Uncoupling Protein 2 Knockdown Research Articles

Mitochondrial Uncoupling Protein-2 Ameliorates Ischemic Stroke by Inhibiting Ferroptosis-Induced Brain Injury and Neuroinflammation.

Ischemic stroke is a devastating disease in which mitochondrial damage or dysfunction substantially contributes to brain injury. Mitochondrial uncoupling protein-2 (UCP2) is a member of the UCP family, which regulates production of mitochondrial superoxide anion. UCP2 is reported to be neuroprotective for ischemic stroke-induced brain injury. However, the molecular mechanisms of UCP2 in ischemic stroke remain incompletely understood. In this study, we investigated whether and how UCP2 modulates neuroinflammation and regulates neuronal ferroptosis following ischemic stroke in vitro and in vivo. Wild-type (WT) and UCP2 knockout (Ucp2-/-) mice were subjected to middle cerebral artery occlusion (MCAO). BV2 cells (mouse microglial cell line) and HT-22 cells (mouse hippocampal neuronal cell line) were transfected with small interfering (si)-RNA or overexpression plasmids to knockdown or overexpress UCP2 levels. Cells were then exposed to oxygen-glucose deprivation and reoxygenation (OGD/RX) to simulate hypoxic injury in vitro. We found that UCP2 expression was markedly reduced in a time-dependent manner in both in vitro and in vivo ischemic stroke models. In addition, UCP2 was mainly expressed in neurons. UCP2 deficiency significantly enlarged infarct volumes, aggravated neurological deficit scores, and exacerbated cerebral edema in mice after MCAO. In vitro knockdown of Ucp2 and in vivo genetic depletion of Ucp2 (Ucp2-/- mice) increased neuronal ferroptosis-related indicators, including Fe2+, malondialdehyde, glutathione, and lipid peroxidation. Overexpression of UCP2 in neuronal cells resulted in reduced ferroptosis. Moreover, knockdown of UCP2 exacerbated neuroinflammation in BV2 microglia and mouse ischemic stroke models, suggesting that endogenous UCP2 inhibits neuroinflammation following ischemic stroke. Upregulation of UCP2 expression in microglia appeared to decrease the release of pro-inflammatory factors and increase the levels of anti-inflammatory factors. Further investigation showed that UCP2 deletion inhibited expression of AMPKα/NRF1 pathway-related proteins, including p-AMPKα, t-AMPKα, NRF1, and TFAM. Thus, UCP2 protects the brain from ischemia-induced ferroptosis by activating AMPKα/NRF1 signaling. Activation of UCP2 represents an attractive strategy for the prevention and treatment of ischemic stroke.

UCP2-SIRT3 Signaling Relieved Hyperglycemia-Induced Oxidative Stress and Senescence in Diabetic Retinopathy.

Diabetic retinopathy (DR) is one of the most common reasons for blindness. uncoupling protein 2 (UCP2), an uncoupling protein located in mitochondria, has been reported to be related to metabolic and vascular diseases. This research aimed to illustrate the function and mechanism of UCP2 in the pathogenesis of DR. Human epiretinal membranes were collected to investigate the expression of UCP2 by quantitative real-time polymerase chain reaction (qRT-PCR) and immunofluorescence. Primary human retinal microvascular endothelial cells (HRECs) were cultured in high glucose (HG) to establish an in vitro cell model for DR. Flow cytometry analysis was used to measure intracellular reactive oxygen species (ROS). Senescence levels were evaluated by the senescence-associated beta-galactosidase (SA-β-gal) assay, the expression of senescence marker P21, and cell-cycle analysis. Adenovirus-mediated UCP2 overexpression or knockdown and specific inhibitors were administered to investigate the underlying regulatory mechanism. Proliferative fibrovascular membranes from patients with DR illustrated the downregulation of UCP2 and sirtuin 3 (SIRT3) by qRT-PCR and immunofluorescence. Persistent hyperglycemia-induced UCP2 downregulation in the progress of DR and adenovirus-mediated UCP2 overexpression protected endothelial cells from hyperglycemia-induced oxidative stress and senescence. Under hyperglycemic conditions, UCP2 overexpression attenuated NAD+ downregulation; hence, it promoted the expression and activity of SIRT3, an NAD+-dependent deacetylase regulating mitochondrial function. 3-TYP, a selective SIRT3 inhibitor, abolished the UCP2-mediated protective effect against oxidative stress and senescence. UCP2 overexpression relieved oxidative stress and senescence based on a novel mechanism whereby UCP2 can regulate the NAD+-SIRT3 axis. Targeting oxidative stress and senescence amelioration, UCP2-SIRT3 signaling may serve as a method for the prevention and treatment of DR and other diabetic vascular diseases.

Uncoupling protein 2 modulates polarization and metabolism of human primary macrophages via glycolysis and the NF‑κB pathway.

