PGC1α-dependent NAD biosynthesis links oxidative metabolism to renal protection

The energetic burden of continuously concentrating solutes against gradients along the tubule may render the kidney especially vulnerable to ischemia. Indeed, acute kidney injury (AKI) affects 3% of all hospitalized patients.1,2 Here we show that the mitochondrial biogenesis regulator, PGC1α,3,4 is a pivotal determinant of renal recovery from injury by regulating NAD biosynthesis. Following renal ischemia, PGC1α−/− mice developed local deficiency of the NAD precursor niacinamide (Nam), marked fat accumulation, and failure to re-establish normal function. Remarkably, exogenous Nam improved local NAD levels, fat accumulation, and renal function in post-ischemic PGC1α−/− mice. Inducible tubular transgenic mice (iNephPGC1α) recapitulated the effects of Nam supplementation, including more local NAD and less fat accumulation with better renal function after ischemia. PGC1α coordinately upregulated the enzymes that synthesize NAD de novo from amino acids whereas PGC1α deficiency or AKI attenuated the de novo pathway. Nam enhanced NAD via the enzyme NAMPT and augmented production of the fat breakdown product beta-hydroxybutyrate (β-OHB), leading to increased prostaglandin PGE2, a secreted autocoid that maintains renal function.5 Nam treatment reversed established ischemic AKI and also prevented AKI in an unrelated toxic model. Inhibition of β-OHB signaling or prostaglandins similarly abolished PGC1α-dependent renoprotection. Given the importance of mitochondrial health in aging and the function of metabolically active organs, the results implicate Nam and NAD as key effectors for achieving PGC1α-dependent stress resistance

Congenital chloride-losing diarrhea in a Mexican child with the novel homozygous SLC26A3 mutation G393W

Congenital chloride diarrhea is an autosomal recessive disease caused by mutations in the intestinal lumenal membrane Cl−/HCO−3 exchanger, SLC26A3. We report here the novel SLC26A3 mutation G393W in a Mexican child, the first such report in a patient from Central America. SLC26A3 G393W expression in Xenopus oocytes exhibits a mild hypomorphic phenotype, with normal surface expression and moderately reduced anion transport function. However, expression of HA-SLC26A3 in HEK-293 cells reveals intracellular retention and greatly decreased steady-state levels of the mutant polypeptide, in contrast to peripheral membrane expression of the wildtype protein. Whereas wildtype HA-SLC26A3 is apically localized in polarized monolayers of filter-grown MDCK cells and Caco2 cells, mutant HA-SLC26A3 G393W exhibits decreased total polypeptide abundance, with reduced or absent surface expression and sparse punctate (or absent) intracellular distribution. The WT protein is similarly localized in LLC-PK1 cells, but the mutant fails to accumulate to detectable levels. We conclude that the chloride-losing diarrhea phenotype associated with homozygous expression of SLC26A3 G393W likely reflects lack of apical surface expression in enterocytes, secondary to combined abnormalities in polypeptide trafficking and stability. Future progress in development of general or target-specific folding chaperonins and correctors may hold promise for pharmacological rescue of this and similar genetic defects in membrane protein targeting

The pathology of eclampsia: An autopsy series

Objective: We describe the main lesions in the liver, brain, and kidney from autopsies of women who died of eclampsia and characterize the endothelial injury. Methods: Cases were identified from a study involving 317 maternal deaths (2003–2006) conducted at the Maputo Central Hospital (Maputo, Mozambique) in association with ISGlobal (Barcelona, Spain). Histology slides along with stains for endothelial, histiocyte, and platelet markers (CD31, CD34, CD68, CD42B) were reviewed to identify the relevant lesions. Malondialdehyde stain was performed to demonstrate free radical generation. Results: Brain lesions were characterized by perivascular “edema” (68.4%), hemorrhage (36.8%), hemosiderin (31.6%), small vessel thrombosis (10.5%), and parenchymal necrosis (15.8%). Liver sections showed periportal/portal necrosis and sinusoidal fibrin (72.2%) with associated hepatic arterial medial necrosis (44.4%). Kidneys showed glomerular endotheliosis. Endothelial, histiocytic, and platelet markers highlighted capillary injury in the otherwise intact brain parenchyma. Stains for free radical formation were positive predominantly in the areas of tissue injury, but intact glial/neuronal elements were focally positive as evidence of widespread oxidative stress. Conclusion: Pathological changes in cases of eclampsia include widespread endothelial/vascular injury in vulnerable organ beds

Exposure to placental ischemia impairs postpartum maternal renal and cardiac function in rats

