Barth Syndrome (BTHS) is a debilitating X-linked genetic disorder caused by mutations in the gene encoding TAFAZZIN, an enzyme responsible for the remodeling of cardiolipin. While cyclic neutropenia is a well-recognized immunological feature of this disease, emerging evidence suggests that lymphopenia may also occur. The objective of this study was to examine the effects of cannabidiol (CBD) on growth, cardiolipin content, and mitochondrial abnormalities in BTHS patient-derived B-lymphoblastoid cells. CBD (1 μM) restored the growth of BTHS B-lymphoblastoids to healthy control levels, but did not alter cell cycle distribution or sub-G1 cell populations, which surprisingly also did not differ from healthy control B-lymphoblastoids. CBD treatment also fully restored the total cellular cardiolipin concentration and reversed the elevation in monolysocardiolipin/cardiolipin ratio in BTHS B-lymphoblastoids to healthy cell levels, but did not restore the cardiolipin fatty acyl composition. Assessment of mitochondrial markers suggested that increased cardiolipin did not result from increased mitochondrial content. This improvement in cardiolipin concentration was associated with a significant increase in the maximal coupled state III respiration of BTHS B-lymphoblastoids, with all five tested BTHS donors exhibiting increased mitochondrial membrane potential following CBD treatment. CBD fully reversed the deficit in succinate dehydrogenase subunit A in BTHS cells, and partially reversed deficits in cytochrome c oxidase subunits I and IV, and partially restored supercomplex I/III2 levels, but did not rescue I/III2/IV levels. This work suggested a potential role for CBD as a therapeutic in BTHS B-lymphopenia that merits further investigation.

Phospholipase A and acyltransferase 1 (PLAAT1) catalyzes O-transacylase, N-transacylase, and phospholipase A1/2 reactions. We have demonstrated that PLAAT1 has O-transacylase activity in vitro using phosphatidylcholine as an acyl donor and monolysocardiolipin (MLCL) as an acyl acceptor, generating cardiolipin. However, a role for PLAAT1 in cardiolipin regulation in vivo has not yet been reported. We generated Plaat1-deficient (Plaat1−/−) mice and studied males and females for gross morphological differences, food intakes, respiratory gas exchange, total energy expenditure, and voluntary activity. We also evaluated cardiac cardiolipin contents, levels of mitochondrial proteins, and exercise capacity. Sex-matched Plaat1−/− mice had highly similar body weights to their wild-type (Wt) littermates, although male Plaat1−/− mice ate less. Male and female Plaat1−/− hearts were 14.2% and 10.6% smaller, respectively. Cardiac cardiolipin levels were ∼one-third lower in male and female Plaat1−/− mice compared to their sex-matched Wt littermates, largely due to lower cardiolipin linoleate. Levels of the mitochondrial protein succinate dehydrogenase complex flavoprotein subunit A were 13.8% and 16.3% lower in male and female Plaat1−/− mice, respectively. Both male and female Plaat1−/− mice had significantly lower oxygen consumption, carbon dioxide production, and total energy expenditure, and male Plaat1−/− mice had lower rearing activity than their sex-matched Wt littermates. While other measures of voluntary activity, including locomotion and ambulation did not differ significantly between genotypes, both males and females had reduced exercise tolerance. This work demonstrates a critical role for PLAAT1 in cardiac cardiolipin content and the regulation of energy metabolism and exercise tolerance in vivo.

