Distinct myocardial triglyceride lipolysis pathways in primary and idiopathic triglyceride deposit cardiomyovasculopathy

Triglyceride deposit cardiomyovasculopathy (TGCV) is a phenotype primarily reported in patients carrying genetic mutations in PNPLA2 encoding adipose triglyceride lipase (ATGL) which releases long chain fatty acid (LCFA) as a major energy source by the intracellular TG hydrolysis. These patients suffered from intractable heart failure requiring cardiac transplantation. Moreover, we identified TGCV patients without PNPLA2 mutations based on pathological and clinical studies. We provided the diagnostic criteria, in which TGCV with and without PNPLA2 mutations were designated as primary TGCV (P-TGCV) and idiopathic TGCV (I-TGCV), respectively. We hereby report clinical profiles of TGCV patients. Between 2014 and 2018, 7 P-TGCV and 18 I-TGCV Japanese patients have been registered in the International Registry. Patients with I-TGCV, of which etiologies and causes are not known yet, suffered from adult-onset severe heart disease, including heart failure and coronary artery disease, associated with a marked reduction in ATGL activity and myocardial washout rate of LCFA tracer, as similar to those with P-TGCV. The present first registry-based study showed that TGCV is an intractable, at least at the moment, and heterogeneous cardiovascular disorder. Show more

Adipose triglyceride lipase (ATGL, also known as PNPLA2) is an essential molecule for hydrolysis of intracellular triglyceride (TG). Genetic ATGL deficiency is a rare multi-systemic neutral lipid storage disease. Information regarding its clinical profile and pathophysiology, particularly for cardiac involvement, is still very limited. A previous middle-aged ATGL-deficient patient in our institute (Case 1) with severe heart failure required cardiac transplantation (CTx) and exhibited a novel phenotype, "Triglyceride deposit cardiomyovasculopathy (TGCV)". Here, we tried to elucidate molecular mechanism underlying TGCV. The subjects were two cases with TGCV, including our second case who was a 33-year-old male patient (Case 2) with congestive heart failure requiring CTx. Case 2 was homozygous for a point mutation in the 5' splice donor site of intron 5 in the ATGL, which results in at least two types of mRNAs due to splicing defects. The myocardium of both patients (Cases 1 and 2) showed up-regulation of peroxisome proliferated activated receptors (PPARs), key transcription factors for metabolism of long chain fatty acids (LCFAs), which was in contrast to these molecules' lower expression in ATGL-targeted mice. We investigated the intracellular metabolism of LCFAs under human ATGL-deficient conditions using patients' passaged skin fibroblasts as a model. ATGL-deficient cells showed higher uptake and abnormal intracellular transport of LCFA, resulting in massive TG accumulation. We used these findings from cardiac specimens and cell-biological experiments to construct a hypothetical model to clarify the pathophysiology of the human disorder. In patients with TGCV, even when hydrolysis of intracellular TG is defective, the marked up-regulation of PPARγ and related genes may lead to increased uptake of LCFAs, the substrates for TG synthesis. This potentially vicious cycle of LCFAs could explain the massive accumulation of TG and severe clinical course for this rare disease. Show more