Metabolic abnormalities, particularly the M1/M2 macrophage imbalance, play a critical role in the development of various diseases, leading to severe inflammatory responses. The present study aimed to investigate the role of uncoupling protein 2 (UCP2) in regulating macrophage polarization, glycolysis, metabolic reprogramming, reactive oxygen species (ROS) and inflammation. Primary human macrophages were first polarized into M1 and M2 subtypes, and these two subtypes were infected by lentivirus-mediated UCP2 overexpression or knockdown, followed by enzyme-linked immunosorbent assay, reverse transcription-quantitative PCR, western blotting and flow cytometry to analyze the effects of UCP2 on glycolysis, oxidative phosphorylation (OXPHOS), ROS production and cytokine secretion, respectively. The results demonstrated that UCP2 expression was suppressed in M1 macrophages and increased in M2 macrophages, suggesting its regulatory role in macrophage polarization. UCP2 overexpression decreased macrophage glycolysis, increased OXPHOS, decreased ROS production, and led to the conversion of M1 polarization to M2 polarization. This process involved NF-κB signaling to regulate the secretion profile of cytokines and chemokines and affected the expression of key enzymes of glycolysis and a key factor for maintaining mitochondrial homeostasis (nuclear respiratory factor 1). UCP2 knockdown in M2 macrophages exacerbated inflammation and oxidative stress by promoting glycolysis, which was attenuated by the glycolysis inhibitor 2-deoxyglucose. These findings highlight the critical role of UCP2 in regulating macrophage polarization, metabolism, inflammation and oxidative stress through its effects on glycolysis, providing valuable insights into potential therapeutic strategies for macrophage-driven inflammatory and metabolic diseases.

Exploring a new mechanism between lactate and VSMC calcification: PARP1/POLG/UCP2 signaling pathway and imbalance of mitochondrial homeostasis

Lactate leads to the imbalance of mitochondria homeostasis, which then promotes vascular calcification. PARP1 can upregulate osteogenic genes and accelerate vascular calcification. However, the relationship among lactate, PARP1, and mitochondrial homeostasis is unclear. The present study aimed to explore the new molecular mechanism of lactate to promote VSMC calcification by evaluating PARP1 as a breakthrough molecule. A coculture model of VECs and VSMCs was established, and the model revealed that the glycolysis ability and lactate production of VECs were significantly enhanced after incubation in DOM. Osteogenic marker expression, calcium deposition, and apoptosis in VSMCs were decreased after lactate dehydrogenase A knockdown in VECs. Mechanistically, exogenous lactate increased the overall level of PARP and PARylation in VSMCs. PARP1 knockdown inhibited Drp1-mediated mitochondrial fission and partially restored PINK1/Parkin-mediated mitophagy, thereby reducing mitochondrial oxidative stress. Moreover, lactate induced the translocation of PARP1 from the nucleus to the mitochondria, which then combined with POLG and inhibited POLG-mediated mitochondrial DNA synthesis. This process led to the downregulation of mitochondria-encoded genes, disturbance of mitochondrial respiration, and inhibition of oxidative phosphorylation. The knockdown of PARP1 could partially reverse the damage of mitochondrial gene expression and function caused by lactate. Furthermore, UCP2 was upregulated by the PARP1/POLG signal, and UCP2 knockdown inhibited Drp1-mediated mitochondrial fission and partially recovered PINK1/Parkin-mediated mitophagy. Finally, UCP2 knockdown in VSMCs alleviated DOM-caused VSMC calcification in the coculture model. The study results thus suggest that upregulated PARP1 is involved in the mechanism through which lactate accelerates VSMC calcification partly via POLG/UCP2-caused unbalanced mitochondrial homeostasis.

Matrine alleviates oxidative stress and ferroptosis in severe acute pancreatitis-induced acute lung injury by activating the UCP2/SIRT3/PGC1α pathway.

Acute lung injury (ALI) is one of the most serious complications of severe acute pancreatitis (SAP). Matrine is well known for its powerful antioxidant and antiapoptotic properties, although its specific mechanism of action in SAP-ALI is unknown. In this study, we examined the effects of matrine on SAP-associated ALIand the specific signaling pathways implicated in SAP-induced ALI, such as oxidative stress, the UCP2-SIRT3-PGC1α pathway, and ferroptosis. The administration of caerulein and lipopolysaccharide (LPS) to UCP2-knockout (UCP2-/-) and wild-type (WT) mice that were pretreated with matrine resulted in pancreatic and lung injury. Changes in reactive oxygen species (ROS) levels, inflammation, and ferroptosis in BEAS-2B and MLE-12 cells were measured following knockdown or overexpression and LPS treatment. Matrine inhibited excessive ferroptosis and ROS production by activating the UCP2/SIRT3/PGC1α pathway while reducing histological damage, edema, myeloperoxidase activity and proinflammatory cytokine expression in the lung. UCP2 knockout decreased the anti-inflammatory properties of matrine and reduced the therapeutic effects of matrine on ROS accumulation and ferroptosis hyperactivation. LPS-induced ROS production and ferroptosis activation in BEAS-2B cells and MLE-12 cells were further enhanced by knockdown of UCP2, but this effect was rescued by UCP2 overexpression. This study demonstrated that matrine reduced inflammation, oxidative stress, and excessive ferroptosis in lung tissue during SAP by activating the UCP2/SIRT3/PGC1α pathway, demonstrating its therapeutic potential in SAP-ALI.