INTRODUCTION: Women with a history of preeclampsia (PE) have an increased risk to develop cardiovascular and renal diseases later in life, but the mechanisms underlying this effect are unknown. In rats, we assessed whether placental ischemia results in long-term effects on the maternal cardiovascular and renal systems using the Reduced Uterine Perfusion Pressure (RUPP) model for PE. METHODS: Sprague-Dawley rats received either a SHAM or RUPP operation at gestational day 14. The rats were followed for eight weeks after delivery (SHAM n=12, RUPP n=21) at which time mean arterial pressure (MAP; conscious), 24-hour albuminuria, GFR (transcutaneous, FITC-sinistrin), and cardiac function (Vevo 770 system) were assessed. Subsequently, all rats were sacrificed for mesenteric artery vasorelaxation and histology of heart and kidney. RESULTS: At eight weeks after delivery, there was no difference in MAP and albuminuria. However, RUPP rats showed a significantly reduced GFR [2.61 ± 0.53 vs 3.37 ± 0.74ml/min; p=0.01]. Ultrasound showed comparable cardiac structure, but RUPP rats had a lower left ventricular ejection fraction (62 ± 7 vs 69 ± 10%; p=0.04). Heart and kidney histology was not different between SHAM or RUPP rats. Furthermore, there were no differences in endothelial dependent or independent vasorelaxation. CONCLUSIONS: We show that exposure to placental ischemia in rats is accompanied by functional disturbances in maternal renal and cardiac function eight weeks after a preeclamptic pregnancy. However, these changes were not dependent on differences in blood pressure, small artery vasorelaxation, or cardiac and renal structure at this time point postpartum

Exposure to placental ischemia impairs postpartum maternal renal and cardiac function in rats

INTRODUCTION: Women with a history of preeclampsia (PE) have an increased risk to develop cardiovascular and renal diseases later in life, but the mechanisms underlying this effect are unknown. In rats, we assessed whether placental ischemia results in long-term effects on the maternal cardiovascular and renal systems using the Reduced Uterine Perfusion Pressure (RUPP) model for PE. METHODS: Sprague-Dawley rats received either a SHAM or RUPP operation at gestational day 14. The rats were followed for eight weeks after delivery (SHAM n=12, RUPP n=21) at which time mean arterial pressure (MAP; conscious), 24-hour albuminuria, GFR (transcutaneous, FITC-sinistrin), and cardiac function (Vevo 770 system) were assessed. Subsequently, all rats were sacrificed for mesenteric artery vasorelaxation and histology of heart and kidney. RESULTS: At eight weeks after delivery, there was no difference in MAP and albuminuria. However, RUPP rats showed a significantly reduced GFR [2.61 ± 0.53 vs 3.37 ± 0.74ml/min; p=0.01]. Ultrasound showed comparable cardiac structure, but RUPP rats had a lower left ventricular ejection fraction (62 ± 7 vs 69 ± 10%; p=0.04). Heart and kidney histology was not different between SHAM or RUPP rats. Furthermore, there were no differences in endothelial dependent or independent vasorelaxation. CONCLUSIONS: We show that exposure to placental ischemia in rats is accompanied by functional disturbances in maternal renal and cardiac function eight weeks after a preeclamptic pregnancy. However, these changes were not dependent on differences in blood pressure, small artery vasorelaxation, or cardiac and renal structure at this time point postpartum

Disconnecting Mitochondrial Content from Respiratory Chain Capacity in PGC-1-Deficient Skeletal Muscle

The transcriptional coactivators PGC-1α and PGC-1β are widely thought to be required for mitochondrial biogenesis and fiber typing in skeletal muscle. Here, we show that mice lacking both PGC-1s in myocytes do indeed have profoundly deficient mitochondrial respiration but, surprisingly, have preserved mitochondrial content, isolated muscle contraction capacity, fiber-type composition, in-cage ambulation, and voluntary running capacity. Most of these findings are recapitulated in cell culture and, thus, are cell autonomous. Functional electron microscopy reveals normal cristae density with decreased cytochrome oxidase activity. These data lead to the following surprising conclusions: (1) PGC-1s are in fact dispensable for baseline muscle function, mitochondrial content, and fiber typing, (2) endurance fatigue at low workloads is not limited by muscle mitochondrial capacity, and (3) mitochondrial content and cristae density can be dissociated from respiratory capacity

RNAi modulation of placental sFLT1 for the treatment of preeclampsia

Preeclampsia is a placentally induced hypertensive disorder of pregnancy that is associated with substantial morbidity and mortality to mothers and fetuses. Clinical manifestations of preterm preeclampsia result from excess circulating soluble vascular endothelial growth factor receptor FLT1 (sFLT1 or sVEGFR1) of placental origin. Here we identify short interfering RNAs (siRNAs) that selectively silence the three sFLT1 mRNA isoforms primarily responsible for placental overexpression of sFLT1 without reducing levels of full-length FLT1mRNA. Full chemical stabilization in the context of hydrophobic modifications enabled productive siRNA accumulation in the placenta (up to 7% of injected dose) and reduced circulating sFLT1 in pregnant mice (up to 50%). In a baboon preeclampsia model, a single dose of siRNAs suppressed sFLT1 overexpression and clinical signs of preeclampsia. Our results demonstrate RNAi-based extrahepatic modulation of gene expression with nonformulated siRNAs in nonhuman primates and establish a path toward a new treatment paradigm for patients with preterm preeclampsia