Abstract Body (Do not enter title and authors here): Background: Duchenne muscular dystrophy (DMD) is a chronic inflammatory myopathy in which the onset of cardiac dysfunction occurs at the later stage of disease pathogenesis and is one of the predominant causes of mortality. Myocardial inflammation is observed in DMD patients with heart failure. Lymph transport function plays a pivotal role in the regulation of inflammation. However, scientific evidence on the roles of cardiac lymphatics in DMD-associated cardiomyopathy remains obscure.
Aims: Our aim was to investigate whether changes in lymphatic structure and function causing inflammation in the heart, consequently leading to DMD cardiomyopathy in the D2.mdx mice model.
Methods: Lymph transport function in heart and lower limbs was measured in the control and D2.mdx mice at different age groups using microlymphangiography. Echocardiography, gene expression profile for inflammation and pathological lymphangiogenesis in the hearts of these mice were determined. Adeno-associated virus (AAV)-mediated or transgenic expression of vascular endothelial growth factor-D (VEGF-D) was performed in 1-month-old control and D2.mdx mice to promote therapeutic lymphangiogenesis. Two months after overexpression of VEGF-D, lymph transport and inflammatory statuses were measured in these mice.
Results: Gene expression profile revealed a significant increase in the proinflammatory and lymphangiogenic markers in the D2.mdx mice at the earlier stage (2-4 months old) when compared to the control group. Immunofluorescence image of the heart tissue showed elevated levels of LYVE-1 expression in the D2.mdx animals. Echocardiography demonstrated that D2.mdx mouse hearts exhibited a concentric left ventricular (LV) hypertrophy phenotype (decrease in the LV inner diameter; increase in the posterior wall thickness and increase in LV ejection fraction %) only at the later stages (9-12 months old). Additionally, VEGF-D overexpression in D2.mdx mice exhibited a significant improvement in lymph transport and reduced inflammatory status in heart and skeletal muscles when compared to the control groups.
Conclusion: While impaired lymph transport and increased inflammatory cardiac lymphangiogenesis observed in the 2-4 month-old D2.mdx mice, hypertrophy phenotype was observed in the 9-12-month old D2.mdx mice. AAV mediated or transgenic approach of therapeutic lymphangiogenesis improved the lymph transport and reduced inflammation in the D2.mdx animals.