Uncoupling Protein 5 Research Articles

Familial globular glial tauopathy linked to MAPT mutations: molecular neuropathology and seeding capacity of a prototypical mixed neuronal and glial tauopathy

Globular glial tauopathy (GGT) is a progressive neurodegenerative disease involving the grey matter and white matter (WM) and characterized by neuronal deposition of hyper-phosphorylated, abnormally conformed, truncated, oligomeric 4Rtau in neurons and in glial cells forming typical globular astrocyte and oligodendrocyte inclusions (GAIs and GOIs, respectively) and coiled bodies. Present studies centre on four genetic GGT cases from two unrelated families bearing the P301T mutation in MAPT and one case of sporadic GGT (sGGT) and one case of GGT linked to MAPT K317M mutation, for comparative purposes. Clinical and neuropathological manifestations and biochemical profiles of phospho-tau are subjected to individual variations in patients carrying the same mutation, even in carriers of the same family, independently of the age of onset, gender, and duration of the disease. Immunohistochemistry, western blotting, transcriptomic, proteomics and phosphoproteomics, and intra-cerebral inoculation of brain homogenates to wild-type (WT) mice were the methods employed. In GGT cases linked to MAPT P301T mutation, astrocyte markers GFAP, ALDH1L1, YKL40 mRNA and protein, GJA1 mRNA, and AQ4 protein are significantly increased; glutamate transporter GLT1 (EAAT2) and glucose transporter (SLC2A1) decreased; mitochondrial pyruvate carrier 1 (MPC1) increased, and mitochondrial uncoupling protein 5 (UCP5) almost absent in GAIs in frontal cortex (FC). Expression of oligodendrocyte markers OLIG1 and OLIG2mRNA, and myelin-related genes MBP, PLP1, CNP, MAG, MAL, MOG, and MOBP are significantly decreased in WM; CNPase, PLP1, and MBP antibodies reveal reduction and disruption of myelinated fibres; and SMI31 antibodies mark axonal damage in the WM. Altered expression of AQ4, GLUC-t, and GLT-1 is also observed in sGGT and in GGT linked to MAPT K317M mutation. These alterations point to primary astrogliopathy and oligodendrogliopathy in GGT. In addition, GGT linked to MAPT P301T mutation proteotypes unveil a proteostatic imbalance due to widespread (phospho)proteomic dearrangement in the FC and WM, triggering a disruption of neuron projection morphogenesis and synaptic transmission. Identification of hyper-phosphorylation of variegated proteins calls into question the concept of phospho-tau-only alteration in the pathogenesis of GGT. Finally, unilateral inoculation of sarkosyl-insoluble fractions of GGT homogenates from GGT linked to MAPT P301T, sGGT, and GGT linked to MAPT K317M mutation in the hippocampus, corpus callosum, or caudate/putamen in wild-type mice produces seeding, and time- and region-dependent spreading of phosphorylated, non-oligomeric, and non-truncated 4Rtau and 3Rtau, without GAIs and GOIs but only of coiled bodies. These experiments prove that host tau strains are important in the modulation of cellular vulnerability and phenotypes of phospho-tau aggregates.

Neuroprotection and acidosis induced by cortical spreading depression.

Dear editor We read with interest the article “Cortical spreading depression produces a neuroprotective effect activating mitochondrial uncoupling protein-5″ published in Neuropsychiatr Dis Treat by Viggiano et al.1 The authors showed that cerebral spreading depression (CSD) triggered uncoupling protein-5 (UCP-5),1 which had been reported to exert a long-term effect upon neuron protection.2 The result is another piece in CSD literature on modifying gene expressions to provide neuroprotection to subsequent ischemic episodes.3,4 An unmentioned but additional factor for neuroprotection in CSD could be acidosis. Acidosis is a known consequence of CSD.5 In the literature, brief acidosis in ischemic conditions when oxygen supply is low has been shown to be cytoprotective and neuroprotective,6–10 a result related sometimes to the concept of the “pH paradox.”9,11,12 Acidosis had been reported to reduce stroke infarct size with CO2 applied for a short time after reperfusion6 as well as during ischemic stroke.10 Brief acidosis applied after birth asphyxia7 was reported to successfully suppress brain alkalosis, which led to seizures. Hence, brief and relatively mild acidosis induced under the condition of CSD may be one of the neuroprotective factors for CSD. The role of acidosis in neuroprotection by CSD warrants further investigation. Interestingly, CSD-induced acidosis could be one explanation of impaired cerebral vascular reactivity13–16 after CSD. It has been reported that once tissue reaches a certain low pH threshold, blood flow increase would be insignificant in response to even stronger CO2 challenge.10

