Leigh Syndrome French Canadian Research Articles

Human induced pluripotent stem cells (hiPSCs) derived cells reflect tissue specificity found in patients with Leigh syndrome French Canadian variant (LSFC).

Leigh syndrome French Canadian type (LSFC) is a recessive neurodegenerative disease characterized by tissue-specific deficiency in cytochrome c oxidase (COX), the fourth complex in the oxidative phosphorylation system. LSFC is caused by mutations in the leucine rich pentatricopeptide repeat containing gene (LRPPRC). Most LSFC patients in Quebec are homozygous for an A354V substitution that causes a decrease in the expression of the LRPPRC protein. While LRPPRC is ubiquitously expressed and is involved in multiple cellular functions, tissue-specific expression of LRPPRC and COX activity is correlated with clinical features. In this proof-of-principle study, we developed human induced pluripotent stem cell (hiPSC)-based models from fibroblasts taken from a patient with LSFC, homozygous for the LRPPRC*354V allele, and from a control, homozygous for the LRPPRC*A354 allele. Specifically, for both of these fibroblast lines we generated hiPSC, hiPSC-derived cardiomyocytes (hiPSC-CMs) and hepatocyte-like cell (hiPSC-HLCs) lines, as well as the three germ layers. We observed that LRPPRC protein expression is reduced in all cell lines/layers derived from LSFC patient compared to control cells, with a reduction ranging from ∼70% in hiPSC-CMs to undetectable levels in hiPSC-HLC, reflecting tissue heterogeneity observed in patient tissues. We next performed exploratory analyses of these cell lines and observed that COX protein expression was reduced in all cell lines derived from LSFC patient compared to control cells. We also observed that mutant LRPPRC was associated with altered expression of key markers of endoplasmic reticulum stress response in hiPSC-HLCs but not in other cell types that were tested. While this demonstrates feasibility of the approach to experimentally study genotype-based differences that have tissue-specific impacts, this study will need to be extended to a larger number of patients and controls to not only validate the current observations but also to delve more deeply in the pathogenic mechanisms of LSFC.

Genetic therapy in a mitochondrial disease model suggests a critical role for liver dysfunction in mortality.

The clinical and largely unpredictable heterogeneity of phenotypes in patients with mitochondrial disorders demonstrates the ongoing challenges in the understanding of this semi-autonomous organelle in biology and disease. Previously, we used the gene-breaking transposon to create 1200 transgenic zebrafish strains tagging protein-coding genes (Ichino et al., 2020), including the lrpprc locus. Here, we present and characterize a new genetic revertible animal model that recapitulates components of Leigh Syndrome French Canadian Type (LSFC), a mitochondrial disorder that includes diagnostic liver dysfunction. LSFC is caused by allelic variations in the LRPPRC gene, involved in mitochondrial mRNA polyadenylation and translation. lrpprc zebrafish homozygous mutants displayed biochemical and mitochondrial phenotypes similar to clinical manifestations observed in patients, including dysfunction in lipid homeostasis. We were able to rescue these phenotypes in the disease model using a liver-specific genetic model therapy, functionally demonstrating a previously under-recognized critical role for the liver in the pathophysiology of this disease.

Poly (A) tail length of human mitochondrial mRNAs is tissue-specific and a mutation in LRPPRC results in transcript-specific patterns of deadenylation

Mutations in LRPPRC cause Leigh Syndrome French Canadian (LSFC), an early onset neurodegenerative disease, with differential tissue involvement. The molecular basis for tissue specificity in this disease remains unknown. LRPPRC, an RNA binding protein, forms a stable complex with SLIRP, which binds to, and stabilizes mitochondrial mRNAs. In cell culture and animal models, loss of LRPPRC function results in transcript-specific alterations in the steady-state levels of mitochondrial mRNAs and poly (A) tail length, the mechanisms for which are not understood. The poly (A) tail length of mitochondrial mRNAs has not been investigated in human tissues from heathy subjects or LSFC patients. Here we have mapped the 3′-termini of mature mitochondrial mRNAs in three tissues (skeletal muscle, heart, and liver) from a healthy individual and an LSFC patient. We show that the poly (A) tail length of mitochondrial mRNAs varies amongst tissues, and that the missense mutation in LRPPRC that causes LSFC results in tissue- and transcript-specific deadenylation of a subset of mitochondrial mRNAs, likely contributing the nature and severity of the biochemical phenotype in different tissues. We also found a relatively large fraction of short transcripts lacking a stop codon, some with short poly (A) tails, in patient tissue, suggesting that mutations in LRPPRC may also impair proper 3′ end processing of some mRNAs.

