Ablation of PGC-1β Results in Defective Mitochondrial Activity, Thermogenesis, Hepatic Function, and Cardiac Performance

The transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator-1β (PGC-1β) has been implicated in important metabolic processes. A mouse lacking PGC-1β (PGC1βKO) was generated and phenotyped using physiological, molecular, and bioinformatic approaches. PGC1βKO mice are generally viable and metabolically healthy. Using systems biology, we identified a general defect in the expression of genes involved in mitochondrial function and, specifically, the electron transport chain. This defect correlated with reduced mitochondrial volume fraction in soleus muscle and heart, but not brown adipose tissue (BAT). Under ambient temperature conditions, PGC-1β ablation was partially compensated by up-regulation of PGC-1α in BAT and white adipose tissue (WAT) that lead to increased thermogenesis, reduced body weight, and reduced fat mass. Despite their decreased fat mass, PGC1βKO mice had hypertrophic adipocytes in WAT. The thermogenic role of PGC-1β was identified in thermoneutral and cold-adapted conditions by inadequate responses to norepinephrine injection. Furthermore, PGC1βKO hearts showed a blunted chronotropic response to dobutamine stimulation, and isolated soleus muscle fibres from PGC1βKO mice have impaired mitochondrial function. Lack of PGC-1β also impaired hepatic lipid metabolism in response to acute high fat dietary loads, resulting in hepatic steatosis and reduced lipoprotein-associated triglyceride and cholesterol content. Altogether, our data suggest that PGC-1β plays a general role in controlling basal mitochondrial function and also participates in tissue-specific adaptive responses during metabolic stress

Predicting breast cancer response to neoadjuvant treatment using multi-feature MRI: results from the I-SPY 2 TRIAL.

Dynamic contrast-enhanced (DCE) MRI provides both morphological and functional information regarding breast tumor response to neoadjuvant chemotherapy (NAC). The purpose of this retrospective study is to test if prediction models combining multiple MRI features outperform models with single features. Four features were quantitatively calculated in each MRI exam: functional tumor volume, longest diameter, sphericity, and contralateral background parenchymal enhancement. Logistic regression analysis was used to study the relationship between MRI variables and pathologic complete response (pCR). Predictive performance was estimated using the area under the receiver operating characteristic curve (AUC). The full cohort was stratified by hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) status (positive or negative). A total of 384 patients (median age: 49 y/o) were included. Results showed analysis with combined features achieved higher AUCs than analysis with any feature alone. AUCs estimated for the combined versus highest AUCs among single features were 0.81 (95% confidence interval [CI]: 0.76, 0.86) versus 0.79 (95% CI: 0.73, 0.85) in the full cohort, 0.83 (95% CI: 0.77, 0.92) versus 0.73 (95% CI: 0.61, 0.84) in HR-positive/HER2-negative, 0.88 (95% CI: 0.79, 0.97) versus 0.78 (95% CI: 0.63, 0.89) in HR-positive/HER2-positive, 0.83 (95% CI not available) versus 0.75 (95% CI: 0.46, 0.81) in HR-negative/HER2-positive, and 0.82 (95% CI: 0.74, 0.91) versus 0.75 (95% CI: 0.64, 0.83) in triple negatives. Multi-feature MRI analysis improved pCR prediction over analysis of any individual feature that we examined. Additionally, the improvements in prediction were more notable when analysis was conducted according to cancer subtype

PGC1βKO Hearts Display a Blunted Heart Rate Response to Dobutamine Stimulation In Vivo

<div><p>PGC1βKO and WT littermates (male, 26-wk-old) were treated as stated in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0040369#s4" target="_blank">Material and Methods</a> and infused with 10 or 40 ng/min/g BW dobutamine to measure in vivo hemodynamic responses WT, solid line; KO, dashed line.</p> <p>(A) Percentage change in heart rate from basal during dobutamine infusion.</p> <p>(B and C) Measurement of ventricular performance, <i>dP</i>/<i>dt</i>, during infusion. The arrow marks the increase in dobutamine concentration in the infusion from 10 to 40 ng/min/g BW. <i>n</i> = 5 mice per genotype.</p></div