Endothelial UCP2 Is a Mechanosensitive Suppressor of Atherosclerosis.

Background:Inflamed endothelial cells (ECs) trigger atherogenesis, especially at arterial regions experiencing disturbed blood flow. UCP2 (Uncoupling protein 2), a key mitochondrial antioxidant protein, improves endothelium-dependent relaxation in obese mice. However, whether UCP2 can be regulated by shear flow is unknown, and the role of endothelial UCP2 in regulating inflammation and atherosclerosis remains unclear. This study aims to investigate the mechanoregulation of UCP2 expression in ECs and the effect of UCP2 on endothelial inflammation and atherogenesis.Methods:In vitro shear stress simulation system was used to investigate the regulation of UCP2 expression by shear flow. EC-specific Ucp2 knockout mice were used to investigate the role of UCP2 in flow-associated atherosclerosis.Results:Shear stress experiments showed that KLF2 (Krüppel-like factor 2) mediates fluid shear stress-dependent regulation of UCP2 expression in human aortic and human umbilical vein ECs. Unidirectional shear stress, statins, and resveratrol upregulate whereas oscillatory shear stress and proinflammatory stimuli inhibit UCP2 expression through altered KLF2 expression. KLF2 directly binds to UCP2 promoter to upregulate its transcription in human umbilical vein ECs. UCP2 knockdown induced expression of genes involved in proinflammatory and profibrotic signaling, resulting in a proatherogenic endothelial phenotype. EC-specific Ucp2 deletion promotes atherogenesis and collagen production. Additionally, we found endothelial Ucp2 deficiency aggravates whereas adeno-associated virus-mediated EC-Ucp2 overexpression inhibits carotid atherosclerotic plaque formation in disturbed flow-enhanced atherosclerosis mouse model. RNA-sequencing analysis revealed FoxO1 (forkhead box protein O1) as the major proinflammatory transcriptional regulator activated by UCP2 knockdown, and FoxO1 inhibition reduced vascular inflammation and disturbed flow-enhanced atherosclerosis. We showed further that UCP2 level is critical for phosphorylation of AMPK (AMP-activated protein kinase), which is required for UCP2-induced inhibition of FoxO1.Conclusions:Altogether, our studies uncover that UCP2 is novel mechanosensitive gene under the control of fluid shear stress and KLF2 in ECs. UCP2 expression is critical for endothelial proinflammatory response and atherogenesis. Therapeutic strategies enhancing UCP2 level may have therapeutic potential against atherosclerosis.

Oxidative Crosstalk with Venular Capillary Mitochondria Mediates Barrier Failure in Acute Lung Injury

OBJECTIVE. To elucidate mechanisms underlying alveolar‐capillary crosstalk in the context of lipopolysaccharide (LPS)‐induced Acute Lung Injury (ALI), which causes The Acute Respiratory Distress Syndrome (ARDS).HYPOTHESISOxidative crosstalk between alveolar epithelium and adjacent endothelium causes mitochondrial injury and barrier failure in Acute Lung InjuryMETHODS. We instilled LPS (5mg/kg) by the intranasal (i.n.) route in anesthetized mice. We evaluated microvascular endothelia of isolated blood‐perfused mouse lungs by confocal microscopy, and ALI by bronchoalveolar lavage (BAL) 48h later. For microscopy, we gave the potentiometric mitochondrial dye MTDR, and the reactive oxygen species (ROS) indicator DCF by intravascular infusion. We determined the role of endothelial uncoupling protein 2 (UCP2) by (1) UCP2 knockdown in endothelia by vascular siRNA injection, and (2) endothelial‐specific knockout of UCP2. We transfected alveolar epithelium by i.n. instillation of catalase‐expressing plasmid, or depleted neutrophils by intraperitoneal injection of anti‐Gr1 antibody, 24 hours before i.n. LPS. We quantified barrier permeability through BAL protein content.RESULTS. Confocal imaging indicated that baseline fluorescence intensity of both endothelial MTDR and DCF was steady, indicating that endothelial mitochondrial potential and endothelial ROS were stable. However, 48 hours after LPS instillation, MTDR fluorescence decreased in venular capillaries more than in alveolar capillaries (n=4, p<0.05), indicating endothelial mitochondrial depolarization. Simultaneously, DCF fluorescence increased in venular capillaries more than in alveolar capillaries (n=4, p<0.05), indicating an increase in endothelial ROS. LPS instillation increased BAL protein (n=4, p<0.05). Knockdown of endothelial UCP2 expression, or expression of transfected catalase in the alveolar epithelium blocked LPS‐induced endothelial mitochondrial depolarization and BAL protein increase (p<0.05). Endothelial‐specific knockout of UCP2, but not neutrophil depletion, blocked LPS‐induced BAL protein increase (p<0.05).CONCLUSIONS. We show here for the first time that the hyper‐permeable responses of LPS‐induced ALI result from mitochondrial depolarization in venular capillaries. Transfer of H2O2 from alveoli, not neutrophils activated UCP2, causing proton influx into the mitochondrial matrix. Our findings reveal a novel mechanism of LPS‐induced ALI, implicating mitochondria‐oxidant coupling in barrier failure. Thus, UCP2 presents a potential therapeutic target for ARDS.