Humoral responses to the measles, mumps and rubella vaccine are impaired in Leigh Syndrome French Canadian patients.

Leigh Syndrome French Canadian (LSFC) is a rare autosomal recessive metabolic disorder characterized by severe lactic acidosis crises and early mortality. LSFC patients carry mutations in the Leucine Rich Pentatricopeptide Repeat Containing (LRPPRC) gene, which lead to defects in the respiratory chain complexes and mitochondrial dysfunction. Mitochondrial respiration modulates cellular metabolic activity, which impacts many cell types including the differentiation and function of immune cells. Hence, we postulated that, in addition to neurological and metabolic disorders, LSFC patients may show impaired immune activity. To gain insight into the quality of the immune response in LSFC patients, we examined the response to the measles, mumps and rubella (MMR) vaccine by measuring antibody titers to MMR in the plasma. In a cohort of eight LSFC patients, the response to the MMR vaccine was variable, with some individuals showing antibodies to all three viruses, while others had antibodies to two or fewer viruses. These results suggest that the mutations in the LRPPRC gene present in LSFC patients may affect the immune response to vaccines. Monitoring vaccine response in this fragile population should be considered to ensure full protection against pathogens.

Novel LRPPRC compound heterozygous mutation in a child with early-onset Leigh syndrome French-Canadian type: case report of an Italian patient

BackgroundMitochondrial diseases, also known as oxidative phosphorylation (OXPHOS) disorders, with a prevalence rate of 1:5000, are the most frequent inherited metabolic diseases. Leigh Syndrome French Canadian type (LSFC), is caused by mutations in the nuclear gene (2p16) leucine-rich pentatricopeptide repeat-containing (LRPPRC). It is an autosomal recessive neurogenetic OXPHOS disorder, phenotypically distinct from other types of Leigh syndrome, with a carrier frequency up to 1:23 and an incidence of 1:2063 in the Saguenay-Lac-St Jean region of Quebec. Recently, LSFC has also been reported outside the French-Canadian population.Patient presentationWe report a male Italian (Sicilian) child, born preterm at 28 + 6/7 weeks gestation, carrying a novel LRPPRC compound heterozygous mutation, with facial dysmorphisms, neonatal hypotonia, non-epileptic paroxysmal motor phenomena, and absent sucking-swallowing-breathing coordination requiring, at 4.5 months, a percutaneous endoscopic gastrostomy tube placement. At 5 months brain Magnetic Resonance Imaging showed diffuse cortical atrophy, hypoplasia of corpus callosum, cerebellar vermis hypoplasia, and unfolded hippocampi. Both auditory and visual evoked potentials were pathological. In the following months Video EEG confirmed the persistence of sporadic non epileptic motor phenomena. No episode of metabolic decompensation, acidosis or ketosis, frequently observed in LSFC has been reported. Actually, aged 14 months corrected age for prematurity, the child shows a severe global developmental delay. Metabolic investigations and array Comparative Genomic Hybridization (aCGH) results were normal. Whole-genome sequencing (WGS) found a compound heterozygous mutation in the LRPPRC gene, c.1921–7A > G and c.2056A > G (p.Ile686Val), splicing-site and missense variants, inherited from the mother and the father, respectively.ConclusionsWe first characterized the clinical and molecular features of a novel LRPPRC variant in a male Sicilian child with early onset encephalopathy and psychomotor impairment. Our patient showed a phenotype characterized by a severe neurodevelopmental delay and absence of metabolic decompensation attributable to a probable residual enzymatic activity. LRPPRC is a rare cause of metabolic encephalopathy outside of Québec. Our patient adds to and broaden the spectrum of LSFC phenotypes. WGS analysis is a pivotal genetic test and should be performed in infants and children with hypotonia and developmental delay in whom metabolic investigations and aCGH are normal.

