous System (CNS) inflammation, which accentuates HIV- associated neurological disorders, triggered both directly or indirectly by the drug. We used the well-established human innate immune macrophage cell line system (THP1) to demonstrate that Reactive Oxygen Species (ROS) immediately induced by Meth play a role in the increased transcription of inflammatory genes, in interaction with HIV-1 Tat peptide. Meth and Tat, alone and together, affect early events of transcriptional activity, as indicated by changes in RNA polymerase (RNAPol) recruitment patterns throughout the genome, via ROS-dependent and -independent mechanisms. IL1β (IL1β) and TNF α (TNFα), two genes with defining roles in the inflammatory response, were both activated in a ROS-dependent manner. We found that this effect occurred via the activation of the activator protein 1 (AP-1) comprising cFOS and cJUN transcription factors and regulated by the SRC kinase. HIV-1 Tat, which was also able to induce the production of ROS, did not further impact the effects of ROS in the context of Meth, but promoted gene activity independently from ROS, via additional transcription factors. For instance, HIV-1 Tat increased NFkB activation and activated gene clusters regulated by Tata box binding peptide, ING4 and IRF2. Importantly, HIV-1 Tat decreased the expression of anti-oxidant genes, where its suppression of the detoxifying machinery may contribute to the aggravation of oxidative stress induced by ROS in the context of Meth. Our results provide evidence of effects of Meth via ROS and interactions with HIV Tat that promote the transcription of inflammatory genes such as IL1β and TNFα.

Why succinate? Physiological regulation by a mitochondrial coenzyme Q sentinel

Metabolites once considered solely in catabolism or anabolism turn out to have key regulatory functions. Among these, the citric acid cycle intermediate succinate stands out owing to its multiple roles in disparate pathways, its dramatic concentration changes and its selective cell release. Here we propose that succinate has evolved as a signaling modality because its concentration reflects the coenzyme Q (CoQ) pool redox state, a central redox couple confined to the mitochondrial inner membrane. This connection is of general importance because CoQ redox state integrates three bioenergetic parameters: mitochondrial electron supply, oxygen tension and ATP demand. Succinate, by equilibrating with the CoQ pool, enables the status of this central bioenergetic parameter to be communicated from mitochondria to the rest of the cell, into the circulation and to other cells. The logic of this form of regulation explains many emerging roles of succinate in biology, and suggests future research questions.

Cysteine 253 of UCP1 regulates energy expenditure and sex-dependent adipose tissue inflammation

Uncoupling protein 1 (UCP1) is a major regulator of brown and beige adipocyte energy expenditure and metabolic homeostasis. However, the widely employed UCP1 loss-of-function model has recently been shown to have a severe deficiency in the entire electron transport chain of thermogenic fat. As such, the role of UCP1 in metabolic regulation in vivo remains unclear. We recently identified cysteine-253 as a regulatory site on UCP1 that elevates protein activity upon covalent modification. Here, we examine the physiological importance of this site through the generation of a UCP1 cysteine-253-null (UCP1 C253A) mouse, a precise genetic model for selective disruption of UCP1 in vivo. UCP1 C253A mice exhibit significantly compromised thermogenic responses in both males and females but display no measurable effect on fat accumulation in an obesogenic environment. Unexpectedly, we find that a lack of C253 results in adipose tissue redox stress, which drives substantial immune cell infiltration and systemic inflammatory pathology in adipose tissues and liver of male, but not female, mice. Elevation of systemic estrogen reverses this male-specific pathology, providing a basis for protection from inflammation due to loss of UCP1 C253 in females. Together, our results establish the UCP1 C253 activation site as a regulator of acute thermogenesis and sex-dependent tissue inflammation.

