Lessons from genetically engineered animal models. IV. Nitric oxide synthase gene knockout mice

Area of Science:

• Physiology
• Biochemistry
• Pharmacology

Background:

• Nitric oxide (NO) is a critical signaling molecule involved in numerous biological functions.
• Three primary nitric oxide synthase (NOS) isoforms—neuronal (nNOS), endothelial (eNOS), and inducible (iNOS)—exhibit distinct tissue distributions and functions.
• Conventional pharmacological tools struggle to differentiate NOS isoforms or model chronic NO depletion.

Purpose of the Study:

• To elucidate the specific physiological roles of NO produced by nNOS, eNOS, and iNOS.
• To investigate the consequences of life-long deficiency of each NOS isoform using knockout mouse models.
• To identify compensatory mechanisms and redundant pathways in NO signaling.

Main Methods:

• Generation and analysis of nNOS, eNOS, and iNOS knockout mice.
• Assessment of physiological functions including neurotransmission, blood flow regulation, and inflammatory responses.
• Evaluation of tissue injury and susceptibility to inflammatory conditions and septic shock.

Main Results:

• NO from nNOS acts as a major inhibitory neurotransmitter.
• NO from eNOS is crucial for physiological blood flow regulation.
• NO from iNOS contributes to hypotension in severe inflammation.
• NOS-deficient mice exhibit distinct phenotypes: nNOS-deficient mice show gastric issues, eNOS-deficient mice have hypotension, and iNOS-deficient mice display altered inflammatory and septic shock responses.

Conclusions:

• Knockout mouse models effectively distinguish the specific roles of NO from each NOS isoform.
• Life-long NOS deficiency leads to significant and distinct physiological alterations.
• These findings highlight the complex and isoform-specific contributions of nitric oxide to health and disease.