Peptidyl arginine deiminase inhibition alleviates angiotensin II-induced fibrosis

OBJECTIVES

The conversion of protein arginine residues to citrulline by calcium-dependent peptidyl arginine deiminases (PADs) has been implicated in the pathogenesis of several diseases, indicating that PADs are therapeutic targets. A recent study indicated that PAD4 regulates age-related organ fibrosis and dysfunction; however, the specific role of this PAD and its citrullination substrate remains unclear. We investigated whether pharmacological inhibition of PAD activity could affect the progression of fibrosis and restore heart function.

METHODS

Cardiac hypertrophy was induced by chronic infusion of angiotensin (Ang) II. After 2 weeks of AngII infusion, a PAD inhibitor (Cl-amidine hydrochloride) or vehicle (saline) was injected every other day for the next 14 days together with the continued administration of AngII for a total of up to 28 days. Cardiac fibrosis and remodeling were evaluated by quantitative heart tissue histology, echocardiography, and mass spectrometry.

RESULTS

A reverse AngII-induced effect was observed in PAD inhibitor-treated mice (n=6) compared with AngII vehicle-treated mice, as indicated by a significant reduction in the heart/body ratio (AngII: 6.51±0.8 mg/g vs. Cl-amidine: 5.27±0.6 mg/g), a reduction in fibrosis (AngII: 2.1-fold increased vs. Cl-amidine: 1.8-fold increased), and a reduction in left ventricular posterior wall diastole (LWVPd) (AngII: 1.1±0.04 vs. Cl-amidine: 0.78±0.02 mm). Label-free quantitative proteomics analysis of heart tissue indicated that proteins involved in fibrosis (e.g., periostin), cytoskeleton organization (e.g., transgelin), and remodeling (e.g., myosin light chain, carbonic anhydrase) were normalized by Cl-amidine treatment.

CONCLUSION

Our findings demonstrate that pharmacological inhibition of PAD may be an effective strategy to attenuate cardiac fibrosis.

Inhibition of Netosis with PAD Inhibitor Attenuates Endotoxin Shock Induced Systemic Inflammation

Neutrophils play a pivotal role in innate immunity by releasing neutrophils extracellular traps (NETs). Excessive NETs are detrimental to the local tissue and further exacerbate inflammation. Protein arginine deiminases (PAD) mediate histone citrullination and NET formation that, in turn, exacerbate endotoxin shock damages. In this study, we further investigated the molecular mechanism underlying PAD and NETs in endotoxic stress in mice. The control group mice were injected with solvent, the LPS endotoxic shock group mice were intraperitoneally injected with LPS at 35 mg/kg only, while the LPS and PAD inhibitor YW3-56 treatment group mice were injected with YW3-56 at 10 mg/kg prior to the LPS injection. YW3-56 significantly prolonged the survival time of the LPS-treated mice. NETs, cfDNA, and inflammatory factors were detected by ELISA in serum, paitoneal cavity, and lung at 24 h after LPS administration. Lung injuries were detected by immunostaining, and lung tissue transcriptomes were analyzed by RNA-seq at 24 h after LPS administration. We found that YW3-56 altered neutrophil tissue homeostasis, inhibited NET formation, and significantly decreased cytokines (IL-6, TNFα and IL-1β) levels, cytokines gene expression, and lung tissue injury. In summary, NET formation inhibition offers a new avenue to manage inflammatory damages under endotoxic stress.

Peptidyl arginine deiminase inhibitor effect on hepatic fibrogenesis in a CCl4 pre-clinical model of liver fibrosis

Having previously shown that levels of the citrullinated vimentin peptide VICM are raised in liver fibrosis in rats, we aimed to investigate whether inhibition of citrullination as measured by VICM levels could affect fibrogenesis.

METHODS

Fibrogenesis was evaluated by quantitative histology and circulating levels of collagen type III in a carbon tetrachloride (CCl4) rat model of liver fibrosis for 6 weeks (n=40+10 untreated controls). The first treatment group (n=20) was treated exclusively with CCl4 for the duration of the study.The second treatment group (n=20) was additionally treated, for the same period, with N-a-benzoyl-N5-(2 Chloro-1-iminoethyl)-L-Ornithine amide, a known PAD inhibitor.

RESULTS

All 40 CCl4 treated animals showed a statistically significant increase in total collagen (p<0.0001) and C3M levels (p<0.001) compared with controls assessed by quantitative histology. Animals additionally treated with the PAD inhibitor showed a statistically significant increase when compared with controls for both total collagen (p<0.001) and C3M levels (p<0.0001) but no statistically difference when compared with animals treated only with CCl4. The mean systemic level of VICM in control animals was 115 ng/ml at 6 weeks. In CCl4-treated animals, mean systemic VICM levels increased 324% at week 6 (p<0.001). The mean level of the marker in CCl4-treated rats was not statistically significant from that in controls (P>0.05). In PAD-treated animals VICM levels were 51% (P<0.05) lower than in non-PAD CCl4-treated animals.

CONCLUSION

The PAD inhibitor did not reduce fibrogenesis in this preclinical model. However circulating VICM marker levels were decreased in the presence of the PAD inhibitor.