Potential Contribution of the Intestinal Microbiome to Phenethylamine-Induced Hyperthermia

Phenethylamines (e.g., methamphetamine) are a common source of drug toxicity. Phenethylamine-induced hyperthermia (PIH) can activate a cascade of events that may result in rhabdomyolysis, coagulopathy, and even death. Here, we review recent evidence that suggests a potential link between the gut-brain axis and PIH. Within the preoptic area of the hypothalamus, phenethylamines lead to changes in catecholamine levels, that activate the sympathetic nervous system (SNS) and increase the peripheral levels of norepinephrine (NE), resulting in: (1) the loss of heat dissipation through α1 adrenergic receptor (α1-AR)-mediated vasoconstriction, (2) heat generation through β-AR activation and subsequent free fatty acid (FFA) activation of uncoupling proteins (UCPs) in brown and white adipose tissue, and (3) alteration of the gut microbiome and its link to the gut-brain axis. Recent studies have shown that phenethylamine derivatives can influence the composition of the gut microbiome and thus its metabolic potential. Phenethylamines increase the relative level of Proteuswhich has been linked to enhanced NE turnover. Bidirectional fecal microbial transplants (FMT) between PIH-tolerant and PIH-naïve rats demonstrated that the transplantation of gut microbiome can confer phenotypic hyperthermic and tolerant responses to phenethylamines. These phenethylamine-mediated changes in the gut microbiome were also associated with epigenetic changes in the mediators of thermogenesis. Given the significant role that the microbiome has been shown to play in the maintenance of body temperature, we outline current studies demonstrating the effects of phenethylamines on the gut microbiome and how these microbiome changes may mechanistically contribute to alterations in body temperature.

Macrophages and brown adipocytes cross-communicate to modulate a thermogenic program following methamphetamine exposure

Hyperthermia is a potentially lethal side-effect of Methamphetamine (Meth), a stimulant drug. Activation of non-shivering thermogenesis in brown adipose tissue (BAT) is partly responsible for Meth-induced rise in temperature, with contributing sympathetic neurotransmitters, such as norepinephrine (NE), and reactive oxygen species (ROS). However, the mechanisms controlling the development of a molecular thermogenic program in brown adipocytes (BA) following Meth are unknown. We hypothesize that Meth and NE affect BAT cells, BA and macrophages, to modify their physiology and interactions, with consequences to thermogenic genes. We also hypothesize that ROS play a critical role in signaling transcription of thermogenic genes and their regulatory components. Using primary BA and macrophage cultures, we measured Meth and NE interference with physiological and phenotypic measures that are relevant to thermogenesis in BAT. Meth caused both BA and macrophages to decrease mitochondrial maximal capacity and increase ROS. In BA, the thermogenic genes UCP1, PPARγ, PGC1α and GADD45γ were transcriptionally increased by Meth in a ROS-dependent manner. In macrophages, Meth increased oxidative stress response and caused a predominance of M2 subset markers. BA transcriptional changes in response to Meth and NE were significantly controlled by macrophages. The results suggest that BA and macrophages respond to Meth and NE, with effects on mitochondrial functions and transcription of genes involved in thermogenesis. ROS-dependent signals in BA and cellular interactions between BA and macrophages synergize to regulate the BAT environment and control critical pathways leading to Meth-hyperthermia.

Human Immunodeficiency Virus Type 1 and Methamphetamine-Mediated Mitochondrial Damage and Neuronal Degeneration in Human Neurons

Methamphetamine, a potent psychostimulant, is a highly addictive drug commonly used by persons living with HIV (PLWH), and its use can result in cognitive impairment and memory deficits long after its use is discontinued. Although the mechanism(s) involved with persistent neurological deficits is not fully known, mitochondrial dysfunction is a key component in methamphetamine neuropathology. Specific mitochondrial autophagy (mitophagy) and mitochondrial fusion and fission are protective quality control mechanisms that can be dysregulated in HIV infection, and the use of methamphetamine can further negatively affect these protective cellular mechanisms. Here, we observed that treatment of human primary neurons (HPNs) with methamphetamine and HIV gp120 and Tat increase dynamin-related protein 1 (DRP1)-dependent mitochondrial fragmentation and neuronal degeneration. Methamphetamine and HIV proteins increased microtubule-associated protein 1 light chain 3 beta-II (LC3B-II) lipidation and induced sequestosome 1 (SQSTM1, p62) translocation to damaged mitochondria. Additionally, the combination inhibited autophagic flux, increased reactive oxygen species (ROS) production and mitochondrial damage, and reduced microtubule-associated protein 2 (MAP2) dendrites in human neurons. N-Acetylcysteine (NAC), a strong antioxidant and ROS scavenger, abrogated DRP1-dependent mitochondrial fragmentation and neurite degeneration. Thus, we show that methamphetamine combined with HIV proteins inhibits mitophagy and induces neuronal damage, and NAC reverses these deleterious effects on mitochondrial function.IMPORTANCE Human and animal studies show that HIV infection, combined with the long-term use of psychostimulants, increases neuronal stress and the occurrence of HIV-associated neurocognitive disorders (HAND). On the cellular level, mitochondrial function is critical for neuronal health. In this study, we show that in human primary neurons, the combination of HIV proteins and methamphetamine increases oxidative stress, DRP1-mediated mitochondrial fragmentation, and neuronal injury manifested by a reduction in neuronal network and connectivity. The use of NAC, a potent antioxidant, reversed the neurotoxic effects of HIV and methamphetamine, suggesting a novel approach to ameliorate the effects of HIV- and methamphetamine-associated cognitive deficits.

