Ageing Causes Ultrastructural Modification to Calcium Release Units and Mitochondria in Cardiomyocytes

Abstract

Ageing is associated with an increase in the incidence of heart failure, even if the existence of a real age-related cardiomyopathy remains controversial. Effective contraction and relaxation of cardiomyocytes depend on efficient production of ATP (handled by mitochondria) and on proper Ca2+ supply to myofibrils during excitation–contraction (EC) coupling (handled by Ca2+ release units, CRUs). Here, we analyzed mitochondria and CRUs in hearts of adult (4 months old) and aged (≥24 months old) mice. Analysis by confocal and electron microscopy (CM and EM, respectively) revealed an age-related loss of proper organization and disposition of both mitochondria and EC coupling units: (a) mitochondria are improperly disposed and often damaged (percentage of severely damaged mitochondria: adults 3.5 ± 1.1%; aged 16.5 ± 3.5%); (b) CRUs that are often misoriented (longitudinal) and/or misplaced from the correct position at the Z line. Immunolabeling with antibodies that mark either the SR or T-tubules indicates that in aged cardiomyocytes the sarcotubular system displays an extensive disarray. This disarray could be in part caused by the decreased expression of Cav-3 and JP-2 detected by western blot (WB), two proteins involved in formation of T-tubules and in docking SR to T-tubules in dyads. By WB analysis, we also detected increased levels of 3-NT in whole hearts homogenates of aged mice, a product of nitration of protein tyrosine residues, recognized as marker of oxidative stress. Finally, a detailed EM analysis of CRUs (formed by association of SR with T-tubules) points to ultrastructural modifications, i.e., a decrease in their frequency (adult: 5.1 ± 0.5; aged: 3.9 ± 0.4 n./50 μm2) and size (adult: 362 ± 40 nm; aged: 254 ± 60 nm). The changes in morphology and disposition of mitochondria and CRUs highlighted by our results may underlie an inefficient supply of Ca2+ ions and ATP to the contractile elements, and possibly contribute to cardiac dysfunction in ageing.

Unilateral Acute Renal Ischemia-Reperfusion Injury Induces Cardiac Dysfunction through Intracellular Calcium Mishandling

“…Our results establish an early impairment in cardiomyocyte contraction-relaxation processes after 7 days of renal I/R that is chiefly due to: (1) a decrease in systolic Ca 2+ release, observed as a reduction in Ca 2+ transient amplitude; (2) an increase in the decay time constant of Ca 2+ transients; and (3) a depressed SR Ca 2+ load. The Ca 2+ handling abnormalities, together with the compromised contraction-relaxation cycle in cardiomyocytes observed 7 days post-renal I/R, are similar to what is observed in several models of HF [19][20][21]. Our data indicate that Ca 2+ reuptake into the SR is impaired in ventricular cardiomyocytes after 7 days of renal I/R, which is considered an early phase of kidney injury.…”

“…This could be explained by the reduction in expression or activity of SERCA 2a . Similar to that which occurs in HF [21], the decline in SERCA 2a function might explain the depletion of Ca 2+ stores in the SR, the lower transient amplitudes and the impaired cellular contractility. These activities recovered 15 days after renal I/R in mice and were similar to cardiomyocytes from sham mice.…”

The Role of Oxidative Stress in the Aging Heart

“…Several genetic, molecular and biochemical abnormalities are involved in the structural and functional myocardial changes during aging [ 9 , 26 , 35 , 36 , 37 ]. These abnormalities are mainly characterized by changes in contractile proteins and cardiac excitation-contraction coupling, decreased contractile response to β-adrenergic stimulation, increased systemic and myocardial oxidative stress and renin–angiotensin activity, and metabolic changes [ 3 , 26 , 27 ].…”

“…Contraction of myocytes depends on the adequate supply of both ATP and Ca 2+ . Most of the Ca 2+ needed for contraction is released by the sarcoplasmatic reticulum (SR) and ATP is provided by mitochondria [ 35 ]. During the excitation-contraction (EC) coupling, the transverse tubules allow the transduction of the action potential into Ca 2+ release from the intracellular stores [ 145 ].…”

A Lombard Variety of Sweet Pepper Regulating Senescence and Proliferation: The Voghera Pepper

“…However, nuclear morphology seems to be unaffected by the aging process. Ultrastructural age-related changes have been extensively reported in the literature during the last century [ 48 ], such as the relationship between mitochondrial alteration and reactive oxygen species overproduction in the aging process [ 49 , 50 , 51 ]. Our pepper extracts seem to be able to increase the number of mitochondria in aged NHDF, suggesting a possible beneficial effect of pepper supplementation in the maintenance of functional and morphological integrity and consequently reducing the onset of the redox state in old NHDF.…”