Regulatory role of PDK1 via integrated gene analysis of mitochondria-immune response in periodontitis

AIMS

To investigate the association between mitochondrial events and immune response in periodontitis and related regulatory genes.

MAIN METHODS

Gene expression profiles in gingival tissues were retrieved from the Gene Expression Omnibus. Mitochondria-immune response-related differentially expressed genes (MIR-DEGs) between the healthy and periodontitis samples were determined. WGCNA, GO, and KEGG were used to investigate the function and the enriched pathways of MIR-DEGs. The correlation between MIR-DEGs expression and clinical probing pocket depth was analyzed. The MIR-DEGs were further identified and verified in animal samples. A periodontitis model was established in C57BL/6 mice with silk ligation. Micro-computed tomography was used to assess alveolar bone loss. Western blot, quantitative real-time polymerase chain reaction, and immunohistochemical analyses further validated the differential expression of the MIR-DEGs.

KEY FINDINGS

A total of ten MIR-DEGs (CYP24A1, PRDX4, GLDC, PDK1, BCL2A1, CBR3, ARMCX3, BNIP3, IFI27, and UNG) were identified, the expression of which could effectively distinguish patients with periodontitis from the healthy controls. Enhanced immune response was detected in the periodontitis group with that in the healthy controls, especially in B cells. PDK1 was a critical MIR-DEG correlated with B cell immune response and clinical periodontal probing pocket depth. Both animal and clinical periodontal samples presented higher gene and protein expression of PDK1 than the control samples. Additionally, PDK1 colocalized with B cells in both animal and clinical periodontal tissues.

SIGNIFICANCE

Mitochondria participate in the regulation of the immune response in periodontitis. PDK1 may be the key mitochondria-related gene regulating B-cell immune response in periodontitis.

Upregulation of the AMPK-FOXO1-PDK4 pathway is a primary mechanism of pyruvate dehydrogenase activity reduction in tafazzin-deficient cells

Barth syndrome (BTHS) is a rare disorder caused by mutations in the TAFAZZIN gene. Previous studies from both patients and model systems have established metabolic dysregulation as a core component of BTHS pathology. In particular, features such as lactic acidosis, pyruvate dehydrogenase (PDH) deficiency, and aberrant fatty acid and glucose oxidation have been identified. However, the lack of a mechanistic understanding of what causes these conditions in the context of BTHS remains a significant knowledge gap, and this has hindered the development of effective therapeutic strategies for treating the associated metabolic problems. In the current study, we utilized tafazzin-knockout C2C12 mouse myoblasts (TAZ-KO) and cardiac and skeletal muscle tissue from tafazzin-knockout mice to identify an upstream mechanism underlying impaired PDH activity in BTHS. This mechanism centers around robust upregulation of pyruvate dehydrogenase kinase 4 (PDK4), resulting from hyperactivation of AMP-activated protein kinase (AMPK) and subsequent transcriptional upregulation by forkhead box protein O1 (FOXO1). Upregulation of PDK4 in tafazzin-deficient cells causes direct phospho-inhibition of PDH activity accompanied by increased glucose uptake and elevated intracellular glucose concentration. Collectively, our findings provide a novel mechanistic framework whereby impaired tafazzin function ultimately results in robust PDK4 upregulation, leading to impaired PDH activity and likely linked to dysregulated metabolic substrate utilization. This mechanism may underlie previously reported findings of BTHS-associated metabolic dysregulation.

Pyruvate dehydrogenase kinase 2 knockdown restores the ability of amyotrophic lateral sclerosis-linked SOD1G93A rat astrocytes to support motor neuron survival by increasing mitochondrial respiration

Amyotrophic lateral sclerosis (ALS) is characterized by progressive motor neuron (MN) degeneration. Various studies using cellular and animal models of ALS indicate that there is a complex interplay between MN and neighboring non-neuronal cells, such as astrocytes, resulting in noncell autonomous neurodegeneration. Astrocytes in ALS exhibit a lower ability to support MN survival than nondisease-associated ones, which is strongly correlated with low-mitochondrial respiratory activity. Indeed, pharmacological inhibition of pyruvate dehydrogenase kinase (PDK) led to an increase in the mitochondrial oxidative phosphorylation pathway as the primary source of cell energy in SOD1G93A astrocytes and restored the survival of MN. Among the four PDK isoforms, PDK2 is ubiquitously expressed in astrocytes and presents low expression levels in neurons. Herein, we hypothesize whether selective knockdown of PDK2 in astrocytes may increase mitochondrial activity and, in turn, reduce SOD1G93A-associated toxicity. To assess this, cultured neonatal SOD1G93A rat astrocytes were incubated with specific PDK2 siRNA. This treatment resulted in a reduction of the enzyme expression with a concomitant decrease in the phosphorylation rate of the pyruvate dehydrogenase complex. In addition, PDK2-silenced SOD1G93A astrocytes exhibited restored mitochondrial bioenergetics parameters, adopting a more complex mitochondrial network. This treatment also decreased lipid droplet content in SOD1G93A astrocytes, suggesting a switch in energetic metabolism. Significantly, PDK2 knockdown increased the ability of SOD1G93A astrocytes to support MN survival, further supporting the major role of astrocyte mitochondrial respiratory activity in astrocyte-MN interactions. These results suggest that PDK2 silencing could be a cell-specific therapeutic tool to slow the progression of ALS.

Long non-coding RNA NEAT1 promotes aerobic glycolysis and progression of cervical cancer through WNT/β-catenin/PDK1 axis

BACKGROUND

Cervical cancer is one of the most common gynecological cancers. Accumulated evidence shows that long non-coding RNAs (lncRNAs) play essential roles in cervical cancer occurrence and progression, but their specific functions and mechanisms remain to be further explored.

METHODS

The RT-qPCR assay was used to detect the expression of NEAT1 in cervical cancer tissues and cell lines. CCK-8, colony formation, flow cytometry, western blotting, and Transwell assays were used to evaluate the impact of NEAT1 on the malignant behavior of cervical cancer cells. Glucose consumption, lactate production, ATP levels, ROS levels, MMP levels, and the mRNA expressions of glycolysis-related genes and tricarboxylic acid cycle-related genes were detected to analyze the effect of NEAT1 on metabolism reprograming in cervical cancer cells. The expressions of PDK1, β-catenin and downstream molecules of the WNT/β-catenin signaling pathway in cervical cancer cells and tissues were detected by western blotting, RT-qPCR, immunofluorescence and immunohistochemistry assays.

RESULTS

This study investigated the role and possible molecular mechanism of lncRNA nuclear paraspeckle assembly transcript 1 (NEAT1) in cervical cancer. Our results showed that NEAT1 was highly expressed in cervical cancer tissues and cell lines. Downregulation of NEAT1 inhibited the proliferation, migration, invasion and glycolysis of cervical cancer cells, while overexpression of NEAT1 led to the opposite effects. Mechanistically, NEAT1 upregulated pyruvate dehydrogenase kinase (PDK1) through the WNT/β-catenin signaling pathway, which enhanced glycolysis and then facilitated cervical cancer metastasis. Furthermore, NEAT1 maintained the protein stability of β-catenin but did not affect its mRNA level. We also excluded the direct binding of NEAT1 to the β-catenin protein via RNA pull-down assay. The suppressive impact of NEAT1 knockdown on cell proliferation, invasion, and migration was rescued by β-catenin overexpression. The WNT inhibitor iCRT3 attenuated the carcinogenic effect induced by NEAT1 overexpression.