Hypothalamic CDK4 regulates thermogenesis by modulating sympathetic innervation of adipose tissues

This study investigated the role of CDK4 in the oxidative metabolism of brown adipose tissue (BAT). BAT from Cdk4^−/− mice exhibited fewer lipids and increased mitochondrial volume and expression of canonical thermogenic genes, rendering these mice more resistant to cold exposure. Interestingly, these effects were not BAT cell‐autonomous but rather driven by increased sympathetic innervation. In particular, the ventromedial hypothalamus (VMH) is known to modulate BAT activation via the sympathetic nervous system. We thus examined the effects of VMH neuron‐specific Cdk4 deletion. These mice display increased sympathetic innervation and enhanced cold tolerance, similar to Cdk4^−/− mice, in addition to browning of scWAT. Overall, we provide evidence showing that CDK4 modulates thermogenesis by regulating sympathetic innervation of adipose tissue depots through hypothalamic nuclei, including the VMH. This demonstrates that CDK4 not only negatively regulates oxidative pathways, but also modulates the central regulation of metabolism through its action in the brain.

Sex differences and Tat expression affect dopaminergic receptor expression and response to antioxidant treatment in methamphetamine-sensitized HIV Tat transgenic mice

Methamphetamine (Meth) abuse is a common HIV comorbidity. Males and females differ in their patterns of Meth use, associated behaviors, and responses, but the underlying mechanisms and impact of HIV infection are unclear. Transgenic mice with inducible HIV-1 Tat protein in the brain (iTat) replicate many neurological aspects of HIV infection in humans. We previously showed that Tat induction enhances the Meth sensitization response associated with perturbation of the dopaminergic system, in male iTat mice. Here, we used the iTat mouse model to investigate sex differences in individual and interactive effects of Tat and Meth challenge on locomotor sensitization, brain expression of dopamine receptors (DRDs) and regulatory adenosine receptors (ADORAs). Because Meth administration increases the production of reactive oxygen species (ROS), we also determined whether the effects of Meth could be rescued by concomitant treatment with the ROS scavenger N-acetyl cysteine (NAC). After Meth sensitization and a 7-day abstinence period, groups of Tat+ and Tat-male and female mice were challenged with Meth in combination with NAC. We confirmed that Tat expression and Meth challenge suppressed DRD mRNA and protein in males and females' brains, and showed that females were particularly susceptible to the effects of Meth on D1-like and D2-like DRD subtypes and ADORAs. The expression of these markers differed strikingly between males and females, and between females in different phases of the estrous cycle, in a Tat -dependent manner. NAC attenuated Meth-induced locomotor sensitization and preserved DRD expression in all groups except for Tat + females. These data identify complex interactions between sex, Meth use, and HIV infection on addiction responses, with potential implications for the treatment of male and female Meth users in the context of HIV, especially those with cognitive disorders.

Systems Biology Analysis of the Antagonizing Effects of HIV-1 Tat Expression in the Brain over Transcriptional Changes Caused by Methamphetamine Sensitization

