Effects of immunosuppressive treatment on microsomal prostaglandin E synthase 1 and cyclooxygenases expression in muscle tissue of patients with polymyositis or dermatomyositis

Abstract

Objectives: To investigate the expression of microsomal prostaglandin E (PGE) synthase 1 (mPGES-1) and cyclooxygenase (COX) in muscle biopsies from patients with polymyositis or dermatomyositis before and after conventional immunosuppressive treatment.

Methods: mPGES-1 and COX expression was evaluated by immunohistochemistry in muscle tissue from healthy individuals and from patients with polymyositis or dermatomyositis before and after conventional immunosuppressive treatment. The number of inflammatory cell infiltrates, T lymphocytes and macrophages was estimated before and after treatment. To localise the mPGES-1 expression double immunofluorescence was performed with antibodies against mPGES-1, CD3, CD68, CD163 and a fibroblast marker. A functional index was used to assess muscle function.

Results: In patients with myositis, mPGES-1, COX-2 and COX-1 expression was significantly higher compared to healthy individuals and associated with inflammatory cells. Double immunofluorescence demonstrated a predominant expression of mPGES-1 in macrophages. Conventional immunosuppressive treatment resulted in improved but still lower muscle function than normal. A decreased number of CD68-positive macrophages and reduced COX-2 expression in muscle tissue was also seen. By contrast, following the same treatment no significant changes were observed in muscle tissue regarding number of infiltrates, T lymphocytes, CD163-positive macrophages or mPGES-1 protein levels.

Conclusions: Increased expression of mPGES-1, COX-1 and COX-2 at protein level was observed in muscle tissue from patients with myositis compared to healthy individuals. Conventional immunosuppressive treatment led to a significant downregulation of COX-2 in myositis muscle tissue. However, the expression of mPGES-1 and COX-1 remained unchanged indicating a role of these enzymes in the chronicity of these diseases.

Figure 1. A schematic overview of the prostaglandin (PG) biosynthesis cascade.

Figure 2. Immunohistochemical staining (brown) for (A, B) microsomal prostaglandin E synthase (mPGES)-1, (C, D) cyclooxygenase (COX)-1 and (E, F) COX-2 in representative muscle tissue sections counterstained with haematoxylin (A, C, E) from patients with polymyositis and (B, D, F) from healthy individuals (original magnification ×500).

Figure 3. Expression of microsomal prostaglandin E synthase (mPGES)-1, cytosolic PGES (cPGES), cyclooxygenase (COX)-1 and COX-2 in muscle tissue from patients with polymyositis or dermatomyositis and from healthy individuals. Results are expressed as positive cell score mean (standard error of mean (SEM)). *p<0.05, patients vs healthy individuals.

Figure 4. Double fluorescence staining demonstrating cellular localisation of microsomal prostaglandin E synthase (mPGES)-1: (A) mPGES-1 positive (green) cells, (B) CD163 positive (red) cells and (C) double stained (yellow) cells in representative muscle tissue section from the patient with polymyositis (original magnification ×250).

Figure 5. A. Expression of microsomal prostaglandin E synthase (mPGES)-1 and related enzymes in muscle tissues of patients with polymyositis or dermatomyositis before and after conventional treatment. Results are expressed as positive cell score mean (standard error of mean (SEM)). B. Expression of cyclooxygenase (COX)-2 in muscle tissues of patients with polymyositis or dermatomyositis before and after conventional treatment. Results are expressed as positive cell score. C. Number of inflammatory cells in muscle tissue from patients with polymyositis and dermatomyositis before and after conventional treatment. Results are expressed as percentage of the total area of counterstained tissue. D. Effects of conventional treatment on muscle function in patients with polymyositis or dermatomyositis. Results are expressed as percentage of functional index (FI) for each patient. *p<0.05, before vs after treatment.