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Mitochondrial retrograde signaling connects respiratory capacity to thermogenic gene expression.

ABSTRACT: Mitochondrial respiration plays a crucial role in determining the metabolic state of brown adipose tissue (BAT), due to its direct roles in thermogenesis, as well as through additional mechanisms. Here, we show that respiration-dependent retrograde signaling from mitochondria to nucleus contributes to genetic and metabolic reprogramming of BAT. In mouse BAT, ablation of LRPPRC (LRP130), a potent regulator of mitochondrial transcription and respiratory capacity, triggers down-regulation of thermogenic genes, promoting a storage phenotype in BAT. This retrograde regulation functions by inhibiting the recruitment of PPAR? to the regulatory elements of thermogenic genes. Reducing cytosolic Ca2+ reverses the attenuation of thermogenic genes in brown adipocytes with impaired respiratory capacity, while induction of cytosolic Ca2+ is sufficient to attenuate thermogenic gene expression, indicating that cytosolic Ca2+ mediates mitochondria-nucleus crosstalk. Our findings suggest respiratory capacity governs thermogenic gene expression and BAT function via mitochondria-nucleus communication, which in turn leads to either a thermogenic or storage mode.

SUBMITTER: Nam M

PROVIDER: S-EPMC5435730 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

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Mitochondrial retrograde signaling connects respiratory capacity to thermogenic gene expression.

Nam Minwoo M Akie Thomas E TE Sanosaka Masato M Craige Siobhan M SM Kant Shashi S Keaney John F JF Cooper Marcus P MP

Scientific reports 20170517 1

Mitochondrial respiration plays a crucial role in determining the metabolic state of brown adipose tissue (BAT), due to its direct roles in thermogenesis, as well as through additional mechanisms. Here, we show that respiration-dependent retrograde signaling from mitochondria to nucleus contributes to genetic and metabolic reprogramming of BAT. In mouse BAT, ablation of LRPPRC (LRP130), a potent regulator of mitochondrial transcription and respiratory capacity, triggers down-regulation of thermo ...[more]

PMID: 28515438

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Project description:Akt, a serine/threonine kinase has been shown to stimulate glycolysis in cancer cells but its role in mitochondrial respiration is unknown. Using PTEN-knockout mouse embryonic fibroblasts (MEF(PTEN-/-)) with hyper-activated Akt as a cell model, we observed a higher respiratory capacity in MEF(PTEN-/-) compared to the wildtype (MEF(WT)). The respiratory phenotype observed in MEF(PTEN-/-) was reproduced in MEF(WT) by gene silencing of PTEN which substantiated its role in regulating mitochondrial function. The increased activities of the respiratory complexes (RCs) I, III and IV were retained in the same relative proportions as those present in MEF(WT), alluding to a possible co-ordinated regulation by PTEN/Akt. Using LY294002 (a PI3K inhibitor) and Akt inhibitor IV, we showed that the regulation of enzyme activities and protein expressions of the RCs was dependent on PI3K/Akt. There was insignificant difference in the protein expressions of mitochondrial transcription factor: peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and its downstream targets, the nuclear respiratory factor 1 (NRF-1) and mitochondrial transcription factor A (mtTFA) between MEF(PTEN-/-) and MEF(WT). Similarly, mRNA levels of the same subunits of the RCs detected in Western blots were not significantly different between MEF(PTEN-/-) and MEF(WT) suggesting that the regulation by Akt on mitochondrial function was probably not via gene transcription. On the other hand, a decrease of total 4E-BP1 with a higher expression of its phosphorylated form relative to total 4E-BP1 was found in MEF(PTEN-/-), which inferred that the regulation of mitochondrial respiratory activities by Akt was in part through this protein translation pathway. Notably, gene silencing of 4E-BP1 up-regulated the protein expressions of all RCs and the action of 4E-BP1 appeared to be specific to these mitochondrial proteins. In conclusion, PTEN inactivation bestowed a bioenergetic advantage to the cells by up-regulating mitochondrial respiratory capacity through the 4E-BP1-mediated protein translation pathway.

Project description:The mitochondrial and nuclear genomes contribute to mitochondrial function, and when mitochondrial function is compromised, mitochondrial retrograde signaling alters nuclear gene expression. We performed gene expression profiling of engineered cells that had mitochondria containing a disease-associated mutation that causes mitochondrial dysfunction. By generating networks of transcription factors that targeted these genes, the authors revealed putative mitochondrial retrograde signaling pathways. One such pathway involved retinoic acid receptor alpha (RXRA), the mRNA for which was reduced in the mutant cells. Network analysis and experiments in cells suggested that mitochondrial dysfunction caused by the mutation initiated a positive feedback loop that aggravated mitochondrial dysfunction: Reduced RXRA abundance further compromised expression of genes encoding products involved in mitochondrial function and translation. This gene-transcription factor mapping-network approach may reveal targets for therapeutic intervention of diseases associated with mitochondrial dysfunction. To investigate retrograde signaling pathways induced by the mitochondrial dysfunction caused by the mt3243 mutation, we generated the three types of cybrid cells using a mitochondria-mediated transformation method. Cells lacking mtDNA (rho0) were fused with mtDNAs with the mt3243 mutation isolated from platelets of a diabetic patient with sensorineural hearing loss. We then isolated three types of cybrid cells: W cells had wild-type mtDNA (3243A homoplasmy), H cells had both the mutant and wild-type mtDNA (3243A/G heteroplasmy) with 70% of the mtDNA containing 3243G, and M cells with only mutant mtDNA (3243G homoplasmy). Gene expression profiles of cybrid cells were generated using Illumina HumanHT-12-v3-BeadChip (Illumina, San Diego, CA), which includes 49,896 probes corresponding to 25,202 annotated genes. According to the Illumina protocols, three biological triplicates of each type of cybrid cells were analyzed. Total RNA (500ng) was isolated from cybrid cells using RNeasy Mini Kit (Qiagen, GmbH, Germany). RNA integrity number (RIN) was in the range of RIN = 9.2 and 10 when measured with an Agilent 2100 Bioanalyzer. RNA was reversely transcribed and amplified using IlluminaTotalPrep RNA amplification kit (Ambion, Austin, TX). In vitro transcription was then carried out to prepare cRNA. The cRNAs were hybridized to the array and then labeled with Cy3-streptavidin (Amersham Bioscience, Little Chalfont, UK). The fluorescent signal on the array was measured with a BeadStation 500 System (Illumina, San Diego, CA).

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Mitochondrial retrograde signaling connects respiratory capacity to thermogenic gene expression.

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Mitochondrial retrograde signaling connects respiratory capacity to thermogenic gene expression.

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