Cardiomyocytes Derived from Induced Pluripotent Stem Cells as a Disease Model for Propionic Acidemia

Understanding the Pathogenesis of Cardiac Complications in Patients with Propionic Acidemia and Exploring Therapeutic Alternatives for Those Who Are Not Eligible or Are Waiting for Liver Transplantation

The guidelines for the management of patients affected by propionic acidemia (PA) recommend standard cardiac therapy in the presence of cardiac complications. A recent revision questioned the impact of high doses of coenzyme Q10 on cardiac function in patients with cardiomyopathy (CM). Liver transplantation is a therapeutic option for several patients since it may stabilize or reverse CM. Both the patients waiting for liver transplantation and, even more, the ones not eligible for transplant programs urgently need therapies to improve cardiac function. To this aim, the identification of the pathogenetic mechanisms represents a key point. Aims: This review summarizes: (1) the current knowledge of the pathogenetic mechanisms underlying cardiac complications in PA and (2) the available and potential pharmacological options for the prevention or the treatment of cardiac complications in PA. To select articles, we searched the electronic database PubMed using the Mesh terms "propionic acidemia" OR "propionate" AND "cardiomyopathy" OR "Long QT syndrome". We selected 77 studies, enlightening 12 potential disease-specific or non-disease-specific pathogenetic mechanisms, namely: impaired substrate delivery to TCA cycle and TCA dysfunction, secondary mitochondrial electron transport chain dysfunction and oxidative stress, coenzyme Q10 deficiency, metabolic reprogramming, carnitine deficiency, cardiac excitation-contraction coupling alteration, genetics, epigenetics, microRNAs, micronutrients deficiencies, renin-angiotensin-aldosterone system activation, and increased sympathetic activation. We provide a critical discussion of the related therapeutic options. Current literature supports the involvement of multiple cellular pathways in cardiac complications of PA, indicating the growing complexity of their pathophysiology. Elucidating the mechanisms responsible for such abnormalities is essential to identify therapeutic strategies going beyond the correction of the enzymatic defect rather than engaging the dysregulated mechanisms. Although these approaches are not expected to be resolutive, they may improve the quality of life and slow the disease progression. Available pharmacological options are limited and tested in small cohorts. Indeed, a multicenter approach is mandatory to strengthen the efficacy of therapeutic options.

Dysregulated Cell Homeostasis and miRNAs in Human iPSC-Derived Cardiomyocytes from a Propionic Acidemia Patient with Cardiomyopathy

Propionic acidemia (PA) disorder shows major involvement of the heart, among other alterations. A significant number of PA patients develop cardiac complications, and available evidence suggests that this cardiac dysfunction is driven mainly by the accumulation of toxic metabolites. To contribute to the elucidation of the mechanistic basis underlying this dysfunction, we have successfully generated cardiomyocytes through the differentiation of induced pluripotent stem cells (iPSCs) from a PCCB patient and its isogenic control. In this human cellular model, we aimed to examine microRNAs (miRNAs) profiles and analyze several cellular pathways to determine miRNAs activity patterns associated with PA cardiac phenotypes. We have identified a series of upregulated cardiac-enriched miRNAs and alterations in some of their regulated signaling pathways, including an increase in the expression of cardiac damage markers and cardiac channels, an increase in oxidative stress, a decrease in mitochondrial respiration and autophagy; and lipid accumulation. Our findings indicate that miRNA activity patterns from PA iPSC-derived cardiomyocytes are biologically informative and advance the understanding of the molecular mechanisms of this rare disease, providing a basis for identifying new therapeutic targets for intervention strategies.

Mitochondrial damage in renal epithelial cells is potentiated by protein exposure in propionic aciduria

Propionic aciduria (PA) is caused by deficiency of the mitochondrial enzyme propionyl-CoA carboxylase (PCC). Due to inefficient propionate catabolism patients are endangered by life-threatening ketoacidotic crisis. Protein and amino acid restriction are major therapeutic pillars. However, long-term complications like neurological deterioration and cardiac abnormalities cannot be prevented. Chronic kidney disease (CKD), which is a well-known characteristic of methylmalonic aciduria two enzymatic steps downstream from PCC, has been recognized as a novel late-onset complication in PA. The pathophysiology of CKD in PA is unclear. We investigated mitochondrial structure and metabolism in human renal tubular cells of healthy controls and PA patients. The cells were exposed to either standard cell culture conditions (NT), high protein (HP) or high concentrations of isoleucine and valine (I/V). Mitochondrial morphology changed to condensed, fractured morphology in PA cells irrespective of the cell culture medium. HP and I/V exposure, however, potentiated oxidative stress in PA cells. Mitochondrial mass was enriched in PA cells, and further increased by HP and I/V exposure suggesting a need for compensation. Alterations in the tricarboxylic acid cycle intermediates and accumulation of medium- and long-chain acylcarnitines pointed to altered mitochondrial energy metabolism. Mitophagy was silenced while autophagy as cellular defense mechanisms was highly active in PA cells. The data demonstrate that PA is associated with renal mitochondrial damage which is aggravated by protein and I/V load. Preservation of mitochondrial energy homeostasis in renal cells may be a potential future therapeutic target.