CONCLUSION

In summary, these findings indicated that NEAT1 may contribute to the progression of cervical cancer by activating the WNT/β-catenin/PDK1 signaling axis.

Abrogating PDK4 activates autophagy-dependent ferroptosis in breast cancer via ASK1/JNK pathway

BACKGROUND

Targeting ferroptosis mediated by autophagy presents a novel therapeutic approach to breast cancer, a mortal neoplasm on the global scale. Pyruvate dehydrogenase kinase isozyme 4 (PDK4) has been denoted as a determinant of breast cancer metabolism. The target of this study was to untangle the functional mechanism of PDK4 in ferroptosis dependent on autophagy in breast cancer.

METHODS

RT-qPCR and western blotting examined PDK4 mRNA and protein levels in breast cancer cells. Immunofluorescence staining appraised light chain 3 (LC3) expression. Fe (2 +) assay estimated total iron level. Relevant assay kits and C11-BODIPY (591/581) staining evaluated lipid peroxidation level. DCFH-DA staining assayed intracellular reactive oxygen species (ROS) content. Western blotting analyzed the protein levels of autophagy, ferroptosis and apoptosis-signal-regulating kinase 1 (ASK1)/c-Jun N-terminal kinase (JNK) pathway-associated proteins.

RESULTS

PDK4 was highly expressed in breast cancer cells. Knockdown of PDK4 induced the autophagy of breast cancer cells and 3-methyladenine (3-MA), an autophagy inhibitor, countervailed the promoting role of PDK4 interference in ferroptosis in breast cancer cells. Furthermore, PDK4 knockdown activated ASK1/JNK pathway and ASK1 inhibitor (GS-4997) partially abrogated the impacts of PDK4 absence on the autophagy and ferroptosis in breast cancer cells.

CONCLUSION

To sum up, deficiency of PDK4 activated ASK1/JNK pathway to stimulate autophagy-dependent ferroptosis in breast cancer.

A tryptophan-derived uremic metabolite/Ahr/Pdk4 axis governs skeletal muscle mitochondrial energetics in chronic kidney disease

Chronic kidney disease (CKD) causes accumulation of uremic metabolites that negatively affect skeletal muscle. Tryptophan-derived uremic metabolites are agonists of the aryl hydrocarbon receptor (AHR), which has been shown to be activated in CKD. This study investigated the role of the AHR in skeletal muscle pathology of CKD. Compared with controls with normal kidney function, AHR-dependent gene expression (CYP1A1 and CYP1B1) was significantly upregulated in skeletal muscle of patients with CKD, and the magnitude of AHR activation was inversely correlated with mitochondrial respiration. In mice with CKD, muscle mitochondrial oxidative phosphorylation (OXPHOS) was markedly impaired and strongly correlated with the serum level of tryptophan-derived uremic metabolites and AHR activation. Muscle-specific deletion of the AHR substantially improved mitochondrial OXPHOS in male mice with the greatest uremic toxicity (CKD + probenecid) and abolished the relationship between uremic metabolites and OXPHOS. The uremic metabolite/AHR/mitochondrial axis in skeletal muscle was verified using muscle-specific AHR knockdown in C57BL/6J mice harboring a high-affinity AHR allele, as well as ectopic viral expression of constitutively active mutant AHR in mice with normal renal function. Notably, OXPHOS changes in AHRmKO mice were present only when mitochondria were fueled by carbohydrates. Further analyses revealed that AHR activation in mice led to significantly increased pyruvate dehydrogenase kinase 4 (Pdk4) expression and phosphorylation of pyruvate dehydrogenase enzyme. These findings establish a uremic metabolite/AHR/Pdk4 axis in skeletal muscle that governs mitochondrial deficits in carbohydrate oxidation during CKD.

Pan-cancer analysis reveals PDK family as potential indicators related to prognosis and immune infiltration

Pyruvate dehydrogenase kinases (PDKs) play a key role in glucose metabolism by exerting negative regulation over pyruvate dehyrogenase complex (PDC) activity through phosphorylation. Inhibition of PDKs holds the potential to enhance PDC activity, prompting cells to adopt a more aerobic metabolic profile. Consequently, PDKs emerge as promising targets for condition rooted in metabolic dysregulation, including malignance and diabetes. However, a comprehensive exploration of the distinct contribution of various PDK family members, particularly PDK3, across diverse tumor types remain incomplete. This study undertakes a systematic investigation of PDK family expression patterns, forging association with clinical parameters, using data from the TCGA and GTEx datasets. Survival analysis of PDKs is executed through both Kaplan-Meier analysis and COX regression analysis. Furthermore, the extent of immune infiltration is assessed by leveraging the CIBERSORT algorithm. Our study uncovers pronounced genetic heterogeneity among PDK family members, coupled with discernible clinical characteristic. Significantly, the study establishes the potential utility of PDK family genes as prognostic indicators and as predictors of therapeutic response. Additionally, our study sheds light on the immune infiltration profile of PDK family. The results showed the intimate involvement of these genes in immune-related metrics, including immune scoring, immune subtypes, tumor-infiltrating lymphocytes, and immune checkpoints expression. In sum, the findings of this study offer insightful strategies to guide the therapeutic direction, aiming at leveraging the impact of PDK family genes in cancer treatment.

Unveiling the clinical and electrophysiological profile of CMTX6: Insights from two Brazilian families

BACKGROUND AND AIMS

X-linked Charcot-Marie-Tooth disease type 6 (CMTX6) is an extremely rare condition associated with mutations in the PDK3 gene. To date, only three families from different countries have been reported (Australia, South Korea, and Germany). In this study, we sought to provide a comprehensive clinical and electrophysiological characterization of two Brazilian families.

METHODS

We conducted comprehensive clinical assessments, extensive electrophysiological evaluations, and performed whole-exome sequencing in the probands to investigate the genetic basis of the disease.

RESULTS

Males in the family carrying the Arg162His mutation displayed early-onset motor and/or sensory axonal neuropathy, absence of tendon jerks, pes cavus, and frequently reported pain. Females in the same family exhibited a milder phenotype of the disease with later onset and some remained asymptomatic into their 50s. In the unrelated family with a single affected male, the clinical presentation was characterized by severe progressive sensorimotor polyneuropathy accompanied by neuropathic pain.

INTERPRETATION

We report two Brazilian families with CMTX6 including one harboring a previously unpublished variant in the PDK3 gene, which co-segregates with the disease as expected in a X-linked disease. Notably, the clinical presentations across the five families with available descriptions, including our study, share striking similarities. Furthermore, the proximity of the three reported mutations suggests potential functional similarities and common underlying mechanisms. This study contributes to the growing knowledge of CMTX6 and underscores the importance of international collaborations in studying rare genetic disorders.

Deficiency of Pdk1 drives heart failure by impairing taurine homeostasis through Slc6a6

3-Phosphoinositide-dependent protein kinase-1 (Pdk1) as a serine/threonine protein kinase plays a critical role in multiple signaling pathways. Analysis of the gene expression omnibus database showed that Pdk1 was significantly downregulated in patients with heart diseases. Gene set enrichment analysis of the proteomics dataset identified apoptotic- and metabolism-related signaling pathways directly targeted by Pdk1. Previously, our research indicated that Pdk1 deletion-induced metabolic changes might be involved in the pathogenesis of heart failure; however, the underlying mechanism remains elusive. Here, we demonstrated that deficiency of Pdk1 resulted in apoptosis, oxidative damage, and disturbed metabolism, both in vivo and in vitro. Furthermore, profiling of metabonomics by 1 H-NMR demonstrated that taurine was the major differential metabolite in the heart of Pdk1-knockout mice. Taurine treatment significantly reduced the reactive oxygen species production and apoptosis, improved cardiac function, and prolonged the survival time in Pdk1 deficient mice. Proteomic screening identified solute carrier family 6 member 6 (Slc6a6) as the downstream that altered taurine levels in Pdk1-expression cells. Consistently, cellular apoptosis and oxidative damage were rescued by Slc6a6 in abnormal Pdk1 expression cells. These findings collectively suggest that Pdk1 deficiency induces heart failure via disturbances in taurine homeostasis, triggered by Slc6a6.

