NRAP marks adaptive premyofibril-like structures during pathological cardiac remodeling
T Yang, Z Liu, S HuAbstract
Background
Nebulin-related anchoring protein (NRAP) is essential for myofibrillogenesis during embryonic heart development. However, its spatio-temporal dynamics and functional significance in pathological cardiac remodeling remain poorly understood.
Purpose
To investigate the expression, localization, and structural role of NRAP in cardiomyocytes during cardiac remodeling.
Methods
Integrated transcriptomic and proteomic analyses were performed on left ventricular tissues from mice eight weeks post-transverse aortic constriction (TAC) or sham surgery. NRAP expression levels were quantified via qPCR and Western blot. The subcellular localization and ultrastructure of NRAP in murine and human failing hearts were characterized using confocal microscopy, stochastic optical reconstruction microscopy (STORM), and transmission electron microscopy (TEM).
Results
NRAP expression was significantly upregulated (2.33-fold, p < 0.01) in murine hearts eight weeks post-TAC, compared to sham controls. Immunofluorescence revealed that while NRAP was strictly localized within approximately one sarcomere length of the intercalated disc (ID) in sham hearts, it redistributed into prominent, premyofibril-like structures extending several micrometers from the ID into the sarcoplasm in TAC hearts. These structures co-localized with non-muscle myosin IIA (NMIIA) and other actin-binding proteins, including XIRP2 and FLNC. TEM confirmed ultrastructural hallmarks of premyofibrils, such as Z-bodies and unaligned filaments, specifically in the ID-adjacent regions of TAC hearts. Notably, in end-stage failing human hearts, NRAP was highly expressed in only a sparse subset of cardiomyocytes; however, within these cells, it exhibited a widespread intracellular distribution, contrasting with the generalized ID-localized pattern observed in TAC hearts, suggesting a more advanced remodeling pattern in chronic failure.
Conclusions
We identified a distinctive redistribution of NRAP marking premyofibril-like structures during cardiac remodeling. These findings suggest that NRAP-mediated de novo myofibril assembly may represent an adaptive mechanism in response to chronic pressure overload.Figure