# Relative Quantitation of EFNA1 Expression in Mouse Heart Tissue Histologic Sections Using MALDI-MSI

## TL;DR

This paper describes a new method to measure EFNA1 levels in mouse heart tissue using MALDI-MSI, which could help understand heart disease and treatments.

## Contribution

The paper introduces an optimized MALDI-MSI method for relative quantitation of EFNA1 in cardiac tissue.

## Key findings

- EFNA1 levels in healthy myocardium are approximately 50 ng per 9.43 mm³ tissue section.
- MALDI-MSI can provide anatomical distribution and relative quantitation of EFNA1 in cardiac tissue.
- The method is compared with routine western blotting for validation.

## Abstract

EFNA1 (ephrinA1), a highly expressed tyrosine kinase receptor-ligand in healthy cardiomyocytes, is reduced following myocardial infarction (MI). A single intramyocardial injection of chimeric EFNA1-Fc at the time of ischemia mitigates the injury in both reperfused and non-reperfused mouse myocardium by reducing apoptosis, necrosis, and inflammation. Recently, we have successfully imaged and qualitatively identified endogenous EFNA1 pre- and post-MI using matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) coupled with a time-of-flight mass spectrometer (MALDI/TOF MS). Building on our previous work, we are currently focused on understanding and characterizing EFNA1’s role in cardiac tissue by developing an integrated quantitative method to determine endogenous levels of EFNA1 using MALDI-MSI technologies. Herein, we have optimized a method for the relative quantitation of endogenous tryptic EFNA1 peptides detected in the murine heart as compared with routine western blotting. In healthy myocardium, there was approximately 50 ng of endogenous EFNA1 per section of 9.43 mm3 tissue, or roughly 12 pg/µg of homogenized tissue. MALDI-MSI thus provides a tool for determining the anatomical distribution and relative quantitation of endogenous EFNA1 in cardiac tissue. Future applications of these tools will allow us to investigate the dynamic changes in EFNA1 expression profile that occur in pathological states such as myocardial infarction and upon therapeutic treatments.