BCKDK modification enhances the anticancer efficacy of CAR-T cells by reprogramming branched chain amino acid metabolism.

Altered branched chain amino acids (BCAAs), including leucine, isoleucine, and valine, are frequently observed in patients with advanced cancer. We evaluated the efficacy of chimeric antigen receptor (CAR) T cell-mediated cancer cell lysis potential in the immune microenvironment of BCAA supplementation and deletion. BCAA supplementation increased cancer cell killing percentage, while accelerating BCAA catabolism and decreasing BCAA transporter decreased cancer cell lysis efficacy. We thus designed BCKDK engineering CAR T cells for the reprogramming of BCAA metabolism in the tumor microenvironment based on the genotype and phenotype modification. BCKDK overexpression (OE) in CAR-T cells significantly improved cancer cell lysis, while BCKDK knockout (KO) resulted in inferior lysis potential. In an in vivo experiment, BCKDK-OE CAR-T cell treatment significantly prolonged the survival of mice bearing NALM6-GL cancer cells, with the differentiation of central memory cells and an increasing proportion of CAR-T cells in the peripheral circulation. BCKDK-KO CAR-T cell treatment resulted in shorter survival and a decreasing percentage of CAR-T cells in the peripheral circulation. In conclusion, BCKDK-engineered CAR-T cells exert a distinct phenotype for superior anticancer efficiency.

BCKDK deficiency: a treatable neurodevelopmental disease amenable to newborn screening.

There are few causes of treatable neurodevelopmental diseases described to date. Branched-chain ketoacid dehydrogenase kinase (BCKDK) deficiency causes branched-chain amino acid (BCAA) depletion and is linked to a neurodevelopmental disorder characterized by autism, intellectual disability and microcephaly. We report the largest cohort of patients studied, broadening the phenotypic and genotypic spectrum. Moreover, this is the first study to present newborn screening findings and mid-term clinical outcome. In this cross-sectional study, patients with a diagnosis of BCKDK deficiency were recruited via investigators' practices through a MetabERN initiative. Clinical, biochemical and genetic data were collected. Dried blood spot (DBS) newborn screening (NBS) amino acid profiles were retrieved from collaborating centres and compared to a healthy newborn reference population. Twenty-one patients with BCKDK mutations were included from 13 families. Patients were diagnosed between 8 months and 16 years (mean: 5.8 years, 43% female). At diagnosis, BCAA levels (leucine, valine and isoleucine) were below reference values in plasma and in CSF. All patients had global neurodevelopmental delay; 18/21 had gross motor function (GMF) impairment with GMF III or worse in 5/18, 16/16 intellectual disability, 17/17 language impairment, 12/17 autism spectrum disorder, 9/21 epilepsy, 12/15 clumsiness, 3/21 had sensorineural hearing loss and 4/20 feeding difficulties. No microcephaly was observed at birth, but 17/20 developed microcephaly during follow-up. Regression was reported in six patients. Movement disorder was observed in 3/21 patients: hyperkinetic movements (1), truncal ataxia (1) and dystonia (2). After treatment with a high-protein diet (≥ 2 g/kg/day) and BCAA supplementation (100-250 mg/kg/day), plasma BCAA increased significantly (P < 0.001), motor functions and head circumference stabilized/improved in 13/13 and in 11/15 patients, respectively. Among cases with follow-up data, none of the three patients starting treatment before 2 years of age developed autism at follow-up. The patient with the earliest age of treatment initiation (8 months) showed normal development at 3 years of age. NBS in DBS identified BCAA levels significantly lower than those of the normal population. This work highlights the potential benefits of dietetic treatment, in particular early introduction of BCAA. Therefore, it is of utmost importance to increase awareness about this treatable disease and consider it as a candidate for early detection by NBS programmes.

Identification of putative allosteric inhibitors of BCKDK via virtual screening and biological evaluation.