Methamphetamine (Meth) abuse is common among humans with immunodeficiency virus (HIV). The HIV-1 regulatory protein, trans-activator of transcription (Tat), has been described to induce changes in brain gene transcription that can result in impaired reward circuitry, as well as in inflammatory processes. In transgenic mice with doxycycline-induced Tat protein expression in the brain, i.e., a mouse model of neuroHIV, we tested global gene expression patterns induced by Meth sensitization. Meth-induced locomotor sensitization included repeated daily Meth or saline injections for seven days and Meth challenge after a seven-day abstinence period. Brain samples were collected 30 min after the Meth challenge. We investigated global gene expression changes in the caudate putamen, an area with relevance in behavior and HIV pathogenesis, and performed pathway and transcriptional factor usage predictions using systems biology strategies. We found that Tat expression alone had a very limited impact in gene transcription after the Meth challenge. In contrast, Meth-induced sensitization in the absence of Tat induced a global suppression of gene transcription. Interestingly, the interaction between Tat and Meth broadly prevented the Meth-induced global transcriptional suppression, by maintaining regulation pathways, and resulting in gene expression profiles that were more similar to the controls. Pathways associated with mitochondrial health, initiation of transcription and translation, as well as with epigenetic control, were heavily affected by Meth, and by its interaction with Tat in anti-directional ways. A series of systems strategies have predicted several components impacted by these interactions, including mitochondrial pathways, mTOR/RICTOR, AP-1 transcription factor, and eukaryotic initiation factors involved in transcription and translation. In spite of the antagonizing effects of Tat, a few genes identified in relevant gene networks remained downregulated, such as sirtuin 1, and the amyloid precursor protein (APP). In conclusion, Tat expression in the brain had a low acute transcriptional impact but strongly interacted with Meth sensitization, to modify effects in the global transcriptome.

Thyroid hormone (T3) stimulates brown adipose tissue activation via mitochondrial biogenesis and MTOR-mediated mitophagy

The thyroid hormone triiodothyronine (T₃) activates thermogenesis by uncoupling electron transport from ATP synthesis in brown adipose tissue (BAT) mitochondria. Although T₃ can induce thermogenesis by sympathetic innervation, little is known about its cell autonomous effects on BAT mitochondria. We thus examined effects of T₃ on mitochondrial activity, autophagy, and metabolism in primary brown adipocytes and BAT and found that T₃ increased fatty acid oxidation and mitochondrial respiration as well as autophagic flux, mitophagy, and mitochondrial biogenesis. Interestingly, there was no significant induction of intracellular reactive oxygen species (ROS) despite high mitochondrial respiration and UCP1 induction by T₃. However, when cells were treated with Atg5 siRNA to block autophagy, induction of mitochondrial respiration by T₃ decreased, and was accompanied by ROS accumulation, demonstrating a critical role for autophagic mitochondrial turnover. We next generated an Atg5 conditional knockout mouse model (Atg5 cKO) by injecting Ucp1 promoter-driven Cre-expressing adenovirus into Atg5^Flox/Flox mice to examine effects of BAT-specific autophagy on thermogenesis in vivo. Hyperthyroid Atg5 cKO mice exhibited lower body temperature than hyperthyroid or euthyroid control mice. Metabolomic analysis showed that T₃ increased short and long chain acylcarnitines in BAT, consistent with increased β-oxidation. T₃ also decreased amino acid levels, and in conjunction with SIRT1 activation, decreased MTOR activity to stimulate autophagy. In summary, T₃ has direct effects on mitochondrial autophagy, activity, and turnover in BAT that are essential for thermogenesis. Stimulation of BAT activity by thyroid hormone or its analogs may represent a potential therapeutic strategy for obesity and metabolic diseases. Abbreviations: ACACA: acetyl-Coenzyme A carboxylase alpha; AMPK: AMP-activated protein kinase; Acsl1: acyl-CoA synthetase long-chain family member 1; ATG5: autophagy related 5; ATG7: autophagy related 7; ATP: adenosine triphosphate; BAT: brown adipose tissue; cKO: conditional knockout; COX4I1: cytochrome c oxidase subunit 4I1; Cpt1b: carnitine palmitoyltransferase 1b, muscle; CQ: chloroquine; DAPI: 4',6-diamidino-2-phenylindole; DIO2: deiodinase, iodothyronine, type 2; DMEM: Dulbecco's modified Eagle's medium; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; Fabp4: fatty acid binding protein 4, adipocyte; FBS: fetal bovine serum; FCCP: carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone; FGF: fibroblast growth factor; FOXO1: forkhead box O1; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; Gpx1: glutathione peroxidase 1; Lipe: lipase, hormone sensitive; MAP1LC3B: microtubule-associated protein 1 light chain 3; mRNA: messenger RNA; MTORC1: mechanistic target of rapamycin kinase complex 1; NAD: nicotinamide adenine dinucleotide; Nrf1: nuclear respiratory factor 1; OCR: oxygen consumption rate; PBS: phosphate-buffered saline; PCR: polymerase chain reaction; PPARGC1A: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; Pnpla2: patatin-like phospholipase domain containing 2; Prdm16: PR domain containing 16; PRKA: protein kinase, AMP-activated; RPS6KB: ribosomal protein S6 kinase; RFP: red fluorescent protein; ROS: reactive oxygen species; SD: standard deviation; SEM: standard error of the mean; siRNA: small interfering RNA; SIRT1: sirtuin 1; Sod1: superoxide dismutase 1, soluble; Sod2: superoxide dismutase 2, mitochondrial; SQSTM1: sequestosome 1; T₃: 3,5,3'-triiodothyronine; TFEB: transcription factor EB; TOMM20: translocase of outer mitochondrial membrane 20; UCP1: uncoupling protein 1 (mitochondrial, proton carrier); ULK1: unc-51 like kinase 1; VDAC1: voltage-dependent anion channel 1; WAT: white adipose tissue.