MTORC1 is required for expression of LRPPRC and cytochrome-c oxidase but not HIF-1α in Leigh syndrome French Canadian type patient fibroblasts.

Leigh syndrome French Canadian type (LSFC) is a mitochondrial disease caused by mutations in the leucine-rich pentatricopeptide repeat-containing (LRPPRC) gene leading to a reduction of cytochrome-c oxidase (COX) expression reaching 50% in skin fibroblasts. We have shown that under basal conditions, LSFC and control cells display similar ATP levels. We hypothesized that this occurs through upregulation of mechanistic target of rapamycin (mTOR)-mediated metabolic reprogramming. Our results showed that compared with controls, LSFC cells exhibited an upregulation of the mTOR complex 1 (mTORC1)/p70 ribosomal S6 kinase pathway and higher levels of hypoxia-inducible factor 1α (HIF-1α) and its downstream target pyruvate dehydrogenase kinase 1 (PDHK1), a regulator of mitochondrial pyruvate dehydrogenase 1 (PDH1). Consistent with these signaling alterations, LSFC cells displayed a 40-61% increase in [U-13C6]glucose contribution to pyruvate, lactate, and alanine formation, as well as higher levels of the phosphorylated and inactive form of PDH1-α. Interestingly, inhibition of mTOR with rapamycin did not alter HIF-1α or PDHK1 protein levels in LSFC fibroblasts. However, this treatment increased PDH1-α phosphorylation in control and LSFC cells and reduced ATP levels in control cells. Rapamycin also decreased LRPPRC expression by 41 and 11% in LSFC and control cells, respectively, and selectively reduced COX subunit IV expression in LSFC fibroblasts. Taken together, our data demonstrate the importance of mTORC1, independent of the HIF-1α/PDHK1 axis, in maintaining LRPPRC and COX expression in LSFC cells.

Leigh Syndrome French Canadian Type Patient Fibroblasts Exhibit Energy Metabolism Adaptations Through a Warburg‐like Effect

Background & ObjectiveLSFC is a recessive mitochondrial disease caused by mutations in the LRPPRC gene resulting in a decrease in the LRPPRC protein. This leads to a tissue‐specific reduction of complex IV or cytochrome c oxidase (COX). Our previous work in LSFC fibroblasts demonstrated several mitochondrial functional abnormalities including reduced mitochondrial membrane potential, fragmentation of the mitochondrial network and impaired oxidative phosphorylation capacity. Despite these abnormalities, LSFC fibroblasts did not display any reduction in ATP levels, suggesting the activation of compensatory mechanisms. We hypothesized that mTORC1‐mediated glycolytic ATP production, also known as Warburg effect, might compensate for mitochondrial dysfunction. To address this question, we evaluated glycolytic flux and the Akt/mTORC1 signaling pathway, using LSFC and control skin fibroblasts as a model.ResultsOur results showed numerous adaptations of LSFC energy metabolism. Metabolic flux analysis revealed that glucose contribution to pyruvate, lactate and alanine formation was respectively increased by 41%, 61%, and 52% (p≤0.05) in LSFC fibroblasts compared to controls. At the molecular level, the Akt/mTORC1 pathway was up regulated in LSFC cells compared to controls (pAkt 111%, p≤0.05; Akt 44%, p≤0.001; mTOR 51%, p≤0.01). This includes enhanced phosphorylation of mTORC1 downstream targets p70S6K by 105% (p≤0.05); as well as an increase in the expression of the transcription factor HIF‐1α by 200% (p≤0.01). The level of pyruvate dehydrogenase kinase 1 (PDHK1), a HIF‐1α downstream target and an inhibitor of mitochondrial glucose oxidation via pyruvate dehydrogenase 1 (PDH1) phosphorylation, was also up regulated by 150% (p≤0.05) in LSFC cells. Consistent with these results, we observed an increase of PDH1 phosphorylation by 94% (p≤0.01) in LSFC cells compared to controls. To further delineate the role of mTORC1 pathway in these adaptations, we inhibited its activity with rapamycin. mTORC1 inhibition did not affect HIF‐1α or PDHK1 expression. However, rapamycin was associated with increased PDH1 phosphorylation (p≤0.05) by 37% and 42% in LSFC and control fibroblasts, respectively. Rapamycin also reduced ATP levels by 8% (p=0.07) in LSFC fibroblasts comparatively to 15% (p≤0.05) in controls. Interestingly, rapamycin decreased LRPPRC expression by 41% (p≤0.01) in LSFC cells compared to only 11% (p≤0.05) reduction in control. This was associated with a selective reduction of COX expression in LSFC (32%, p≤0.01) fibroblasts, while we did not observe any change in expression of the others mitochondrial complexes.ConclusionLSFC fibroblasts maintain ATP levels probably through a “Warburg‐like effect”; for which mTORC1 is not the primary regulator. mTORC1 activation, however, appears important for LRPPRC and therefore, COX expression in LSFC fibroblasts.Support or Funding InformationSupported by: Association de l'acidose lactique and CIHR Emerging Team Grant