Identified eleven exon variants in PKD1 and PKD2 genes that altered RNA splicing by minigene assay

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a common monogenic multisystem disease caused primarily by mutations in the PKD1 gene or PKD2 gene. There is increasing evidence that some of these variants, which are described as missense, synonymous or nonsense mutations in the literature or databases, may be deleterious by affecting the pre-mRNA splicing process.

RESULTS

This study aimed to determine the effect of these PKD1 and PKD2 variants on exon splicing combined with predictive bioinformatics tools and minigene assay. As a result, among the 19 candidate single nucleotide alterations, 11 variants distributed in PKD1 (c.7866C > A, c.7960A > G, c.7979A > T, c.7987C > T, c.11248C > G, c.11251C > T, c.11257C > G, c.11257C > T, c.11346C > T, and c.11393C > G) and PKD2 (c.1480G > T) were identified to result in exon skipping.

CONCLUSIONS

We confirmed that 11 variants in the gene of PKD1 and PKD2 affect normal splicing by interfering the recognition of classical splicing sites or by disrupting exon splicing enhancers and generating exon splicing silencers. This is the most comprehensive study to date on pre-mRNA splicing of exonic variants in ADPKD-associated disease-causing genes in consideration of the increasing number of identified variants in PKD1 and PKD2 gene in recent years. These results emphasize the significance of assessing the effect of exon single nucleotide variants in ADPKD at the mRNA level.

CircRAD54L2 promotes triple-negative breast cancer progression by regulating the miR-888 family/PDK1 axis

BACKGROUND

The long-term prognosis of breast cancer with metastasis remains extremely poor. Genetic alterations in tumor cells result in cellular heterogeneity, promoting cancer cells invasion and colonization in some organs during the metastatic process. CircRNAs are very promising as critical biological markers and precise diagnoses in identifying disease mechanisms and developing new methods for effective treatment. However, the role of aberrant expression of circRNAs in breast cancer progression remains largely unknown.

METHODS

RNase R treatment and quantitative RT-PCR (qRT-PCR) were performed for circRNA detection. Transwell chamber assays were used to examine the chemotactic migration and invasion of breast cancer cells.

RESULTS

This study identified and characterized the circRAD54L2 originating from exon 1, 2, 3, and 4 of the RAD54L2 gene. Importantly, we found that circRAD54L2, rather than RAD54L2 linear mRNA, was significantly upregulated in breast cancer cell lines. Furthermore, we found that inhibiting circRAD54L2 expression markedly reduced the invasion, metastasis, and proliferation of breast cancer cells via sponging of the miR-888 family, which downregulated the expression of pyruvate dehydrogenase kinase 1 (PDK1).

CONCLUSION

Our results showed that circRAD54L2 could regulate PDK1 expression by sponging the miR-888 family competing for the ceRNA mechanism, indicating that circRAD54L2 may act as an essential upstream regulator and providing further mechanistic evidence to support the notion that circRAD54L2/miR-888s/PDK1 is a promising therapeutic target in the treatment of breast cancer.

FOXM1 regulates glycolysis in nasopharyngeal carcinoma cells through PDK1

The transcription factor forkhead box M1 (FOXM1) is a well-known proto-oncogene that plays a significant role in the pathogenesis of various human cancers. However, the regulatory role and underlying mechanisms of FOXM1 in nasopharyngeal carcinoma (NPC) metabolism remain unclear. We demonstrated that FOXM1 could positively regulate glycolysis in NPC cells. Functional studies have shown that pyruvate dehydrogenase kinase 1 (PDK1) is involved in FOXM1-regulated lactate production, ATP generation and glycolysis. FOXM1 binds directly to the PDK1 promoter region and increases the expression of PDK1 at the transcriptional level, leading to the phosphorylation of pyruvate dehydrogenase (PDH) at serine 293, inhibiting its activity. Knocking down FOXM1 using specific short hairpin RNAs (shRNAs) can significantly decrease glycolysis and the expression of PDK1 in NPC cells. Furthermore, microenvironmental factors can increase the expression of FOXM1 by regulating hypoxia-inducible factor 1α (HIF-1α) expression. Clinical data and in vivo studies confirmed the positive roles of FOXM1/PDK1 in NPC proliferation and progression. In conclusion, our findings revealed that FOXM1 regulates glycolysis and proliferation of NPC through PDK1-mediated PDH phosphorylation. Therefore, targeting the FOXM1-PDK1 axis may be a potential therapeutic strategy for NPC.

Crosstalk of LncRNA HOTAIR and SP1-mediated repression of PDK1 contributes to β-Elemene-inhibited proliferation of hepatocellular carcinoma cells

ETHNOPHARMACOLOGICAL RELEVANCE

Hepatocellular carcinoma (HCC) is a liver malignancy which lacks effective treatment and has a poor prognosis. β-Elemene refers to a natural Curcuma wenyujin-derived single molecular entity, which exhibits various biological activities, and is especially well-known for it's antitumor properties.

AIM OF THE RESEARCH

LncRNA HOTAIR, SP1, and PDK1 have displayed oncogenic roles in many tumors, participating in the initiation and progression of cancers by mediating multiple signaling pathways. However, there are only a few reports about their roles and mutual relationship in the growth of HCC cells. Therefore, this study aimed to investigate the expression of LncRNA HOTAIR, SP1, and PDK1 and their interaction with β-Elemene in HCC cells.

MATERIALS AND METHODS

MTT, a Colony formation assay, and flow cytometry were employed to evaluate the growth of HCC and LO2 cells under β-Elemene. LncRNA HOTAIR, SP1 and PDK1 plasmids were transfected into HCC cells by a transient transfection assay, and the expression and interaction of LncRNA HOTAIR, SP1 and PDK1 were assessed via qRT-PCR and western blotting.

RESULTS

β-Elemene suppressed HCC cell growth through the downregulation of LncRNA HOTAIR, SP1 and PDK1. The results demonstrated a reciprocal interaction among LncRNA HOTAIR, SP1 and PDK1. Exogenous overexpression LncRNA HOTAIR or SP1 eliminated the suppressive effects of β-Elemene on them, and both of which regulated PDK1 expression in HCC cells. Additionally, exogenously overexpressed SP1 or LncRNA HOTAIR prevented β-Elemene inhibition of the protein-level expression of PDK1, whereas overexpressing PDK1 had no effect on SP1, though it still weakened the inhibition of cell growth and LncRNA HOTAIR expression by β-Elemene.

CONCLUSION

β-Elemene suppresses HCC cell proliferation via through the regulation of LncRNA HOTAIR, SP1, PDK1 and their interaction.