Barth Syndrome (BTHS) is an ultra-rare, X-linked mitochondrial disorder caused by a variety of different mutations in the cardiolipin remodeling gene TAFAZZIN that results in cardiac and skeletal myopathy, as well as immunological deficits. Epstein-Barr virus-mediated transformation of B-lymphocytes has been used to generate B-lymphoblastoid cells that retain many of the characteristics of the initial cell line, but can be propagated extensively in culture to generate biological materials enabling study of the basic, natural function of this enzyme in cells, as well as disease-relevant effects and interventions. Notably, these model lines from individual donors are of particular value for understanding a disease with variable penetrance such as BTHS, where variation in genetic background can alter symptom severity considerably, even among closely-related individuals with the same mutation. Here, we review the generation, benefits, and limitations of the B-lymphoblastoid cell model in BTHS research, and provide an overview of recent advances in understanding the role of TAFAZZIN in mitochondrial biology from this model. Implications of these findings for understanding the pathology of BTHS, and determining future directions, are also provided, along with a review of recent advances in our understanding of the mechanism of TAFAZZIN function in cardiolipin degradation, remodeling and stability.

The effects of lithium (Li) isotopes and their impact on biological processes have recently gained increased attention due to the significance of Li as a pharmacological agent and the potential that Li isotopic effects in neuroscience contexts may constitute a new example of quantum effects in biology. Previous studies have shown that the two Li isotopes, which differ in mass and nuclear spin, have unusual different effects in vivo and in vitro and, although some molecular targets for Li isotope fractionation have been proposed, it is not known whether those result in observable downstream neurophysiological effects. In this work we studied fluxes of Li+, sodium (Na+) and calcium (Ca2+) ions in the mitochondrial sodium/calcium/lithium exchanger (NCLX), the only transporter known with recognized specificity for Li+. We studied the effect of Li+ isotopes on Ca2+ efflux from heart mitochondria in comparison to natural Li+ and Na+ using Ca2+-induced fluorescence and investigated a possible Li isotope fractionation in mitochondria using inductively coupled plasma mass spectrometry (ICP-MS). Our fluorescence data indicate that Ca2+ efflux increases with higher concentrations of either Li+ or Na+. We found that the simultaneous presence of Li+ and Na+ increases Ca2+ efflux compared to Ca2+ efflux caused by the same concentration of Li+ alone. However, no differentiation in the Ca2+ efflux between the two Li+ isotopes was observed, either for Li+ alone or in mixtures of Li+ and Na+. Our ICP-MS data demonstrate that there is selectivity between Na+ and Li+ (greater Na+ than Li+ uptake) and, most interestingly, between the Li+ isotopes (greater 6Li+ than 7Li+ uptake) by the inner mitochondrial membrane. In summary, we observed no Li+ isotope differentiation for Ca2+ efflux in mitochondria via NCLX but found a Li+ isotope fractionation during Li+ uptake by mitochondria with NCLX active or blocked. Our results suggest that the transport of Li+ via NCLX is not the main pathway for Li+ isotope fractionation and that this differentiation does not affect Ca2+ efflux in mitochondria. Therefore, explaining the puzzling effects of Li+ isotopes observed in other contexts will require further investigation to identify the molecular targets for Li+ isotope differentiation.

Adipose tissue stores triacylglycerol (TAG) in lipid droplets (LD) and release fatty acids upon lipolysis during energy shortage. We identify ApoL6 as a LD-associated protein mainly found in adipose tissue, specifically in adipocytes. ApoL6 expression is low during fasting but induced upon feeding. ApoL6 knockdown results in smaller LD with lower TAG content in adipocytes, while ApoL6 overexpression causes larger LD with higher TAG content. We show that the ApoL6 affects adipocytes through inhibition of lipolysis. While ApoL6, Perilipin 1 (Plin1), and HSL can form a complex on LD, C-terminal ApoL6 directly interacts with N-terminal Plin1 to prevent Plin1 binding to HSL, to inhibit lipolysis. Thus, ApoL6 ablation decreases white adipose tissue mass, protecting mice from diet-induced obesity, while ApoL6 overexpression in adipose brings obesity and insulin resistance, making ApoL6 a potential future target against obesity and diabetes.

