Supplementary Material for: Expression of High Mobility Group Protein B1 in Cardiac Tissue of Elderly Patients with Coronary Artery Disease with or without Inflammatory Rheumatic Disease

Background: It is known from clinical practice and
observational studies that elderly patients with a diagnosis of
inflammatory rheumatic diseases (IRD) bear a significantly increased
risk for cardiovascular diseases such as coronary artery disease (CAD)
and heart failure. The molecular mechanism, however, is still not known.
Recently, high mobility group protein B1 (HMGB1), a ubiquitous, highly
conserved single polypeptide expressed in all mammal eukaryotic cells,
has been identified to mediate myocardial dysfunction in vitro once
released from the nuclei of cardiomyocytes. Objective: To
investigate whether HMGB1 and its receptors are expressed in cardiac
muscles of elderly patients with CAD with or without IRD. Methods:
HMGB1 and its 3 well-known receptors, receptor for advanced glycation
end products, Toll-like receptor 2 (TLR2), and TLR4, were examined by
immunohistochemistry on myocardial biopsy specimens from 18 elderly
patients with CAD (10 with IRD, 8 without IRD). Furthermore, total HMGB1
protein levels were measured by Western blot from the cardiac biopsies
in 5 patients with and 5 without IRD. Results: Pathologic
cytosolic HMGB1 in cardiomyocytes was massively recorded in all patients
with IRD, but only slightly expressed in 1 patient without IRD. Total
HMGB1 levels were also consistently lower in myocardial muscle biopsies
of patients with IRD compared to those without IRD. Furthermore, all 3
HMGB1 receptors were expressed in cardiomyocytes of all patients. Conclusion:
The increased cytosolic expression of HMGB1 in cardiomyocytes and the
lower total amount of HMGB1 in the cardiac specimens of IRD patients is
consistent with a greater release of HMGB1 from the myocardial nuclei in
IRD than non-IRD individuals. Thus, the HMGB1 signaling pathways may be
more easily activated in elderly CAD patients with concomitant IRD and
trigger a detrimental inflammatory process causing severe cardiovascular
problems. Therefore, targeting HMGB1 in IRD patients might reduce the
risk for cardiovascular events.