Reactive oxygen species (ROS) and mitochondrial defects in neurons are implicated in neurodegenerative disease. Here, we find that a key consequence of ROS and neuronal mitochondrial dysfunction is ...the accumulation of lipid droplets (LD) in glia. In Drosophila, ROS triggers c-Jun-N-terminal Kinase (JNK) and Sterol Regulatory Element Binding Protein (SREBP) activity in neurons leading to LD accumulation in glia prior to or at the onset of neurodegeneration. The accumulated lipids are peroxidated in the presence of ROS. Reducing LD accumulation in glia and lipid peroxidation via targeted lipase overexpression and/or lowering ROS significantly delays the onset of neurodegeneration. Furthermore, a similar pathway leads to glial LD accumulation in Ndufs4 mutant mice with neuronal mitochondrial defects, suggesting that LD accumulation following mitochondrial dysfunction is an evolutionarily conserved phenomenon, and represents an early, transient indicator and promoter of neurodegenerative disease.
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•Lipid droplets (LD) are transient and occur prior to neurodegeneration in flies and mice•LD are present in glia and induced by neuronal increase of ROS, JNK, and SREBP•Reduction of ROS by antioxidants, lipases, or lower JNK or SREBP, delay degeneration•Neurodegeneration in mice with ROS/lipid droplets can be delayed with antioxidants
Lipid droplet accumulation in glial cells, driven by mitochondrial defects and ROS in neurons, contribute to neurodegeneration in a Drosophila model, with evidence of a conserved mechanism in mice.
Transcriptional cascades that operate over the course of lineage development are fundamental mechanisms that control cellular differentiation. In the developing central nervous system (CNS), these ...mechanisms are well characterized during neurogenesis, but remain poorly defined during neural stem cell commitment to the glial lineage. NFIA is a transcription factor that plays a crucial role in the onset of gliogenesis; we found that its induction is regulated by the transcription factor Sox9 and that this relationship mediates the initiation of gliogenesis. Subsequently, Sox9 and NFIA form a complex and coregulate a set of genes induced after glial initiation. Functional studies revealed that a subset of these genes, Apcdd1 and Mmd2, perform key migratory and metabolic roles during astro-gliogenesis, respectively. In sum, these studies delineate a transcriptional regulatory cascade that operates during the initiation of gliogenesis and identifies a unique set of genes that regulate key aspects of astro-glial precursor physiology during development.
► Sox9 directly regulates NFIA induction during the initiation of gliogenesis ► Sox9 and NFIA associate and coregulate a set of genes during gliogenesis ► Mmd2 is a target of Sox9/NFIA that regulates glial precursor energy metabolism ► Apcdd1 is a target of Sox9/NFIA that mediates astrocyte precursor migration
Transcriptional cascades are fundamental mechanisms that control lineage development. Kang et al. report that Sox9 and NFIA comprise such a transcriptional cascade during neural stem cell commitment to the glial lineage. Furthermore, Sox9 and NFIA associate and coregulate a select set of glial-specific genes.
Here, we utilized spontaneous models of pancreatic and lung cancer to examine how neoantigenicity shapes tumor immunity and progression. As expected, neoantigen expression during lung adenocarcinoma ...development leads to T cell-mediated immunity and disease restraint. By contrast, neoantigen expression in pancreatic ductal adenocarcinoma (PDAC) results in exacerbation of a fibro-inflammatory microenvironment that drives disease progression and metastasis. Pathogenic TH17 responses are responsible for this neoantigen-induced tumor progression in PDAC. Underlying these divergent T cell responses in pancreas and lung cancer are differences in infiltrating conventional dendritic cells (cDCs). Overcoming cDC deficiency in early-stage PDAC leads to disease restraint, while restoration of cDC function in advanced PDAC restores tumor-restraining immunity and enhances responsiveness to radiation therapy.
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•Neoantigen expression elicits pathogenic T cell response accelerating PDAC•cDC dysfunction precludes early TH1 and CTL response to PDAC neoantigens•Increasing cDCs in early PDAC lesions restores anti-tumor T cell immunity•Restoring cDC function in advanced PDAC improves efficacy of radiation therapy
Hegde et al. identify divergent T cell responses in lung cancer and pancreatic ductal adenocarcinoma (PDAC) caused by differences in conventional dendritic cell (cDC) infiltration. Mobilization of cDCs in PDAC models enhances CD8+ T cell and TH1 activity to reduce tumor growth and increase response to therapy.