Objective: Lipotoxic injury from renal lipid accumulation in obesity and type 2 diabetes (T2D) is implicated in associated kidney damage. However, models examining effects of renal ectopic lipid accumulation independent of obesity or T2D are lacking. We generated renal tubule specific adipose triglyceride lipase knockout (RT-SAKO) mice to determine if this targeted triacylglycerol (TAG) over-storage affects glycemic control and kidney health. Methods: Male and female RT-SAKO mice and their control littermates were tested for changes in glycemic control at 10-12 and 16-18 weeks of age. Markers of kidney health and blood lipid and hormone concentrations were analyzed. Kidney and blood lysophosphatidic acid (LPA) levels were measured, and a role for LPA in mediating impaired glycemic control was evaluated using the LPA receptor 1/3 inhibitor Ki-16425. Results: All groups remained insulin sensitive, but 16- to 18 -week-old male RT-SAKO mice became glucose intolerant, without developing kidney inflammation or fibrosis. Rather, these mice displayed lower circulating insulin and glucagon-like peptide 1 (GLP-1) levels. Impaired firstphase glucose -stimulated insulin secretion was detected and restored by Exendin-4. Kidney and blood LPA levels were elevated in older male but not female RT-SAKO mice, associated with increased kidney diacylglycerol kinase epsilon. Inhibition of LPA-mediated signaling restored serum GLP-1 levels, first -phase insulin secretion, and glucose tolerance. Conclusions: TAG over -storage alone is insufficient to cause renal tubule lipotoxicity. This work is the first to show that endogenously derived LPA modulates GLP-1 levels in vivo, demonstrating a new mechanism of kidney-gut -pancreas crosstalk to regulate insulin secretion and glucose homeostasis. (c) 2024 The Authors. Published by Elsevier GmbH. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Barth syndrome (BTHS) is caused by mutations in tafazzin resulting in deficits in cardiolipin remodeling that alter major metabolic processes. The tafazzin gene is encoded on the X chromosome, and therefore BTHS primarily affects males. Female carriers are typically considered asymptomatic, but age-related changes have been reported in female carriers of other X-linked disorders. Therefore, we examined the phenotype of female mice heterozygous for deletion of the tafazzin gene (Taz-HET) at 3 and 12 months of age. Food intakes, body masses, lean tissue and adipose depot weights, daily activity levels, metabolic measures, and exercise capacity were assessed. Age-related changes in mice resulted in small but significant genotype-specific differences in Taz-HET mice compared with their female Wt littermates. By 12 months, Taz-HET mice weighed less than Wt controls and had smaller gonadal, retroperitoneal, and brown adipose depots and liver and brain masses, despite similar food consumption. Daily movement, respiratory exchange ratio, and total energy expenditure did not vary significantly between the age-matched genotypes. Taz-HET mice displayed improved glucose tolerance and insulin sensitivity at 12 months compared with their Wt littermates but had evidence of slightly reduced exercise capacity. Tafazzin mRNA levels were significantly reduced in the cardiac muscle of 12-month-old Taz-HET mice, which was associated with minor but significant alterations in the heart cardiolipin profile. This work is the first to report the characterization of a model of female carriers of heterozygous tafazzin deficiency and suggests that additional study, particularly with advancing age, is warranted.

Barth syndrome (BTHS) is an X-linked mitochondrial disease caused by mutations in the gene encoding for tafazzin (TAZ), a key enzyme in the remodeling of cardiolipin. Mice with a germline deficiency in Taz have been generated (Taz-KO) but not yet fully characterized. We performed physiological assessments of 3-, 6-, and 12-month-old male Taz-KO mice, including measures of perinatal survival, growth, lifespan, gross anatomy, whole-body energy and substrate metabolism, glucose homeostasis, and exercise capacity. Taz-KO mice displayed reduced viability, with lower-than-expected numbers of mice recorded at 4 weeks of age, and a shortened lifespan due to disease progression. At all ages, Taz-KO mice had lower body weights compared with wild-type (Wt) littermates despite similar absolute food intakes. This finding was attributed to reduced adiposity and diminutive organs and tissues, including heart and skeletal muscles. Although there were no differences in basal levels of locomotion between age-matched genotypes, indirect calorimetry studies showed higher energy expenditure measures and respiratory exchange ratios in Taz-KO mice. At the youngest age, Taz-KO mice had comparable glucose tolerance and insulin action to Wt mice, but while these measures indicated metabolic impairments in Wt mice with advancing age that were likely associated with increasing adiposity, Taz-KO mice were protected. Comparisons across the three age-cohorts revealed a significant and more severe deterioration of exercise capacity in Taz-KO mice than in their Wt littermate controls. The Taz-KO mouse model faithfully recapitulates important aspects of BTHS, and thus provides an important new tool to investigate pathophysiological mechanisms and potential therapies.