Role of the sympathetic nervous system in regulation of the sodium glucose cotransporter 2

BACKGROUND

The sympathetic nervous system (SNS) regulates glucose metabolism in various organs including the kidneys. The sodium glucose cotransporter 2 (SGLT2) mediates glucose reabsorption in renal proximal tubules and its inhibition has been shown to improve glucose control, cardiovascular and renal outcomes. We hypothesized that SNS-induced alterations of glucose metabolism may be mediated via regulation of SGLT2.

METHOD

We used human renal proximal tubule cells to investigate the effects of noradrenaline on SGLT2 regulation. Mice fed a high-fat diet were oral gavaged with dapagliflozin and the expression of noradrenaline and tyrosine hydroxylase was measured in the kidney and heart.

RESULTS

Noradrenaline treatment resulted in a pronounced increase in SGLT2 and interleukin (IL)-6 expression in HK2 cells and promoted translocation of SGLT2 to the cell surface. In vivo, dapagliflozin treatment resulted in marked glucosuria in high-fat diet-fed mice. SGLT2 inhibition significantly reduced high-fat diet-induced elevations of tyrosine hydroxylase and noradrenaline in the kidney and heart. We also aimed to assess the levels of hypertension-related cytokines in the kidneys of our mice treated with and without dapagliflozin. Excitingly, we demonstrate that SGLT2 inhibition with dapagliflozin promoted a trend towards reduced tumour necrosis factor-alpha and elevated IL-1β protein levels in the kidney.

CONCLUSION

Our in-vitro and in-vivo studies provide first evidence for an important cross-talk between the SNS and SGLT2 regulation that may not only account for SNS-induced alterations of glucose metabolism but potentially contribute to cardiovascular and renal protection observed with SGLT2 inhibitors.

Body temperature regulation and drugs of abuse

Phenethylamine-induced hyperthermia can occur following exposure to several different types of illicit stimulants, such as amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine ("Molly"), synthetic cathinones ("bath salts"), and N-methoxybenyl ("NBOMe"), to name a few. Peripheral norepinephrine release mediated by these sympathomimetic agents induces a double-edged sword of heat accumulation through β-adrenoreceptor-dependent activation of uncoupling protein (UCP1 and 3)-regulated thermogenesis and loss of heat dissipation through α₁-adrenoreceptor-mediated vasoconstriction. Additionally, thyroid hormones are important determinants of the capacity of thermogenesis induced by phenethylamines through the regulation of free fatty acid release and the transcriptional activation of a host of metabolic genes, including adrenergic receptors and mitochondrial uncoupling proteins. Here, we review the central and peripheral mechanistic "triggers" of phenethylamine-induced hyperthermia and outline potential pharmacologic interventions for managing phenethylamine-induced hyperthermia based on these recently discovered hyperthermia mediators.