Impact of Sodium Dichloroacetate Alone and in Combination Therapies on Lung Tumor Growth and Metastasis

Metabolic reprogramming has been recognized as an essential emerging cancer hallmark. Dichloroacetate (DCA), an inhibitor of pyruvate dehydrogenase kinase (PDK), has been reported to have anti-cancer effects by reversing tumor-associated glycolysis. This study was performed to explore the anti-cancer potential of DCA in lung cancer alone and in combination with chemo- and targeted therapies using two non-small cell lung cancer (NSCLC) cell lines, namely, A549 and LNM35. DCA markedly caused a concentration- and time-dependent decrease in the viability and colony growth of A549 and LNM35 cells in vitro. DCA also reduced the growth of tumor xenografts in both a chick embryo chorioallantoic membrane and nude mice models in vivo. Furthermore, DCA decreased the angiogenic capacity of human umbilical vein endothelial cells in vitro. On the other hand, DCA did not inhibit the in vitro cellular migration and invasion and the in vivo incidence and growth of axillary lymph nodes metastases in nude mice. Treatment with DCA did not show any toxicity in chick embryos and nude mice. Finally, we demonstrated that DCA significantly enhanced the anti-cancer effect of cisplatin in LNM35. In addition, the combination of DCA with gefitinib or erlotinib leads to additive effects on the inhibition of LNM35 colony growth after seven days of treatment and to synergistic effects on the inhibition of A549 colony growth after 14 days of treatment. Collectively, this study demonstrates that DCA is a safe and promising therapeutic agent for lung cancer.

Cryptotanshinone, a novel PDK 4 inhibitor, suppresses bladder cancer cell invasiveness via the mTOR/β‑catenin/N‑cadherin axis

The phosphorylation of pyruvate dehydrogenase (PDH) by pyruvate dehydrogenase kinase (PDK) 4 inhibits its ability to induce a glycolytic shift. PDK4 expression is upregulated in various types of human cancer. Because PDK4 regulation is critical for metabolic changes in cancer cells, it is an attractive target for cancer therapy given its ability to shift glucose metabolism. It was previously shown that a novel PDK4 inhibitor, cryptotanshinone (CPT), suppressed the three‑dimensional (3D)‑spheroid formation of pancreatic and colorectal cancer cells. In the present study, the effects of CPT on the invasiveness of bladder cancer cells were investigated. CPT significantly suppressed the invasiveness and 3D‑spheroid formation of T24 and J82 bladder cancer cells. CPT also suppressed the phosphorylation of PDH and β‑catenin, as well as the expression of N‑cadherin, which are all critical for inducing epithelial‑mesenchymal transition (EMT). The knockdown of β‑catenin or PDK4 using specific small interfering RNAs suppressed N‑cadherin expression and invasiveness in T24 cells. An mTOR inhibitor also suppressed the phosphorylation of β‑catenin and N‑cadherin expression. Furthermore, CPT injection significantly suppressed pancreatic tumor growth and peritoneal dissemination of highly metastatic SUIT‑2 pancreatic cancer cells in a mouse orthotopic pancreatic cancer model, without evident toxicity. Moreover, immunohistochemistry analyses demonstrated decreased β‑catenin expression in CPT‑treated pancreatic tumors compared with control tumors. Taken together, these results indicate that CPT reduced the invasiveness and metastasis of bladder cancer cells by suppressing EMT via the mTOR/β‑catenin/N‑cadherin pathway.

LINC00662 modulates cervical cancer cell proliferation, invasion, and apoptosis via sponging miR-103a-3p and upregulating PDK4

Cervical cancer (CC) is one of the most common cancers among women with high recurrence rates all over the world. Recently, the molecular mechanism of CC has been gradually uncovered in accumulating reports. This study aimed to investigate the function and upstream regulation mechanism of pyruvate dehydrogenase kinase 4 (PDK4) in CC cells, which was verified as an oncogene in several cancers. Through RT-qPCR assay, we discovered that PDK4 was highly expressed in CC cells. Then, it was demonstrated in function assays that PDK4 facilitated CC cell proliferation and invasion, but inhibited CC cell apoptosis. Next, we sought to determine the upstream genes of PDK4, and miR-103a-3p was identified to target PDK4. Then, through bioinformatics tools and a range of mechanism assays, long intergenic non-protein coding RNA 662 (LINC00662) was verified as the sponge of miR-103a-3p. Moreover, LINC00662 positively modulated PDK4 expression via competitively binding to miR-103a-3p in CC cells. Subsequently, rescue assays demonstrated that LINC00662 accelerated CC cell proliferation and inhibited cell apoptosis through upregulating PDK4. Furthermore, forkhead box A1 (FOXA1) was verified to activate transcription of both LINC00662 and PDK4. Taken together, our study revealed a novel ceRNA pattern of LINC00662/miR-103a-3p/PDK4 with FOXA1 as a transcription factor of LINC00662 and PDK4 in CC cells.

PDK4 dictates metabolic resistance to ferroptosis by suppressing pyruvate oxidation and fatty acid synthesis

Although induction of ferroptosis, an iron-dependent form of non-apoptotic cell death, has emerged as an anticancer strategy, the metabolic basis of ferroptotic death remains poorly elucidated. Here, we show that glucose determines the sensitivity of human pancreatic ductal carcinoma cells to ferroptosis induced by pharmacologically inhibiting system xc-. Mechanistically, SLC2A1-mediated glucose uptake promotes glycolysis and, thus, facilitates pyruvate oxidation, fuels the tricyclic acid cycle, and stimulates fatty acid synthesis, which finally facilitates lipid peroxidation-dependent ferroptotic death. Screening of a small interfering RNA (siRNA) library targeting metabolic enzymes leads to identification of pyruvate dehydrogenase kinase 4 (PDK4) as the top gene responsible for ferroptosis resistance. PDK4 inhibits ferroptosis by blocking pyruvate dehydrogenase-dependent pyruvate oxidation. Inhibiting PDK4 enhances the anticancer activity of system xc- inhibitors in vitro and in suitable preclinical mouse models (e.g., a high-fat diet diabetes model). These findings reveal metabolic reprogramming as a potential target for overcoming ferroptosis resistance.

PDK4 promotes tumorigenesis and cisplatin resistance in lung adenocarcinoma via transcriptional regulation of EPAS1

The use of cisplatin for the treatment of non-small cell lung cancer has long been constrained by the rapid acquisition of tumor cell chemoresistance. In the present study, we sought to better elucidate the molecular mechanisms underlying this resistance phenotype. To that end, we assessed gene expression patterns in cisplatin-resistant lung adenocarcinoma cells, revealing pyruvate dehydrogenase lipoamide kinase isozyme 4 (PDK4) to be the most up-regulated kinase in resistant cells. We further found PDK4 upregulation to be directly linked with the acquisition of chemoresistance, driving enhanced tumor cell growth in vitro and in vivo. In clinical samples, we also found that PDK4 upregulation was detectable in patients with lung adenocarcinoma and that it was correlated with a poorer prognosis for these patients. From a mechanistic perspective, we further determined that PDK4 was able to promote lung adenocarcinoma cell growth and cisplatin resistance at least in part via regulating endothelial PAS domain-containing protein 1 (EPAS1) expression, thus highlighting PDK4 as a potentially viable therapeutic target in efforts to treat lung adenocarcinoma patients that have become resistant to cisplatin.

