Studying monogenic mitochondrial cardiomyopathies may yield insights into mitochondrial roles in cardiac development and disease. Here, we combine patient-derived and genetically engineered iPSCs with tissue engineering to elucidate the pathophysiology underlying the cardiomyopathy of Barth syndrome (BTHS), a mitochondrial disorder caused by mutation of the gene Tafazzin (TAZ). Using BTHS iPSC-derived cardiomyocytes (iPSC-CMs), we defined metabolic, structural, and functional abnormalities associated with TAZ mutation. BTHS iPSC-CMs assembled sparse and irregular sarcomeres, and engineered BTHS “heart on chip” tissues contracted weakly. Gene replacement and genome editing demonstrated that TAZ mutation is necessary and sufficient for these phenotypes. Sarcomere assembly and myocardial contraction abnormalities occurred in the context of normal whole cell ATP levels. Excess levels of reactive oxygen species mechanistically linked TAZ mutation to impaired cardiomyocyte function. Our study provides new insights into the pathogenesis of Barth syndrome, suggests new treatment strategies, and advances iPSC-based in vitro modeling of cardiomyopathy.

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Using exome sequencing, we identify SERAC1 mutations as the cause of MEGDEL syndrome, a recessive disorder of dystonia and deafness with Leigh-like syndrome, impaired oxidative phosphorylation and 3-methylglutaconic aciduria. We localized SERAC1 at the interface between the mitochondria and the endoplasmic reticulum in the mitochondria-associated membrane fraction that is essential for phospholipid exchange. A phospholipid analysis in patient fibroblasts showed elevated concentrations of phosphatidylglycerol-34:1 (where the species nomenclature denotes the number of carbon atoms in the two acyl chains:number of double bonds in the two acyl groups) and decreased concentrations of phosphatidylglycerol-36:1 species, resulting in an altered cardiolipin subspecies composition. We also detected low concentrations of bis(monoacyl-glycerol)-phosphate, leading to the accumulation of free cholesterol, as shown by abnormal filipin staining. Complementation of patient fibroblasts with wild-type human SERAC1 by lentiviral infection led to a decrease and partial normalization of the mean ratio of phosphatidylglycerol-34:1 to phosphatidylglycerol-36:1. Our data identify SERAC1 as a key player in the phosphatidylglycerol remodeling that is essential for both mitochondrial function and intracellular cholesterol trafficking.

Peroxisomes play a major role in human cellular lipid metabolism, including the beta-oxidation of fatty acids. The most frequent peroxisomal disorder is X-linked adrenoleukodystrophy (X-ALD), which is caused by mutations in the ABCD1 gene. The protein involved, called ABCD1, or alternatively ALDP, is a member of the ATP-binding-cassette (ABC) transporter family and is located in the peroxisomal membrane. The biochemical hallmark of X-ALD is the accumulation of very long-chain fatty acids (VLCFAs), due to an impaired peroxisomal beta-oxidation. Although this suggests a role of ALDP in VLCFA import, no experimental evidence is available to substantiate this. In the yeast Saccharomyces cerevisiae, peroxisomes are the exclusive site of fatty acid beta-oxidation. Earlier work has shown that uptake of fatty acids into peroxisomes may occur via two routes, either as free fatty acids thus requiring intraperoxisomal activation into acyl-CoA esters or as long-chain acyl-CoA esters. The latter route involves the two peroxisomal half ABC transporters Pxa1p and Pxa2p that form a heterodimeric complex in the peroxisomal membrane. Using different strategies, including the analysis of intracellular acyl-CoA esters by tandem-MS, we show that the Pxa1p/Pxa2p heterodimer is involved in the transport of a spectrum of acyl-CoA esters. Interestingly, we found that the mutant phenotype of the pxa1/pxa2Delta mutant can be rescued, at least partially, by the sole expression of the human ABCD1 cDNA coding for ALDP, the protein that is defective in the human disease X-linked adrenoleukodystrophy. Our data indicate that ALDP can function as a homodimer and is involved in the transport of acyl-CoA esters across the peroxisomal membrane.

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The development of Alzheimer's disease (AD) is closely connected with cholesterol metabolism. Cholesterol increases the production and deposition of amyloid-beta (Abeta) peptides that result in the formation of amyloid plaques, a hallmark of the pathology. In the brain, cholesterol is synthesized in situ but cannot be degraded nor cross the blood-brain barrier. The major exportable form of brain cholesterol is 24S-hydroxycholesterol, an oxysterol generated by the neuronal cholesterol 24-hydroxylase encoded by the CYP46A1 gene. We report that the injection of adeno-associated vector (AAV) encoding CYP46A1 in the cortex and hippocampus of APP23 mice before the onset of amyloid deposits markedly reduces Abeta peptides, amyloid deposits and trimeric oligomers at 12 months of age. The Morris water maze (MWM) procedure also demonstrated improvement of spatial memory at 6 months, before the onset of amyloid deposits. AAV5-wtCYP46A1 vector injection in the cortex and hippocampus of amyloid precursor protein/presenilin 1 (APP/PS) mice after the onset of amyloid deposits also reduced markedly the number of amyloid plaques in the hippocampus, and to a less extent in the cortex, 3 months after the injection. Our data demonstrate that neuronal overexpression of CYP46A1 before or after the onset of amyloid plaques significantly reduces Abeta pathology in mouse models of AD.

