LOX Enzyme May Serve as Scleroderma Biomarker, Therapeutic Target

The molecule lysyl oxidase (LOX) plays key roles in promoting skin and lung scarring in scleroderma and may serve as a potential biomarker and therapeutic target for the disease, a study suggests. 

The study, “Lysyl Oxidase Directly Contributes to Extracellular Matrix Production and Fibrosis in Systemic Sclerosis,” was published in the American Journal of Physiology–Lung Cellular and Molecular Physiology.

A hallmark of scleroderma is the accumulation of scar tissue caused by the excess production of collagen, a major component of the extracellular matrix (ECM) — a meshwork of proteins and carbohydrates outside the cell, acting as a scaffold that gives tissues structural integrity and strength.

Although treatment options have become available for lung fibrosis (scarring), their efficacy is limited in people with scleroderma. 

“These drugs merely slow the progression of the disease,” Carol Feghali-Bostwick, PhD, the study’s senior author and professor at the Medical University of South Carolina, said in a university press release. “They don’t stop it. They don’t reverse it. New drug targets are urgently needed.” 

LOX is an enzyme whose primary role is to crosslink ECM proteins such as collagen, increasing the ECM’s strength and stability. Also, LOX is known to regulate gene activity and modulate cell signaling pathways. 

Prior studies found that people with scleroderma had increased levels of LOX in the skin and blood compared to healthy controls, and that the amount of the enzyme circulating in blood matched the extent of skin fibrosis in these patients.

In the new study, researchers set out to investigate further the role of LOX in scleroderma development using tissue from patients and a mouse model of lung fibrosis. 

LOX levels were measured in lung fibroblasts, cells that generate collagen, isolated from nine healthy controls, 12 scleroderma patients with pulmonary fibrosis, nine individuals with scleroderma and pulmonary hypertension, and 10 people with idiopathic pulmonary fibrosis (IPF). 

Results showed that LOX expression — meaning the levels of its messenger RNA, the intermediate molecule between DNA and protein — was significantly higher in lung fibroblasts from scleroderma patients compared to both controls and IPF patients, with the highest levels found in participants with scleroderma and pulmonary fibrosis. 

Inducing lung fibrosis in mice increased LOX expression in the lungs by 2.8 times at 10 days after induction compared to control mice. Then, the team found that the anti-fibrotic molecule E4 nearly normalized LOX protein and activity levels in the blood of mice three weeks after administration.

“It’s exciting that LOX is a biomarker that goes up when we induce lung fibrosis in the mice and goes down when we improve the fibrosis,” said Feghali-Bostwick. “Having a good biomarker of fibrosis would be invaluable because it would allow us to monitor the response to therapy in patients.”

Treating lung fibroblasts isolated from healthy individuals with LOX protein significantly increased mRNA levels of collagen and the protein fibronectin, another critical component of the ECM. LOX also increased its own production in cultured human lung tissues. 

Notably, blocking LOX activity failed to completely stop the LOX-induced ECM production, suggesting that LOX has disease-related functions independent of its crosslinking role, the team said.

The data also showed that administering LOX to mice with fibrosis via a viral vector worsened pulmonary scarring, and also raised collagen and fibronectin levels.

In a parallel approach, providing LOX to skin cultured from healthy donors led to an increase in skin thickness and to increased production of collagen and LOX itself. 

“Our findings in lung and skin tissues thus demonstrate that LOX can induce a fibrotic phenotype [manifestation] in more than one organ,” the researchers wrote. “Further, LOX can positively regulate its own expression, providing a positive feedback loop.”

An examination of ECM components found that LOX significantly increased the production of the pro-inflammatory protein interleukin-6 (IL-6) in lung fibroblasts, and in cultured lung and skin tissues. Blocking IL-6 reduced collagen production in skin and lung tissues from scleroderma and IPF patients, suggesting that “LOX regulation of ECM production is in part via IL-6,” the scientists added.

Finally, they found that a protein called c-Fos regulated the production of IL-6 in fibroblasts by binding to a specific region in the IL-6 gene. Blocking c-Fos significantly reduced LOX induction of IL-6 production. 

“In summary, we have demonstrated that measuring LOX levels and activity serves as a novel biomarker of fibroproliferative disorders and for monitoring response to therapy and that LOX overexpression may play a pathogenic [disease-related] role in fibrosis,” the investigators concluded. 

“We propose that LOX is a novel therapeutic target for fibroproliferative disorders such as [scleroderma] and development of therapies, such as E4, that reduce LOX levels and activity are likely to improve organ fibrosis,” they added.