Pdgfrβ+ Mural Preadipocytes Contribute to Adipocyte Hyperplasia Induced by High-Fat-Diet Feeding and Prolonged Cold Exposure in Adult Mice

The expansion of white adipose tissue (WAT) in obesity involves de novo differentiation of new adipocytes; however, the cellular origin of these cells remains unclear. Here, we utilize Zfp423(GFP) reporter mice to characterize adipose mural (Pdgfrβ(+)) cells with varying levels of the preadipocyte commitment factor Zfp423. We find that adipose tissue contains distinct mural populations, with levels of Zfp423 distinguishing adipogenic from inflammatory-like mural cells. Using our "MuralChaser" lineage tracking system, we uncover adipose perivascular cells as developmental precursors of adipocytes formed in obesity, with adipogenesis and precursor abundance regulated in a depot-dependent manner. Interestingly, Pdgfrβ(+) cells do not significantly contribute to the initial cold-induced recruitment of beige adipocytes in WAT; it is only after prolonged cold exposure that these cells differentiate into beige adipocytes. These results provide genetic evidence for a mural cell origin of white adipocytes in obesity and suggest that beige adipogenesis may originate from multiple sources.

Zfp423 Maintains White Adipocyte Identity through Suppression of the Beige Cell Thermogenic Gene Program

The transcriptional regulators Ebf2 and Prdm16 establish and maintain the brown and/or beige fat cell identity. However, the mechanisms operating in white adipocytes to suppress the thermogenic gene program and maintain an energy-storing phenotype are less understood. Here, we report that the transcriptional regulator Zfp423 is critical for maintaining white adipocyte identity through suppression of the thermogenic gene program. Zfp423 expression is enriched in white versus brown adipocytes and suppressed upon cold exposure. Doxycycline-inducible inactivation of Zfp423 in mature adipocytes, combined with β-adrenergic stimulation, triggers a conversion of differentiated adiponectin-expressing inguinal and gonadal adipocytes into beige-like adipocytes; this reprogramming event is sufficient to prevent and reverse diet-induced obesity and insulin resistance. Mechanistically, Zfp423 acts in adipocytes to inhibit the activity of Ebf2 and suppress Prdm16 activation. These data identify Zfp423 as a molecular brake on adipocyte thermogenesis and suggest a therapeutic strategy to unlock the thermogenic potential of white adipocytes in obesity.

Brown adipose tissue derived VEGF-A modulates cold tolerance and energy expenditure

We recently reported that local overexpression of VEGF-A in white adipose tissue (WAT) protects against diet-induced obesity and metabolic dysfunction. The observation that VEGF-A induces a “brown adipose tissue (BAT)-like” phenotype in WAT prompted us to further explore the direct function of VEGF-A in BAT. We utilized a doxycycline (Dox)-inducible, brown adipocyte-specific VEGF-A transgenic overexpression model to assess direct effects of VEGF-A in BAT in vivo. We observed that BAT-specific VEGF-A expression increases vascularization and up-regulates expression of both UCP1 and PGC-1α in BAT. As a result, the transgenic mice show increased thermogenesis during chronic cold exposure. In diet-induced obese mice, introducing VEGF-A locally in BAT rescues capillary rarefaction, ameliorates brown adipocyte dysfunction, and improves deleterious effects on glucose and lipid metabolism caused by a high-fat diet challenge. These results demonstrate a direct positive role of VEGF-A in the activation and expansion of BAT.

Xbp1s-FoxO1 axis governs lipid accumulation and contractile performance in heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is now the dominant form of heart failure and one for which no efficacious therapies exist. Obesity and lipid mishandling greatly contribute to HFpEF. However, molecular mechanism(s) governing metabolic alterations and perturbations in lipid homeostasis in HFpEF are largely unknown. Here, we report that cardiomyocyte steatosis in HFpEF is coupled with increases in the activity of the transcription factor FoxO1 (Forkhead box protein O1). FoxO1 depletion, as well as over-expression of the Xbp1s (spliced form of the X-box-binding protein 1) arm of the UPR (unfolded protein response) in cardiomyocytes each ameliorates the HFpEF phenotype in mice and reduces myocardial lipid accumulation. Mechanistically, forced expression of Xbp1s in cardiomyocytes triggers ubiquitination and proteasomal degradation of FoxO1 which occurs, in large part, through activation of the E3 ubiquitin ligase STUB1 (STIP1 homology and U-box-containing protein 1) a novel and direct transcriptional target of Xbp1s. Our findings uncover the Xbp1s-FoxO1 axis as a pivotal mechanism in the pathogenesis of cardiometabolic HFpEF and unveil previously unrecognized mechanisms whereby the UPR governs metabolic alterations in cardiomyocytes.