Abnormal accumulation of branched-chain amino acids (BCAAs) can lead to metabolic diseases and cancers. Branched-chain α-keto acid dehydrogenase kinase (BCKDK) is a key negative regulator of BCAA catabolism, and targeting BCKDK provides a promising therapeutic approach for diseases caused by BCAA accumulation. Here, we screened PPHN and POAB as novel putative allosteric inhibitors by integrating allosteric binding site prediction, large-scale ligand database virtual screening, and bioactivity evaluation assays. Both of them showed a high binding affinity to BCKDK, with Kd values of 3.9 µM and 1.86 µM, respectively. In vivo experiments, the inhibitors demonstrated superior kinase inhibitory activity and notable antiproliferative and proapoptotic effects on diverse cancer cells. Finally, bulk RNA-seq analysis revealed that PPHN and POAB suppressed cell growth through a range of signalling pathways. Taken together, our findings highlight two novel BCKDK inhibitors as potent therapeutic candidates for metabolic diseases and cancers associated with BCAA dysfunctional metabolism.

The Role of Branched Chain Ketoacid Dehydrogenase Kinase (BCKDK) in Skeletal Muscle Biology and Pathogenesis.

Muscle wasting can be caused by nutrition deficiency and inefficient metabolism of amino acids, including Branched Chain Amino Acids (BCAAs). Branched Chain Amino Acids are a major contributor to the metabolic needs of healthy muscle and account for over a tenth of lean muscle mass. Branched chain alpha-ketoacid dehydrogenase (BCKD) is the rate limiting enzyme of BCAA metabolism. Inhibition of BCKD is achieved through a reversible phosphorylation event by Branched Chain a-ketoacid dehydrogenase kinase (BCKDK). Our study set out to determine the importance of BCKDK in the maintenance of skeletal muscle. We used the Gene Expression Omnibus Database to understand the role of BCKDK in skeletal muscle pathogenesis, including aging, muscular disease, and interrupted muscle metabolism. We found BCKDK expression levels were consistently decreased in pathologic conditions. These results were most consistent when exploring muscular disease followed by aging. Based on our findings, we hypothesize that decreased BCKDK expression alters BCAA catabolism and impacts loss of normal muscle integrity and function. Further research could offer valuable insights into potential therapeutic strategies for addressing muscle-related disorders.

Branched-chain keto-acid dehydrogenase kinase regulates vascular permeability and angiogenesis to facilitate tumor metastasis in renal cell carcinoma.

Branched-chain keto-acid dehydrogenase kinase (BCKDK) is the rate-limiting enzyme of branched-chain amino acid (BCAA) metabolism. In the last six years, BCKDK has been used as a kinase to promote tumor proliferation and metastasis. Renal cell carcinoma (RCC) is a highly vascularized tumor. A high degree of vascularization promotes tumor metastasis. Our objective is to explore the relationship between BCKDK and RCC metastasis and its specific mechanism. In our study, BCKDK is highly expressed in renal clear cell carcinoma and promotes the migration of clear cell renal cell carcinoma (ccRCC). Exosomes from ccRCC cells can promote vascular permeability and angiogenesis, especially when BCKDK is overexpressed in ccRCC cells. BCKDK can also augment the miR-125a-5p expression in ccRCC cells and derived exosomes, thereby decreasing the downstream target protein VE-cadherin level, weakening adhesion junction expression, increasing vascular permeability, and promoting angiogenesis in HUVECs. The novel BCKDK/Exosome-miR-125a-5p/VE-cadherin axis regulates intercellular communication between ccRCC cells and HUVECs. BCKDK plays a critical role in renal cancer metastasis, may be used as a molecular marker of metastatic ccRCC, and even may become a potential target of clinical anti-vascular therapy for ccRCC.

The ubiquitin ligase UBE3B, disrupted in intellectual disability and absent speech, regulates metabolic pathways by targeting BCKDK.

