Deregulation of Ca2+-Signaling Systems in White Adipocytes, Manifested as the Loss of Rhythmic Activity, Underlies the Development of Multiple Hormonal Resistance at Obesity and Type 2 Diabetes.

Egor A Turovsky,Maria V Turovskaya,Vladimir V Dynnik

doi:10.3390/ijms22105109

Abstract

Various types of cells demonstrate ubiquitous rhythmicity registered as simple and complex Ca2+-oscillations, spikes, waves, and triggering phenomena mediated by G-protein and tyrosine kinase coupled receptors. Phospholipase C/IP3-receptors (PLC/IP3R) and endothelial NO-synthase/Ryanodine receptors (NOS/RyR)–dependent Ca2+ signaling systems, organized as multivariate positive feedback generators (PLC-G and NOS-G), underlie this rhythmicity. Loss of rhythmicity at obesity may indicate deregulation of these signaling systems. To issue the impact of cell size, receptors’ interplay, and obesity on the regulation of PLC-G and NOS-G, we applied fluorescent microscopy, immunochemical staining, and inhibitory analysis using cultured adipocytes of epididumal white adipose tissue of mice. Acetylcholine, norepinephrine, atrial natriuretic peptide, bradykinin, cholecystokinin, angiotensin II, and insulin evoked complex [Ca2+]i responses in adipocytes, implicating NOS-G or PLC-G. At low sub-threshold concentrations, acetylcholine and norepinephrine or acetylcholine and peptide hormones (in paired combinations) recruited NOS-G, based on G proteins subunits interplay and signaling amplification. Rhythmicity was cell size- dependent and disappeared in hypertrophied cells filled with lipids. Contrary to control cells, adipocytes of obese hyperglycemic and hypertensive mice, growing on glucose, did not accumulate lipids and demonstrated hormonal resistance being non responsive to any hormone applied. Preincubation of preadipocytes with palmitoyl-L-carnitine (100 nM) provided accumulation of lipids, increased expression and clustering of IP3R and RyR proteins, and partially restored hormonal sensitivity and rhythmicity (5–15% vs. 30–80% in control cells), while adipocytes of diabetic mice were not responsive at all. Here, we presented a detailed kinetic model of NOS-G and discussed its control. Collectively, we may suggest that universal mechanisms underlie loss of rhythmicity, Ca2+-signaling systems deregulation, and development of general hormonal resistance to obesity.

Highlights

Intracellular calcium-signaling machinery is known to be implicated in the regulation of diverse cellular functions in many types of cells and tissues
We investigate the impact of cell size of cultured cells on rhythmicity; the role of influx signaling axes recruited by ACh, NE, angiotensin II (AngII), CCK, BK, and insulin (Ins) acting via GPCR and RTK; receptors’ interplay at sub-threshold concentrations of hormones applied; the mechanisms of self-control based on the amplification of main positive feedback loops (PFL) by other kinase-dependent loops; and the impact of obesity on the regulation of phospholipase C (PLC)-G and NOS-G
We will show that the diversity of responses depends on the type of hormone involved, positive feedback Ca2+-signaling system engaged, and morphological heterogeneity, which may be characterized by cell size, lipid droplet number, and, apparently, the volume of cytoplasm

Summary

Introduction

Intracellular calcium-signaling machinery is known to be implicated in the regulation of diverse cellular functions in many types of cells and tissues. The temporal patterns of calcium response to hormonal signal in various types of cells may include a slow or steep rise of [Ca2+]i and Ca2+spikes [5,6], simple and complex Ca2 oscillations [7,8,9,10,11,12,13], triggering phenomena (switching of the system between two states with different [Ca2+]i levels) [8], or intra-and intercellular Ca2+-waves [10,14,15]. Many missing links remain in the mechanisms that orchestrate intracellular rhythmicity and intercellular waves’ propagation, despite their extreme importance

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