Circulating progranulin in human infants: relation to prenatal growth and early postnatal nutrition.

BACKGROUND: Progranulin (PGRN) displays pleiotropic biological functions and has been proposed as a biomarker for metabolic diseases. We longitudinally assessed PGRN concentrations in infants born appropriate (AGA) or small for gestational age (SGA), the latter being at risk for obesity and type 2 diabetes, especially if they experience an excessive postnatal catch-up in weight and are formula-fed (FF). METHODS: The study population consisted of 183 infants who were exclusively breast-fed [(BF), AGA, n = 66; SGA, n = 40], or FF (AGA, n = 31; SGA, n = 46) over the first 4 months. Assessments included auxology, fasting glucose, insulin, IGF-1, high-molecular-weight adiponectin, PGRN and body composition (by DXA), at birth, and at age 4 and 12 months. RESULTS: PGRN levels were low at birth and unaffected by prenatal growth. PGRN increased at 4 and 12 months, although to a lesser extent in SGA infants, and was unrelated to the mode of feeding. PGRN correlated with markers of adiposity, inflammation and insulin resistance in both AGA and SGA infants, especially in those FF. CONCLUSIONS: The attenuated increase of PGRN levels in SGA infants over the first year of life, along with the association to markers of unhealthy metabolic profile, might point to a role of PGRN in future disease risks. IMPACT: Progranulin (PGRN) displays pleiotropic biological functions and has been proposed as a biomarker for metabolic diseases. In healthy infants, PGRN concentrations are low at birth and experience a significant and progressive increase up to age 12 months, which is less marked in infants born small for gestational age (SGA) and is unrelated to the mode of feeding. Circulating PGRN is related to markers of adiposity, inflammation, and insulin sensitivity, especially in formula-fed SGA infants. PGRN may play a role in the metabolic adaptations of SGA infants during early life, potentially contributing to the risk for obesity and type 2 diabetes in this population.

The splicing factor SF3B1 is involved in brown adipocyte thermogenic activation.

The ability of alternative splicing mechanisms to control gene expression is increasingly being recognized as relevant for adipose tissue function. The expression of SF3B1, a key component of the SF3B complex directly involved in spliceosome formation, was previously reported to be significantly induced in brown adipose tissue under cold-induced thermogenic activation. Here, we identify that noradrenergic cAMP-mediated thermogenic stimulation increases SF3B1 expression in brown and beige adipocytes. We further show that pladienolide-B, a drug that binds SF3B1 to inhibit pre-mRNA splicing by targeting the SF3B complex, down-regulates key components of the thermogenic machinery (e.g., UCP1 gene expression), differentially alters the expression of alternative splicing-regulated transcripts encoding molecular actors involved in the oxidative metabolism of brown adipocytes (e.g., peroxisome proliferator-activated receptor-gamma co-activator-alpha [PGC-1α] and cytochrome oxidase subunit 7a genes), and impairs the respiratory activity of brown adipocytes. Similar alterations were found in brown adipocytes with siRNA-mediated knockdown of SF3B1 protein levels. Our findings collectively indicate that SF3B1 is a key factor in the appropriate thermogenic activation of differentiated brown adipocytes. This work exemplifies the importance of splicing processes in adaptive thermogenesis and suggests that pharmacological tools, such as pladienolide-B, may be used to modulate brown adipocyte thermogenic activity.

Blood Sampling for Arteriovenous Difference Measurements Across Interscapular Brown Adipose Tissue in Rat.

A classic physiological approach to assess the specific uptake or release of circulating factors in organs and tissues is to measure concentration differences between venous and arterial blood. For interscapular brown adipose tissue (iBAT), the anatomic distribution of its vascularization, which drains most of the blood into Sulzer's vein, allows for local measurement of arteriovenous differences. The use of this procedure to monitor oxygen concentration changes was fundamental for the recognition of BAT as the main site of adaptive non-shivering thermogenesis. More recently, this technique has regained importance as a means to identify BAT-secreted regulatory molecules, such as fibroblast growth factor-21 and the chemokine CXCL14. In this chapter, we provide a detailed description of an optimized and feasible protocol to determine arteriovenous differences across iBAT. We include tips and practical advice for using this powerful tool to study BAT metabolism and secretory activity in rats as an experimental model.

A Differential Pattern of Batokine Expression in Perivascular Adipose Tissue Depots From Mice.

Depending on its anatomical placement, perivascular adipose tissue (PVAT) has been found to possess features more (e.g., aortic thoracic) or less (e.g., aortic abdominal) similar to brown/beige adipose tissue in mice, whereas PVAT surrounding the mesenteric arteries and the caudal part of abdominal aorta is similar to white fat. PVAT is thought to influence vascular function through the effects of adipose-secreted molecules on vessels. Brown adipose tissue was recently shown to play differential secretory role via secretion of the so-called batokines but the involvement of differential batokine production in PVAT brown/beige plasticity was unclear. The current study characterizes for the first time the expression of batokines at aortic thoracic PVAT (tPVAT) and aortic abdominal PVAT (aPVAT) in comparison with typical brown and white adipose depots, in basal and thermogenically activated conditions. We found that both PVAT depots increased their expression of genes encoding the batokines bone morphogenetic protein-8b (BMP8B), fibroblast growth factor-21 (FGF21), and kininogen-2 (KNG2) in response to cold, indicating that, under cold-induced thermogenic activation, both thoracic aorta and abdominal aorta would experience intense local exposure to these PVAT-secreted batokines. In contrast, the gene expression levels of growth/differentiation factor-15 and vascular endothelial growth factor-A were induced only in tPVAT. Under short-term high-fat diet-induced thermogenic activation, the thoracic aorta would be specifically exposed to a local increase in PVAT-originating BMP8B, FGF21, and KNG2. Our data support the notion that acquisition of a brown/beige phenotype in PVAT is associated with upregulation of batokines, mainly BMP8B, FGF21, and KNG2, that can differentially target the vascular system.

The multifaceted role of cell cycle regulators in the coordination of growth and metabolism.

Adapting to changes in nutrient availability and environmental conditions is a fundamental property of cells. This adaptation requires a multi-directional coordination between metabolism, growth, and the cell cycle regulators (consisting of the family of cyclin-dependent kinases (CDKs), their regulatory subunits known as cyclins, CDK inhibitors, the retinoblastoma family members, and the E2F transcription factors). Deciphering the mechanisms accountable for this coordination is crucial for understanding various patho-physiological processes. While it is well established that metabolism and growth affect cell division, this review will focus on recent observations that demonstrate how cell cycle regulators coordinate metabolism, cell cycle progression, and growth. We will discuss how the cell cycle regulators directly regulate metabolic enzymes and pathways and summarize their involvement in the endolysosomal pathway and in the functions and dynamics of mitochondria.