Kaufman oculocerebrofacial syndrome (KOS) is a recessive neurodevelopmental disorder characterized by intellectual disability and lack of speech. KOS is caused by inactivating mutations in UBE3B, but the underlying biological mechanisms are completely unknown. We found that loss of Ube3b in mice resulted in growth retardation, decreased grip strength, and loss of vocalization. The brains of Ube3b-/- mice had hypoplasia of the corpus callosum, enlarged ventricles, and decreased thickness of the somatosensory cortex. Ube3b-/- cortical neurons had abnormal dendritic morphology and synapses. We identified 22 UBE3B interactors and found that branched-chain α-ketoacid dehydrogenase kinase (BCKDK) is an in vivo UBE3B substrate. Since BCKDK targets several metabolic pathways, we profiled plasma and cortical metabolomes from Ube3b-/- mice. Nucleotide metabolism and the tricarboxylic acid cycle were among the pathways perturbed. Substrate-induced mitochondrial respiration was reduced in skeletal muscle but not in liver of Ube3b-/- mice. To assess the relevance of these findings to humans, we identified three KOS patients who had compound heterozygous UBE3B mutations. We discovered changes in metabolites from similar pathways in plasma from these patients. Collectively, our results implicate a disease mechanism in KOS, suggest that it is a metabolic encephalomyopathy, and provide an entry to targeted therapies.

Novel Loss of Function Variant in BCKDK Causes a Treatable Developmental and Epileptic Encephalopathy.

Branched-chain amino acids (BCAA) are essential amino acids playing crucial roles in protein synthesis and brain neurotransmission. Branched-chain ketoacid dehydrogenase (BCKDH), the flux-generating step of BCAA catabolism, is tightly regulated by reversible phosphorylation of its E1α-subunit. BCKDK is the kinase responsible for the phosphorylation-mediated inactivation of BCKDH. In three siblings with severe developmental delays, microcephaly, autism spectrum disorder and epileptic encephalopathy, we identified a new homozygous in-frame deletion (c.999_1001delCAC; p.Thr334del) of BCKDK. Plasma and cerebrospinal fluid concentrations of BCAA were markedly reduced. Hyperactivity of BCKDH and over-consumption of BCAA were demonstrated by functional tests in cells transfected with the mutant BCKDK. Treatment with pharmacological doses of BCAA allowed the restoring of BCAA concentrations and greatly improved seizure control. Behavioral and developmental skills of the patients improved to a lesser extent. Importantly, a retrospective review of the newborn screening results allowed the identification of a strong decrease in BCAA concentrations on dried blood spots, suggesting that BCKDK is a new treatable metabolic disorder probably amenable to newborn screening programs.

Mitochondrial response to the BCKDK-deficiency: Some clues to understand the positive dietary response in this form of autism.

Mutations on the mitochondrial-expressed Branched Chain α-Keto acid Dehydrogenase Kinase (BCKDK) gene have been recently associated with a novel dietary-treatable form of autism. But, being a mitochondrial metabolism disease, little is known about the impact on mitochondrial performance. Here, we analyze the mitochondrial response to the BCKDK-deficiency in patient's primary fibroblasts by measuring bioenergetics, ultra-structural and dynamic parameters. A two-fold increase in superoxide anion production, together with a reduction in ATP-linked respiration and intracellular ATP levels (down to 60%) detected in mutants fibroblasts point to a general bioenergetics depletion that could affect the mitochondrial dynamics and cell fate. Ultrastructure analysis of BCKDK-deficient fibroblasts shows an increased number of elongated mitochondria, apparently associated with changes in the mediator of inner mitochondria membrane fusion, GTPase OPA1 forms, and in the outer mitochondrial membrane, mitofusin 2/MFN2. Our data support a possible hyperfusion response of BCKDK-deficient mitochondria to stress. Cellular fate also seems to be affected as these fibroblasts show an altered proportion of the cells on G0/G1 and G2/M phases. Knockdown of BCKDK gene in control fibroblasts recapitulates most of these features. Same BCKDK-knockdown in a MSUD patient fibroblasts unmasks the direct involvement of the accelerated BCAAs catabolism in the mitochondrial dysfunction. All these data give us a clue to understand the positive dietary response to an overload of branched-chain amino acids. We hypothesize that a combination of the current therapeutic option with a protocol that considers the oxidative damage and energy expenditure, addressing the patients' individuality, might be useful for the physicians.

