NEU Insights and Development of Potential Therapeutics for Pulmonary Fibrosis
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Date
2020-11-24
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Abstract
Fibrosing diseases involve the formation of inappropriate scar tissue, but what drives fibrosis is unclear. Idiopathic pulmonary fibrosis involves the formation of excess scar tissue in the lungs. Sialidases (also called neuraminidases) are enzymes that desialylate glycoconjugates by cleaving terminal sialic acids from the glycoconjugates. Our lab previously found that a sialylated serum glycoprotein called serum amyloid P (SAP) inhibits fibrosis, and that sialidases attenuate SAP function. Mammals have four different sialidases, NEU1 – 4. In this dissertation, I show that extensive desialylation of glycoconjugates and upregulation of the sialidase NEU3 is observed in the fibrotic lesions in human and mouse lungs. NEU3 is upregulated in the bronchoalveolar lavage (BAL) fluid of the fibrotic mouse lungs in bleomycin-induced pulmonary fibrosis mouse model studies. Fibrosis-associated signals such as transforming growth factor-β1 (TGF-β1) and interleukin (IL)-6 upregulate NEU3 in a variety of human lung cells. Conversely, recombinant human NEU3 upregulates extracellular accumulation of active TGF-β1 and upregulates IL-6 in human peripheral blood mononuclear cells (PBMC). NEU3 also desialylates the human latency associated glyco-peptide (LAP) protein, which holds TGF-β1 in an inactive state, releasing active TGF-β1. Compared to wild-type mice, mice lacking NEU3 have significantly less bleomycin-induced pulmonary fibrosis, reduced TGF-β1 staining in the lungs after bleomycin-assault, and reduced protein, cells, and IL-6 levels in the lung fluid, providing genetic evidence for the role of NEU3 in pulmonary fibrosis in mice. Two small molecule sialidase inhibitors, DANA and oseltamivir (Tamiflu), work well on viral and mouse sialidases, but relatively poorly on human sialidases. In the bleomycin-induced pulmonary fibrosis mouse model, daily intraperitoneal injections of either DANA or oseltamivir at 10 mg / kg, starting at day 10 after bleomycin insult, strongly attenuated pulmonary fibrosis at day 21. The currently studied NEU3 inhibitors have relatively poor efficacies; thus, we designed a new class of small molecule NEU3 inhibitors. Some of our designed inhibitors have nanomolar IC50 values for the inhibition of recombinant human NEU3 releasing active TGF-β1 from the recombinant human latent TGF-β1, and inhibition of the NUE3-induced accumulation of IL-6 in human PBMC. One of our small molecule inhibitors given as daily 0.1 mg/kg injections, and two inhibitors as daily 1 mg/ kg injections, starting at day 10 after bleomycin insult, strongly attenuated pulmonary fibrosis at day 21 in the bleomycin-induced fibrosis mouse model. All of these results suggest that a NEU3-to-fibrosis-to-NEU3 positive feedback loop helps to potentiate pulmonary fibrosis. NEU3 could be a suitable target to develop treatments for lung fibrosis and our NEU3 inhibitors might be effective as therapeutics for fibrosing diseases.
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Pulmonary fibrosis, Therapeutics