Methamphetamine Augments Concurrent Astrocyte Mitochondrial Stress, Oxidative Burden, and Antioxidant Capacity: Tipping the Balance in HIV-Associated Neurodegeneration

Methamphetamine (METH) use, with and without human immunodeficiency virus (HIV)-1 comorbidity, exacerbates neurocognitive decline. Oxidative stress is a probable neurotoxic mechanism during HIV-1 central nervous system infection and METH abuse, as viral proteins, antiretroviral therapy and METH have each been shown to induce mitochondrial dysfunction. However, the mechanisms regulating mitochondrial homeostasis and overall oxidative burden in astrocytes are not well understood in the context of HIV-1 infection and METH abuse. Here, we report METH-mediated dysregulation of astrocyte mitochondrial morphology and function during prolonged exposure to low levels of METH. Mitochondria became larger and more rod shaped with METH when assessed by machine learning, segmentation analyses. These changes may be mediated by elevated mitofusin expression coupled with inhibitory phosphorylation of dynamin-related protein-1, which regulate mitochondrial fusion and fission, respectively. While METH decreased oxygen consumption and ATP levels during acute exposure, chronic treatment of 1 to 2 weeks significantly enhanced both when tested in the absence of METH. Together, these changes significantly increased not only expression of antioxidant proteins, augmenting the astrocyte's oxidative capacity, but also oxidative damage. We propose that targeting astrocytes to reduce their overall oxidative burden and expand their antioxidant capacity could ultimately tip the balance from neurotoxicity towards neuroprotection.

Mitochondrial reactive oxygen species and adipose tissue thermogenesis: Bridging physiology and mechanisms

Brown and beige adipose tissues can catabolize stored energy to generate heat, relying on the principal effector of thermogenesis: uncoupling protein 1 (UCP1). This unique capability could be leveraged as a therapy for metabolic disease. Numerous animal and cellular models have now demonstrated that mitochondrial reactive oxygen species (ROS) signal to support adipocyte thermogenic identity and function. Herein, we contextualize these findings within the established principles of redox signaling and mechanistic studies of UCP1 function. We provide a framework for understanding the role of mitochondrial ROS signaling in thermogenesis together with testable hypotheses for understanding mechanisms and developing therapies.

The complementary and divergent roles of uncoupling proteins 1 and 3 in thermoregulation

KEY POINTS

Both uncoupling protein 1 (UCP1) and UCP3 are important for mammalian thermoregulation. UCP1 and UCP3 in brown adipose tissue mediate early and late phases of sympathomimetic thermogenesis, respectively. Lipopolysaccharide thermogenesis requires skeletal muscle UCP3 but not UCP1. Acute noradrenaline-induced hyperthermia requires UCP1 but not UCP3. Loss of both UCP1 and UCP3 accelerate the loss of body temperature compared to UCP1KO alone during acute cold exposure.

ABSTRACT

Uncoupling protein 1 (UCP1) is the established mediator of brown adipose tissue-dependent thermogenesis. In contrast, the role of UCP3, expressed in both skeletal muscle and brown adipose tissue, in thermoregulatory physiology is less well understood. Here, we show that mice lacking UCP3 (UCP3KO) have impaired sympathomimetic (methamphetamine) and completely abrogated lipopolysaccharide (LPS) thermogenesis, but a normal response to noradrenaline. By comparison, UCP1 knockout (UCP1KO) mice exhibit blunted methamphetamine and fully inhibited noradrenaline thermogenesis, but an increased febrile response to LPS. We further establish that mice lacking both UCP1 and 3 (UCPDK) fail to show methamphetamine-induced hyperthermia, and have a markedly accelerated loss of body temperature and survival after cold exposure compared to UCP1KO mice. Finally, we show that skeletal muscle-specific human UCP3 expression is able to significantly rescue LPS, but not sympathomimetic thermogenesis blunted in UCP3KO mice. These studies identify UCP3 as an important mediator of physiological thermogenesis and support a renewed focus on targeting UCP3 in metabolic physiology.

Modulation of anti-cancer drug sensitivity through the regulation of mitochondrial activity by adenylate kinase 4

BACKGROUND

Adenylate kinase is a key enzyme in the high-energy phosphoryl transfer reaction in living cells. An isoform of this enzyme, adenylate kinase 4 (AK4), is localized in the mitochondrial matrix and is believed to be involved in stress, drug resistance, malignant transformation in cancer, and ATP regulation. However, the molecular basis for the AK4 functions remained to be determined.