Two novel mutations in the BCKDK (branched-chain keto-acid dehydrogenase kinase) gene are responsible for a neurobehavioral deficit in two pediatric unrelated patients.

Inactivating mutations in the BCKDK gene, which codes for the kinase responsible for the negative regulation of the branched-chain α-keto acid dehydrogenase complex (BCKD), have recently been associated with a form of autism in three families. In this work, two novel exonic BCKDK mutations, c.520C>G/p.R174G and c.1166T>C/p.L389P, were identified at the homozygous state in two unrelated children with persistently reduced body fluid levels of branched-chain amino acids (BCAAs), developmental delay, microcephaly, and neurobehavioral abnormalities. Functional analysis of the mutations confirmed the missense character of the c.1166T>C change and showed a splicing defect r.[520c>g;521_543del]/p.R174Gfs1*, for c.520C>G due to the presence of a new donor splice site. Mutation p.L389P showed total loss of kinase activity. Moreover, patient-derived fibroblasts showed undetectable (p.R174Gfs1*) or barely detectable (p.L389P) levels of BCKDK protein and its phosphorylated substrate (phospho-E1α), resulting in increased BCKD activity and the very rapid BCAA catabolism manifested by the patients' clinical phenotype. Based on these results, a protein-rich diet plus oral BCAA supplementation was implemented in the patient homozygous for p.R174Gfs1*. This treatment normalized plasma BCAA levels and improved growth, developmental and behavioral variables. Our results demonstrate that BCKDK mutations can result in neurobehavioral deficits in humans and support the rationale for dietary intervention.

FYN-mediated phosphorylation of BCKDK at Y151 promotes GBM proliferation by increasing the oncogenic metabolite N-acetyl-L-alanine.

Branched chain α-keto acid dehydrogenase kinase (BCKDK) is a key enzyme involved in the metabolism of branched-chain amino acids (BCAAs). Its potential as a therapeutic target and prognostic factor for a variety of cancers has been widely reported. In this study, we investigated the expression of BCKDK in clinical glioma samples and found that BCKDK was significantly overexpressed in glioblastoma (GBM) and was associated with its poor prognosis. We further found that BCKDK is phosphorylated by tyrosine protein kinase Fyn at Y151, which increases its catalytic activity and stability, and demonstrate through in vivo and in vitro experiments that BCKDK phosphorylation promotes GBM cell proliferation. In addition, we found that the levels of the metabolite N-acetyl-L-alanine (NAAL) in GBM cells with high BCKDK were higher than those in the silencing group, and silencing or inhibition of BCKDK promotes the expression of ACY1, an enzyme that catalyzes the hydrolysis of NAAL into acetic acid and alanine. Exogenous addition of NAAL can activate the ERK signaling pathway and promote the proliferation of GBM cells. Taken together, we identified a novel mechanism of BCKDK activation and found NAAL is a novel oncogenic metabolite. Our study confirms the importance of the Fyn-BCKDK-ACY1-NAAL signalling axis in the development of GBM and suggests that p-BCKDK (Y151) and NAAL can serve as potential predictors of GBM progression and prognosis.

Cross-talk between BCKDK-mediated phosphorylation and STUB1-dependent ubiquitination degradation of BCAT1 promotes GBM progression.

