Nitric oxide signals are interlinked with calcium signals in normal pancreatic stellate cells upon oxidative stress and inflammation

Abstract

The mammalian diffuse stellate cell system comprises retinoid-storing cells capable of remarkable transformations from a quiescent to an activated myofibroblast-like phenotype. Activated pancreatic stellate cells (PSCs) attract attention owing to the pivotal role they play in development of tissue fibrosis in chronic pancreatitis and pancreatic cancer. However, little is known about the actual role of PSCs in the normal pancreas. These enigmatic cells have recently been shown to respond to physiological stimuli in a manner that is markedly different from their neighbouring pancreatic acinar cells (PACs). Here, we demonstrate the capacity of PSCs to generate nitric oxide (NO), a free radical messenger mediating, for example, inflammation and vasodilatation. We show that production of cytosolic NO in PSCs is unambiguously related to cytosolic Ca2+ signals. Only stimuli that evoke Ca2+ signals in the PSCs elicit consequent NO generation. We provide fresh evidence for the striking difference between signalling pathways in PSCs and adjacent PACs, because PSCs, in contrast to PACs, generate substantial Ca2+-mediated and NOS-dependent NO signals. We also show that inhibition of NO generation protects both PSCs and PACs from necrosis. Our results highlight the interplay between Ca2+ and NO signalling pathways in cell–cell communication, and also identify a potential therapeutic target for anti-inflammatory therapies.

Calcium signalling in the acinar environment of the exocrine pancreas: physiology and pathophysiology

“…These results may indicate the existence of a further necrotic amplification loop in which initial damage to PACs, induced – for example – by FAEEs or a bile acid, causes release of activated trypsin from dying PACs, which in turn activates PSCs to produce Ca 2+ signals, generating NO that may diffuse into neighbouring PACs, thereby causing further cell death (Jakubowska et al . ) and therefore further liberation of trypsin and other proteases (Fig. ).…”

“…These Ca 2+ signals – via NO formation in PSCs and with NO diffusing into adjacent PACs (Jakubowska et al . ) – would contribute to further damage of PACs, which in turn would cause further release of kallikrein leading to a further increase in the BK level and thereby further stimulation of PSCs acting to promote PAC necrosis. We have shown that pharmacological inhibition of NO synthase provides remarkable protection against necrosis (Jakubowska et al .…”

“…We have shown that pharmacological inhibition of NO synthase provides remarkable protection against necrosis (Jakubowska et al . ), but the mechanism by which NO exerts this effect is unknown.…”

“…Because Ca 2+ signals in PSCs generate nitric oxide (NO), whereas this is not the case in PACs, it is possible that the effects of PSC Ca 2+ signals on PACs are mediated by NO diffusing from PSCs into PACs (Jakubowska et al . ).…”

Pancreatic Cancer: Current Status and Challenges

“…KRAS signaling via paracrine signaling promotes a fibro-inflammatory microenvironment by stimulating fibroblasts, PSCs and immune cells [51, 53]. In addition, external stressors that cause activation of PSCs include hypoxia, hyperglycemia, alcohol and metabolites, oxidative stress inducing agents like hydrogen peroxide and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase which is a source of reactive oxygen species (ROS) [51, 52, 55]. Activated PSCs can remain in a perpetually active state secreting a number of factors including ECM proteins (collagen, FN, and laminin), cytokines (like TGF-β, IL-1, IL-8, and IL-15), connective tissue growth factor (CTGF), monocyte chemoattractant protein-1 (MCP-1), and matrix metalloproteinase-2 (MMP-2) that can perpetuate PSCs themselves or mediate their effects on cancer cells [52].…”