Kidney injury initiates metabolic reprogramming in tubule cells that contributes to the development of chronic kidney disease (CKD). Exercise has been associated with beneficial effects in patients ...with CKD. Here we show that the induction of a myokine, irisin, improves kidney energy metabolism and prevents kidney damage. In response to kidney injury, mice with muscle-specific PGC-1α overexpression (mPGC-1α) exhibit reduced kidney damage and fibrosis. Metabolomics analysis reveals increased ATP production and improved energy metabolism in injured kidneys from mPGC-1α mice. We identify irisin as a serum factor that mediates these metabolic effects during progressive kidney injury by inhibiting TGF-β type 1 receptor. Irisin depletion from serum blunts the induction of oxygen consumption rate observed in tubule cells treated with mPGC-1α serum. In mice, recombinant irisin administration attenuates kidney damage and fibrosis and improves kidney functions. We suggest that myokine-mediated muscle-kidney crosstalk can suppress metabolic reprograming and fibrogenesis during kidney disease.
Transmitochondrial cybrids and multiple OMICs approaches were used to understand mitochondrial reprogramming and mitochondria-regulated cancer pathways in triple-negative breast cancer (TNBC). ...Analysis of cybrids and established breast cancer (BC) cell lines showed that metastatic TNBC maintains high levels of ATP through fatty acid β oxidation (FAO) and activates Src oncoprotein through autophosphorylation at Y419. Manipulation of FAO including the knocking down of carnitine palmitoyltransferase-1A (CPT1) and 2 (CPT2), the rate-limiting proteins of FAO, and analysis of patient-derived xenograft models confirmed the role of mitochondrial FAO in Src activation and metastasis. Analysis of TCGA and other independent BC clinical data further reaffirmed the role of mitochondrial FAO and CPT genes in Src regulation and their significance in BC metastasis.
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•Metastatic TNBC is dependent on mitochondrial FAO energy metabolism•FAO activates c-Src via autophosphorylation at residue Y419•CPT genes are critical in TNBC tumor progression and metastasis•Reduction of fat or FAO may provide clinical benefit to TNBC patients
Park et al. show that mitochondrial fatty acid β oxidation is an important energy pathway in metastatic triple-negative breast cancer. Their results uncover the significance of mitochondrial energy reprogramming in the tumor properties of triple-negative breast cancer and regulation of the Src cancer pathway by post-translational modification.
Biallelic pathogenic variants in subunits of succinyl-CoA synthetase (SCS), a tricarboxylic acid (TCA) cycle enzyme, are associated with mitochondrial encephalomyopathy in humans. SCS catalyzes the ...interconversion of succinyl-CoA to succinate, coupled to substrate-level phosphorylation of either ADP or GDP, within the TCA cycle. SCS-deficient encephalomyopathy typically presents in infancy and early childhood, with many patients succumbing to the disease during childhood. Common symptoms include abnormal brain MRI, basal ganglia lesions and cerebral atrophy, severe hypotonia, dystonia, progressive psychomotor regression, and growth deficits. Although subunits of SCS were first identified as causal genes for progressive metabolic encephalomyopathy in the early 2000s, recent investigations are now beginning to unravel the pathomechanisms underlying this metabolic disorder. This article reviews the current understanding of SCS function within and outside the TCA cycle as it relates to the complex and multifactorial mechanisms underlying SCS-related mitochondrial encephalomyopathy.
An increasing number of genes required for mitochondrial biogenesis, dynamics, or function have been found to be mutated in metabolic disorders and neurological diseases such as Leigh Syndrome. In a ...forward genetic screen to identify genes required for neuronal function and survival in Drosophila photoreceptor neurons, we have identified mutations in the mitochondrial methionyl-tRNA synthetase, Aats-met, the homologue of human MARS2. The fly mutants exhibit age-dependent degeneration of photoreceptors, shortened lifespan, and reduced cell proliferation in epithelial tissues. We further observed that these mutants display defects in oxidative phosphorylation, increased Reactive Oxygen Species (ROS), and an upregulated mitochondrial Unfolded Protein Response. With the aid of this knowledge, we identified MARS2 to be mutated in Autosomal Recessive Spastic Ataxia with Leukoencephalopathy (ARSAL) patients. We uncovered complex rearrangements in the MARS2 gene in all ARSAL patients. Analysis of patient cells revealed decreased levels of MARS2 protein and a reduced rate of mitochondrial protein synthesis. Patient cells also exhibited reduced Complex I activity, increased ROS, and a slower cell proliferation rate, similar to Drosophila Aats-met mutants.
