Impaired Plakophilin-2 in obesity breaks cell cycle dynamics to breed adipocyte senescence

The desmosome comes into focus

The desmosome is a cell-cell adhesive junction that provides integrity and mechanical resistance to tissues through its attachment to the intermediate filament cytoskeleton. Defects in desmosomes cause diseases impacting the heart, epidermis, and other epithelia. In this review, we provide a historical perspective on the discovery of the desmosome and how the evolution of cellular imaging technologies revealed insights into desmosome structure and function. We also discuss recent findings using contemporary imaging approaches that have informed the molecular order, three-dimensional architecture, and associations of desmosomes with organelles such as the endoplasmic reticulum. Finally, we provide an updated model of desmosome molecular organization and speculate upon novel functions of this cell junction as a signaling center for sensing mechanical and other forms of cell stress.

Desmosomes at a glance

Desmosomes are relatives of ancient cadherin-based junctions, which emerged late in evolution to ensure the structural integrity of vertebrate tissues by coupling the intermediate filament cytoskeleton to cell-cell junctions. Their ability to dynamically counter the contractile forces generated by actin-associated adherens junctions is particularly important in tissues under high mechanical stress, such as the skin and heart. Much more than the simple cellular 'spot welds' depicted in textbooks, desmosomes are in fact dynamic structures that can sense and respond to changes in their mechanical environment and external stressors like ultraviolet light and pathogens. These environmental signals are transmitted intracellularly via desmosome-dependent mechanochemical pathways that drive the physiological processes of morphogenesis and differentiation. This Cell Science at a Glance article and the accompanying poster review desmosome structure and assembly, highlight recent insights into how desmosomes integrate chemical and mechanical signaling in the epidermis, and discuss desmosomes as targets in human disease.

Ex vivo Anti-Senescence Activity of N-Acetylcysteine in Visceral Adipose Tissue of Obese Volunteers

INTRODUCTION

Excessive visceral adiposity is known to drive the onset of metabolic derangements, mostly involving oxidative stress, prolonged inflammation, and cellular senescence. N-acetylcysteine (NAC) is a synthetic form of l-cysteine with potential antioxidant, anti-inflammatory, and anti-senescence properties. This ex-vivo study aimed to determine the effect of NAC on some markers of senescence including β-galactosidase activity and p16, p53, p21, IL-6, and TNF-α gene expressions in visceral adipose tissue in obese adults.

METHODS

This ex-vivo experimental study involved 10 obese participants who were candidates for bariatric surgery. Duplicate biopsies from the abdominal visceral adipose tissue were obtained from the omentum. The biopsies were treated with or without NAC (5 and 10 mm). To evaluate adipose tissue senescence, beta-galactosidase (β-gal) activity and the expression of P16, P21, P53, IL-6, and TNF-α were determined. ANOVA test was employed to analyze the varying markers of cellular senescence and inflammation between treatment groups.

RESULTS

The NAC at concentrations of 5 mm and 10 mm resulted in a noteworthy reduction β-gal activity compared to the control group (p < 0.001). Additionally, the expression of P16, P21, and IL-6 was significantly reduced following treatment with NAC (5 mm) and NAC (10 mm) compared to the control group (All p < 0.001).

DISCUSSION/CONCLUSION

Taken together, these data suggest the senotherapeutic effect of NAC, as it effectively reduces the activity of SA-β-gal and the expression of IL-6, P16, and P21 genes in the visceral adipose tissue of obese individuals.

Plakoglobin regulates adipocyte differentiation independently of the Wnt/β-catenin signaling pathway

The scaffold protein 14-3-3ζ is an established regulator of adipogenesis and postnatal adiposity. We and others have demonstrated the 14-3-3ζ interactome to be diverse and dynamic, and it can be examined to identify novel regulators of physiological processes, including adipogenesis. In the present study, we sought to determine if factors that influence adipogenesis during the development of obesity could be identified in the 14-3-3ζ interactome found in white adipose tissue of lean or obese TAP-tagged-14-3-3ζ overexpressing mice. Using mass spectrometry, differences in the abundance of novel, as well as established, adipogenic factors within the 14-3-3ζ interactome could be detected in adipose tissues. One novel candidate was revealed to be plakoglobin, the homolog of the known adipogenic inhibitor, β-catenin, and herein, we report that plakoglobin is involved in adipocyte differentiation. Plakoglobin is expressed in murine 3T3-L1 cells and is primarily localized to the nucleus, where its abundance decreases during adipogenesis. Depletion of plakoglobin by siRNA inhibited adipogenesis and reduced PPARγ2 expression, and similarly, plakoglobin depletion in human adipose-derived stem cells also impaired adipogenesis and reduced lipid accumulation post-differentiation. Transcriptional assays indicated that plakoglobin does not participate in Wnt/β-catenin signaling, as its depletion did not affect Wnt3a-mediated transcriptional activity. Taken together, our results establish plakoglobin as a novel regulator of adipogenesis in vitro and highlights the ability of using the 14-3-3ζ interactome to identify potential pro-obesogenic factors.