Developmental programming by high fructose decreases phosphorylation efficiency in aging offspring brain mitochondria, correlating with enhanced UCP5 expression.

Fructose has recently been observed to affect brain metabolism and cognitive function in adults. Yet, possible late-onset effects by gestational fructose exposure have not been examined. We evaluated mitochondrial function in the brain of aging (15 months) male offspring of Fischer F344 rat dams fed a high-fructose diet (50% energy from fructose) during gestation and lactation. Maternal fructose exposure caused a significantly lower body weight of the offspring throughout life after weaning, while birth weight, litter size, and body fat percentage were unaffected. Isolated brain mitochondria displayed a significantly increased state 3 respiration of 8%, with the substrate combinations malate/pyruvate, malate/pyruvate/succinate, and malate/pyruvate/succinate/rotenone, as well as a significant decrease in the P/O2 ratio, compared with the control. Uncoupling protein 5 (UCP5) protein levels increased in the fructose group compared with the control (P=0.03) and both UCP5 mRNA and protein levels were inversely correlated with the P/O2 ratio (P=0.008 and 0.03, respectively), suggesting that UCP5 may have a role in the observed decreased phosphorylation efficiency. In conclusion, maternal high-fructose diet during gestation and lactation has long-term effects (fetal programming) on brain mitochondrial function in aging rats, which appears to be linked to an increase in UCP5 protein levels.

Regulated expression of neuronal SIRT1 and related genes by aging and neuronal β2-containing nicotinic cholinergic receptors

Longevity genes attenuate the aging process, but their expression in the brain during aging remains unknown. Loss of the majority of heteromeric brain nicotinic acetylcholine receptors (nAChRs) results in premature brain aging, and altered regulation of longevity genes could be involved. Using in situ hybridization, the expression of SIRT1, Ku70, Nampt, p53, forkhead Box O3 (FoxO3), and mitochondria uncoupling protein 5 (UCP5) was determined in neocortex and hippocampus of young adult 3-month and middle-aged 18-month-old wild-type (WT), and age-matched mice lacking β2* heteromeric nAChRs (β2-/-). Age-related structural changes were detected in WT mice. In particular, cortical thickness was decreased but neuronal density increased, and hippocampal volume increased with age. In contrast, young β2-/- mice exhibited increased cortical neuronal density, and with age, cortical thickness decreased more dramatically, and hippocampal volume did not increase. Thus, young β2-/- mice exhibited cortical signs of aging, and aging was accelerated at 18 months. The longevity genes probed exhibited similar expression patterns in frontal brain structures, with strong expression in hippocampus, medial habenula (MHb), and cortex. In WT mice, age significantly decreased expression of all genes except SIRT1 in cortical structures, and a similar pattern was detected in the MHb. Genotype had no effect on expression in young adults in either cortex or MHb, but increased mRNA expression of SIRT1, Nampt, and Ku70 was detected in cortex, hippocampus, and MHb of aged β2-/- mice compared with WT mice. This is the first study to determine age-related expression of survival genes in forebrain areas. Although, structural changes indicative of accelerated aging are evident in young β2-/- mice, the data suggest that nAChRs do not directly regulate expression of survival genes. However, loss of β2* nAChRs could result in augmented cellular stress, which indirectly increases expression of SIRT1, Nampt, and Ku70 as an adaptive response to provide protection against neurodegeneration.