Two insults often underlie a variety of eye diseases including glaucoma, optic atrophy, and retinal degeneration--defects in mitochondrial function and aberrant Rhodopsin trafficking. Although ...mitochondrial defects are often associated with oxidative stress, they have not been linked to Rhodopsin trafficking. In an unbiased forward genetic screen designed to isolate mutations that cause photoreceptor degeneration, we identified mutations in a nuclear-encoded mitochondrial gene, ppr, a homolog of human LRPPRC. We found that ppr is required for protection against light-induced degeneration. Its function is essential to maintain membrane depolarization of the photoreceptors upon repetitive light exposure, and an impaired phototransduction cascade in ppr mutants results in excessive Rhodopsin1 endocytosis. Moreover, loss of ppr results in a reduction in mitochondrial RNAs, reduced electron transport chain activity, and reduced ATP levels. Oxidative stress, however, is not induced. We propose that the reduced ATP level in ppr mutants underlies the phototransduction defect, leading to increased Rhodopsin1 endocytosis during light exposure, causing photoreceptor degeneration independent of oxidative stress. This hypothesis is bolstered by characterization of two other genes isolated in the screen, pyruvate dehydrogenase and citrate synthase. Their loss also causes a light-induced degeneration, excessive Rhodopsin1 endocytosis and reduced ATP without concurrent oxidative stress, unlike many other mutations in mitochondrial genes that are associated with elevated oxidative stress and light-independent photoreceptor demise.
ABAT is a key enzyme responsible for catabolism of principal inhibitory neurotransmitter γ-aminobutyric acid (GABA). We report an essential role for ABAT in a seemingly unrelated pathway, ...mitochondrial nucleoside salvage, and demonstrate that mutations in this enzyme cause an autosomal recessive neurometabolic disorder and mtDNA depletion syndrome (MDS). We describe a family with encephalomyopathic MDS caused by a homozygous missense mutation in ABAT that results in elevated GABA in subjects’ brains as well as decreased mtDNA levels in subjects’ fibroblasts. Nucleoside rescue and co-IP experiments pinpoint that ABAT functions in the mitochondrial nucleoside salvage pathway to facilitate conversion of dNDPs to dNTPs. Pharmacological inhibition of ABAT through the irreversible inhibitor Vigabatrin caused depletion of mtDNA in photoreceptor cells that was prevented through addition of dNTPs in cell culture media. This work reveals ABAT as a connection between GABA metabolism and nucleoside metabolism and defines a neurometabolic disorder that includes MDS.
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•ABAT converts dNDP to dNTP in the mitochondrial nucleoside salvage pathway•Inhibition of ABAT causes decreased copy number of mitochondrial genome•mtDNA depletion induced by ABAT inhibition is rescued by dNTP supplementation in vitro•ABAT causes human mitochondrial DNA depletion syndrome
ABAT is a key enzyme responsible for catabolism of principal inhibitory neurotransmitter γ-aminobutyric acid (GABA). Besse et al. report an essential role for ABAT in a seemingly unrelated pathway, mitochondrial nucleoside salvage, and demonstrate that mutations in this enzyme cause autosomal recessive mtDNA depletion syndrome.
Nuclear genetic disorders causing mitochondrial DNA (mtDNA) depletion are clinically and genetically heterogeneous, and the molecular etiology remains undiagnosed in the majority of cases. Through ...whole-exome sequencing, we identified recessive nonsense and splicing mutations in FBXL4 segregating in three unrelated consanguineous kindreds in which affected children present with a fatal encephalopathy, lactic acidosis, and severe mtDNA depletion in muscle. We show that FBXL4 is an F-box protein that colocalizes with mitochondria and that loss-of-function and splice mutations in this protein result in a severe respiratory chain deficiency, loss of mitochondrial membrane potential, and a disturbance of the dynamic mitochondrial network and nucleoid distribution in fibroblasts from affected individuals. Expression of the wild-type FBXL4 transcript in cell lines from two subjects fully rescued the levels of mtDNA copy number, leading to a correction of the mitochondrial biochemical deficit. Together our data demonstrate that mutations in FBXL4 are disease causing and establish FBXL4 as a mitochondrial protein with a possible role in maintaining mtDNA integrity and stability.
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