Subpleural Microvascular Dysfunction in the Intact Mouse Lung in Conjunction with Increased Blood Glucose Levels, Oxidative Stress and Altered Nitric Oxide Signaling in a Model of Type‐1 Diabetes

Abstract

Microvascular dilation important for distributing the blood glucose load to peripheral tissues, such as skeletal muscle, is inhibited by the loss of bioavailable nitric oxide (NO) in diabetes. The lungs could also be a target since NO signaling modulates alveolar perfusion. We tested the hypothesis that diabetes‐induced oxidative stress with subsequent over‐expression of inducible NO synthase (iNOS) and increased protein nitrosylation, leads to decreased bioavailable NO and consequently to pulmonary microvascular dysfunction. Effects of acute NO synthase (NOS) inhibition with L‐NAME on sub‐pleural pulmonary arterioles and alveoli were examined in streptozotocin‐treated C57BL/6J mice (STZ) and saline‐treated controls (Control). Microvascular changes were assessed by intra‐vital microscopy of the intact right lung in anesthetized mice (7 to 11 months old) with open chest and ventilated lungs when the lungs were statically held inflated for brief periods. Pulmonary arteriolar diameters and alveoli were measured before and after acute administration of L‐NAME, a nitric oxide synthase (NOS) inhibitor. L‐NAME significantly increased arteriolar tone in control mice (n=5). In contrast, tone decreased in STZ mice (n=5). Fixed lung tissue sections from these experiments were stained for superoxide detection by fluorescence microscopy (DHE staining) and immuno‐stained for iNOS expression and protein nitrosylation (3‐nitrotyrosine, 3‐NT) by immunohistochemistry. Superoxide formation significantly increased in STZ (22.8 ± 15.0%, p = 0.02) compared to Control (3.8 ± 1.0%) and correlated with increased blood glucose levels in STZ (372.2 ± 43.3 mg/dL) compared to Control (103.8 ± 8.8 mg/dL). Expression of iNOS also increased significantly in STZ (4.7 ± 3.1%, p = 0.009) compared to Control (0.06 ± 0.07%) as did 3‐NT formation in STZ (5.4 ± 5.5%, p = 0.008 compared to Control (0.007 ± 0.01%). Our data suggest that diabetes‐induced systemic effects alter lung endothelial signaling. Control mice had a physiological vasoconstrictor response to L‐NAME likely due to the loss of the vasodilator influence of bioavailable NO. In contrast, NOS inhibition with L‐NAME appeared to have a vasodilator effect in STZ mice by decreasing formation of a vasoconstrictor, or unmasking a vasodilator. DHE staining and 3‐NT immunoreactivity indicated increased oxidative stress related to blood glucose levels. We conclude that diabetes may adversely affect lung microvasculature by decreasing NO bioavailability and inducing oxidative injury. Altered NO‐induced responses may cause pulmonary endothelial injury and microvascular dysfunction leading to ventilation‐perfusion abnormalities that exacerbate systemic complications of diabetes.Support or Funding InformationUniversity of Louisville, School of Medicine Collaborative Enhancement GrantThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.