Pro‐inflammatory Cytokines Increase Glycolysis through Upregulation of Uncoupling Protein and Akt Activation in Colorectal Cancer Cells

Non‐cancerous colonocytes use butyrate, which is a short‐chain fatty acid derived from the fermentation of dietary fiber, as a primary energy source. In contrast, cancerous colonocytes use glucose as their preferred energetic substrate and undergo enhanced glycolysis or the Warburg effect. It has been reported that increased production of pro‐inflammatory cytokines such as interleukin1 beta and tumor necrosis factor alpha (TNFalpha) promote glycolysis. Previously, we have shown that interleukin1 beta increased glycolysis and decreased butyrate oxidation. However, the mechanism underlying how this pro‐inflammatory cytokine increased glycolysis was unclear. Here, we have discovered that Uncoupling Protein 2 (UCP2) appears to mediate the elevation in glycolysis induced by interleukin1 beta. UCP2 is a mitochondrial protein that transports the protons back into the mitochondrial matrix, thus dissipating the proton gradient and reducing ATP production. UCP2 is upregulated in various cancers such as breast, prostate, skin, and colorectal cancers. We hypothesize that interleukin1 beta promotes glycolysis by upregulating UCP2 and activating Akt in colorectal cancer cells. We have found colorectal cancer cells treated with interleukin1 beta showed elevated UCP2 expression and increased Akt activation. Next, we utilized the Seahorse XFe24 analyzer to check whether interleukin1 beta affects proton leak and ATP production in colorectal cancer cells. Preliminary data suggests that interleukin1 beta increases proton leak and decreases ATP production in mitochondria, which is consistent with the upregulation of UCP2 and demonstrates a functional consequence. To study whether UCP2 mediates the interleukin1 beta effect toward increasing glycolysis, we created a stable UCP2 knockdown in colorectal cancer cells and tested whether colorectal cancer cells that had diminished UCP2 from the RNAi knockdown did not show an increase in glycolysis when treated with interleukin1 beta as compared to RNAi mock colorectal cancer cells. Our preliminary data allude to a role for UCP2 in mediating the interleukin1 beta induced increase in glycolysis observed in colorectal cancer cells.

Endothelial Cells Mediated by UCP2 Control the Neurogenic-to-Astrogenic Neural Stem Cells Fate Switch During Brain Development.

During mammalian cortical development, neural stem/progenitor cells (NSCs) gradually alter their characteristics, and the timing of generation of neurons and glial cells is strictly regulated by internal and external factors. However, whether the blood vessels located near NSCs affect the neurogenic‐to‐gliogenic transition remain unknown. Here, it is demonstrated that endothelial uncoupling protein 2 (UCP2) deletion reduces blood vessel diameter and affects the transition timing of neurogenesis and gliogenesis. Deletion of endothelial UCP2 results in a persistent increase in astrocyte production at the postnatal stage. Mechanistically, the endothelial UCP2/ROS/ERK1/2 pathway increases chymase‐1 expression to enhance angiotensin II (AngII) secretion outside the brain endothelium. The endotheliocyte‐driven AngII‐gp130‐JAK‐STAT pathway also regulates gliogenesis initiation. Moreover, endothelial UCP2 knockdown decreases human neural precursor cell (hNPC) differentiation into neurons and accelerates hNPC differentiation into astrocytes. Altogether, this work provides mechanistic insights into how endothelial UCP2 regulates the neurogenic‐to‐gliogenic fate switch in the developing neocortex.

Impact of UCP2 depletion on heat stroke-induced mitochondrial function in human umbilical vein endothelial cells