Introduction: Cardiolipin is produced de novo in an immature form, and must be remodeled to contain a fatty acyl profile that is functionally appropriate for the mitochondria in a specific tissue. We have recently discovered that phospholipase A and acyltransferase 1 (PLAAT1) has transacylase activity using monolysocardiolipin as an acyl acceptor, and phosphatidylcholine as an acyl donor, and that cells overexpressing PLAAT1 have higher levels of total cardiolipin, supporting a role for this enzyme in cardiolipin remodeling in vivo. We have generated Plaat1 global knockout mice ( Plaat1-/-) to study the role of this enzyme in whole body physiology. Objectives and methods: The objective of this study was to perform an initial physiological characterization of Plaat1-/- mice, with an emphasis on measures related to mitochondrial function. Activity levels, oxygen utilization, carbon dioxide production, respiratory exchange ratio (RER), and exercise capacity were measured and compared between Plaat1-/- and wildtype mice within sexes. Hypotheses:: We anticipate that altered cardiolipin remodeling due to Plaat1 deficiency will adversely affect mitochondrial function, resulting in changes in bioenergetic metabolism and exercise capacity. As compared to controls, we hypothesize that Plaat1-/- mice will have reduced activity levels and impaired exercise tolerance, but increased oxygen consumption rates and carbon dioxide production, with an elevated RER due to dependance on glycolysis. Increased heat production is also predicted due to an expected increased dissipation of the proton gradient. Results: Male Plaat1-/- mice had 42.1% ± 17.2% lower rearing activity over 24 hours compared to wildtype mice (n=6-8, P<0.05), but no differences in X- or Y-directional locomotor activity, while female Plaat1-/- mice did not differ from their wildtype ( Wt) littermates in these measures. However, Female Plaat1-/- mice had 31.9% ± 14.4% lower oxygen utilization (P<0.05), 34.3% ± 11.5% lower carbon dioxide production (P<0.05), and 45.8% ± 13.9% lower heat production (P<0.01) over 24 h when compared to Wt controls. Both male and female Plaat1-/- mice ran significantly shorter distances in a treadmill time-to-exhaustion test (P<0.05). Male Plaat1-/- mice had a mean run time of 32.4±2.3 minutes (min) before exhaustion compared to Wt littermates (35.8±2.3 min), while female Plaat1-/- mice had mean run times of 34.6±2.1 min compared to Wt littermates (38.3±1.9 min). Interestingly, however, when mice were subjected to two treadmill tests, 1-hour apart, male Wt mice displayed significantly decreased performance from their initial test (-6.7% ± 2.3%), but Plaat1-/- mice did not. Conclusions: Our initial physiological characterization demonstrates differences in behaviour, respiration, and exercise tolerance in both males and females deficient in Plaat1, supporting a role for this enzyme in whole body bioenergetic metabolism and exercise tolerance. This work is supported by the Barth Syndrome Foundation, and the Natural Sciences and Engineering Research Council of Canada (NSERC). R.E.D. was a recipient of an Early Investigator Award from the Canadian Lipoprotein Conference. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Barth syndrome (BTHS) is caused by mutations in the TAZ gene encoding the cardiolipin remodeling enzyme, Tafazzin. The study objective was to quantitatively examine growth characteristics and mitochondrial morphology of transformed lymphoblast cell lines derived from five patients with BTHS relative to five healthy controls, as well as the therapeutic potential of oleoylethanolamide (OEA) and linoleoylethanolamide (LEA). These bioactive lipids both activate PPARα, which may be therapeutic. BTHS lymphoblasts grew more slowly than controls, suggesting lymphopenia merits clinical investigation. Treatment of BTHS lymphoblasts with OEA, but not LEA, significantly restored mitochondrial membrane potential, as well as colony growth in all BTHS lymphoblast lines, although a full growth rescue was not achieved. Quantification analysis of electron micrographs from three BTHS and healthy lymphoblast donors indicated similar numbers of mitochondria per cell, but lower average cristae length per mitochondrion, and higher mitochondrial density. Additionally, BTHS lymphoblasts had larger mitochondria, and a higher percentage of abnormally large mitochondria (> 1 μm2) than healthy controls. Notably, OEA treatment significantly restored mitochondrial size, without affecting density or cristae lengths. Cardiolipin total content, relative linoleic acid content and monolysocardiolipin:cardiolipin ratios were not improved by OEA, indicating that effects on growth, and mitochondrial morphology and function, occurred without resolving this deficit. However, immunoblotting showed higher levels of OPA1, a biomarker for mitochondrial fusion, in BTHS lymphoblasts, which was attenuated by OEA treatment, implicating altered mitochondrial dynamics in the pathology and treatment of BTHS.

