Inhibiting BCKDK in triple negative breast cancer suppresses protein translation, impairs mitochondrial function, and potentiates doxorubicin cytotoxicity.

Triple-negative breast cancers (TNBCs) are characterized by poor survival, prognosis, and gradual resistance to cytotoxic chemotherapeutics, like doxorubicin (DOX). The clinical utility of DOX is limited by its cardiotoxic and chemoresistant effects that manifest over time. To induce chemoresistance, TNBC rewires oncogenic gene expression and cell signaling pathways. Recent studies have demonstrated that reprogramming of branched-chain amino acids (BCAAs) metabolism facilitates tumor growth and survival. Branched-chain ketoacid dehydrogenase kinase (BCKDK), a regulatory kinase of the rate-limiting enzyme of the BCAA catabolic pathway, is reported to activate RAS/RAF/MEK/ERK signaling to promote tumor cell proliferation. However, it remains unexplored if BCKDK action remodels TNBC proliferation and survival per se and influences susceptibility to DOX-induced genotoxic stress. TNBC cells treated with DOX exhibited reduced BCKDK expression and intracellular BCKAs. Genetic and pharmacological inhibition of BCKDK in TNBC cell lines also showed a similar reduction in intracellular and secreted BCKAs. BCKDK silencing in TNBC cells downregulated mitochondrial metabolism genes, reduced electron complex protein expression, oxygen consumption, and ATP production. Transcriptome analysis of BCKDK silenced cells confirmed dysregulation of mitochondrial metabolic networks and upregulation of the apoptotic signaling pathway. Furthermore, BCKDK inhibition with concurrent DOX treatment exacerbated apoptosis, caspase activity, and loss of TNBC proliferation. Inhibition of BCKDK in TNBC also upregulated sestrin 2 and concurrently decreased mTORC1 signaling and protein synthesis. Overall, loss of BCKDK action in TNBC remodels BCAA flux, reduces protein translation triggering cell death, ATP insufficiency, and susceptibility to genotoxic stress.

The Opioid Awareness and Support Team: an innovative example of medical education and community partnership.

The Opioid Awareness and Support Team (OAST) at the Memorial University Faculty of Medicine is a novel student-led initiative designed to supplement medical student learning related to opioid use disorder and the opioids crisis. OAST has focused on grounding educational initiatives related to opioid use disorder in the local community context, working with community partners, and bringing in individuals with lived experience. We present initial findings from an Opioid Education Day that suggest student-led supplemental education for medical students can improve student knowledge surrounding opioid use.

L'équipe d'aide et de sensibilisation aux opioïdes (OAST) est une initiative des étudiants de la faculté de médecine de l'Université Memorial qui apporte un complément à la formation que reçoivent les étudiants sur le trouble lié à l'usage d'opioïdes. L'OAST s'est efforcée d'inscrire les initiatives éducatives liées à la crise des opïodes dans un contexte local en collaboration avec des partenaires communautaires et de faire participer des personnes ayant une expérience de terrain. Nous présentons les résultats préliminaires d'une journée de sensibilisation aux opioïdes qui suggèrent que cette activité éducative menée par les étudiants en médecine peut améliorer les connaissances des apprenants sur la consommation d'opioïdes.

Branched-chain ketoacid overload inhibits insulin action in the muscle.

Branched-chain α-keto acids (BCKAs) are catabolites of branched-chain amino acids (BCAAs). Intracellular BCKAs are cleared by branched-chain ketoacid dehydrogenase (BCKDH), which is sensitive to inhibitory phosphorylation by BCKD kinase (BCKDK). Accumulation of BCKAs is an indicator of defective BCAA catabolism and has been correlated with glucose intolerance and cardiac dysfunction. However, it is unclear whether BCKAs directly alter insulin signaling and function in the skeletal and cardiac muscle cell. Furthermore, the role of excess fatty acids (FAs) in perturbing BCAA catabolism and BCKA availability merits investigation. By using immunoblotting and ultra-performance liquid chromatography MS/MS to analyze the hearts of fasted mice, we observed decreased BCAA-catabolizing enzyme expression and increased circulating BCKAs, but not BCAAs. In mice subjected to diet-induced obesity (DIO), we observed similar increases in circulating BCKAs with concomitant changes in BCAA-catabolizing enzyme expression only in the skeletal muscle. Effects of DIO were recapitulated by simulating lipotoxicity in skeletal muscle cells treated with saturated FA, palmitate. Exposure of muscle cells to high concentrations of BCKAs resulted in inhibition of insulin-induced AKT phosphorylation, decreased glucose uptake, and mitochondrial oxygen consumption. Altering intracellular clearance of BCKAs by genetic modulation of BCKDK and BCKDHA expression showed similar effects on AKT phosphorylation. BCKAs increased protein translation and mTORC1 activation. Pretreating cells with mTORC1 inhibitor rapamycin restored BCKA's effect on insulin-induced AKT phosphorylation. This study provides evidence for FA-mediated regulation of BCAA-catabolizing enzymes and BCKA content and highlights the biological role of BCKAs in regulating muscle insulin signaling and function.

Role of branched-chain amino acid-catabolizing enzymes in intertissue signaling, metabolic remodeling, and energy homeostasis.

Beyond their contribution as fundamental building blocks of life, branched-chain amino acids (BCAAs) play a critical role in physiologic and pathologic processes. Importantly, BCAAs are associated with insulin resistance, obesity, cardiovascular disease, and genetic disorders. However, several metabolome-wide studies in recent years could not attribute alterations in systemic BCAAs as the sole driver of endocrine perturbations, suggesting that a snapshot of global BCAA changes does not always reveal the underlying modifications. Because enzymes catabolizing BCAAs have a unique distribution, it is plausible that the tissue-specific roles of BCAA-catabolic enzymes could precipitate changes in systemic BCAA levels, flux, and action. We review the genetic and pharmacological approaches dissecting the role of BCAA-catabolic enzyme dysfunctions. We summarized emerging evidence on BCAA metabolic intermediates, tissue specificity of BCAA-catabolizing enzymes, and crosstalk between different metabolites in driving metabolic maladaptation in health and pathology. This review substantiates the understanding that tissue-specific dysfunction of the BCAA-catabolic enzymes and accumulating intermediary metabolites could act as better surrogates of metabolic imbalances, highlighting the biochemical communication among the nutrient triad of BCAAs, glucose, and fatty acid.-Biswas, D., Duffley, L., Pulinilkunnil, T. Role of branched-chain amino acid-catabolizing enzymes in intertissue signaling, metabolic remodeling, and energy homeostasis.