Branched-chain amino acid transferase 1 (BCAT1) is highly expressed in multiple cancers and is associated with poor prognosis, particularly in glioblastoma (GBM). However, the post-translational modification (PTM) mechanism of BCAT1 is unknown. Here, we investigated the cross-talk mechanisms between phosphorylation and ubiquitination modifications in regulating BCAT1 activity and stability. We found that BCAT1 is phosphorylated by branched chain ketoacid dehydrogenase kinase (BCKDK) at S5, S9, and T312, which increases its catalytic and antioxidant activity and stability. STUB1 (STIP1 homology U-box-containing protein 1), the first we found and reported E3 ubiquitin ligase of BCAT1, can also be phosphorylated by BCKDK at the S19 site, which disrupts the interaction with BCAT1 and inhibits its degradation. In addition, we demonstrate through in vivo and in vitro experiments that BCAT1 phosphorylation inhibiting its ubiquitination at multiple sites is associated with GBM proliferation and that inhibition of the BCKDK-BCAT1 axis enhances the sensitivity to temozolomide (TMZ). Overall, we identified novel mechanisms for the regulation of BCAT1 modification and elucidated the importance of the BCKDK-STUB1-BCAT1 axis in GBM progression.

Bckdk-Mediated Branch Chain Amino Acid Metabolism Reprogramming Contributes to Muscle Atrophy during Cancer Cachexia.

SCOPE: Branched chain amino acids (BCAAs) are essential amino acids and important nutrient signals for energy and protein supplementation. The study uses muscle-specific branched-chain α-keto acid dehydrogenase kinase (Bckdk) conditional knockout (cKO) mice to reveal the contribution of BCAA metabolic dysfunction to muscle wasting. METHOD AND RESULTS: Muscle-specific Bckdk-cKO mice are generated through crossbreeding of Bckdkf/f mice with Myf5Cre mice. Lewis lung cancer (LLC) tumor transplantation is used to establish the cancer cachexia model. The occurrence of cancer cachexia is accelerated in the muscle-specific Bckdk-cKO mice after bearing LLC tumor. Wasting skeletal muscle is characterized by increased protein ubiquitination degradation and impaired protein synthesis. The wasting muscle gastrocnemius is mechanized as a distinct BCAA metabolic dysfunction. Based on the atrophy phenotype resulting from BCAA metabolism dysfunction, the optimized BCAA supplementation improves the survival of cancer cachexia in muscle-specific Bckdk-cKO mice bearing LLC tumors, and improves the occurrence of cancer cachexia. The mechanism of BCAA supplementation on muscle mass preservation is based on the promotion of protein synthesis and the inhibition of protein ubiquitination degradation. CONCLUSIONS: Dysfunctional BCAA metabolism contributes to the inhibition of protein synthesis and increases protein degradation in the cancer cachexia model of muscle-specific Bckdk-cKO mice bearing LLC tumors. The reprogramming of BCAA catabolism exerts therapeutic effects by stimulating protein synthesis and inhibiting protein degradation in skeletal muscle.

Branched-chain amino acid catabolic defect in vascular smooth muscle cells drives thoracic aortic dissection via mTOR hyperactivation.

