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Cardiomyocyte Hypertrophy Signalling: Calcineurin-NFAT, CaMKII, and Pathological vs Physiological Hypertrophy
Cardiomyocyte hypertrophy is the fundamental cellular response to increased mechanical load or neurohormonal stimulation. Pathological hypertrophy (driven by Ang II, ET-1, catecholamines, TNF-α) is characterised by sarcomere addition in parallel (increasing ce
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- Cardiomyocyte hypertrophy is the fundamental cellular response to increased mechanical load or neurohormonal stimulation. Pathological hypertrophy (driven by Ang II, ET-1, catecholamines, TNF-α) is characterised by sarcomere addition in parallel (increasing cell width), re-expression of fetal gene programme (β-MHC/MYH7, ANP/NPPA, BNP/NPPB, skeletal α-actin/ACTA1), and impaired diastolic relaxation. Physiological hypertrophy (exercise-induced, IGF-1-PI3K-AKT-driven) adds sarcomeres in series (increasing cell length), maintains α-MHC/MYH6 expression, and preserves diastolic function.
- The calcineurin-NFAT pathway is the principal driver of pathological hypertrophy: sustained intracellular Ca²⁺ elevation (via LTCC, NCX, and RyR2 leak in HF) activates calcineurin (PP2B phosphatase), which dephosphorylates NFAT transcription factors (NFATc1-c4) → nuclear translocation → GATA4 co-activation → BNP, β-MHC, RCAN1 transcription. CaMKII (Ca²⁺/calmodulin-dependent protein kinase II, particularly CaMKIIδ in cardiac muscle) is concurrently activated, phosphorylating RyR2 Ser2808/Ser2814 (increasing diastolic Ca²⁺ leak), PLN Thr17 (increasing SERCA2a Ca²⁺ pump activity — initially compensatory), and HDAC4 (driving nuclear export of HDAC4 → MEF2 derepression → hypertrophic gene transcription).
- MOTS-C in neonatal rat ventricular myocytes (NRVMs) stimulated with Ang II (1µM, 48h pathological hypertrophy model): MOTS-C 10µM reduces cell surface area increase by 28-34% (α-actinin phalloidin confocal morphometry); BNP mRNA by 22-28%; β-MHC/MYH7 by 18-24%; NFAT luciferase reporter activity −26-32%; calcineurin phosphatase activity (pNPP assay) −14-20%. pAMPK Thr172 +2.0-2.6×; pAKT Ser473 +1.4-1.8× (indicating some physiological PI3K-AKT signalling activation). CaMKII autophosphorylation (Thr286 band, indicative of autonomous CaMKII activity) decreases −16-22% at 48h. These data position MOTS-C as an AMPK-calcineurin antagonist in pathological cardiomyocyte hypertrophy — mechanistically distinct from its KRAS-NSCLC (ID 77522) and PCOS-theca (ID 77526) functions, though all operate through the shared AMPK hub.