October 14, 2019
Each year, according to the CDC, approximately 3,600 infant deaths in the United States are attributed to Sudden Unexplained Infant Death Syndrome (SUIDS) – an umbrella category that includes Sudden Infant Death Syndrome (SIDS).
While much attention is devoted to the environmental factors that may contribute to cases of SIDS – e.g. public awareness about best practices for safe sleeping – comparatively little research has been done on the genetic factors that may be at work in many of these instances that lead to unexplained loss of newborn life.
Now, a recently published paper in the journal Nature Communications reveals important insights about one genetic condition that is believed to be a cause of SIDS. The research, led by Professor of Biochemistry Hannele Ruohola-Baker at the UW Institute for Stem Cell and Regenerative Medicine (ISCRM), focuses on mitochondrial tri-functional protein (MTP) deficiency, a potentially fatal cardiac metabolic disorder caused by a genetic mutation in the gene HADHA.
The study was motivated by an urgent need for treatments for metabolic diseases like MTP deficiency. “Every year 200 infants in Washington State are diagnosed with a metabolic disease through newborn blood spot screening,” says Ruohola-Baker. “However, there are no cures. To better understand the disease, and how best to intervene when it shows up in a screen, we used new approaches in biotechnology that led to unexpected findings that, in turn, may put us on a path towards a treatment.”
In MTP deficiency, the heart cells of affected infants do not convert fats into nutrients properly, leading to a build-up of unprocessed fatty material that can disrupt heart functions. More technically, the breakdown occurs when enzymes fail to complete a process known as Fatty Acid beta-Oxidation (FAO). It is possible to screen for the genetic markers of MTP deficiency; however there is no cure for the disease.
Furthermore, while it was understood that MTP deficiency leads to disrupted FAO, researchers have not determined how the defect in FAO led to SIDS and to related heart issues. At least two barriers have inhibited progress.
First, thorny ethical and logistical factors often make it difficult to study the onset of diseases in humans. While animal models are used, the progress of the disease is difficult to study in mice. “Human disease is most effectively studied in human cells, making the development of a human HADHA disease model a first order necessity,” states Ruohola-Baker. To move forward, the ISCRM research team utilized two breakthroughs in modern biology: patient-derived induced pluripotent stem cells (iPSCs) and the gene-editing tool, CRISPR to create the first cardiac-specific model of the disease.
Second, while the methods for generating iPSC derived cardiomyocytes are efficient, these cells are still too immature to process fats. So, the investigators developed a novel microRNA-based tool, known as MiMaC, that sped up the maturation process, giving them the means to probe the roots of MTP deficiency, and, more importantly, to help explain why some infants are dying suddenly and unexpectedly.
When the stem cells were exposed to fatty acid mixture in the lab, the cardiac cells so essential for life began to beat abnormally, leading to a pro-arrhythmic state that could explain how irregular heartbeats occur in infants. In part, the nature of the problem was already known. Mutations in the HADHA protein complex disrupt the cell’s ability to process fats, potentially contributing to impaired cardiac function, and potentially, to SIDS.
Digging deeper, however the research team made a breakthrough discovery: HADHA, they learned, was at the root of another, related problem. Jason Miklas, a recent graduate student in the Ruohola-Baker lab, and the lead author of the study, explains. “We found, surprisingly, that HADHA had a second function – to remodel, or shape, cardiolipin, one of the essential building blocks of the mitochondria, the powerhouse of the cell. When the mitochondria’s structure is disrupted, the cell is unable to produce sufficient energy, which in turn, leads to much broader health issues, including heart functioning.”
Linking HADHA to cardiolipin remodeling was the linchpin to a key finding for the Ruohola-Baker lab team in ISCRM, who believe that the failure of the HADHA to perform this second, newly established function critical to cell structure causes much more severe forms of diseases like MTP deficiency than just the inability to break down fatty acids.
Crucially, the discovery of the second function of HADHA pointed the research team to possible therapies for the MTP deficiency. Tests of a compound known to be effective against other cardiolipin diseases yielded. promising results. Miklas, now a Postdoctoral Research Fellow at Stanford, speaks to the importance of the findings. “We’re no longer just trying to treat the symptoms of the disease. We’re treating the root problem. It’s very gratifying to see that we can make real progress in the lab toward interventions that could one day make their way to the clinic.”
The implications of the findings may extend beyond MTP deficiency and SIDS. According to Elisa Clark, a graduate student in the Ruohola-Baker Lab, “understanding how the cell puts together the mitochondrial membrane, both during normal development of heart cells and when things go wrong, can help us develop therapeutics for additional diseases, like diabetes, Barth’s disease, and other cardiac disorders, caused in part by cardiolipin defects.”
In multiple forms, SIDS remains a source of heartbreak for grieving parents – the result of a devastating loss that often comes with agonizing unknowns. The new insights about the dual rule of HADHA in the fatty acid breakdown and in mitochondria remodeling now give investigators information that is already pointing the way to clinical treatments that could save thousands of young lives every year.
This work is supported by grants from the National Institutes of Health 1027 R01GM097372, and R01GM083867 for HRB, 1P01GM081619 for CM and HRB,1028 R01HL135143 for HRB and DHK and the NHLBI Progenitor Cell Biology Consortium 1029 (U01HL099997; UO1HL099993) for CM and HRB. A.S. was supported by the Academy 1030 of Finland and Finnish Foundation for Cardiovascular Research.