Whole genome siRNA cell-based screen links mitochondria to Akt signaling network through uncoupling of electron transport chain

Forkhead transcription factors (FOXOs) alter a diverse array of cellular processes including the cell cycle, oxidative stress resistance, and aging. Insulin/Akt activation directs phosphorylation and cytoplasmic sequestration of FOXO away from its target genes and serves as an endpoint of a complex signaling network. Using a human genome small interfering RNA (siRNA) library in a cell-based assay, we identified an extensive network of proteins involved in nuclear export, focal adhesion, and mitochondrial respiration not previously implicated in FOXO localization. Furthermore, a detailed examination of mitochondrial factors revealed that loss of uncoupling protein 5 (UCP5) modifies the energy balance and increases free radicals through up-regulation of uncoupling protein 3 (UCP3). The increased superoxide content induces c-Jun N-terminal kinase 1 (JNK1) kinase activity, which in turn affects FOXO localization through a compensatory dephosphorylation of Akt. The resulting nuclear FOXO increases expression of target genes, including mitochondrial superoxide dismutase. By connecting free radical defense and mitochondrial uncoupling to Akt/FOXO signaling, these results have implications in obesity and type 2 diabetes development and the potential for therapeutic intervention.

Mitochondrial UCP5 is neuroprotective by preserving mitochondrial membrane potential, ATP levels, and reducing oxidative stress in MPP + and dopamine toxicity

We explored the protective mechanisms of human neuronal mitochondrial uncoupling protein-5 (UCP5) in MPP +- and dopamine-induced toxicity after its stable overexpression in SH-SY5Y cells. We raised specific polyclonal antibodies. Overexpressed UCP5 localized in mitochondria but not in cytosol. UCP5 overexpression increased proton leak, decreased mitochondrial membrane potential (MMP), reduced ATP production, and increased overall oxygen consumption (demonstrating uncoupling activity). UCP5 overexpression did not affect other neuronal UCP expression (UCP2 and UCP4). Overexpressing UCP5 is protective against MPP +- and dopamine-induced toxicity. MPP + and dopamine exposure for 6 h reduced MMP and increased superoxide levels. ATP levels in UCP5-overexpressing cells were preserved under MPP + and dopamine toxicity, comparable to levels in untreated vector controls. At 24 h, UCP5 overexpression preserved MMP, ATP levels, and cell survival; attenuated superoxide generation; and maintained oxidative phosphorylation as indicated by lower lactate levels. MPP + and dopamine exposure induced UCP5 mRNA transcription but did not decrease transcript degradation, as inhibition of transcription by actinomycin-D abolished induction by either toxin. Compared with our previous studies on UCP4, we observed functional differences between UCP4 and UCP5 in enhancing mitochondrial efficiency. These neuronal UCP homologues may work synergistically to maintain oxidative balance (through uncoupling activities) and ATP production (by modifying MMP).

Hydrogen Peroxide Regulates the Mitochondrial Content of Uncoupling Protein 5 in Colon Cancer Cells

Uncoupling protein-2 (UCP2) and uncoupling protein-5 (UCP5) are ion carriers located in the inner mitochondrial membrane that mediate a regulated discharge of the proton gradient generated by the respiratory chain and are possibly involved in the protection against free radical production. Mitochondrial dysfunction is involved in the pathogenesis of colon cancer for which UCP2 has been proposed as a potential therapeutic target. The object of this study was to investigate the possible effects of mitochondrial dysfunction and oxidative stress on the mitochondrial content of UCP2 and UCP5 in colonic cells. Proliferation rate/index, antioxidant systems, reactive oxygen species, oxidative damage, mitochondrial markers and protein expression of UCP2 and UCP5 were analysed in non-metastatic HT-29 cells, metastatic SW-620 cells, and in a HT-29 differentiated derivative (Glu-R). In this study, we found a clear relationship between mitochondrial dysfunction in colonic epithelial cells and the levels of UCP2 and UCP5 proteins. Furthermore, hydrogen peroxide was responsible for the coordinated activation of the antioxidant response and the increase of UCP5 protein levels. Our findings suggest that uncoupling activity could act as a local feedback mechanism to limit the enhanced steady-state H₂O₂ production in dysfunctional mitochondria of colonic cells.