A Metabolic Signature of Mitochondrial Dysfunction Revealed through a Monogenic Form of Leigh Syndrome

SUMMARYA decline in mitochondrial respiration represents the root cause of a large number of inborn errors of metabolism. It is also associated with common age-associated diseases and the aging process. To gain insight into the systemic, biochemical consequences of respiratory chain dysfunction, we performed a case-control, prospective metabolic profiling study in a genetically homogenous cohort of patients with Leigh syndrome French Canadian variant, a mitochondrial respiratory chain disease due to loss-of-function mutations in LRPPRC. We discovered 45 plasma and urinary analytes discriminating patients from controls, including classic markers of mitochondrial metabolic dysfunction (lactate and acylcarnitines), as well as unexpected markers of cardiometabolic risk (insulin and adiponectin), amino acid catabolism linked to NADH status (α-hydroxybutyrate), and NAD+ biosynthesis (kynurenine and 3-hydroxyanthranilic acid). Our study identifies systemic, metabolic pathway derangements that can lie downstream of primary mitochondrial lesions, with implications for understanding how the organelle contributes to rare and common diseases.

Mitochondrial vulnerability and increased susceptibility to nutrient-induced cytotoxicity in fibroblasts from leigh syndrome French canadian patients.

Mutations in LRPPRC are responsible for the French Canadian variant of Leigh Syndrome (LSFC), a severe disorder characterized biochemically by a tissue-specific deficiency of cytochrome c oxidase (COX) and clinically by the occurrence of severe and deadly acidotic crises. Factors that precipitate these crises remain unclear. To better understand the physiopathology and identify potential treatments, we performed a comprehensive analysis of mitochondrial function in LSFC and control fibroblasts. Furthermore, we have used this cell-based model to screen for conditions that promote premature cell death in LSFC cells and test the protective effect of ten interventions targeting well-defined aspects of mitochondrial function. We show that, despite maintaining normal ATP levels, LSFC fibroblasts present several mitochondrial functional abnormalities under normal baseline conditions, which likely impair their capacity to respond to stress. This includes mitochondrial network fragmentation, impaired oxidative phosphorylation capacity, lower membrane potential, increased sensitivity to Ca2+-induced permeability transition, but no changes in reactive oxygen species production. We also show that LSFC fibroblasts display enhanced susceptibility to cell death when exposed to palmitate, an effect that is potentiated by high lactate, while high glucose or acidosis alone or in combination were neutral. Furthermore, we demonstrate that compounds that are known to promote flux through the electron transport chain independent of phosphorylation (methylene blue, dinitrophenol), or modulate fatty acid (L-carnitine) or Krebs cycle metabolism (propionate) are protective, while antioxidants (idebenone, N-acetyl cysteine, resveratrol) exacerbate palmitate plus lactate-induced cell death. Collectively, beyond highlighting multiple alterations in mitochondrial function and increased susceptibility to nutrient-induced cytotoxicity in LSFC fibroblasts, these results raise questions about the nature of the diets, particularly excess fat intake, as well as on the use of antioxidants in patients with LSFC and, possibly, other COX defects.