PDK2-enhanced glycolysis promotes fibroblast proliferation in thyroid-associated ophthalmopathy

The study aimed to investigate the role of pyruvate dehydrogenase kinase (PDK) in regulating glycolysis and proliferation of perimysial orbital fibroblasts (pOFs) during the pathogenesis of thyroid-associated ophthalmopathy (TAO). EdU and BrdU incorporation assays were performed to examine cell proliferation. Lactate production and oxygen consumption assays were conducted to evaluate glycolysis. Real-time PCR was adapted to quantify PDK mRNA levels. Capillary Western immunoassay was adapted to quantify PDK2, Akt, pAkt308 and GAPDH in protein samples. The TAO pOFs exhibited stronger proliferation activity, higher intracellular lactate concentration, and lower oxygen consumption rate than the control pOFs. The PDK inhibitor dichloroacetic acid (DCA) dose-dependently suppressed the proliferation of both TAO and control pOFs. DCA reduced lactate production and promoted oxygen consumption in the TAO pOFs but showed no significant effects on glycolysis in the control pOFs. Among four PDK isotypes, PDK2 was overexpressed in the TAO pOFs. The potential PDK signaling mediator, cytoplasmic Akt, was more abundant in TAO pOFs than control pOFs. Knockdown of PDK2 resulted in lower lactate production, stronger oxygen consumption, weaker proliferation activity, and less cytoplasmic Akt in the TAO pOFs but showed no significant effects in the control pOFs. The Akt inhibitor MK2206 suppressed proliferation in both TAO and control pOFs, and lactate production was inhibited by MK2206 in the TAO OFs but not the control pOFs. To conclude, PDK2 overexpression enhances glycolysis and promotes proliferation via Akt signaling in the TAO pOFs. These findings yield insights that PDK2 is a potential therapeutic target for TAO treatment.

Malic Enzyme 1 Is Associated with Tumor Budding in Oral Squamous Cell Carcinomas

Budding at the tumor invasive front has been correlated with the malignant properties of many cancers. Malic enzyme 1 (ME1) promotes the Warburg effect in cancer cells and induces epithelial–mesenchymal transition (EMT) in oral squamous cell carcinoma (OSCC). Therefore, we investigated the role of ME1 in tumor budding in OSCC. Tumor budding was measured in 96 human OSCCs by immunostaining for an epithelial marker (AE1/AE3), and its expression was compared with that of ME1. A significant correlation was observed between tumor budding and ME1 expression. The correlation increased with the progression of cancer. In human OSCC cells, lactate secretion decreased when lactate fermentation was suppressed by knockdown of ME1 and lactate dehydrogenase A or inhibition of pyruvate dehydrogenase (PDH) kinase. Furthermore, the extracellular pH increased, and the EMT phenotype was suppressed. In contrast, when oxidative phosphorylation was suppressed by PDH knockdown, lactate secretion increased, extracellular pH decreased, and the EMT phenotype was promoted. Induction of chemical hypoxia in OSCC cells by CoCl₂ treatment resulted in increased ME1 expression along with HIF1α expression and promotion of the EMT phenotype. Hypoxic conditions also increased matrix metalloproteinases expression and decreased mitochondrial membrane potential, mitochondrial oxidative stress, and extracellular pH. Furthermore, the hypoxic treatment resulted in the activation of Yes-associated protein (YAP), which was abolished by ME1 knockdown. These findings suggest that cancer cells at the tumor front in hypoxic environments increase their lactate secretion by switching their energy metabolism from oxidative phosphorylation to glycolysis owing to ME1 overexpression, decrease in extracellular pH, and YAP activation. These alterations enhance EMT and the subsequent tumor budding. Tumor budding and ME1 expression are thus considered useful markers of OSCC malignancy, and ME1 is expected to be a relevant target for molecular therapy.

Epigenetic Reprogramming of Cancer-Associated Fibroblasts Deregulates Glucose Metabolism and Facilitates Progression of Breast Cancer

The mechanistic contributions of cancer-associated fibroblasts (CAFs) in breast cancer progression remain to be fully understood. While altered glucose metabolism in CAFs could fuel cancer cells, how such metabolic reprogramming emerges and is sustained needs further investigation. Studying fibroblasts isolated from patients with benign breast tissues and breast cancer, in conjunction with multiple animal models, we demonstrate that CAFs exhibit a metabolic shift toward lactate and pyruvate production and fuel biosynthetic pathways of cancer cells. The depletion or suppression of the lactate production of CAFs alter the tumor metabolic profile and impede tumor growth. The glycolytic phenotype of the CAFs is in part sustained through epigenetic reprogramming of HIF-1α and glycolytic enzymes. Hypoxia induces epigenetic reprogramming of normal fibroblasts, resulting in a pro-glycolytic, CAF-like transcriptome. Our findings suggest that the glucose metabolism of CAFs evolves during tumor progression, and their breast cancer-promoting phenotype is partly mediated by oxygen-dependent epigenetic modifications.

STAT3-dependent analysis reveals PDK4 as independent predictor of recurrence in prostate cancer

Prostate cancer (PCa) has a broad spectrum of clinical behavior; hence, biomarkers are urgently needed for risk stratification. Here, we aim to find potential biomarkers for risk stratification, by utilizing a gene co-expression network of transcriptomics data in addition to laser-microdissected proteomics from human and murine prostate FFPE samples. We show up-regulation of oxidative phosphorylation (OXPHOS) in PCa on the transcriptomic level and up-regulation of the TCA cycle/OXPHOS on the proteomic level, which is inversely correlated to STAT3 expression. We hereby identify gene expression of pyruvate dehydrogenase kinase 4 (PDK4), a key regulator of the TCA cycle, as a promising independent prognostic marker in PCa. PDK4 predicts disease recurrence independent of diagnostic risk factors such as grading, staging, and PSA level. Therefore, low PDK4 is a promising marker for PCa with dismal prognosis.

Synovial fibroblast-derived exosomal microRNA-106b suppresses chondrocyte proliferation and migration in rheumatoid arthritis via down-regulation of PDK4

Fibroblast-derived exosomes have been reported to transfer microRNAs to recipient cells, where they regulate target gene expression, which is of interest for understanding the basic biology of inflammation, tissue homeostasis, and development of therapeutic approaches. Initial microarray-based analysis carried out in this study identified the rheumatoid arthritis (RA)-related differentially expressed gene pyruvate dehydrogenase kinase 4 (PDK4). Subsequently, the upstream regulatory microRNA-106b (miR-106b) of PDK4 was predicted with bioinformatic analyses. A collagen-induced arthritis (CIA)-induced mouse model was established, and exosomes were isolated from synovial fibroblasts (SFs) and transferred into chondrocytes to identify the role of exosomes in rheumatoid arthritis (RA). We found that PDK4 was poorly expressed in RA cartilage tissues and chondrocytes, while miR-106b was highly expressed in RA SFs and SF-derived exosomes. Notably, PDK4 was confirmed as a target gene of miR-106b. Over-expression of PDK4 promoted the proliferation and migration abilities of chondrocytes and inhibited their apoptosis as well as affected the receptor activator of nuclear factor kappa B ligand (RANKL)/RANK/osteoprotegerin (OPG) system. Meanwhile, miR-106b was delivered from SFs to chondrocytes through exosomes, which suppressed chondrocyte proliferation and migration and accelerated apoptosis as well as affected the RANKL/RANK/OPG system via down-regulation of PDK4. Furthermore, in vivo results validated that miR-106b inhibition could relieve CIA-induced RA. Taken together, SF-derived exosomal miR-106b stimulates RA initiation by targeting PDK4, indicating a physiologically validated potential approach for the prevention and treatment of RA. KEY MESSAGES: PDK4 is decreased in chondrocytes of RA, while miR-106b is increased in SFBs. PDK4 promotes proliferation and migration of chondrocytes. miR-106b could target 3'UTR of PDK4 gene. SFB-exosomal miR-106b inhibits proliferation and migration of chondrocytes. Inhibition of miR-106b attenuates RA progression in a CIA mouse model.