Objective The incidence rate of heat stroke (HS) has increased, with high morbidity and mortality rates, in recent years. Previous studies have suggested that vascular endothelial cell injury is one of the main pathological features of HS. Uncoupling protein 2 (UCP2) exhibits antioxidant activity under various stress conditions. This study aims to investigate the role of UCP2 in HS-induced vascular endothelial injury. Method To explore the mechanisms mediating vascular endothelial cell injury induced by HS, we established an HS model of HUVECs in vitro. The percentage of cell death and viability induced by HS were assessed using annexin V-FITC/PI staining and CCK8 assays. HS-induced mitochondrial membrane potential (ΔΨm) was detected by JC-1 staining. HS-induced mitochondrial superoxide was measured by MitoSOX staining, and analyzed by flow cytometry. UCP2, Drp1, phosphorylated Drp1, OPA1, and Mfn2 expression levels were measured by western blotting. Results HS triggered mitochondrial fragmentation and UCP2 upregulation in a time-dependent manner in HUVECs. As a specific Drp1 inhibitor, Mdivi‐1 pretreatment significantly promoted mitochondrial fission and apoptosis in HS-induced HUVECs. In addition, siRNA-mediated UCP2 knockdown further aggravated mitochondrial fragmentation and ΔΨm depolarization and increased mitochondrial ROS production and cell apoptosis in HS-induced HUVECs, which were abolished by Drp1 inhibition. Conclusion Our results indicate that UCP2 protects against HS-induced vascular endothelial damage and that it enhances mitochondrial function. These findings reveal that UCP2 can be a potential contributor to mechanism-based therapeutic strategies for HS.

Neuroprotection of retinal cells by Caffeic Acid Phenylethyl Ester（CAPE) is mediated by mitochondrial uncoupling protein UCP2

Oxidative stress due to mitochondrial produced reactive oxygen species is a major cause of damage seen in many retinal degenerative diseases. Caffeic acid phenylethyl ester （CAPE） is protective agent in multiple tissues and is reported to have anti-oxidant properties. Systemically applied CAPE protected retinal ganglion cells from ischemic injury induced by increased intraocular pressure. CAPE provided complete protection for ARPE19 retinal pigment epithelial cells against tert-butyl hydrogen peroxide and reduced both basal and LPS-stimulated ROS production. The major effect of CAPE was mediated by the mitochondrial uncoupling protein UCP2 since both pharmacological inhibition of UCP2 and siRNA-induced knockdown removed the ability of CAPE to block ROS production. Based on common structural features, CAPE may be acting as a mimetic of the natural UCP2 homeostatic regulator 4-hydroxy-2-nonenal. CAPE may provide a valuable tool to treat oxidative stress-related damage in retinal and other degenerative diseases.

Klotho inhibits H2 O2 -induced oxidative stress and apoptosis in periodontal ligament stem cells by regulating UCP2 expression.

Periodontitis, a human chronic inflammatory disease, has affected the lives of millions of individuals. Periodontal ligament stem cells (PDLSCs), derived from the periodontal ligament, exhibit tissue specificity and impaired differentiation ability and are closely associated with tissue regeneration in periodontitis. Klotho, a single-pass transmembrane protein, has been reported to positively affect H2 O2 -induced oxidative stress and inflammation in PDLSCs. The ultimate damage of oxidative stress stimulation in PDLSCs was cell apoptosis, which was also the major lesion in periodontitis. Thus, the present study aimed to figure out the effect of klotho on H2 O2 -injured PDLSCs and its underlying mechanism to provide new therapeutic targets in periodontitis. The expression of klotho and uncoupling protein 2 (UCP2) was investigated in the gingival tissues, gingival crevicular fluid (GCF), and periodontal ligament stem cells (PDLSCs) in patients with chronic periodontitis. Then, under klotho treatment, oxidative stress was evaluated by measuring SOD and GSH-PX levels. Cell apoptosis and cell necrosis were also detected by measuring the cell death-relevant proteins, including Caspase-3, BAX, Bcl, MLKL, RIP1, and RIP3. Finally, a rescue assay was performed by inhibiting the expression of UCP2. The results showed that klotho and UCP2 were downregulated in patients with chronic periodontitis. In addition, klotho upregulated the production of UCP2 in H2 O2 -treated PDLSCs. Klotho inhibited H2 O2 -induced oxidative stress and cellular loss in PDLSCs, moreover, the rescue assay suggested that UCP2 knockdown suppressed the effects of klotho on PDLSCs. In conclusion, this study showed that klotho inhibits H2 O2 -induced oxidative stress and apoptosis in PDLSCs by regulating UCP2 expression. This novel discovery might provide a potential target for chronic periodontitis treatment.

Role and mechanism of FLNa and UCP2 in the development of cervical cancer.