Metabolic reprogramming of vascular smooth muscle cell (VSMC) plays a critical role in the pathogenesis of thoracic aortic dissection (TAD). Previous researches have mainly focused on dysregulation of fatty acid or glucose metabolism, while the impact of amino acids catabolic disorder in VSMCs during the development of TAD remains elusive. Here, we identified branched-chain amino acid (BCAA) catabolic defect as a metabolic hallmark of TAD. The bioinformatics analysis and data from human aorta revealed impaired BCAA catabolism in TAD individuals. This was accompanied by upregulated branched-chain α-ketoacid dehydrogenase kinase (BCKDK) expression and BCKD E1 subunit alpha (BCKDHA) phosphorylation, enhanced vascular inflammation, and hyperactivation of mTOR signaling. Further in vivo experiments demonstrated that inhibition of BCKDK with BT2 (a BCKDK allosteric inhibitor) treatment dephosphorylated BCKDHA and re-activated BCAA catabolism, attenuated VSMCs phenotypic switching, alleviated aortic remodeling, mitochondrial reactive oxygen species (ROS) damage and vascular inflammation. Additionally, the beneficial actions of BT2 were validated in a TNF-α challenged murine VSMC cell line. Meanwhile, rapamycin conferred similar beneficial effects against VSMC phenotypic switching, cellular ROS damage as well as inflammatory response. However, co-treatment with MHY1485 (a classic mTOR activator) reversed the beneficial effects of BT2 by reactivating mTOR signaling. Taken together, the in vivo and in vitro evidence showed that impairment of BCAA catabolism resulted in aortic accumulation of BCAA and further caused VSMC phenotypic switching, mitochondrial ROS damage and inflammatory response via mTOR hyperactivation. BCKDK and mTOR signaling may serve as the potential drug targets for the prevention and treatment of TAD.

CRISPR-RfxCas13d screening uncovers Bckdk as a post-translational regulator of the maternal-to-zygotic transition in teleosts.

The Maternal-to-Zygotic transition (MZT) is a reprograming process encompassing zygotic genome activation (ZGA) and the clearance of maternally-provided mRNAs. While some factors regulating MZT have been identified, there are thousands of maternal RNAs whose function has not been ascribed yet. Here, we have performed a proof-of-principle CRISPR-RfxCas13d maternal screening targeting mRNAs encoding protein kinases and phosphatases in zebrafish and identified Bckdk as a novel post-translational regulator of MZT. Bckdk mRNA knockdown caused epiboly defects, ZGA deregulation, H3K27ac reduction and a partial impairment of miR-430 processing. Phospho-proteomic analysis revealed that Phf10/Baf45a, a chromatin remodeling factor, is less phosphorylated upon Bckdk depletion. Further, phf10 mRNA knockdown also altered ZGA and Phf10 constitutively phosphorylated rescued the developmental defects observed after bckdk mRNA depletion. Altogether, our results demonstrate the competence of CRISPR-RfxCas13d screenings to uncover new regulators of early vertebrate development and shed light on the post-translational control of MZT mediated by protein phosphorylation.

Computational structural genomics and clinical evidence suggest BCKDK gain-of-function may cause a potentially asymptomatic maple syrup urine disease phenotype.

Maple syrup urine disease (MSUD) is a disorder of branched-chain amino acid metabolism caused by a defect in the branched-chain α-ketoacid dehydrogenase (BCKD) complex (OMIM #248600). The hallmark presentation is encephalopathic crisis in neonates, but can also present with metabolic decompensation, developmental delays, and feeding difficulties. Biochemical evidence for MSUD includes elevated branched-chain amino acids (BCAA) and the pathognomonic presence of alloisoleucine. The BCKD complex contains several subunits associated with autosomal recessive MSUD, while its regulatory proteins have less well-defined disease associations. We report on two families with the same BCKDK variant (c.1115C>G (p.Thr372Arg)). Probands were detected on newborn screening and demonstrated biochemical evidence of MSUD. The variant was identified in reportedly asymptomatic parents and additional family members who had elevated BCAA and alloisoleucine, following an autosomal dominant pattern of inheritance. To better define the functional effect of the variant on the kinase, we completed molecular modeling using sequence-based (2D), structural-based (3D), and dynamic-based (4D) analyses. The BCKDK variant modeling indicated a gain-of-function which leads to impaired BCAA catabolism consistent with the biochemical evidence in this cohort. Combining the evidence gained from molecular modeling with the absence of metabolic decompensation in our patients and several adult family members, despite encountering stressors typically problematic in classic MSUD, we suggest that heterozygous gain-of-function variants in BCKDK may represent a novel biochemical phenotype of MSUD with a benign clinical course.