METHODS

HeLa cells were transiently transfected with an AK4 small interfering RNA (siRNA), an AK4 short hairpin RNA (shRNA) plasmid, a control shRNA plasmid, an AK4 expression vector, and a control expression vector to examine the effect of the AK4 expression on cell proliferation, sensitivity to anti-cancer drug, metabolome, gene expression, and mitochondrial activity.

RESULTS

AK4 knockdown cells treated with short hairpin RNA increased ATP production and showed greater sensitivity to hypoxia and anti-cancer drug, cis-diamminedichloro-platinum (II) (CDDP). Subcutaneous grafting AK4 knockdown cells into nude mice revealed that the grafted cells exhibited both slower proliferation and reduced the tumor sizes in response to CDDP. AK4 knockdown cell showed a increased oxygen consumption rate with FCCP treatment, while AK4 overexpression lowered it. Metabolome analysis showed the increased levels of the tricarboxylic acid cycle intermediates, fumarate and malate in AK4 knockdown cells, while AK4 overexpression lowered them. Electron microscopy detected the increased mitochondrial numbers in AK4 knockdown cells. Microarray analysis detected the increased gene expression of two key enzymes in TCA cycle, succinate dehydrogenase A (SDHA) and oxoglutarate dehydrogenease L (OGDHL), which are components of SDH complex and OGDH complex, supporting the metabolomic results.

CONCLUSIONS

We found that AK4 was involved in hypoxia tolerance, resistance to anti-tumor drug, and the regulation of mitochondrial activity. These findings provide a new potential target for efficient anticancer therapies by controlling AK4 expression.

Effects of acute and chronic systemic methamphetamine on respiratory, cardiovascular and metabolic function, and cardiorespiratory reflexes

KEY POINTS

Methamphetamine (METH) abuse is escalating worldwide, with the most common cause of death resulting from cardiovascular failure and hyperthermia; however, the underlying physiological mechanisms are poorly understood. Systemic administration of METH in anaesthetised rats reduced the effectiveness of some protective cardiorespiratory reflexes, increased central respiratory activity independently of metabolic function, and increased heart rate, metabolism and respiration in a pattern indicating that non-shivering thermogenesis contributes to the well-described hyperthermia. In animals that showed METH-induced behavioural sensitisation following chronic METH treatment, no changes were evident in baseline cardiovascular, respiratory and metabolic measures and the METH-evoked effects in these parameters were similar to those seen in saline-treated or drug naïve animals. Physiological effects evoked by METH were retained but were neither facilitated nor depressed following chronic treatment with METH. These data highlight and identify potential mechanisms for targeted intervention in patients vulnerable to METH overdose. Methamphetamine (METH) is known to promote cardiovascular failure or life-threatening hyperthermia; however, there is still limited understanding of the mechanisms responsible for evoking the physiological changes. In this study, we systematically determined the effects on both autonomic and respiratory outflows, as well as reflex function, following acute and repeated administration of METH, which enhances behavioural responses. Arterial pressure, heart rate, phrenic nerve discharge amplitude and frequency, lumbar and splanchnic sympathetic nerve discharge, interscapular brown adipose tissue and core temperatures, and expired CO2 were measured in urethane-anaesthetised male Sprague-Dawley rats. Novel findings include potent increases in central inspiratory drive and frequency that are not dependent on METH-evoked increases in expired CO2 levels. Increases in non-shivering thermogenesis correlate with well-described increases in body temperature and heart rate. Unexpectedly, METH evoked minor effects on both sympathetic outflows and mean arterial pressure. METH modified cardiorespiratory reflex function in response to hypoxia, hypercapnia and baroreceptor unloading. Chronically METH-treated rats failed to exhibit changes in baseline sympathetic, cardiovascular, respiratory and metabolic parameters. The tonic and reflex cardiovascular, respiratory and metabolic responses to METH challenge were similar to those seen in saline-treated and drug naive animals. Overall, these findings describe independent and compound associations between physiological systems evoked by METH and serve to highlight that a single dose of METH can significantly impact basic homeostatic systems and protective functions. These effects of METH persist even following chronic METH treatment.