Acetate supplementation restores chromatin accessibility and promotes tumor cell differentiation under hypoxia

Despite the fact that Otto H. Warburg discovered the Warburg effect almost one hundred years ago, why cancer cells waste most of the glucose carbon as lactate remains an enigma. Warburg proposed a connection between the Warburg effect and cell dedifferentiation. Hypoxia is a common tumor microenvironmental stress that induces the Warburg effect and blocks tumor cell differentiation. The underlying mechanism by which this occurs is poorly understood, and no effective therapeutic strategy has been developed to overcome this resistance to differentiation. Using a neuroblastoma differentiation model, we discovered that hypoxia repressed cell differentiation through reducing cellular acetyl-CoA levels, leading to reduction of global histone acetylation and chromatin accessibility. The metabolic switch triggering this global histone hypoacetylation was the induction of pyruvate dehydrogenase kinases (PDK1 and PDK3). Inhibition of PDKs using dichloroacetate (DCA) restored acetyl-CoA generation and histone acetylation under hypoxia. Knocking down PDK1 induced neuroblastoma cell differentiation, highlighting the critical role of PDK1 in cell fate control. Importantly, acetate or glycerol triacetate (GTA) supplementation restored differentiation markers expression and neuron differentiation under hypoxia. Moreover, ATAC-Seq analysis demonstrated that hypoxia treatment significantly reduced chromatin accessibility at RAR/RXR binding sites, which can be restored by acetate supplementation. In addition, hypoxia-induced histone hypermethylation by increasing 2-hydroxyglutarate (2HG) and reducing α-ketoglutarate (αKG). αKG supplementation reduced histone hypermethylation upon hypoxia, but did not restore histone acetylation or differentiation markers expression. Together, these findings suggest that diverting pyruvate flux away from acetyl-CoA generation to lactate production is the key mechanism that Warburg effect drives dedifferentiation and tumorigenesis. We propose that combining differentiation therapy with acetate/GTA supplementation might represent an effective therapy against neuroblastoma.

Mitochondrial Substrate Utilization Regulates Cardiomyocyte Cell Cycle Progression

The neonatal mammalian heart is capable of regeneration for a brief window of time after birth. However, this regenerative capacity is lost within the first week of life, which coincides with a postnatal shift from anaerobic glycolysis to mitochondrial oxidative phosphorylation, particularly towards fatty-acid utilization. Despite the energy advantage of fatty-acid beta-oxidation, cardiac mitochondria produce elevated rates of reactive oxygen species when utilizing fatty acids, which is thought to play a role in cardiomyocyte cell-cycle arrest through induction of DNA damage and activation of DNA-damage response (DDR) pathway. Here we show that inhibiting fatty-acid utilization promotes cardiomyocyte proliferation in the postnatatal heart. First, neonatal mice fed fatty-acid deficient milk showed prolongation of the postnatal cardiomyocyte proliferative window, however cell cycle arrest eventually ensued. Next, we generated a tamoxifen-inducible cardiomyocyte-specific, pyruvate dehydrogenase kinase 4 (PDK4) knockout mouse model to selectively enhance oxidation of glycolytically derived pyruvate in cardiomyocytes. Conditional PDK4 deletion resulted in an increase in pyruvate dehydrogenase activity and consequently an increase in glucose relative to fatty-acid oxidation. Loss of PDK4 also resulted in decreased cardiomyocyte size, decreased DNA damage and expression of DDR markers and an increase in cardiomyocyte proliferation. Following myocardial infarction, inducible deletion of PDK4 improved left ventricular function and decreased remodelling. Collectively, inhibition of fatty-acid utilization in cardiomyocytes promotes proliferation, and may be a viable target for cardiac regenerative therapies.

Overexpression of PDK2 and PDK3 reflects poor prognosis in acute myeloid leukemia

Acute myeloid leukemia (AML) is a hematological malignancy characterized by the proliferation of immature myeloid cells, with impaired differentiation and maturation. Pyruvate dehydrogenase kinase (PDK) is a pyruvate dehydrogenase complex (PDC) phosphatase inhibitor that enhances cell glycolysis and facilitates tumor cell proliferation. Inhibition of its activity can induce apoptosis of tumor cells. Currently, little is known about the role of PDKs in AML. Therefore, we screened The Cancer Genome Atlas (TCGA) database for de novo AML patients with complete clinical information and PDK family expression data, and 84 patients were included for the study. These patients did not undergo allogeneic hematopoietic stem cell transplantation (allo-HSCT). Univariate analysis showed that high expression of PDK2 was associated with shorter EFS (P = 0.047), and high expression of PDK3 was associated with shorter OS (P = 0.026). In multivariate analysis, high expression of PDK3 was an independent risk factor for EFS and OS (P < 0.05). In another TCGA cohort of AML patients who underwent allo-HSCT (n = 71), PDK expression was not associated with OS (all P > 0.05). Our results indicated that high expressions of PDK2 and PDK3, especially the latter, were poor prognostic factors of AML, and the effect could be overcome by allo-HSCT.

LncRNA AC093818.1 accelerates gastric cancer metastasis by epigenetically promoting PDK1 expression

Gastric cancer (GC) is a highly prevalent type of metastatic tumor. The mechanisms underlying GC metastasis are poorly understood. Some long noncoding RNAs (lncRNAs) reportedly play key roles in regulating metastasis of GC. However, the biological roles of five natural antisense lncRNAs (AC093818.1, CTD-2541M15.1, BC047644, RP11-597M12.1, and RP11-40A13.1) in GC metastasis remain unclear. In this study, the expression of these lncRNAs was measured by quantitative reverse transcription-polymerase chain reaction. Migration and invasion were evaluated by wound-healing and the Transwell assay, respectively. Stable cells were injected into the tail veins of nude mice. Sections of collected lung and liver tissues were stained using hematoxylin and eosin. Protein expression was analyzed by western blot. RNA immunoprecipitation (RIP) assay was used to verify whether the STAT3 and SP1 transcription factors bound to AC093818.1 in GC cells. Expression levels of the five lncRNAs, especially AC093818.1, were significantly upregulated in metastatic GC tissues relative to those in nonmetastatic GC tissues. AC093818.1 expression was correlated with invasion, lymphatic metastasis, distal metastasis, and tumor-node-metastasis stage. AC093818.1 expression was highly sensitive and specific in the diagnosis of metastatic or nonmetastatic GC. AC093818.1 overexpression promoted GC migration and invasion in vitro and in vivo. AC093818.1 overexpression increased PDK1, p-AKT1, and p-mTOR expression levels. AC093818.1 silencing decreased these expressions. AC093818.1 bound to transcription factors STAT3 and SP1, and SP1 or STAT3 silencing could alleviated the effect of AC093818.1 overexpression. The data demonstrate that lncRNA AC093818.1 accelerates gastric cancer metastasis by epigenetically promoting PDK1 expression. LncRNA AC093818.1 may be a potential therapeutic target for metastatic GC.