MitoNEET-Parkin Effects in Pancreatic α- and β-Cells, Cellular Survival, and Intrainsular Cross Talk

Mitochondrial metabolism plays an integral role in glucose-stimulated insulin secretion (GSIS) in β-cells. In addition, the diabetogenic role of glucagon released from α-cells plays a major role in the etiology of both type 1 and type 2 diabetes because unopposed hyperglucagonemia is a pertinent contributor to diabetic hyperglycemia. Titrating expression levels of the mitochondrial protein mitoNEET is a powerful approach to fine-tune mitochondrial capacity of cells. Mechanistically, β-cell-specific mitoNEET induction causes hyperglycemia and glucose intolerance due to activation of a Parkin-dependent mitophagic pathway, leading to the formation of vacuoles and uniquely structured mitophagosomes. Induction of mitoNEET in α-cells leads to fasting-induced hypoglycemia and hypersecretion of insulin during GSIS. MitoNEET-challenged α-cells exert potent antiapoptotic effects on β-cells and prevent cellular dysfunction associated with mitoNEET overexpression in β-cells. These observations identify that reduced mitochondrial function in α-cells exerts potently protective effects on β-cells, preserving β-cell viability and mass.

Compromised responses to dietary methionine restriction in adipose tissue but not liver of ob/ob mice

OBJECTIVE

Dietary methionine restriction (MR) reduces adiposity and hepatic lipids and increases overall insulin sensitivity in part by reducing lipogenic gene expression in liver, inducing browning of white adipose tissue (WAT), and enhancing the lipogenic and oxidative capacity of the remodeled WAT.

METHODS

Ob/ob mice have compromised β-adrenergic receptor expression in adipose tissue and were used to test whether MR could ameliorate obesity, insulin resistance, and disordered lipid metabolism.

RESULTS

In contrast to responses in wild-type mice, MR failed to slow accumulation of adiposity, increase lipogenic and thermogenic gene expression in adipose tissue, reduce serum insulin, or increase serum adiponectin in ob/ob mice. However, MR produced comparable reductions in hepatic lipids and lipogenic gene expression in both genotypes. In addition, MR was fully effective in increasing insulin sensitivity in adiponectin(-/-) mice.

CONCLUSIONS

These findings show that diet-induced changes in hepatic lipid metabolism are independent of weight loss and remodeling of WAT and are not required for insulin sensitization. In contrast, the failure of ob/ob mice to mount a normal thermogenic response to MR suggests that the compromised responsiveness of adipose tissue to SNS input is an important component of the inability of the diet to correct their obesity and insulin resistance.

Autonomous interconversion between adult pancreatic α-cells and β-cells after differential metabolic challenges

Background

Evidence hints at the ability of β-cells to emerge from non-β-cells upon genetic or pharmacological interventions. However, their quantitative contributions to the process of autonomous β-cell regeneration without genetic or pharmacological manipulations remain to be determined.

Methods & results

Using PANIC-ATTAC mice, a model of titratable, acute β-cell apoptosis capable of autonomous, and effective islet mass regeneration, we demonstrate that an extended washout of residual tamoxifen activity is crucial for β-cell lineage tracing studies using the tamoxifen-inducible Cre/loxP systems. We further establish a doxycycline-inducible system to label different cell types in the mouse pancreas and pursued a highly quantitative assessment to trace adult β-cells after various metabolic challenges. Beyond proliferation of pre-existing β-cells, non-β-cells contribute significantly to the post-challenge regenerated β-cell pool. α-cell trans-differentiation is the predominant mechanism upon post-apoptosis regeneration and multiparity. No contributions from exocrine acinar cells were observed. During diet-induced obesity, about 25% of α-cells arise de novo from β-cells. Ectopic expression of Nkx6.1 promotes α-to-β conversion and insulin production.

Conclusions

We identify the origins and fates of adult β-cells upon post-challenge upon autonomous regeneration of islet mass and establish the quantitative contributions of the different cell types using a lineage tracing system with high temporal resolution.

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Insufficient washout for tamoxifen leads to β-cell lineage tracing artifacts.

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Inter-conversion between α- and β-cells after differential metabolic challenges.

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Developmental distance and precursor population determine conversion efficiency.

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Nkx6.1 promotes α-to-β conversion.