Glucagon-like peptide-1 (GLP-1) potentiates glucose-stimulated insulin secretion (GSIS). While dozens of compounds stimulate GLP-1 secretion, few inhibit. Reduced GLP-1 secretion and impaired GSIS occur in chronic inflammation. Lysophosphatidic acids (LPAs) are bioactive phospholipids elevated in inflammation. The aim of this study was to test whether LPA inhibits GLP-1 secretion in vitro and in vivo. GLUTag L-cells were treated with various LPA species, with or without LPA receptor (LPAR) antagonists, and media GLP-1 levels, cellular cyclic AMP and calcium ion concentrations, and DPP4 activity levels were analyzed. Mice were injected with LPA, with or without LPAR antagonists, and serum GLP-1 and DPP4 activity were measured. GLUTag GLP-1 secretion was decreased ~70–90% by various LPAs. GLUTag expression of Lpar1, 2, and 3 was orders of magnitude higher than Lpar4, 5, and 6, implicating the former group in this effect. In agreement, inhibition of GLP-1 secretion was reversed by the LPAR1/3 antagonist Ki16425, the LPAR1 antagonists AM095 and AM966, or the LPAR2 antagonist LPA2-antagonist 1. We hypothesized involvement of Gαi-mediated LPAR activity, and found that intracellular cyclic AMP and calcium ion concentrations were decreased by LPA, but restored by Ki16425. Mouse LPA injection caused an ~50% fall in circulating GLP-1, although only LPAR1 or LPAR1/3 antagonists, but not LPAR2 antagonism, prevented this. GLUTag L-cell and mouse serum DPP4 activity was unchanged by LPA or LPAR antagonists. LPA therefore impairs GLP-1 secretion in vitro and in vivo through Gαi-coupled LPAR1/3 signaling, providing a new mechanism linking inflammation with impaired GSIS.

