Glucocorticoids promote structural and functional maturation of foetal cardiomyocytes: a role for PGC-1α

Glucocorticoid levels rise dramatically in late gestation to mature foetal organs in readiness for postnatal life. Immature heart function may compromise survival. Cardiomyocyte glucocorticoid receptor (GR) is required for the structural and functional maturation of the foetal heart in vivo, yet the molecular mechanisms are largely unknown. Here we asked if GR activation in foetal cardiomyocytes in vitro elicits similar maturational changes. We show that physiologically relevant glucocorticoid levels improve contractility of primary-mouse-foetal cardiomyocytes, promote Z-disc assembly and the appearance of mature myofibrils, and increase mitochondrial activity. Genes induced in vitro mimic those induced in vivo and include PGC-1α, a critical regulator of cardiac mitochondrial capacity. SiRNA-mediated abrogation of the glucocorticoid induction of PGC-1α in vitro abolished the effect of glucocorticoid on myofibril structure and mitochondrial oxygen consumption. Using RNA sequencing we identified a number of transcriptional regulators, including PGC-1α, induced as primary targets of GR in foetal cardiomyocytes. These data demonstrate that PGC-1α is a key mediator of glucocorticoid-induced maturation of foetal cardiomyocyte structure and identify other candidate transcriptional regulators that may play critical roles in the transition of the foetal to neonatal heart

Functional crosstalk of PGC-1 coactivators and inflammation in skeletal muscle pathophysiology

Skeletal muscle is an organ involved in whole body movement and energy metabolism with the ability to dynamically adapt to different states of (dis-)use. At a molecular level, the peroxisome proliferator-activated receptor γ coactivators 1 (PGC-1s) are important mediators of oxidative metabolism in skeletal muscle and in other organs. Musculoskeletal disorders as well as obesity and its sequelae are associated with PGC-1 dysregulation in muscle with a concomitant local or systemic inflammatory reaction. In this review, we outline the function of PGC-1 coactivators in physiological and pathological conditions as well as the complex interplay of metabolic dysregulation and inflammation in obesity with special focus on skeletal muscle. We further put forward the hypothesis that, in this tissue, oxidative metabolism and inflammatory processes mutually antagonize each other. The nuclear factor κB (NF-κB) pathway thereby plays a key role in linking metabolic and inflammatory programs in muscle cells. We conclude this review with a perspective about the consequences of such a negative crosstalk on the immune system and the possibilities this opens for clinical applications

Genetic targeting of chemical indicators in vivo

Fluorescent protein reporters have become the mainstay for tracing cellular circuitry in vivo but are limited in their versatility. Here we generated Cre-dependent reporter mice expressing the Snap-tag to target synthetic indicators to cells. Snap-tag labeling worked efficiently and selectively in vivo, allowing for both the manipulation of behavior and monitoring of cellular fluorescence from the same reporter