Partial suppression of BCAA catabolism as a potential therapy for BCKDK deficiency.

Branched chain ketoacid dehydrogenase kinase (BCKDK) deficiency is a recently described inherited neurometabolic disorder of branched chain amino acid (BCAA) metabolism implying increased BCAA catabolism. It has been hypothesized that a severe reduction in systemic BCAA levels underlies the disease pathophysiology, and that BCAA supplementation may ameliorate disease phenotypes. To test this hypothesis, we characterized a recent mouse model of BCKDK deficiency and evaluated the efficacy of enteral BCAA supplementation in this model. Surprisingly, BCAA supplementation exacerbated neurodevelopmental deficits and did not correct biochemical abnormalities despite increasing systemic BCAA levels. These data suggest that aberrant flux through the BCAA catabolic pathway, not just BCAA insufficiency, may contribute to disease pathology. In support of this conclusion, genetic re-regulation of BCAA catabolism, through Dbt haploinsufficiency, partially rescued biochemical and behavioral phenotypes in BCKDK deficient mice. Collectively, these data raise into question assumptions widely made about the pathophysiology of BCKDK insufficiency and suggest a novel approach to develop potential therapies for this disease.

Loss of BCAA catabolism enhances Rab1A-mTORC1 signaling activity and promotes tumor proliferation in NSCLC.

BACKGROUND: Non-small cell lung cancer (NSCLC) is a leading cause of cancer death. Branched-chain amino acid (BCAA) homeostasis is important for normal physiological metabolism. Branched-chain keto acid dehydrogenase kinase (BCKDK) is a rate-limiting enzyme involved in BCAA degradation. BCAA metabolism has been highlighted in human cancers. The aberrant activation of mTORC1 has been implicated in tumor progression. Rab1A is a small GTPase, an activator of mTORC1, and an oncogene. This study aimed to reveal the specific role of BCKDK-BCAA-Rab1A-mTORC1 signaling in NSCLC. METHODS: We analyzed a cohort of 79 patients with NSCLC and 79 healthy controls. Plasma BCAA assays, immunohistochemistry, and network and pathway analyses were performed. The stable cell lines BCKDK-KD, BCKDK-OV A549, and H1299 were constructed. BCKDK, Rab1A, p-S6 and S6 were detected using western blotting to explore their molecular mechanisms of action in NSCLC. The effects of BCAA and BCKDK on the apoptosis and proliferation of H1299 cells were detected by cell function assays. RESULTS: We demonstrated that NSCLC was primarily involved in BCAA degradation. Therefore, combining BCAA, CEA, and Cyfra21-1 is clinically useful for treating NSCLC. We observed a significant increase in BCAA levels, downregulation of BCKDHA expression, and upregulation of BCKDK expression in NSCLC cells. BCKDK promotes proliferation and inhibits apoptosis in NSCLC cells, and we observed that BCKDK affected Rab1A and p-S6 in A549 and H1299 cells via BCAA modulation. Leucine affected Rab1A and p-S6 in A549 and H1299 cells and affected the apoptosis rate of H1299 cells. In conclusion, BCKDK enhances Rab1A-mTORC1 signaling and promotes tumor proliferation by suppressing BCAA catabolism in NSCLC, suggesting a new biomarker for the early diagnosis and identification of metabolism-based targeted approaches for patients with NSCLC.

Mitophagy in Astrocytes Is Required for the Health of Optic Nerve.