Tissue-specific cardiolipin fatty acyl profiles are achieved by remodeling of de novo synthesized cardiolipin, and four remodeling enzymes have thus far been identified. We studied the enzyme phospholipase A and acyltransferase 1 (PLAAT1), and we report the discovery that it has phosphatidylcholine (PC):monolysocardiolipin (MLCL) transacylase activity. Subcellular localization was analyzed by differential centrifugation and immunoblotting. Total levels of major phospholipids, and the fatty acyl profile of cardiolipin, were analyzed in HEK293 cells expressing murine PLAAT1 using gas chromatography. Apparent enzyme kinetics of affinity-purified PLAAT1 were calculated using radiochemical enzyme assays. This enzyme was found to localize predominantly to the endoplasmic reticulum (ER) but was detected at low levels in the mitochondria-associated ER matrix. Cells expressing PLAAT1 had higher levels of total cardiolipin, but not other phospholipids, and it was primarily enriched in the saturated fatty acids myristate, palmitate, and stearate, with quantitatively smaller increases in the n-3 polyunsaturated fatty acids linolenate, eicosatrienoate, and eicosapentanoate and the monounsaturated fatty acid erucate. Affinity-purified PLAAT1 did not catalyze the transacylation of MLCL using 1-palmitoyl-2-[14C]-linoleoyl-PC as an acyl donor. However, PLAAT1 had an apparent Vmax of 1.61 μmol/min/mg protein and Km of 126 μM using [9,10-3H]-distearoyl-PC as an acyl donor, and 0.61 μmol/min/mg protein and Km of 16 μM using [9,10-3H]-dioleoyl-PC. PLAAT1 is therefore a novel PC:MLCL transacylase.

Background The endoplasmic reticulum senses alterations to cellular homeostasis that activates the unfolded protein response (UPR). UPR proteins are known to aid in regulating glucose and lipid metabolism. CREB3 is a UPR-associated transcription factor whose potential role in regulating energy metabolism remains unclear. Methods Eight-week-old wild-type (WT) and Creb3 +/− mice were placed on control and high-fat diets (HFD) for 8 weeks, and metabolic phenotypes characterized by weekly weighing, indirect calorimetry, body composition scans, glucose tolerance tests, plasma analysis, tissue lipid quantifications and gene/protein expression analysis. Results HFD weight gain in Creb3 +/− males was reduced by 34% ( p < 0.0001) and females by 39.5% ( p = 0.014) from their WT counterparts. No differences were found in HFD food intake or total fecal lipids between genotypes. Creb3 +/− mice had increased energy expenditure and respiratory exchange ratios ( p = 0.002) relative to WT. Creb3 +/− mice had significant reductions in absolute fat and lean tissue, while Creb3 +/− females had significant reductions in body fat% and increased lean% composition ( p < 0.0001) compared to WT females. Creb3 +/− mice were protected from HFD-induced basal hyperglycemia (males p < 0.0001; females p = 0.0181). Creb3 +/− males resisted HFD-induced hepatic lipid accumulation ( p = 0.025) and glucose intolerance compared to WT ( p < 0.0001) while Creb3 +/− females were protected from lipid accumulation in skeletal muscle ( p = 0.001). Despite the metabolic differences of Creb3 +/− mice on HFD, lipid plasma profiles did not significantly differ from WT. Fasted Creb3 +/− mice additionally revealed upregulation of hepatic energy expenditure and gluconeogenic genes such as Pgc-1a and Gr (glucocorticoid receptor) ( p < 0.05), respectively. Conclusions Reduced expression of CREB3 increased energy expenditure and the respiratory exchange ratio, and protected mice from HFD-induced weight gain, basal hyperglycemia, and sex-specific tissue lipid accumulation. We postulate that CREB3 is a novel key regulator of diet-induced obesity and energy metabolism that warrants further investigation as a potential therapeutic target in metabolic disorders.

ABSTRACT ApoL6 is a new LD-associated protein containing an apoprotein-like domain, expressed mainly in adipose tissue, specifically in adipocytes. ApoL6 expression is low in fasting but induced upon feeding. ApoL6 knockdown results in smaller LD with lower triglyceride (TAG) content in adipocytes, while ApoL6 overexpression causes larger LD with higher TAG content. We show that ApoL6 effect in adipocytes is by inhibition of lipolysis. While ApoL6, Perilipin 1 (Plin1) and HSL can form a complex on LD, C-terminal domain of ApoL6 directly interacts with Plin1, to compete with Plin1 binding to HSL through Plin1 N-terminal domain, thereby keeping HSL in a “stand by” status. Thus, ApoL6 ablation decreases WAT mass, protecting mice from diet-induced obesity, while adipose overexpression increases WAT mass to bring obesity and insulin resistance with hepatosteatosis, making ApoL6 a potential future target against obesity and diabetes.

