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Spatiotemporal relation between gap junctions and fascia adherens junctions during postnatal development of human
N S Peters1, N J Severs, S M Rothery
1Department of Cardiac Medicine, National Heart & Lung Institute, London, England.
Insights
The distribution of gap junctions and fascia adherens in the human heart changes significantly during childhood, impacting electromechanical coupling and myocardial adaptability. These changes continue until about age 6, affecting the heart's ability to remodel.
Area of Science:
- Cardiovascular Biology
- Developmental Biology
- Cell Biology
Background:
- The postnatal human heart grows and adapts to hemodynamic changes, but its capacity for growth and remodeling declines with age.
- This decline may be linked to age-dependent alterations in intercellular junctions (gap junctions and fascia adherens) that mediate electrical and mechanical coupling between myocytes.
- Understanding these changes is crucial for comprehending myocardial development and adaptability.
Purpose of the Study:
- To investigate age-dependent changes in the distribution of gap junctions and fascia adherens in postnatal human ventricular myocardium.
- To explore the spatial relationship between gap junctions and fascia adherens during myocardial maturation.
- To determine if these changes continue into early childhood.
Main Methods:
- Quantitative immunohistochemical localization of connexin43 (gap junctions) and N-cadherin (fascia adherens) in ventricular myocardium from 23 pediatric surgical patients (4 weeks to 15 years).
- Confocal microscopy for junctional protein distribution.
- Correlative immunogold and standard electron microscopy to confirm junctional contacts and spatial relationships.
Main Results:
- In neonates, connexin43 gap junctions are punctately distributed across myocytes; with age, they become confined to transverse terminals, forming intercalated disks.
- The proportion of transversely arrayed gap junctions increased linearly with age, reaching the adult pattern around 6 years.
- Fascia adherens junctions showed similar age-related progression, and their association with gap junctions increased with maturation.
Conclusions:
- Spatiotemporal patterns of intercellular junctions (gap junctions and fascia adherens) are coordinated during postnatal human ventricular development, continuing until approximately 6 years of age.
- The increasing association between gap junctions and fascia adherens parallels the ventricle's functional shift from rapid growth to stable adult function.
- These age-related junctional changes may influence myocardial remodeling capacity in response to physiological or pathological demands.
Background:
The growing postnatal human heart maintains electromechanical function while undergoing substantial changes of cellular topology and myocardial architecture. The capacity for growth and remodeling of ventricular myocardium in adaptation to the hemodynamic changes of early infancy later declines. This decline is associated with changes in electromechanical properties of the myocardium, which suggest that the electrical and mechanical interactions between the myocytes may change in an age-dependent manner. Thus, reduction in the capacity for myocardial growth and adaptability may relate to age-dependent alterations in the patterns of the intercellular junctions that mediate electrical and mechanical coupling. We therefore examined the hypotheses that (1) age-dependent changes in the distribution patterns of gap junctions and fasciae adherentes, the intercellular junctions responsible, respectively, for electrical and mechanical coupling, accompany postnatal development in the human heart and that (2) such changes continue into the first few years of childhood. Further, the spatial relation between the two types of junction, for which a close association has been hypothesized as necessary, was explored.
Methods And Results:
Ventricular myocardial gap-junction distribution was investigated in 23 pediatric surgical patients (4 weeks to 15 years old) by quantitative immunohistochemical localization of the principal cardiac gap-junctional protein, connexin43, using confocal microscopy. Immunolocalization of fascia adherens junctions by labeling N-cadherin, and correlative immunogold and standard electron microscopy, were performed in parallel. In the neonate, connexin43 gap junctions have a punctate distribution over the entire surface of the ventricular myocytes. With advancing age, gap junctions become progressively confined to the transverse terminals of the cell, ie, toward the distribution within the intercalated disk characteristic of the adult ventricle. The transversely arrayed proportion of gap-junctional label showed a linear increase with age (R = .88, P < .001), reaching the adult pattern at about 6 years, and the fascia adherens junctions showed a similar progression. Electron microscopy confirmed the changing pattern of junctional contacts and demonstrated that initially gap junctions and adhering junctions are frequently not closely adjacent but become increasingly so with maturation of the intercalated disk.
Conclusions:
Changes in the spatiotemporal patterns of the intercellular junctions responsible for electrical and mechanical coupling are closely coordinated in postnatal human ventricular myocardium and continue to about 6 years of age. Over this period there is a close and increasing association between the gap junctions and fascia adherens junctions. These changes in the distribution of intercellular electrical and adhering junctions may parallel the changing functional requirements of the ventricle, from a distribution that facilitates the remodeling necessitated by rapid growth and changing hemodynamics to that of the relatively stable and rapidly conducting adult myocardium. These age-related changes may also diminish the ability for appropriate myocardial remodeling in response to physiological, pathological, or surgical hemodynamic alterations.