SUN1 accumulation as a mechanism of impaired mechanotransduction in human lamin a/c cardiomyopathy

Background Lamin A/C Cardiomyopathy (LMNA) is a highly penetrant genetic cardiomyopathy marked by early arrhythmias, sudden cardiac death, and progression towards end-stage heart failure. Despite its severity, the mechanism of mechanotransduction in LMNA disease progression is poorly defined and there is an urgent unmet need to identify mechanisms and develop new therapeutic targets [1]. Focal adhesion complexes (FACs) integrate mechanical forces and connect the sarcolemma to the nuclear membrane via the LINC complex [2,3]. SUN1, a key LINC complex protein has been shown to accumulate in LMNA-patient derived human induced pluripotent stem cell cardiomyocytes (hiPSC-CMs), however its role in human LMNA disease progression is not known [4]. Purpose To investigate if altered mechanotransduction as measured by real-time sarolemmal tension is an early driver of LMNA cardiomyopathy and to determine the mechanistic role of SUN1 accumulation in disease progression. Methods Control and LMNA patient-derived hiPSC-CMs were transfected with a novel bioluminescence resonance energy transfer (BRET) vinculin tension sensor [5] to image real time sarcolemmal tension, where a higher BRET ratio indicates lower sarcolemmal tension (Figure 1A). Both control and LMNA hiPSC-CMs underwent immunocytochemistry (ICC) for Lamin A, and western blot for SUN1. SUN1 knockdown was performed to assess therapeutic reversibility. Adult human heart tissue from control donor hearts and LMNA patients at the time of transplant underwent immunohistochemistry (IHC) for SUN1. Results LMNA hiPSC-CMs demonstrated a significantly higher FAC size and lower density of distribution compared to the linear FAC arrays evenly distributed in control hiPSC-CMs (Figure 1B & 1D). BRET imaging indicated a significantly higher BRET ratio in LMNA hiPSC-CMs than controls, indicating lower sarcolemmal tension (Figure 1C & 1E). SUN1 expression was elevated by 1.5x in both early-stage LMNA (hiPSC-CM, Figure 2A) and late-stage LMNA (human heart tissue, Figure 2B), demonstrating persistent SUN1 accumulation throughout the disease progression. ICC staining of Lamin A in hiPSC-CMs showed abnormal folding and buckling in LMNA CMs, with a decrease in circularity. SUN1 Knockdown in LMNA hiPSC-CMs significantly improved abnormal nuclear membrane folding and increased circularity back to that of control CMs (Figure 2C & 2D), supporting the role for SUN1-driven nuclear membrane distortion Conclusions This work identified mechanotransduction failure as an early and central mechanism in LMNA cardiomyopathy and demonstrates that SUN1 accumulation is a persistent, targetable driver of nuclear pathology. The rescue of the LMNA phenotype through SUN1 reduction provides the first evidence that modulating LINC complex tension may represent a therapeutic target for LMNA cardiomyopathy. These findings establish SUN1 as a mechanistically grounded novel therapeutic target for LMNA cardiomyopathy.