Barth Syndrome (BTHS) is a rare X-linked genetic disorder caused by mutations in the TAZ gene that encodes for the cardiolipin remodelling enzyme, Tafazzin. This syndrome is characterized by cardiac and skeletal myopathies, as well as immunological deficits that cause significant morbidity and mortality. Study of the molecular pathology of BTHS thus provides insight into the role of cardiolipin and mitochondria in cellular physiology, while addressing a clinically relevant disease. Current treatment options for BTHS are limited, but a recent trial suggests that PPARα activation may be therapeutic. The objective of this study was to quantitatively examine the growth properties and mitochondrial physiology of B-lymphoblasts derived from five donors with BTHS, as well as effects of treatment with oleoylethanolamide (OEA), a bioactive N-acylethanolamine. Cyclic neutropenia is a well-recognized aspect of the pathology of BTHS. We hypothesized that deficits in lymphoblast proliferation would also be evident, and that OEA, which activates receptors including PPARα, would demonstrate therapeutic benefit. One million B-lymphoblasts derived from BTHS donors and age- and sex-matched healthy controls were seeded on day 0 and counted daily for 4 days. On day 4, there were 27.7 ± 4.6% fewer BTHS B-lymphoblasts than control cells (P<0.05), indicating that lymphopenia is likely also a component of BTHS. Treatment of B-lymphoblasts with 1 μM OEA caused no significant effect on control cell numbers, but significantly improved deficits in each of the five BTHS lymphoblast lines, raising the mean cell number on day 4 from 3.74 × 106 to 4.25 × 106 cells, although a full rescue of growth was not achieved. Analysis of electron micrographs of samples from two distinct BTHS B-lymphoblast donors indicated that cells had larger mitochondria as compared with healthy controls (mean of 0.67 ± 0.07 µM2 versus 0.27 ± 0.16 µM2, respectively). OEA decreased mitochondrial size by 53.0 ± 10.9%, while increasing the total mitochondrial number per cell by 92.6 ± 58.6%. OEA reduced the elevated expression of the enzyme CDS1 in BTHS B-lymphoblasts to healthy control levels, suggesting improved cardiolipin levels may play a role. However, an initial donor pair comparison did not show an effect of OEA on cardiolipin content, suggesting other mechanisms should be explored. Higher immunodetectable levels of OPA1, a biomarker of mitochondrial fusion, were found in lymphoblasts from children with BTHS, and were attenuated by OEA. Results from this study newly identify lymphopenia as a probable immunological deficit in BTHS, and suggest that therapies targeting aberrant fission/fusion of the mitochondrial network, rather than cardiolipin content, per se, and may have clinical utility for treatment of this disease.

Delta-6-desaturase (D6D) activity is deficient in MCF-7 and other cancer cell lines, but it is not explained by FADS2 gene mutations. This deficient activity was not ameliorated by induction of the FADS2 gene; therefore, we hypothesized that some of the induced FADS2 transcript variants (tv) may play a negative regulatory role. FADS2_tv1 is the reference FADS2 tv, coding for full-length D6D isoform 1 (D6D-iso1), and alternative transcriptional start sites result in FADS2_tv2 and FADS2_tv3 variants encoding D6D-iso2 and D6D-iso3 isoforms, respectively, which lack the catalytically critical N-terminal domain. In MCF-7 cells, FADS2_tv2 and FADS2_tv3 were expressed at significantly higher levels than FADS2_tv1. Overexpression of FADS2_tv2 in HEK293 cells confirmed that D6D-iso2 is non-functional, and co-transfection demonstrated a dominant-negative role for D6D-iso2 in D6D-iso1 activity regulation. FADS2_tv2 was expressed at higher levels than FADS2_tv1 in HeLa, MDA-MB-435, MCF-10 A, and HT-29 cells, but at lower levels in A549, MDA-MB-231, and LNCaP cells. Overexpression studies indicated roles for FADS2 variants in proliferation and apoptosis regulation, which were also cell-line specific. Increased FADS2_tv2 expression provides a new mechanism to help explain deficient D6D activity in MCF-7 and other cancer cell lines, but it is not a hallmark of malignant cells.

