Endothelial nitric oxide synthase activation and nitric oxide function: new light through old windows

Area of Science:

• Biochemistry
• Cell Biology
• Physiology

Background:

• Endothelial nitric oxide synthase (eNOS) activity is primarily regulated by phosphorylation, auto-regulatory mechanisms, and calcium/calmodulin binding.
• eNOS activation is optimized by specific serine/threonine phosphorylation coupled with elevated intracellular calcium levels.
• Existing knowledge of eNOS regulation is expanded by the identification of a novel 'flexible arm' responsive to redox state.

Discussion:

• Endothelial calcium signaling dynamics vary across physiological states, impacting nitric oxide (NO) production duration and amplitude.
• Altered calcium signaling, particularly capacitative entry, affects agonist responses and is implicated in conditions like preeclampsia during pregnancy.
• The concept of 'adaptive cell signaling' is introduced to describe modifications in cellular signaling pathways under different physiological conditions.

Key Insights:

• A newly identified 'flexible arm' of eNOS is modulated by the cellular redox state, offering another layer of activity control.
• Changes in endothelial calcium signaling patterns, termed 'adaptive cell signaling,' can prolong NO output and are critical in pregnancy.
• Nitric oxide (NO) plays a role beyond vascular regulation, potentially modulating adrenal cortisol biosynthesis in response to hypoxia.

Outlook:

• Further research is needed to fully elucidate the physiological significance of NO in steroid biosynthesis, particularly cortisol regulation.
• Continued investigation into the mechanisms of adaptive cell signaling and their role in various physiological and pathological states is warranted.
• Despite decades of study, significant aspects of nitric oxide (NO) biosynthesis and function, including eNOS regulation and non-vascular roles, remain areas for future discovery.