The cross-talk of HIV-1 Tat and methamphetamine in HIV-associated neurocognitive disorders

Antiretroviral therapy has dramatically improved the lives of human immunodeficiency virus 1 (HIV-1) infected individuals. Nonetheless, HIV-associated neurocognitive disorders (HAND), which range from undetectable neurocognitive impairments to severe dementia, still affect approximately 50% of the infected population, hampering their quality of life. The persistence of HAND is promoted by several factors, including longer life expectancies, the residual levels of virus in the central nervous system (CNS) and the continued presence of HIV-1 regulatory proteins such as the transactivator of transcription (Tat) in the brain. Tat is a secreted viral protein that crosses the blood–brain barrier into the CNS, where it has the ability to directly act on neurons and non-neuronal cells alike. These actions result in the release of soluble factors involved in inflammation, oxidative stress and excitotoxicity, ultimately resulting in neuronal damage. The percentage of methamphetamine (MA) abusers is high among the HIV-1-positive population compared to the general population. On the other hand, MA abuse is correlated with increased viral replication, enhanced Tat-mediated neurotoxicity and neurocognitive impairments. Although several strategies have been investigated to reduce HAND and MA use, no clinically approved treatment is currently available. Here, we review the latest findings of the effects of Tat and MA in HAND and discuss a few promising potential therapeutic developments.

Reactive oxygen species scavenger N-acetyl cysteine reduces methamphetamine-induced hyperthermia without affecting motor activity in mice

Hyperthermia is a potentially lethal side effect of Methamphetamine (Meth) abuse, which involves the participation of peripheral thermogenic sites such as the Brown Adipose Tissue (BAT). In a previous study we found that the anti-oxidant N-acetyl cysteine (NAC) can prevent the high increase in temperature in a mouse model of Meth-hyperthermia. Here, we have further explored the ability of NAC to modulate Meth-induced hyperthermia in correlation with changes in BAT. We found that NAC treatment in controls causes hypothermia, and, when administered prior or upon the onset of Meth-induced hyperthermia, can ameliorate the temperature increase and preserve mitochondrial numbers and integrity, without affecting locomotor activity. This was different from Dantrolene, which decreased motor activity without affecting temperature. The effects of NAC were seen in spite of its inability to recover the decrease of mitochondrial superoxide induced in BAT by Meth. In addition, NAC did not prevent the Meth-induced decrease of BAT glutathione. Treatment with S-adenosyl-L-methionine, which improves glutathione activity, had an effect in ameliorating Meth-induced hyperthermia, but also modulated motor activity. This suggests a role for the remaining glutathione for controlling temperature. However, the mechanism by which NAC operates is independent of glutathione levels in BAT and specific to temperature. Our results show that, in spite of the absence of a clear mechanism of action, NAC is a pharmacological tool to examine the dissociation between Meth-induced hyperthermia and motor activity, and a drug of potential utility in treating the hyperthermia associated with Meth-abuse.

The heat is on: Molecular mechanisms of drug-induced hyperthermia

Thermoregulation is an essential homeostatic process in which critical mechanisms of heat production and dissipation are controlled centrally in large part by the hypothalamus and peripherally by activation of the sympathetic nervous system. Drugs that disrupt the components of this highly orchestrated multi-organ process can lead to life-threatening hyperthermia. In most cases, hyperthermic agents raise body temperature by increasing the central and peripheral release of thermoregulatory neurotransmitters that ultimately lead to heat production in thermogenic effector organs skeletal muscle (SKM) and brown adipose tissue (BAT). In many cases hyperthermic drugs also decrease heat dissipation through peripheral changes in blood flow. Drug-induced heat production is driven by the stimulation of mechanisms that normally regulate the adaptive thermogenic responses including both shivering and non-shivering thermogenesis (NST) mechanisms. Modulation of the mitochondrial electrochemical proton/pH gradient by uncoupling protein 1 (UCP1) in BAT is the most well characterized mechanism of NST in response to cold, and may contribute to thermogenesis induced by sympathomimetic agents, but this is far from established. However, the UCP1 homologue, UCP3, and the ryanodine receptor (RYR1) are established mediators of toxicant-induced hyperthermia in SKM. Defining the molecular mechanisms that orchestrate drug-induced hyperthermia will be essential in developing treatment modalities for thermogenic illnesses. This review will briefly summarize mechanisms of thermoregulation and provide a survey of pharmacologic agents that can lead to hyperthermia. We will also provide an overview of the established and candidate molecular mechanisms that regulate the actual thermogenic processes in heat effector organs BAT and SKM.