Spontaneous Pulmonary Hypertension Associated With Systemic Sclerosis in P‐Selectin Glycoprotein Ligand 1–Deficient Mice

Abstract

Objective Pulmonary arterial hypertension (PAH), one of the major complications of systemic sclerosis (SSc), is a rare disease with unknown etiopathogenesis and noncurative treatments. As mice deficient in P‐selectin glycoprotein ligand 1 (PSGL‐1) develop a spontaneous SSc‐like syndrome, we undertook this study to analyze whether they develop PAH and to examine the molecular mechanisms involved. Methods Doppler echocardiography was used to estimate pulmonary pressure, immunohistochemistry was used to assess vascular remodeling, and myography of dissected pulmonary artery rings was used to analyze vascular reactivity. Angiotensin II (Ang II) levels were quantified by enzyme‐linked immunosorbent assay, and Western blotting was used to measure Ang II type 1 receptor (AT1R), AT2R, endothelial cell nitric oxide synthase (eNOS), and phosphorylated eNOS expression in lung lysates. Flow cytometry allowed us to determine cytokine production by immune cells and NO production by endothelial cells. In all cases, there were 4–8 mice per experimental group. Results PSGL‐1−/− mice showed lung vessel wall remodeling and a reduced mean ± SD expression of pulmonary AT2R (expression ratio [relative to β‐actin] in female mice age >18 months: wild‐type mice 0.799 ± 0.508 versus knockout mice 0.346 ± 0.229). With aging, female PSGL‐1−/− mice had impaired up‐regulation of estrogen receptor α (ERα) and developed lung vascular endothelial dysfunction coinciding with an increase in mean ± SEM pulmonary Ang II levels (wild‐type 48.70 ± 5.13 pg/gm lung tissue versus knockout 78.02 ± 28.09 pg/gm lung tissue) and a decrease in eNOS phosphorylation, leading to reduced endothelial NO production. These events led to a reduction in the pulmonary artery acceleration time:ejection time ratio in 33% of aged female PSGL‐1−/− mice, indicating pulmonary hypertension. Importantly, we found expanded populations of interferon‐γ–producing PSGL‐1−/− T cells and B cells and a reduced presence of regulatory T cells. Conclusion The absence of PSGL‐1 induces a reduction in Treg cells, NO production, and ERα expression and causes an increase in Ang II in the lungs of female mice, favoring the development of PAH.

PSGL-1 Immune Checkpoint Inhibition for CD4+ T Cell Cancer Immunotherapy

“…Sustaining a more effector-like T cell response is vital for the immune system to control cancer, and PSGL-1 can affect the balance of inflammatory and suppressive cells. As mentioned previously, Selplg −/− mice with DSS-induced colitis show an increased effector T cell to Treg ratio in the colon, a trend that was also observed in the lungs of Selplg −/− mice ( 75 , 175 ). In an experimental autoimmune encephalomyelitis (EAE) model, PSGL-1 on Tregs was found to be necessary for suppression of the late stage T cell response ( 48 ).…”

“…Selplg −/− mice have been shown to develop a systemic sclerosis (SSc)-like syndrome. In these mice, the absence of PSGL-1 led to a notable decrease in Tregs in the lungs and an increase in IFN-γ-producing T cells and macrophages, highlighting the role of PSGL-1 in immunosuppression ( 175 ). Another autoimmunity study of SSc-like disease in Selplg −/− mice found increased serum levels of autoantigens, activated DC and CD4 + T effector cells in the skin, vascular damage, and increased mortality rates in mice due to loss of PSGL-1 ( 176 ).…”

P-selectin glycoprotein ligand 1 deficiency prevents development of acute pancreatitis by attenuating leukocyte infiltration

“…PSGL-1 regulates leukocyte activation, recruitment, and infiltration via binding to E-selectin and P-selectin, which play an important role in initiating inflammatory responses[ 5 ]. Knockdown of PSGL-1 effectively reduces the numbers of circulating neutrophils and monocytes, improves endothelial damage, and decreases blood pressure[ 6 ]. Blocking functional PSGL-1 reduces visceral adipose inflammation and ameliorates endothelial dysfunction in atherosclerosis[ 7 ].…”

Relevance of PSGL-1 Expression in B Cell Development and Activation

“…The relevance of PSGL-1/P-selectin interactions in different animal models of acute inflammation has been well established (21)(22)(23)(24)(25)(26). However, in recent years, a new role in the preservation of immune homeostasis has been described for PSGL-1/P-selectin interaction (27)(28)(29)(30). In human monocyte-derived dendritic cells, interaction between P-selectin and PSGL-1 triggers a tolerogenic program characterized by the increase in IL-10, TGF-b; and IDO mRNA (30).…”

“…Furthermore, PSGL-1 knock-out mice (PSGL-1 −/− ) develop a systemic sclerosis (SSc)-like syndrome recapitulating the hallmarks of human disease: vascular damage, autoimmunity, and skin fibrosis (30). Interestingly, PSGL-1 −/− female mice also develop pulmonary hypertension associated with this scleroderma-like syndrome (27). In the case of P-selectin deficient mice (P-sel −/− ), lack of PSGL-1/P-selectin interaction results in a systemic lupus erythematosus (SLE)-like syndrome, characterized by the production of SLE-specific autoantibodies such as anti-dsDNA or anti-RNP, reduced dermal T effector/Treg ratio, and lung and renal involvement (28).…”