Protein misfolding: an additional player in the stroke-heart syndrome
Authors: Diteepeng T , Puspitasari Y M , Ministrini S , Vdovenko D , Akhmedov A , Beer J H , Ruschitzka F , Paneni F , Camici G G , Luciani M 
Published: November 2023

Abstract

Background
Patients suffering from acute ischemic stroke experience an increased risk of major adverse cardiovascular events, introducing the term of stroke-heart syndrome (SHS). Beside common risk factors, the so-called brain-heart axis represents a relevant yet not fully understood biological matrix driving this multi-organ condition. Together with inflammatory and neurohormonal signals, protein misfolding appears as an additional component of this matrix. In fact, previous studies employing animal models of cerebral ischemia identified wrongly arranged toxic proteins (oligomers). In light of the spreading capabilities of such proteins, we questioned whether protein misfolding plays a role in the SHS.

Purpose
The purpose of this study is to investigate the occurrence of protein misfolding in the post-stroke cardiac dysfunction by assessing presence, origin, localization and routes of oligomers in the heart following an acute ischemic stroke. Its biological and physiological relevance are evaluated by in vivo and in vitro assessments of the myocardium.

Methods
Acute cerebral ischemic injury was induced in the mouse by left transient middle cerebral artery occlusion for 45 minutes followed by 48 hours of reperfusion in 3-4 month-old C57BL/6J wild type males. Sham operated littermate mice were used as controls. Forty-eight hours after acute cerebral ischemia, cardiac function was evaluated by electrocardiography and compared to pre-operative assessment. Organs were harvested after the abovementioned assessment for the localization and semi-quantification of oligomers in heart and lymph nodes. Furthermore, biological responses related to protein homeostasis in the myocardium were assessed on mRNA and protein levels.

Results
Our preliminary results show that acute ischemic stroke is associated with an increased presence of oligomers in the heart. In addition, higher levels of oligomers were detected in axillary lymph nodes isolated from stroke mice, suggesting a possible route of oligomers spreading (Fig 1A). Correlating with oligomers occurrence, molecular analyses showed significant upregulation of the inositol-requiring enzyme 1 (IRE1), and catalase at mRNA level (Fig 1B). On the other hand, the expression of the 78-kDa glucose-regulated protein (GRP78), and catalase significantly decreased at protein level, indicating impaired myocardial protein quality control and oxidative stress after acute ischemic stroke (Fig 1C). Stroke-induced cardiac dysfunction was presented by decreased heart weight to tibia length ratio as well as slower and irregular heart rhythm suggesting signs of arrhythmia (Fig 2).

Conclusions
Acute ischemic stroke is associated with an increased oligomers occurrence in the myocardium and ultimately correlates with altered cardiac resistance against proteotoxicity. Further experiments will be conducted in order to elucidate the role of oligomers as active players or bystanders in the stroke-heart syndrome.