GDF1 is a novel mediator of macrophage infiltration in brown adipose tissue of obese mice

GDF1 ameliorates cognitive impairment induced by hearing loss

Hearing loss is associated with an increased risk of Alzheimer disease (AD). However, the mechanisms of hearing loss promoting the onset of AD are poorly understood. Here we show that hearing loss aggravates cognitive impairment in both wild-type mice and mouse models of AD. Embryonic growth/differentiation factor 1 (GDF1) is downregulated in the hippocampus of deaf mice. Knockdown of GDF1 mimics the detrimental effect of hearing loss on cognition, while overexpression of GDF1 in the hippocampus attenuates the cognitive impairment induced by deafness. Strikingly, overexpression of GDF1 also attenuates cognitive impairment in APP/PS1 transgenic mice. GDF1 activates Akt, which phosphorylates asparagine endopeptidase and inhibits asparagine endopeptidase-induced synaptic degeneration and amyloid-β production. The expression of GDF1 is downregulated by the transcription factor CCAAT-enhancer binding protein-β. These findings indicate that hearing loss could promote AD pathological changes by inhibiting the GDF1 signaling pathway; thus, GDF1 may represent a therapeutic target for AD.

Arsenic suppresses GDF1 expression via ROS-dependent downregulation of specificity protein 1

Inorganic arsenic, an environmental contaminant, has adverse health outcomes. Our previous studies showed that arsenic causes abnormal cardiac development in zebrafish embryos by downregulating Dvr1/GDF1 expression and that folic acid protects against these effects. However, the mechanism by which arsenic represses Dvr1/GDF1 expression remains unknown. Herein, we demonstrate that specificity protein 1 (Sp1) acts as a transcriptional activator of GDF1. Arsenic treatment downregulated Sp1 at both the mRNA and protein level and its downstream targets GDF1 and SIRT1. Chromatin immunoprecipitation analysis showed that the occupancy of Sp1 on the GDF1 or SIRT1 promoter was significantly reduced in response to arsenite. Further investigation showed that Sp1 overexpression inhibited the arsenic-mediated decrease in GDF1 and SIRT1, while Sp1 knockdown had the opposite effect. We found that expression of the oxidative adaptor p66shc was inversely related to that of SIRT1 and that the binding of SIRT1 to the p66shc promoter was sharply attenuated by arsenite treatment. SIRT1 overexpression attenuated p66shc expression but enhanced GDF1 protein expression, while SIRT1 depletion exerted the opposite effect. Both the antioxidants N-acetylcysteine and folic acid reversed the arsenic-mediated repression of Sp1, GDF1 and SIRT1. Moreover, wild-type p66shc overexpression enhanced the arsenic-mediated repression of Sp1, GDF1 and SIRT1, which was accompanied by an increase in intracellular reactive oxygen species (ROS) levels, while both overexpression of a dominant negative p66shcSer36Ala mutant and deficiency in p66shc reversed these effects. Taken together, our results revealed that arsenic suppresses GDF1 expression via the ROS-dependent downregulation of the Sp1/SIRT1 axis, which forms a negative feedback loop with p66shc to regulate oxidative stress. Our findings reveal a novel molecular mechanism underlying arsenic toxicity and provide new insight into the protective effect of folic acid in arsenic-mediated toxicity.

Epigenetic Studies Revealed a Ghost Proteome in PC1/3 KD Macrophages under Antitumoral Resistance Induced by IL-10

Our previous investigation on macrophages has allowed us to show that the inhibition of the enzyme proprotein convertase (PC1/3) controls the activation of macrophages. We demonstrated that PC1/3 knockdown (KD) in macrophages exhibits an increased secretion of proinflammatory and antitumoral factors. In this biological context, we assessed the presence of histone modifications and the presence and contribution of a "ghost proteome" in these macrophages. We identified a set of alternative proteins (AltProts) that have a key role in the regulation of various signaling pathways. In this study, to further investigate the underlying mechanisms involved in the resistance of PC1/3-KD macrophages to anti-inflammatory stimuli, we have conducted a proteomic system biology study to assess the epigenome variation, focusing on histone modifications. Results from our study have indicated the presence of significant variations in histone modifications along with the identification of 28 AltProts, which can be correlated with antitumoral resistance under IL-10 stimulation. These findings highlight a key role of altered epigenome histone modifications in driving resistance and indicate that like the reference proteins, AltProts can have a major impact in the field of epigenetics and regulation of gene expression, as shown in our results.

On the role of macrophages in the control of adipocyte energy metabolism

The crosstalk between macrophages (MΦ) and adipocytes within white adipose tissue (WAT) influences obesity-associated insulin resistance and other associated metabolic disorders, such as atherosclerosis, hypertension and type 2 diabetes. MΦ infiltration is increased in WAT during obesity, which is linked to decreased mitochondrial content and activity. The mechanistic interplay between MΦ and mitochondrial function of adipocytes is under intense investigation, as MΦ and inflammatory pathways exhibit a pivotal role in the reprogramming of WAT metabolism in physiological responses during cold, fasting and exercise. Thus, the underlying immunometabolic pathways may offer therapeutic targets to correct obesity and metabolic disease. Here, I review the current knowledge on the quantity and the quality of human adipose tissue macrophages (ATMΦ) and their impact on the bioenergetics of human adipocytes. The effects of ATMΦ and their secreted factors on mitochondrial function of white adipocytes are discussed, including recent research on MΦ as part of an immune signaling cascade involved in the 'browning' of WAT, which is defined as the conversion from white, energy-storing adipocytes into brown, energy-dissipating adipocytes.