Effect of pH on the structure and function of pyruvate dehydrogenase kinase 3: Combined spectroscopic and MD simulation studies

Pyruvate dehydrogenase kinase-3 (PDK3) plays important role in the glucose metabolism and is associated with cancer progression, and thus being considered as an attractive target for cancer therapy. In this study, we employed spectroscopic techniques to study the structural and conformational changes in the PDK3 at varying pH conditions ranging from pH 2.0 to 12.0. UV/Vis, fluorescence and circular dichroism spectroscopic measurements revealed that PDK3 maintains its native-like structure (both secondary and tertiary) in the alkaline conditions (pH 7.0-12.0). However, a significant loss in the structure was observed under acidic conditions (pH 2.0-6.0). The propensity of aggregate formation at pH 4.0 was estimated by thioflavin T fluorescence measurements. To further complement structural data, kinase activity assay was performed, and maximum activity of PDK3 was observed at pH 7.0-8.0 range; whereas, its activity was lost under acidic pH. To further see conformational changes at atomistic level we have performed all-atom molecular dynamics at different pH conditions for 150 ns. A well defined correlation was observed between experimental and computational studies. This work highlights the significance of structural dependence of pH for wide implications in protein-protein interaction, biological function and drug design procedures.

Aberrant PDK4 Promoter Methylation Preceding Hyperglycemia in a Mouse Model

Diabetic prevalence is at speedy increase globally. Previous studies stated that other than genetics, factors such as environment, lifestyle, and paternal-maternal condition play critical roles in diabetes through DNA methylation in specific areas of the genome. The purpose of this study is to investigate the methylation pattern of the PDK4 promoter in streptozotocin-induced diabetic mice until the 12th week of the observation. The methylation pattern in the blood samples was analyzed periodically, while the pattern in the muscle sample was only analyzed at the end of the experiment using the blood of the sacrificed animals. Three methylated CpG site 1, CpG site 6, and CpG site 7 were analyzed and quantified based on the band density using bisulfite treatment and methylation-specific polymerase chain reaction (PCR). The hyperglycemia period was developed at the 9th week of experiment. However, there was a significant increase of methylation, specifically on CpG site 6 started from week 6 to week 12. This peculiar methylation on CpG site 6 of PDK4 promoter in the blood sample before the hyperglycemic period might serve as a potential biomarker for early detection of diabetes in the patients. No significant difference was found between the methylation level of streptozotocin (STZ)-treated mice and of the control group in the muscle sample.

Hypoxia induction in cultured pancreatic islets enhances endothelial cell morphology and survival while maintaining beta-cell function

Background

Pancreatic islets are heavily vascularized in vivo yet lose this vasculature after only a few days in culture. Determining how to maintain islet vascularity in culture could lead to better outcomes in transplanting this tissue for the treatment of type 1 diabetes as well as provide insight into the complex communication between beta-cells and endothelial cells (ECs). We previously showed that islet ECs die in part due to limited diffusion of serum albumin into the tissue. We now aim to determine the impact of hypoxia on islet vascularization.

Methods

We induced hypoxia in cultured mouse islets using the hypoxia mimetic cobalt chloride (100 μM CoCl₂). We measured the impact on islet metabolism (two-photon NAD(P)H and Rh123 imaging) and function (insulin secretion and survival). We also measured the impact on hypoxia related transcripts (HIF-1α, VEGF-A, PDK-1, LDHA, COX4) and confirmed increased VEGF-A expression and secretion. Finally, we measured the vascularization of islets in static and flowing culture using PECAM-1 immunofluorescence.

Results

CoCl₂ did not induce significant changes in beta cell metabolism (NAD(P)H and Rh123), insulin secretion, and survival. Consistent with hypoxia induction, CoCl₂ stimulated HIF-1α, PDK-1, and LDHA transcripts and also stimulated VEGF expression and secretion. We observed a modest switch to the less oxidative isoform of COX4 (isoform 1 to 2) and this switch was noted in the glucose-stimulated cytoplasmic NAD(P)H responses. EC morphology and survival were greater in CoCl₂ treated islets compared to exogenous VEGF-A in both static (dish) and microfluidic flow culture.

Conclusions

Hypoxia induction using CoCl₂ had a positive effect on islet EC morphology and survival with limited impact on beta-cell metabolism, function, and survival. The EC response appears to be due to endogenous production and secretion of angiogenic factors (e.g. VEGF-A), and mechanistically independent from survival induced by serum albumin.

Therapeutic effect of dichloroacetate against atherosclerosis via hepatic FGF21 induction mediated by acute AMPK activation

Dyslipidemia-induced atherosclerosis, which has a risk of high morbidity and mortality, can be alleviated by metabolic activation associated with mitochondrial function. The effect of dichloroacetate (DCA), a general pyruvate dehydrogenase kinase (PDK) inhibitor, on in vivo energy expenditure in ApoE-/- mice fed a western diet (WD) has not yet been investigated. WD-fed ApoE-/- mice developed atherosclerotic plaques and hyperlipidemia along with obesity, which were significantly ameliorated by DCA administration. Increased oxygen consumption was associated with heat production in the DCA-treated group, with no change in food intake or physical activity compared with those of the control. These processes were correlated with the increased gene expression of Dio2 and Ucp-1, which represents brown adipose tissue (BAT) activation, in both WD-induced atherosclerosis and high-fat-induced obesity models. In addition, we found that DCA stimulated hepatic fibroblast growth factor 21 (Fgf21) mRNA expression, which might be important for lowering lipid levels and insulin sensitization via BAT activation, in a dose- and time-dependent manner associated with serum FGF21 levels. Interestingly, Fgf21 mRNA expression was mediated in an AMP-activated protein kinase (AMPK)-dependent manner within several minutes after DCA treatment independent of peroxisome proliferator-activated receptor alpha (PPARα). Taken together, the results suggest that enhanced glucose oxidation by DCA protects against atherosclerosis by inducing hepatic FGF21 expression and BAT activation, resulting in augmented energy expenditure for heat generation.

HIF-1α/PDK4/autophagy pathway protects against advanced glycation end-products induced vascular smooth muscle cell calcification

Osteogenic differentiation of VSMC is one of the main causes of diabetic vascular calcification, and AGEs accumulation accelerates the calcification of VSMCs in diabetic patients. Autophagy has also been found to play an important role in the process of vascular calcification. However, the potential link between AGEs, autophagy and vascular calcification is still unclear and was investigated in this study. Primary VSMCs were isolated from the thoracic aorta of Sprague Dawley rats and cultured with AGEs-BSA to induce osteogenic differentiation. VSMCs calcification was evaluated by measuring the calcium content, RUNX2 protein levels, and by Alizarin red S staining. We demonstrated that treatment of VSMCs with AGE-BSA increased the expression of HIF-1α and PDK4. AGE-BSA treatment increased LC3-II and decreased p62 protein levels. AGE-BSA exposure enhanced autophagic flux determined by mRFP-GFP-LC3 adenovirus, induced co-localization of LC3-II and LAMP-1, and increased the number of autophagasome under TEM. HIF-1α/PDK4 pathway was activated during AGEs-induced autophagy of VSMCs. In addition, autophagy played a protective role during AGE-induced calcification of VSMCs. In conclusion, AGEs enhance autophagy via the HIF-1α/PDK4 signaling pathway, and autophagy helps attenuate AGE-induced calcification of VSMCs.

