Increased pulmonary arteriolar tone associated with lung oxidative stress and nitric oxide in a mouse model of Alzheimer's disease

Abstract

Vascular dysfunction and decreased cerebral blood flow are linked to Alzheimer's disease (AD). Loss of endothelial nitric oxide (NO) and oxidative stress in human cerebrovascular endothelium increase expression of amyloid precursor protein (APP) and enhance production of the Aβ peptide, suggesting that loss of endothelial NO contributes to AD pathology. We hypothesize that decreased systemic NO bioavailability in AD may also impact lung microcirculation and induce pulmonary endothelial dysfunction. The acute effect of NO synthase (NOS) inhibition on pulmonary arteriolar tone was assessed in a transgenic mouse model (TgAD) of AD (C57BL/6-Tg(Thy1-APPSwDutIowa)BWevn/Mmjax) and age-matched wild-type controls (C57BL/6J). Arteriolar diameters were measured before and after the administration of the NOS inhibitor, L-NAME Lung superoxide formation (DHE) and formation of nitrotyrosine (3-NT) were assessed as indicators of oxidative stress, inducible NOS (iNOS) and tumor necrosis factor alpha (TNF-α) expression as indicators of inflammation. Administration of L-NAME caused either significant pulmonary arteriolar constriction or no change from baseline tone in wild-type (WT) mice, and significant arteriolar dilation in TgAD mice. DHE, 3-NT, TNF-α, and iNOS expression were higher in TgAD lung tissue, compared to WT mice. These data suggest L-NAME could induce increased pulmonary arteriolar tone in WT mice from loss of bioavailable NO In contrast, NOS inhibition with L-NAME had a vasodilator effect in TgAD mice, potentially caused by decreased reactive nitrogen species formation, while significant oxidative stress and inflammation were present. We conclude that AD may increase pulmonary microvascular tone as a result of loss of bioavailable NO and increased oxidative stress. Our findings suggest that AD may have systemic microvascular implications beyond central neural control mechanisms.

Keywords: Amyloid precursor protein; endothelial dysfunction; lung microcirculation; neuroinflammation; reactive nitrogen species.

Figure 1

Comparison of DHE staining in lung tissue samples treated with (SOD+) or without superoxide dismutase (SOD−) in a wild‐type control (WT) and an Alzheimer's model mouse (TgAD). Note that fluorescence intensity decreased after SOD treatment in the TgAD mouse, while the lower levels in the WT mouse remained relatively constant.

Figure 2

Intravital microscopic images of subpleural pulmonary arterioles comparing effects of a nitric oxide inhibitor (L‐NAME, 0.1 mg/kg body weight) on arteriolar diameter in a wild‐type (WT) control mouse and in a Alzheimer's disease model mouse (TgAD). White lines along vessels indicate interior arteriolar diameter. Note constriction in WT and dilation in TgAD.

Figure 3

Comparison of the effect of L‐NAME on the change in parent and daughter branch pulmonary arteriolar diameters from their pre‐L‐NAME baselines in Alzheimer's model mice (TgAD, parent: n = 6) and wild‐type control mice (WT, parent: n = 6). Values are means ± SD. *Significant (P ≤ 0.05) difference between the responses of the TgAD and WT groups.

Figure 4

Pulmonary arteriolar diameter at different mean arterial blood pressures with (black circles) or without (open circles) the presence of L‐NAME. Each pair of diameter measurements is within a single mouse (n = 6).

Figure 5

Left panel: Tumor necrosis factor alpha (TNF‐α) and inducible nitric oxide synthase (iNOS) immunoblotting in lung lysates from wild‐type (WT) and age‐matched transgenic Alzheimer's mice (TgAD) without (A) or with (B) L‐NAME treatment. Right panel: Densitometry quantification of TNF‐α (top panel) and iNOS (bottom panel) immunoreactivity normalized to β‐actin shows significantly increased TNF‐α and iNOS immunoreactivity in TgAD compared to WT mice (*P ≤ 0.05; n = 4). L‐NAME treatment did not significantly alter TNF‐α and iNOS immunoreactivity in any of the groups.

Figure 6

Comparison of inducible nitric oxide synthase (iNOS) expression, superoxide (DHE), and peroxynitrite (3‐NT) formation in lung tissue samples from a wild‐type control (WT) and an age‐matched (20 months) Alzheimer's disease model mouse (TgAD). Note increased fluorescence intensity in the TgAD mouse compared to the WT mouse.

Figure 7

Comparison of mean fluorescence intensity units (FIU) per total tissue sample area for inducible nitric oxide synthase (iNOS) expression, superoxide (DHE), and peroxynitrite (3‐NT) production in Alzheimer's model (TgAD, n = 4, open bars) and wild‐type (WT, n =4, black bars) mice. Values are means ± SD. *Significant (P ≤ 0.05) difference between WT and TgAD.

Figure 8

Comparison of percent of lung tissue exhibiting standard intensity for inducible nitric oxide synthase (iNOS) expression, superoxide (DHE), and peroxynitrite (3‐NT) production in Alzheimer's model (TgAD, n = 4, open bars) and wild‐type (WT, n = 4, black bars) mice. Values are means ± SD. *Significant (P ≤ 0.05) difference between WT and TgAD.