Differences in susceptibility to nutrient‐induced cell death between primary and immortalized Leigh Syndrome French Canadian type (LSFC) patient fibroblasts

LSFC is a monogenic metabolic disease resulting from a mutation in the leucine‐rich pentatricopeptide repeat‐containing (LRPPRC) gene. It is characterized by cytochrome c oxidase (COX) deficiency and episodes of lactic acidosis leading to death at an early age. Recently, we reported that primary (P) LSFC fibroblasts were more susceptible than controls to necrosis induced by nutrient overload (palmitate 1 mM and lactate 10 mM), an effect associated with a lower [ATP] (FASEB J 2011 25:722.15). In this study, we compared P and immortalized (I) LSFC and control fibroblasts. Under basal conditions, control P and I cells displayed similar characteristics regarding (i) LRPPRC localization (immunocytochemistry) and content (Western) as well as (ii) COX activity. Both these parameters showed the expected decrease in LSFC P and I cells. However, compared to P cells, I cells from both groups had higher citrate synthase activity (~25%) and lower [ATP] (~40%). Accordingly, during nutrient overload, I cells were more susceptible than P cells to both necrosis and apoptosis. While this was observed for control and LSFC cells, LSFC I cells remain more susceptible to necrosis compared to their control counterpart. Collectively, our results highlight differences between P and I cells that ought to be considered for data interpretation and study design. (Supported by: Association de l'acidose lactique and CIHR Emerging Team Grant)

Alterations in mitochondrial function in fibroblasts from patients with Leigh Syndrome French Canadian type (LSFC)

LSFC is a monogenic metabolic disease characterized by 1) cytochrome c oxidase deficiency, resulting from a mutation in the leucine‐rich pentatricopeptide repeat motif containing gene LRPPRC, and 2) episodes of lactic acidosis “crisis” leading to death early in life. The mechanisms responsible for these crises remain to be elucidated. In this study, we used fibroblasts from LSFC patients as a working model to test the hypothesis that impaired mitochondrial function and network dynamics in these cells may predispose them to premature death. Calcium retention capacity (CRC), oxygen (O2) consumption, reactive oxygen species production, mitochondrial membrane potential (ΔΨ) and network morphology were assessed in intact or permeabilized control and LSFC fibroblasts. Compared to controls, LSFC fibroblasts showed multiple abnormalities under basal condition, including decreased CRC (36%), O2 consumption (30–59%), ΔΨ (67%) and increased mitochondrial fission. In addition, nutrient overload, which induces premature death of LSFC fibroblasts (FASEB J 2011 25:722.15), exacerbated mitochondrial fission in these cells. Together, these results suggest that mitochondria from LSFC fibroblasts are dysfunctional and this may limit the capacity of these cells to maintain homeostasis, particularly under conditions of nutrient overload. (Supported by: Association de l'acidose lactique and CIHR Emerging Team Grants)

AMP‐activated protein kinase (AMPK) activity in Leigh Syndrome French Canadian Type (LSFC) patient fibroblasts: differences between primary and immortalized cell lines