Recent studies have reported that filamin A (FLNa) and uncoupling protein 2 (UCP2) are highly expressed in various types of cancer, but little is currently known about their roles in cervical cancer (CC). In the present study, immunohistochemical staining of paraffin sections of cervical tissues was performed in order to compare the differential expression of FLNa, UCP2, p16 and Ki67 between CC and high-grade intraepithelial neoplasia (HSIL). UCP2 and FLNa were knocked down in CC cell lines to investigate the effects on cell proliferation, cell cycle arrest, apoptosis, migration and invasion. In addition, the present study investigated the expression of cell-associated proteins [extracellular signal-regulated kinase (ERK), phosphorylated (p) ERK, protein kinase B (AKT), p-AKT and B-cell lymphoma-2 (Bcl-2)] and the mRNA levels of cellular proteins such as Ras, matrix metalloproteinase (MMP)-2 and MMP-9. FLNa and UCP2 expression levels were significantly higher in CC tissues than in HSIL tissues, with no significant differential expression of p16 or Ki67. UCP2 expression was significantly different in patients with clinical stage II or higher or lymph node metastasis compared with in other patients with cervical cancer. FLNa or UCP2 knockdown slowed or decreased SiHa and HeLa cell proliferation, migration and invasion, with no significant change in apoptosis, and downregulated the protein levels of p-ERK1/2, and the mRNA levels of Ras, MMP-2 and MMP-9. UCP2 knockdown arrested the cell cycle at the G2 phase in SiHa and HeLa cells, while FLNa knockdown arrested the cell cycle at the G2 phase in HeLa cells. The results of the present study revealed that FLNa and UCP2 play roles in the development and progression of CC via the Ras/MAPK/ERK signalling pathway. FLNa and UCP2 are superior to p16 and Ki67 for early prediction of CC, indicating that FLNa and UCP2 may be used for the early diagnosis of CC. UCP2 may be used to predict the prognosis of CC.

Genipin enhances the antitumor effect of elesclomol in A549 lung cancer cells by blocking uncoupling protein-2 and stimulating reactive oxygen species production.

The uncoupling protein-2 (UCP2) serves a role in tumor aggressiveness and anticancer resistance, which is considered to be associated with its ability to attenuate reactive oxygen species (ROS) production. We hypothesized that UCP2 may protect cancer cells from elesclomol-induced cytotoxicity, and that this may be overcome by blocking UCP2 function with genipin. In A549 lung cancer cells that exhibited high UCP2 expression, treatment with elesclomol alone induced limited changes in glucose uptake, ROS production and cell survival. By contrast, both UCP2 knockdown and genipin treatment mildly reduced glucose uptake, increased ROS production and decreased cell survival. Combining genipin and elesclomol further reduced glucose uptake and increased cellular and mitochondrial ROS production. Moreover, co-treatment with genipin and elesclomol reduced the colony forming capacity to 50.6±7.4% and the cell survival to 42.0±3.4% of that in the control cells (both P<0.001). Suppression of cell survival by treatment with elesclomol and genipin was enhanced in the presence of an exogenous ROS inducer and attenuated by a ROS scavenger. The cytotoxic effects of combining genipin and elesclomol were accompanied by reduced mitochondrial membrane potential and occurred through apoptosis as demonstrated by Annexin V assay and increased protein cleavage of PARP and caspase-3. Finally, in an A549 ×enograft mouse model, tumor growth was only modestly retarded by treatment with elesclomol or genipin alone, but was markedly suppressed by combining the two drugs compared with that in the control group (P=0.008). Therefore, high UCP2 expression may limit the antitumor effect of elesclomol by attenuating ROS responses, and this may be overcome by co-treatment with genipin; combining elesclomol and genipin may be an effective strategy for treating cancers with high UCP2.

Abstract 1897: Mechanism of MEK inhibitor resistance in triple negative breast cancer

Abstract Background: Triple-negative breast cancer (TNBC) is an aggressive disease associated with recurrence, metastasis, and resistance to chemotherapy and radiation; effective targeted therapies are needed. Although the MEK inhibitors (MEKi) selumetinib (AZD6244) and pimasertib (AS703026) showed therapeutic efficacy in preclinical models, they failed as effective single agents in the clinic due to development of intrinsic resistance. To identify potential mediators of this resistance, we performed a synthetic lethal siRNA screen and identified myeloid cell leukemia-1 (MCL1) as a potential mediator of selumetinib resistance. Mcl-1 is an anti-apoptotic protein that is highly amplified in numerous human cancers and associated with cell immortalization and chemoresistance. We hypothesized that Mcl-1 promotes MEKi resistance in TNBC, and sought to confirm this and discern of mechanisms. Results: We established selumetinib- and pimasertib-resistant clones of TNBC cells SUM-149 and MDA-MB-231 to a final concentration of 15µM selumetinib and 11µM pimasertib by continuous exposure to increasing concentrations over a 6-month period. MEKi-resistant cells showed a significantly higher proliferation rate than the parental cells. More colonies were observed among the MEKi-resistant cells than in the parental cells in a colony formation assay (40%, p=0.05) and a similar outcome was observed in a mammosphere assay (65%, p=0.01), suggesting a higher fraction of tumor-initiating cells. To determine if the Mcl-1-specific inhibitor S63845 could sensitize the MEKi-resistant cells, we treated parental and resistant cells with either selumetinib or pimasertib together with S63845, a highly specific Mcl-1 inhibitor. After treatment with the Mcl-1 inhibitor, the resistant SUM-149 and MDA-MB-231 cells had similar cell proliferation rates to those of their parental counterparts. To extrapolate the mechanism of MEKi resistance, we performed an RT2 Profiler PCR Human Mitochondria Array; mitochondrial uncoupling proteins UCP4 and UCP2 were upregulated in the SUM149 and MDA-MB-231 MEKi-resistant cells, respectively. MDA-MB-231 MEKi-resistant cells had higher levels of glycolysis than the parental control cells, suggesting that the MEKi-resistant cells had undergone a metabolic shift to enhance glycolysis. This is consistent with a observation that metabolic alterations play a part in drug resistance. In addition, the Warbug effect, in which tumor cells adopt aerobic glycolysis, is considered the major adaptive mechanism and increased glycolysis is commonly displayed in resistant cells. Furthermore, knockdown of UCP2 in selumetinib-resistant MDA-MB-231 cells made them ~20% more sensitive to selumetinib. Inhibition of glycolysis using 2-deoxy-D-glucose in combination with MEKi increased drug sensitivity by 20-30%. Conclusion: We found preliminary evidence of a link between Mcl-1 and glycolytic metabolism that may be involved in MEK resistance. We will also design combinational studies of MEKi and Mcl-1 inhibitors in vivo in TNBC models. Citation Format: Maria Gagliardi, Moises Tacam, Lakesla Iles, Yuan Qi, Lajos Pusztai, Debu Tripathy, Geoffrey Bartholomeusz, Chandra Bartholomeusz. Mechanism of MEK inhibitor resistance in triple negative breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1897.

