Titin isoforms are increasingly protected against oxidative modifications in developing rat cardiomyocytes

Area of Science:

• Cardiovascular Physiology
• Molecular Biology
• Biochemistry

Background:

• During perinatal adaptation, titin isoform switching in cardiomyocytes influences passive tension (Fpassive).
• Oxidative stress, including SH-group oxidation and carbonylation, can affect protein function.
• Small heat shock proteins (sHSPs), such as Hsp27 and αB-crystallin, are known to protect proteins from damage.

Purpose of the Study:

• To investigate the impact of titin isoform composition and oxidative insults on cardiomyocyte passive tension during rat heart development.
• To examine the protective role of titin-associated sHSPs (Hsp27 and αB-crystallin) against oxidative damage in cardiomyocytes.

Main Methods:

• Single, permeabilized left ventricular (LV) cardiomyocytes from rats of various ages were exposed to oxidative agents (DTDP for SH-oxidation, Fenton reagents for carbonylation).
• Cardiomyocyte force measurements were performed to determine passive tension (Fpassive).
• Western immunoblot assays quantified oxidized SH-groups, carbonyl-groups in titin, and sHSP expression levels.

Main Results:

• Oxidative insults increased Fpassive more significantly in younger (0- and 7-day-old) rat cardiomyocytes compared to older (21-day-old and adult) ones.
• The susceptibility of titin to SH-group oxidation and carbonylation decreased with cardiomyocyte age.
• Expression levels of Hsp27 and αB-crystallin increased with cardiomyocyte age, mirroring the decline in titin oxidation.

Conclusions:

• Titin oxidation contributes to increased cardiomyocyte passive tension during early postnatal development.
• Upregulation of Hsp27 and αB-crystallin expression provides a protective mechanism against titin oxidation in developing cardiomyocytes.
• These findings highlight a developmental adaptation process involving titin modification and protective protein expression in the rat heart.