Molecular characterization and expression of a novel homolog of uncoupling protein 5 (UCP5) from the eastern oyster Crassostrea virginica (Bivalvia: Ostreidae)

Uncoupling proteins (UCPs) belong to the mitochondrial anion carrier gene family which has been implicated in diverse physiological functions ranging from thermoregulation to antioxidant defense. In mammals, the UCP family is well characterized and contains five members (UCP1-5). In contrast, invertebrate homologues of uncoupling proteins are much less studied both from the viewpoints of structure and function. In this study we report nucleotide and predicted protein structure of an important member of UCP family, UCP5 from eastern oysters Crassostrea virginica. UCP5 from oysters appears to be a close homolog of the mammalian brain mitochondrial carrier protein (BMCP1, or UCP5) and is the first full-length UCP described from a Lophotrochozoan invertebrate. Evolutionary analysis of UCP sequences indicates at least three monophyletic UCP branches (UCP1-3, UCP4 and UCP5) that have diverged early in the evolution, prior to the divergence of vertebrates and invertebrates. In oysters, two forms of UCP5 transcript are found (UCP5S and UCP5L) that differ by 152 bp in length due to the presence of an intron in UCP5L. UCP5 was expressed in all studied oyster tissues, unlike mammals, where UCP5 is predominantly expressed in brains and male gonads. Hypoxia-reoxygenation stress, sublethal Cd exposure (50 μg L − 1 Cd for 56 days) and acclimation to different temperatures (12 and 20 °C) had no significant effect on UCP5 mRNA expression in oysters indicative of its relative unimportance in antioxidant defense and temperature adaptation of oyster mitochondria. These data suggest that despite the relatively high degree of evolutionary conservation of the UCP5 amino acid sequence, its functional significance in mitochondria changed in the course of evolution of mollusks and vertebrates.

Oxygen and oxidative stress modulate the expression of uncoupling protein-5 in vitro and in vivo.

Uncoupling protein 5 (UCP5), also referred to as brain mitochondrial carrier protein (BMCP 1), belongs to the family of mitochondrial membrane transporters known as uncoupling proteins (UCPs)1. Five UCPs have been cloned, named UCP1, UCP2, UCP3, UCP4 and UCP5/BMCP12. It is well established that UCP1, the prototypical UCP expressed only in brown adipocytes, dissipates the mitsochondrial proton gradient across the inner membrane and hence potential energy is lost as heat2. However, it is not known whether UCP 2–5 are true uncoupling proteins and have thermogenic properties or have other in vivo physiological functions. It has been proposed that the novel UCPs might play a role in the regulation of reactive oxygen species (ROS) production3,4 KeywordsUncouple ProteinHypobaric HypoxiaBrown AdipocyteTransient Cerebral IschemiaUCP3 GeneThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

UCP5/BMCP1 transcript isoforms in human skeletal muscle: relationship of the short-insert isoform with lipid oxidation and resting metabolic rates

Uncoupling protein 5 (UCP5) or brain mitochondrial carrier protein-1 (BMCP1) enhances mitochondrial proton leak in vitro and its hepatic and brain expression profiles are modulated by diet and cold exposure in mice. Alternative splicing generates three isoforms: a long form (UCP5L), a short form (UCP5S), and a short form with a 31 amino acid insert (UCP5SI). We investigated the relationship between skeletal muscle UCP5 expression and in vivo energy metabolism in 36 non-diabetic Pima Indians. We determined the expression levels of total UCP5 (UCP5T), and the isoforms UCP5L, UCP5S, and UCP5SI (66.8, 32.5, and 0.8% of UCP5T, respectively). None correlated with body weight or percent body fat. The transcript level of UCP5SI, but not the others, was positively correlated with resting metabolic rate ( r=0.38, P=0.02, adjusted for age, sex, fat mass, and fat-free mass) and lipid oxidation rate (adjusted for age, sex, and percent body fat) during a euglycemic clamp with infusion of insulin at a physiologic concentration ( r=0.42, P=0.01).