Uncoupling protein 2 is upregulated in melanoma cells and contributes to the activation of Akt/mTOR and ERK signaling

The aim of the present study was to characterize the expression of uncoupling protein2 (UCP2) in melanoma and to study the potential mechanisms underlying the involvement of UCP2 in melanomagenesis using human melanoma cell lines. The expression of UCP2 was evaluated in specimens from normal control subjects, patients with compound nevus, and patients with cutaneous and mucosal melanoma. Stable knockdown of UCP2 was achieved in human melanoma cell lines, which were used to examine whether UCP2 knockdown affects the mitochondrial membrane potential and intracellular levels of ATP, reactive oxygen species and lactate. Cell proliferation, invasion, spheroid formation and cisplatin sensitivity were also evaluated in the UCP2 knockdown cells. Finally, the effects of UCP2 knockdown on the Akt/mammalian target of rapamycin (mTOR) and extracellular signal‑regulated kinase (ERK) pathways, which are important oncogenic pathways during melanomagenesis, were evaluated. Relatively high expression of UCP2 was detected in human melanoma specimens, which was correlated with Clark level and Breslow thickness. Knockdown of UCP2 suppressed cell proliferation, invasion and spheroid formation, and increased the sensitivity of melanoma cells to cisplatin. Furthermore, the UCP2 knockdown cells exhibited inhibition of Akt/mTOR signaling and ERK activation. Therefore, human melanoma tissues exhibit relatively high UCP2 expression, which may be implicated in the mechanisms underlying tumor progression. The potential role of UCP2 in melanomagenesis may involve enhancing the Akt/mTOR and mitogen‑activated protein kinase/ERK pathways.

Inhibition of Uncoupling Protein 2 Enhances the Radiosensitivity of Cervical Cancer Cells by Promoting the Production of Reactive Oxygen Species.

Objective The mechanism of enhanced radiosensitivity induced by mitochondrial uncoupling protein UCP2 was investigated in HeLa cells to provide a theoretical basis as a novel target for cervical cancer treatment. Methods HeLa cells were irradiated with 4 Gy X-radiation at 1.0 Gy/min. The expression of UCP2 mRNA and protein was assayed by real-time quantitative polymerase chain reaction and western blotting. UCP2 siRNA and negative control siRNA fragments were constructed and transfected into HeLa cells 24 h after irradiation. The effect of UCP2 silencing and irradiation on HeLa cells was determined by colony formation, CCK-8 cell viability, γH2AX immunofluorescence assay of DNA damage, Annexin V-FITC/PI apoptosis assay, and propidium iodide cell cycle assay. The effects on mitochondrial structure and function were investigated with fluorescent probes including dichlorodihydrofluorescein diacetate (DCFH-DA) assay of reactive oxygen species (ROS), rhodamine 123, and MitoTracker Green assay of mitochondrial structure and function. Results Irradiation upregulated UCP2 expression, and UCP2 knockdown decreased the survival of irradiated HeLa cells. UCP2 silencing sensitized HeLa cells to irradiation-induced DNA damage and led to increased apoptosis, cell cycle arrest in G2/M, and increased mitochondrial ROS. Increased radiosensitivity was associated with an activation of P53, decreased Bcl-2, Bcl-xl, cyclin B, CDC2, Ku70, and Rad51 expression, and increased Apaf-1, cytochrome c, caspase-3, and caspase-9 expression. Conclusions UCP2 inhibition augmented the radiosensitivity of cervical cancer cells, and it may be a potential target of radiotherapy of advanced cervical cancer.