Angiographic Tool to Detect Pulmonary Arteriovenous Malformations in Single Ventricle Physiology

Background

Individuals with single ventricle physiology who are palliated with superior cavopulmonary anastomosis (Glenn surgery) may develop pulmonary arteriovenous malformations (PAVMs). The traditional tools for PAVM diagnosis are often of limited diagnostic utility in this patient population. We sought to measure the pulmonary capillary transit time (PCTT) to determine its value as a tool to identify PAVMs in patients with single ventricle physiology.

Methods

We defined the angiographic PCTT as the number of cardiac cycles required for transit of contrast from the distal pulmonary arteries to the pulmonary veins. Patients were retrospectively recruited from a single quaternary North American pediatric center, and angiographic and clinical data was reviewed. PCTT was calculated in 20 control patients and compared to 20 single ventricle patients at the pre-Glenn, Glenn, and Fontan surgical stages (which were compared with a linear-mixed model). Correlation (Pearson) between PCTT and hemodynamic and injection parameters was assessed using 84 Glenn angiograms. Five independent observers calculated PCTT to measure reproducibility (intra-class correlation coefficient).

Results

Mean PCTT was 3.3 cardiac cycles in the control population, and 3.5, 2.4, and 3.5 in the pre-Glenn, Glenn, and Fontan stages, respectively. PCTT in the Glenn population did not correlate with injection conditions. Intraclass correlation coefficient was 0.87.

Conclusions

Pulmonary angiography can be used to calculate the pulmonary capillary transit time, which is reproducible between observers. PCTT accelerates in the Glenn stage, correlating with absence of direct hepatopulmonary venous flow.

Angiographic tool to detect pulmonary arteriovenous malformations in single ventricle physiology

OBJECTIVE

Individuals with single ventricle physiology who are palliated with superior cavopulmonary anastomosis (Glenn surgery) may develop pulmonary arteriovenous malformations. The traditional tools for pulmonary arteriovenous malformation diagnosis are often of limited diagnostic utility in this patient population. We sought to measure the pulmonary capillary transit time to determine its value as a tool to identify pulmonary arteriovenous malformations in patients with single ventricle physiology.

METHODS

We defined the angiographic pulmonary capillary transit time as the number of cardiac cycles required for transit of contrast from the distal pulmonary arteries to the pulmonary veins. Patients were retrospectively recruited from a single quaternary North American paediatric centre, and angiographic and clinical data were reviewed. Pulmonary capillary transit time was calculated in 20 control patients and compared to 20 single ventricle patients at the pre-Glenn, Glenn, and Fontan surgical stages (which were compared with a linear-mixed model). Correlation (Pearson) between pulmonary capillary transit time and haemodynamic and injection parameters was assessed using angiograms from 84 Glenn patients. Five independent observers calculated pulmonary capillary transit time to measure reproducibility (intraclass correlation coefficient).

RESULTS

Mean pulmonary capillary transit time was 3.3 cardiac cycles in the control population, and 3.5, 2.4, and 3.5 in the pre-Glenn, Glenn, and Fontan stages, respectively. Pulmonary capillary transit time in the Glenn population did not correlate with injection conditions. Intraclass correlation coefficient was 0.87.

CONCLUSIONS

Pulmonary angiography can be used to calculate the pulmonary capillary transit time, which is reproducible between observers. Pulmonary capillary transit time accelerates in the Glenn stage, correlating with absence of direct hepatopulmonary venous flow.

Spatiotemporal dynamics of primary and motile cilia throughout lung development

Cilia are specialized structures found on a variety of mammalian cells, with variable roles in the transduction of mechanical and biological signals (by primary cilia, PC), as well as the generation of fluid flow (by motile cilia). Their critical role in the establishment of a left-right axis in early development is well described, as is the innate immune function of multiciliated upper airway epithelium. By contrast, the dynamics of ciliary status during organogenesis and postnatal development is largely unknown. In this study, we define the progression of ciliary status within the endothelium, epithelium, and mesenchyme of the lung. Remarkably, we find that endothelial cells (ECs) lack PC at all stages of development, except in low numbers in the most proximal portions of the pulmonary arteries. In the lung epithelium, a proximodistal ciliary gradient is established over time, as the uniformly mono-ciliated epithelium transitions into proximal, multiciliated cells, and the distal alveolar epithelium loses its cilia. Mesenchymal cells, interestingly, are uniformly ciliated in early development, but with restriction to PDGFRα+ fibroblasts in the adult alveoli. This dynamic process in multiple cellular populations both challenges prior assertions that PC are found on all cells, and highlights a need to understand their spatiotemporal functions.