The PGC1βKO Mouse Has Altered Metabolism under Standard Environmental Conditions

<div><p>(A) Growth curves of male (left panel) and female (right panel) mice on normal diet. WT (solid circles) and PGC1βKO (open circles) mice, <i>n</i> = 18–21 mice per group.</p> <p>(B) Assessment of fat content by DEXA in 8- and 32-wk-old male WT (solid bars) and PGC1βKO mice (open bars), <i>n</i> = 8–12 mice per group.</p> <p>(C) Representative histological sections of tissues from WAT (<i>n</i> = 6).</p> <p>(D) Size distribution of adipocytes from WT and PGC1βKO mice. Two fields from each section from epididymal adipose tissue depot (<i>n</i> = 4 mice per genotype) were analysed to obtain the mean cell area per animal.</p> <p>(E) Epididymal WAT gene expression from 12-wk-old PGC1βKO (white bars) and WT littermates (black bars). Individual measurements are standardized using 18S, and then the average of the WT group was set to 1. <i>n</i> = 5–8 mice per group.</p></div

PGC1βKO Mice Demonstrate Increased Liver Mass and Development of Fatty Liver after 24 h HFD

<div><p>Female 8-wk-old mice were given normal chow or Surwit HFD (Sur) for 24 h. Tissues were then collected for analysis.</p> <p>(A) Liver weight, as standardized by body weight (LW/BW) for WT (black bars) and PGC1βKO (white bars) after 24 h diets.</p> <p>(B) Representative histological sections from mice given normal or Surwit diet for 24 h. <i>n</i> = 6–7 mice per group.</p></div

PGC-1β Ablation Results in Major Changes in BAT Metabolic Gene Expression

<p>Expression levels of mRNA were assessed on interscapular BAT from 12-wk-old male WT (black bars) and PGC1βKO (white bars) mice. Individual measurements are standardized using 18S, and the average of the WT group set to 1. <i>n</i> = 5–7 mice per group.</p

Isolated Soleus Fibres from PGC1βKO Mice Have Reduced Mitochondrial Activity

<div><p>Soleus fibres were isolated from WT (black bars) and PGC1βKO mice (white bars) and permeabilised to allow measurement of tissue-associated mitochondrial function.</p> <p>(A) Mitochondrial respiratory parameters for state 2 (<i>V</i>₀), state 3 (<i>V</i>_ADP), state 4 (<i>V</i>_oligomycin), and respiratory control ratio (RC).</p> <p>(B) ATP synthesis rates in permeabilised soleus fibres.</p> <p>(C) ATP/O ratio in permeabilised soleus fibres. Data are standardised to mg of muscle dry weight (mgdw). <i>n</i> = 9 WT mice, 11 PGC1βKO mice.</p> <p>(D) A representative electron micrograph of soleus muscle from WT (left panel) and PGC1βKO (right panel) mice.</p></div

Alterations in Gene Expression and Mitochondrial Dimensions in Hearts of PGC1βKO Mice

<div><p>(A) Expression levels of mRNA were assessed on hearts from 24-wk-old male WT (black bars) and PGC1βKO (white bars) mice. Individual measurements are standardized using 18S, and the average of the WT group set to 1. <i>n</i> = 5–7 mice per group.</p> <p>(B) A representative electron micrograph of mitochondria from WT (left panel) and PGC1βKO (right panel) hearts. The bar indicates a measurement of 200 nm.</p> <p>(C) mRNA expression of key genes for mitochondrial function in 24-wk-old WT and PGC1βKO mouse hearts.</p> <p>(D) mRNA expression of key genes for metabolic function in 24-wk-old male WT and PGC1βKO mouse hearts.</p></div

PGC-1β Ablation Reduces ETC Gene and Protein Expression but Mitochondrial Volume Fraction is Unaffected

<div><p>(A and B) Expression levels of (A) nuclear-encoded and (B) mitochondrially encoded genes were assessed on interscapular BAT from 12-wk-old male WT (black bars) and PGC1βKO (white bars) mice. Individual measurements are standardized using 18S, and the average of the WT group set to 1. <i>n</i> = 5–7 mice per group.</p> <p>(C and D) BAT protein levels of ETC and OxPhos components from 15-wk-old female mice were assessed by western blotting of samples from (C) tissues and (D) mitochondrial fractions. WT, black bars and PGC1βKO, white bars. Complex I, α-subcomplex 9 (α-s9); complex II, succinate dehydrogenase subunit B (SDHB); complex III, Fe-S core protein (Fe-S); complex IV, Cox4; complex V, ATP synthase subunit β (ATPβ). <i>n</i> = 5–6 mice for each protein, with the average value of the WT group set to 1. Representative blots showing two samples from each genotype.</p> <p>(E) Representative electron micrographs from BAT of WT (left panel) and PGC1βKO (right panel) mice.</p></div