UCP2 promotes proliferation and chemoresistance through regulating the NF-κB/β-catenin axis and mitochondrial ROS in gallbladder cancer

Uncoupling protein 2 (UCP2) is a mitochondrial anion carrier which plays a key role in energy homeostasis. UCP2 is deregulated in several human cancers and has been suggested to regulate cancer metabolism. However, the role of UCP2 in gallbladder cancer has not been defined.Using clinical samples, we found highly expressed UCP2 in gallbladder cancer tissues, and higher expression levels of UCP2 correlated with worse clinical characteristics. To study whether UCP2 promotes gallbladder cancer growth, UCP2 stable knockdown cells were generated, and cell proliferation was suppressed in these knockdown cells. Further studies demonstrated that glycolysis was inhibited and IKKβ, as well as the downstream signaling molecules NF-κB/FAK/β-catenin, were downregulated in UCP2 knockdown cells. More importantly, gallbladder cancer cells became sensitive to gemcitabine treatments when UCP2 was inhibited. UCP2 knockdown suppressed the activation of the NF-κB/β-catenin axis and promoted the increases in mitochondrial ROS in gallbladder cancer cells exposed to gemcitabine treatments. The UCP2 inhibitor genipin suppressed xenograft tumor growth and sensitized grafted tumors to gemcitabine treatments. These results suggest targeting UCP2 as a novel therapeutic strategy for the treatment of gallbladder cancer.

Direct impact of cisplatin on mitochondria induces ROS production that dictates cell fate of ovarian cancer cells

Patients with high-grade serous ovarian cancer (HGSC) frequently receive platinum-based chemotherapeutics, such as cisplatin. Cisplatin binds to DNA and induces DNA-damage culminating in mitochondria-mediated apoptosis. Interestingly, mitochondrial DNA is critically affected by cisplatin but its relevance in cell death induction is scarcely investigated. We find that cisplatin sensitive HGSC cell lines contain higher mitochondrial content and higher levels of mitochondrial ROS (mtROS) than cells resistant to cisplatin induced cell death. In clonal sub-lines from OVCAR-3 mitochondrial content and basal oxygen consumption rate correlate with sensitivity to cisplatin induced apoptosis. Mitochondria are in two ways pivotal for cisplatin sensitivity because not only knock-down of BAX and BAK but also the ROS scavenger glutathione diminish cisplatin induced apoptosis. Mitochondrial ROS correlates with mitochondrial content and reduction of mitochondrial biogenesis by knock-down of transcription factors PGC1α or TFAM attenuates both mtROS induction and cisplatin induced apoptosis. Increasing mitochondrial ROS by inhibition or knock-down of the ROS-protective uncoupling protein UCP2 enhances cisplatin induced apoptosis. Similarly, enhancing ROS by high-dose ascorbic acid or H2O2 augments cisplatin induced apoptosis. In summary, mitochondrial content and the resulting mitochondrial capacity to produce ROS critically determine HGSC cell sensitivity to cisplatin induced apoptosis. In line with this observation, data from the human protein atlas (www.proteinatlas.org) indicates that high expression of mitochondrial marker proteins (TFAM and TIMM23) is a favorable prognostic factor in ovarian cancer patients. Thus, we propose mitochondrial content as a biomarker for the response to platinum-based therapies. Functionally, this might be exploited by increasing mitochondrial content or mitochondrial ROS production to enhance sensitivity to cisplatin based anti-cancer therapies.

UCP2 silencing aggravates mitochondrial dysfunction in astrocytes under septic conditions

Uncoupling protein 2 (UCP2) plays a positive role in sepsis. However, the role of UCP2 in experimental sepsis in astrocytes remains unknown. The present study was designed to determine whether UCP2 has a protective effect in an experimental sepsis model in astrocytes asnd to clarify the mechanisms responsible for its neuroprotective effects after sepsis. An experimental astrocyte model mimicking sepsis-induced brain injury was established using lipopolysaccharide (LPS) and interferon (IFN)-γ. Additionally, UCP2 knockdown in astrocytes was achieved by adenovirus transfection. Tumor necrosis factor (TNF)-α and interleukin (IL)-1β activity, mitochondrial membrane potential (MMP) and reactive oxygen species (ROS), and adenosine triphosphate (ATP) levels were assessed. The mitochondrial ultrastructure was evaluated, and the expression of UCP2 was determined by western blotting. LPS with IFN-γ co-stimulation increased the mRNA and protein expression levels of UCP2 in astrocytes, damaged the mitochondrial structure, and accelerated the release of TNF-α and IL-1β, resulting in a decrease in the MMP, and the excessive generation of ROS. Moreover, sepsis also caused a reduction in ATP production. The knockdown of UCP2 exacerbated astrocyte injury and mitochondrial impairment. In conclusion, both the function and morphology of mitochondria were damaged in an experimental model of sepsis in astrocytes, and knockdown of UCP2 using shRNA exacerbated this impairment, suggesting that UCP2 has a positive effect on astrocytes as determined in an experimental sepsis model.