Classical rodent obesity models implicate renal steatosis and lipotoxicity in the pathology of type 2 diabetes (T2D), but are confounded by myriad of metabolic changes. To study effects of isolated renal steatosis, we have generated renal tubule-specific adipose triglyceride lipase knockout (RT-SAKO) mice. Initial work from our laboratory has found glucose intolerance, without insulin resistance, in young male RT-SAKO mice, but not in females. Women have an older age of onset of T2D than men, therefore, we have studied the physiology and glycemic control of older female RT-SAKO mice.

Lysophosphatidic acid (lysoPtdOH) levels have previously been reported to decrease in rodents with short-term fasting. We investigated whether a 16 h fast would change expression of autotaxin, the predominant phospholipase D responsible for adipose-derived lysoPtdOH synthesis, or any of the lysophosphatidic acid receptors (1-6) in four white adipose tissue (WAT) depots and interscapular brown adipose tissue (BAT) in male C57Bl/6J mice fed ad libitum, or fasted for 16 h. Aside from small inductions of Lpar1 in epididymal WAT and Lpar2 in epididymal and inguinal WAT, no significant changes were observed in expression of the Lpar family members, or autotaxin in perirenal, retroperitoneal, epididymal, or inguinal WAT or BAT with fasting. Comparison of the relative expression of Lpar1-6 in various depots showed that Lpar6 was the predominant Lpar in both WAT and BAT, and suggests that further work on the adipose-specific role of Lpar6 is warranted.

Lysophosphatidic acids (lysoPtdOH) are involved in several physiological processes including cell proliferation, inflammation, and glucose metabolism. However, measuring lysoPtdOH is challenging due to inadequate extraction techniques, poor chromatographic resolution, or the inability to discriminate between sn-1 and sn-2 regioisomers. In the present work, we developed a high-throughput (10 min run times) ultra-high-performance liquid chromatography-tandem mass spectrometry method capable of discriminating lysoPtdOH species by their fatty acyl composition and sn-localization on glycerol backbones. We quantitated sn-1/sn-2 regioisomeric pairs of lysoPtdOH with 16:0, 18:0, 18:1, 18:2, 20:4, and 22:6 fatty acyl chains using 50 μL of mouse plasma. The method presented here can be expanded to profile more lysoPtdOH species, and has the potential to be used in clinical settings to quickly screen lysoPtdOH profiles. Finally, the ability to discriminate between sn-1 and sn-2 isomers can provide insights regarding the metabolic origins and fates of specific lysoPtdOH molecules.

The apolipoprotein E (APOE) epsilon 4 isoform has been associated with a significantly greater risk of developing late onset Alzheimer's disease (AD). However, the negative effects of APOE-epsilon 4 allele on cognitive function vary across the lifespan: reduced memory and executive function have been found in older individuals but, paradoxically, young APOE-epsilon 4 carriers perform better on cognitive tests and show higher neural efficiency. This study aimed to assess the association between APOE genotype and saccade latency using a prosaccade and antisaccade task in young individuals (N = 97, age: 17-35 years). Results showed that prosaccade latency was significantly delayed in a group of epsilon 4 carriers in comparison to non-carriers, which was due to a lower rate of signal accumulation rather than a change in the criterion threshold. In contrast, there was no significant genotype difference for antisaccade latency in this young cohort. These results indicate that prosaccade latency may be useful in establishing the APOE behavioural phenotype, which could ultimately assist with distinguishing between normal and pathological aging.