Mitochondrial dysfunction in astrocytes has been implicated in the development of various neurological disorders. Mitophagy, mitochondrial autophagy, is required for proper mitochondrial function by preventing the accumulation of damaged mitochondria. The importance of mitophagy, specifically in the astrocytes of the optic nerve (ON), has been little studied. We introduce an animal model in which two separate mutations act synergistically to produce severe ON degeneration. The first mutation is in Cryba1, which encodes ßA3/A1-crystallin, a lens protein also expressed in astrocytes, where it regulates lysosomal pH. The second mutation is in Bckdk, which encodes branched-chain ketoacid dehydrogenase kinase, which is ubiquitously expressed in the mitochondrial matrix and involved in the catabolism of the branched-chain amino acids. BCKDK is essential for mitochondrial function and the amelioration of oxidative stress. Neither of the mutations in isolation has a significant effect on the ON, but animals homozygous for both mutations (DM) exhibit very serious ON degeneration. ON astrocytes from these double-mutant (DM) animals have lysosomal defects, including impaired mitophagy, and dysfunctional mitochondria. Urolithin A can rescue the mitophagy impairment in DM astrocytes and reduce ON degeneration. These data demonstrate that efficient mitophagy in astrocytes is required for ON health and functional integrity.

Evaluation of therapeutic strategies targeting BCAA catabolism using a systems pharmacology model.

Background: Abnormal branched-chained amino acids (BCAA) accumulation in cardiomyocytes is associated with cardiac remodeling in heart failure. Administration of branched-chain α-keto acid dehydrogenase (BCKD) kinase inhibitor BT2 has been shown to reduce cardiac BCAA levels and demonstrated positive effects on cardiac function in a preclinical setting. The current study is focused on evaluating the impact of BT2 on the systemic and cardiac levels of BCAA and their metabolites as well as activities of BCAA catabolic enzymes using a quantitative systems pharmacology model. Methods: The model is composed of an ordinary differential equation system characterizing BCAA consumption with food, disposal in the proteins, reversible branched-chain-amino-acid aminotransferase (BCAT)-mediated transamination to branched-chain keto-acids (BCKA), followed by BCKD-mediated oxidation. Activity of BCKD is regulated by the balance of BCKDK and protein phosphatase 2Cm (PP2Cm) activities, affected by BT2 treatment. Cardiac BCAA levels are assumed to directly affect left ventricular ejection fraction (LVEF). Biochemical characteristics of the enzymes are taken from the public domains, while plasma and cardiac BCAA and BCKA levels in BT2 treated mice are used to inform the model parameters. Results: The model provides adequate reproduction of the experimental data and predicts synchronous BCAA responses in the systemic and cardiac space, dictated by rapid BCAA equilibration between the tissues. The model-based simulations indicate maximum possible effect of BT2 treatment on BCAA reduction to be 40% corresponding to 12% increase in LVEF. Model sensitivity analysis demonstrates strong impact of BCKDK and PP2Cm activities as well as total BCKD and co-substrate levels (glutamate, ketoglutarate and ATP) on BCAA and BCKA levels. Conclusion: Model based simulations confirms using of plasma measurements as a marker of cardiac BCAA changes under BCKDK inhibition. The proposed model can be used for optimization of preclinical study design for novel compounds targeting BCAA catabolism.

The role of branched chain amino acids metabolic disorders in tumorigenesis and progression.

Branched-chain amino acids (BCAAs) are essential amino acids in human bodies. They have complex metabolic pathways and various metabolites. Both BCAAs and its metabolites are involved in various processes such as protein anabolism and catabolism, energy supply, signaling transduction and so on. Previous studies have observed the widely alternations of BCAAs and its related proteins in multiple tumor phenotypes, which suggests that BCAAs metabolic disorders may have emerged as a powerful factor for tumor metabolism reprogramming. BCAAs metabolism has a pivotal role in tumorigenesis and progression, including cell growth, proliferation, migration, invasion, and so on. In this review, we try to shed light on the crucial role of BCAAs metabolic disorders in different tumor types by focusing on the impacts of metabolic disorders of BCAAs and discussing the notable proteins involved in cancer metabolic reprogramming of BCAAs, such as BCAT1/2, BCKDH-BCKDK-PPM1K complex, transporters of BCAAs and its metabolites, transcription factors and so on, and present several possible diagnose approaches and therapies to BCAAs-related cancers.