Dysregulation of cPWWP2A-miR-579 axis mediates dexamethasone-induced cytotoxicity in human osteoblasts

Dexamethasone (DEX) induces significant cytotoxicity to human osteoblasts. cPWWP2A is recently-indentified novel circular RNA (circRNA), acting as an endogenous sponge of microRNA-579 (miR-579). The present study tested the expression and potential functions of the cPWWP2A-miR-579 axis in DEX-treated osteoblasts. We show that cPWWP2A is downregulated in the necrotic femoral head tissues of DEX-taking human patients as well as in DEX-treated human osteoblasts. In OB-6 osteoblastic cells and primary human osteoblasts ectopic overexpression of cPWWP2A potently inhibited DEX-induced miR-579 accumulation, cell death, apoptosis and programmed necrosis. Silencing miR-579, by targeted siRNAs, also attenuated DEX-induced cytotoxicity in human osteoblasts. Significantly, mimicking DEX-induced actions, cPWWP2A silencing or forced miR-579 overexpression induced significant cytotoxicity in human osteoblasts. Further analyses demonstrated that miR-579's targets, including SIRT1 and PDK1 (phosphoinositide-dependent protein kinase 1), were downregulated in DEX-treated osteoblasts. Their levels were decreased as well in the necrotic femoral head tissues of DEX-taking human patients. Taken together we show that dysregulation of the cPWWP2A-miR-579 axis is involved in DEX-induced cytotoxicity in human osteoblasts.

Ku80 promotes melanoma growth and regulates antitumor effect of melatonin by targeting HIF1-α dependent PDK-1 signaling pathway

Melanoma is one of the most malignant and aggressive cancers with high cancer-related deaths. However, it is unclear whether Ku80 regulates tumor growth in human melanoma. In this study, we screened a siRNA library targeting 6024 human genes and identified Ku80 as a potential therapeutic target in melanoma cells. Knockdown of Ku80 significantly suppressed melanoma cell proliferation and induced apoptosis, as well as enhanced the antitumor effect of melatonin in melanoma in vitro and in vivo. Overexpression of Ku80, however, promoted melanoma growth and increased the insensitivity of melanoma cells to melatonin. Mechanistically, we found that Ku80 bound to the PDK1 promoter and activated the transcription of PDK1. Moreover, we showed that the binding of Ku80 at the PDK-1 promoter was HIF1-α dependent, and melatonin degraded HIF1-α in melanoma cells. Furthermore, clinical data revealed that the expression of Ku80 and PDK-1 proteins were positively correlated and elevated in the tumor tissues of melanoma patients, and high expression of Ku80 predicted a poor prognosis in melanoma. Collectively, our study demonstrated that Ku80 promoted melanoma growth and regulated antitumor activity of melatonin by targeting HIF1-α dependent PDK-1 signaling pathway, suggesting that Ku80 may be a potential molecular target for melanoma treatment.

Carnosine inhibits glioblastoma growth independent from PI3K/Akt/mTOR signaling

Glioblastoma is a high-grade glioma with poor prognosis even after surgery and standard therapy. Here, we asked whether carnosine (β-alanyl-L-histidine), a naturally occurring dipeptide, exert its anti-neoplastic effect on glioblastoma cells via PI3K/Akt/mTOR signaling. Therefore, glioblastoma cells from the lines U87 and T98G were exposed to carnosine, to the mTOR inhibitor rapamycin and to the PI3K inhibitor Ly-294,002. Pyruvate dehydrogenase kinase (PDK4) expression, known to be a target of PI3K/Akt/mTOR, and which is also affected by carnosine, was analyzed by RT-qPCR, and reporter gene assays with the human PDK4 promoter were performed. Cell viability was assessed by cell-based assays and mTOR and Akt phosphorylation by Western blotting. Rapamycin and Ly-294,002 increased PDK4 mRNA expression in both cell lines but significance was only reached in U87. Carnosine significantly increased expression in both lines. A significant combinatorial effect of carnosine was only detected in U87 when the dipeptide was combined with Ly-294,002. Reporter gene assays revealed no specific effect of carnosine on the human PDK4 promoter, whereas both inhibitors increased reporter gene expression. Rapamycin reduced phosphorylation of mTOR, and Ly-294,002 that of Akt. A significant reduction of Akt phosphorylation was observed in the presence of carnosine in U87 but not in T98G, and carnosine had no effect on mTOR phosphorylation. Cell viability as determined by ATP in cell lysates was reduced only in the presence of carnosine. We conclude that carnosine’s anti-neoplastic effect is independent from PI3K/Akt/mTOR signaling. As the dipeptide reduced viability in tumor cells that do not respond to PI3K or mTOR inhibitors, it appears to be worth to further investigate the mechanisms by which carnosine exerts its anti-tumor effect and to consider it for therapy, especially as it is a naturally occurring compound that has already been used for the treatment of other diseases without indication of side-effects.

Pyruvate Dehydrogenase Kinase Is a Metabolic Checkpoint for Polarization of Macrophages to the M1 Phenotype

Metabolic reprogramming during macrophage polarization supports the effector functions of these cells in health and disease. Here, we demonstrate that pyruvate dehydrogenase kinase (PDK), which inhibits the pyruvate dehydrogenase-mediated conversion of cytosolic pyruvate to mitochondrial acetyl-CoA, functions as a metabolic checkpoint in M1 macrophages. Polarization was not prevented by PDK2 or PDK4 deletion but was fully prevented by the combined deletion of PDK2 and PDK4; this lack of polarization was correlated with improved mitochondrial respiration and rewiring of metabolic breaks that are characterized by increased glycolytic intermediates and reduced metabolites in the TCA cycle. Genetic deletion or pharmacological inhibition of PDK2/4 prevents polarization of macrophages to the M1 phenotype in response to inflammatory stimuli (lipopolysaccharide plus IFN-γ). Transplantation of PDK2/4-deficient bone marrow into irradiated wild-type mice to produce mice with PDK2/4-deficient myeloid cells prevented M1 polarization, reduced obesity-associated insulin resistance, and ameliorated adipose tissue inflammation. A novel, pharmacological PDK inhibitor, KPLH1130, improved high-fat diet-induced insulin resistance; this was correlated with a reduction in the levels of pro-inflammatory markers and improved mitochondrial function. These studies identify PDK2/4 as a metabolic checkpoint for M1 phenotype polarization of macrophages, which could potentially be exploited as a novel therapeutic target for obesity-associated metabolic disorders and other inflammatory conditions.

High hepatic expression of PDK4 improves survival upon multimodal treatment of colorectal liver metastases

BACKGROUND

Patients with borderline resectable colorectal liver metastases (CRLM) frequently receive neoadjuvant chemotherapy (NC) to reduce tumour burden, thus making surgical resection feasible. Even though NC can induce severe liver injury, most studies investigating tissue-based prognostic markers focus on tumour tissue. Here, we assessed the prognostic significance of pyruvate-dehydrogenase-kinase isoenzyme 4 (PDK4) within liver tissue of patients undergoing surgical resection due to CRLM.

METHODS

Transcript levels of hypoxia-adaptive genes (such as PDK isoenzymes) were assessed in the tissue of healthy liver, corresponding CRLM, healthy colon mucosa and corresponding tumour. Uni- and multivariate analyses were performed. Responses to chemotherapy upon up- or down-regulation of PDK4 were studied in vitro.

RESULTS

PDK4 expression within healthy liver tissue was associated with increased overall survival and liver function following surgical resection of CRLM. This association was enhanced in patients with NC. PDK4 expression in CRLM tissue did not correlate with overall survival. Up-regulation of PDK4 increased the resistance of hepatocytes and colon cancer cells against chemotherapy-induced toxicity, whereas knockdown of PDK4 enhanced chemotherapy-associated cell damage.

CONCLUSION

Our findings suggest that up-regulated PDK4 expression reduces hepatic chemotherapy-induced oxidative stress and is associated with improved postoperative liver function in patients undergoing multimodal treatment and resection of CRLM.