# Hypertension and Diabetes Cooperatively Drive HSP90 Activation, HSP70 Suppression, and Left Ventricular Interstitial Expansion: Relevance to Maladaptive Myocardial Remodeling

## TL;DR

This study shows that high blood pressure and diabetes together cause harmful changes in heart muscle by altering stress proteins and increasing heart tissue damage.

## Contribution

The study reveals a novel synergistic effect of hypertension and diabetes on HSP90 and HSP70 expression and myocardial remodeling.

## Key findings

- HSP90 is strongly upregulated in diabetes and even more so when combined with hypertension.
- HSP70 is suppressed in the combined hypertension and diabetes condition despite some mRNA upregulation.
- The combination of hypertension and diabetes causes significant expansion of heart interstitial tissue.

## Abstract

Background: Arterial hypertension (AH) and insulin-dependent diabetes mellitus (DM) are major comorbid risk factors for accelerated myocardial damage, yet the behavior of key stress-adaptive heat shock proteins HSP70 and HSP90 under combined stress remains unclear. This study aimed to characterize the expression profiles of HSP70 and HSP90 in left ventricular cardiomyocytes during isolated and comorbid AH and DM, and to evaluate their association with structural remodeling and expansion of interstitial elements. Methods: The study was conducted in accordance with the European Convention for the Protection of Vertebrate Animals (ethical approval No. 26, RUDN Institute of Medicine, 18 February 2021) on 25 male rats divided into five groups (n = 5 each): control—38-week-old Wistar–Kyoto (WKY) rats; AH—38-week-old spontaneously hypertensive rats (SHR); long-term AH—57-week-old SHR; DM—38-week-old WKY rats with streptozotocin-induced insulin-dependent DM (65 mg/kg, i.p.); AH+DM—38-week-old SHR with STZ-induced DM. After 30 days of DM, left ventricular (LV) tissue was analyzed by immunohistochemistry (IHC) for HSP70/HSP90 protein expression and by RT-qPCR for mRNA levels. Increased stromal elements in myocardium were quantified morphometrically as interstitial stromal volume fraction (%) on hematoxylin and eosin-stained sections. Results: HSP90 was significantly upregulated in all pathological groups. The most pronounced increase occurred in isolated DM, with a 4.0-fold rise in HSP90-positive area (21.80% vs. 5.45% in control) and a 1.82-fold increase in mRNA. In the AH+DM group, HSP90 mRNA expression was extremely elevated (25.93-fold), accompanied by a 3.7-fold increase in protein. In contrast, HSP70 protein was elevated only in the 38-week AH group (27.68% vs. 19.70% control, p ≤ 0.05), remained unchanged in isolated DM (19.50%), and was significantly reduced in AH+DM (14.71%, p ≤ 0.05), despite a modest 1.64-fold mRNA upregulation in DM. Morphometric analysis revealed progressive expansion of interstitial elements, most severe in AH+DM (9.43% stromal volume vs. 4.81% in control, p ≤ 0.05). Conclusions: Comorbid AH and DM provoke synergistic HSP90 upregulation, while HSP70 expression is markedly suppressed, indicating a shift from an adaptive to a maladaptive cellular-stress response. The imbalance between HSP90 and HSP70 may represent a key molecular mechanism underlying accelerated structural and functional deterioration of the myocardium in cardiometabolic comorbidity.