Bile acids (BAs) are water-soluble end products from cholesterol metabolism and are essential for efficient absorption of dietary lipids. By using targeted somatic mutagenesis of the nuclear receptor liver receptor homolog 1 (LRH-1) in mouse hepatocytes, we demonstrate here that LRH-1 critically regulates the physicochemical properties of BAs. The absence of LRH-1 and subsequent deficiency of Cyp8b1 eliminate the production of cholic acid and its amino acid conjugate taurocholic acid and increase the relative amounts of less amphipathic BA species. Intriguingly, while the expression of Cyp8b1 is almost extinguished in the livers of mice that lack LRH-1, the expression of the rate-limiting enzyme of BA synthesis, i.e., Cyp7a1, remains unchanged. The profound remodeling of the BA composition significantly reduces the efficacy of intestinal absorption of lipids and reuptake of BAs and facilitates the removal of lipids from the body. Our studies unequivocally demonstrate a pivotal role for LRH-1 in determining the composition of BAs, which, in turn has major consequences on whole-body lipid homeostasis.

Cholestatic liver disease is one of the most common metabolic problems associated with total parenteral nutrition (TPN) in preterm infants, and it is strongly related to the duration of TPN ( 1 ). The incidence of parenteral nutrition-associated liver disease (PNALD) in infants who Abstract Total parenteral nutrition (TPN) is associated with the development of parenteral nutrition-associated liver disease (PNALD) in infants. Fish oil-based lipid emulsions can reverse PNALD, yet it is unknown if they can prevent PNALD. We studied preterm pigs administered TPN for 14 days with either 100% soybean oil (IL), 100% fi sh oil (OV), or a mixture of soybean oil, medium chain triglycerides (MCTs), olive oil, and fi sh oil (SL); a group was fed formula enterally (ENT). In TPN-fed pigs, serum direct bilirubin, gamma glutamyl transferase (GGT), and plasma bile acids increased after the 14 day treatment but were highest in IL pigs. All TPN pigs had suppressed hepatic expression of farnesoid X receptor (FXR), cholesterol 7-hydroxylase (CYP7A1), and plasma 7 ␣ -hydroxy-4-cholesten-3-one (C4) concentrations, yet hepatic CYP7A1 protein abundance was increased only in the IL versus ENT group. Organic solute transporter alpha (OST ␣ ) gene expression was the highest in the IL group and paralleled plasma bile acid levels. In cultured hepatocytes, bile acid-induced bile salt export pump (BSEP) expression was inhibited by phytosterol treatment. We show that TPN-fed pigs given soybean oil developed cholestasis and steatosis that was prevented with both This work was supported in part by federal funds from the USDA,, the American Society for Parenteral and Enteral Nutrition, Abbreviations: ALT, alanine aminotransferase; AST, aspartate aminotransferase; BSEP, bile salt export pump; CA, cholic acid; CDCA, chenodeoxycholic acid; C4, 7 ␣ -hydroxy-4-cholesten-3-one; CYP8B1, sterol 12-alpha-hydroxylase; CYP7A1, cholesterol 7-hydroxylase; CYP3A29, cytochrome P450 3A29; CYP27A1, sterol 27-hydroxylase; FGF, fi broblast growth factor; FXR, farnesoid X receptor; GGT, gamma glutamyl transferase; MCT, medium chain triglyceride; MRP3, multidrug resistant protein 3; NTCP, Na + / taurocholate cotransporter; OBCA, obeticholic acid; OST ␣ / ␤ , organic solute transporters alpha and beta; PNALD, parenteral nutrition-associated liver disease; TPN, total parenteral nutrition; UDCA, ursodeoxycholic acid . and immediately placed in cages housed at 31°C to 32°C, as described previously ( 12 ). Based on body weight, pigs delivered from each sow were randomly assigned to one of the three TPN treatment groups or to enteral nutrition (ENT). After delivery, pigs were surgically implanted with catheters into the jugular vein and umbilical artery. Pigs in the enteral group also were implanted with an orogastric feeding tube, whereas TPN groups received a sham puncture. Maternal plasma (16 ml/kg intravenously during the fi rst 24 h) was administered for passive immunological protection. During the 14 day study, pigs received antibiotics (enrofl oxacin 5 mg/kg) intrave...