Background & ObjectiveLSFC is an autosomal recessive disease caused by mutations in the leucine‐rich pentatricopeptide repeat containing protein (LRPPRC) gene resulting in decreased LRPPRC expression. This leads to a tissue‐specific cytochrome c oxidase deficiency and a reduction in energy production. AMPK is a key enzyme in the regulation of energy homeostasis. To test the hypothesis that AMPK activity may differ in LSFC and control cells, we evaluated the phosphorylated and active form of AMPK in primary (P) fibroblasts and, because of the limited availability of P cells, we also tested their immortalized (I) counterparts.ResultsUnder basal conditions, P fibroblasts from LSFC patients and controls showed marginal differences in the levels of phosphorylated AMPK (pAMPK) as well as acetyl‐CoA carboxylase (ACC), one of many AMPK substrates. However, compared to P cells, I cells from both controls and LSFC patients showed a 60% and 80% decrease in pAMPK, respectively. Consistent with pAMPK levels, phosphorylated ACC levels were also decreased in I cells by 58 % in controls and 69% in LSFC patients. The total levels of these proteins were similar in all cases.ConclusionThese results highlight an important decrease in AMPK activity level in I vs. P cells, which may compromise the capacity of these cells to palliate an energy deficit.Supported by: Association de l'acidose lactique and CIHR Emerging Team Grant

Low-Concentration Methylene Blue Maintains Energy Production and Strongly Improves Survival of Leigh Syndrome French Canadian Skin Fibroblasts

Leigh syndrome French Canadian (LSFC) is a recessive disease caused by mutations in the LRPPRC gene (leucine-rich pentatricopeptide repeat containing protein). These mutations induce a cytochrome c oxidase (COX) deficiency resulting in episodes of acute acidotic crisis that will often lead to death. There is no effective treatment. Methylene blue (MB) is a redox dye that increases COX content and activity in vitro and in vivo suggesting that MB could prevent and treat LSFC. In this study, the protective effect of low-concentration MB was tested on two LSFC cell lines, including LSFC-F1, homozygous for the mutation A354V, and LSFC-F2 a compound heterozygous for the mutations A354V and C12775STOP. MB effect on metabolic activity was assessed on both LSFC cells in stable and acidotic conditions. For LSFC-F1, results showed that metabolic activity drastically decline after 96 hours in both conditions but not LSFC-F2 and normal cells. MB completely prevents the decrease of metabolic activity in LSFC-F1. Intracellular ATP content was also measured in both culture media. After 96 hours in acidotic medium, ATP content was almost completely depleted for both LSFC cells. Interestingly, MB completely restores ATP content in LSFC-F1 and LSFC-F2 cells. Finally, MB strongly improves the survival of both LSFC cells.

Abstract 4023: Novel role of neurofibromin in transport of RNA granules

Abstract Neurofibromatosis 1 (NF1) is the most common tumor predisposing syndrome in humans, with an incidence of 1:3500 live births. Neurofibromin, encoded by Nf1, acts as a p21-Ras-GAP to directly interact with and inactivate p21-Ras, through its’ GAP Related Domain (GRD). Evidence suggests that non-Ras-GAP functions mediated through interactions with domains outside of the GRD are of importance. By making a number of NF1-GST domain constructs coupled with differential Mass Spec analysis, we identified LRPPRC and Dynein as previously unreported NF1-TBD interacting proteins. LRPPRC was of interest as it is mutated in the Leigh Syndrome French Canadian (LSFC) variant, a cytochrome-oxidase deficiency syndrome, characterized by neurodegeneration, developmental- mental- and growth-retardation, thereby having some similarities with non-tumor manifestations of NF1. We have established that LRPPRC and neurofibromin interact in vitro by immunoprecipitation and reverse bait immunoprecipitation. Use of a novel Proximity Ligation Assay (PLA) was used to further confirm the interaction in situ in cell lines and clinical tissue cryosections. Towards elucidating the functional relevance of the interaction, we have established that the two proteins complex with microtubules and motor proteins, which indicates a role in microtubule-dependant intracellular transport. Since LRPPRC binds with mRNA and is involved in its nucleocytosolic shuttling, we hypothesize that the cargo transported by this complex could be RNA granules. Mass Spec analysis of NF1 immunoprecipitates revealed a number of proteins that are a part of the RNA granule complex which include RNA binding proteins and proteins involved in mRNA translation. By performing RNA Immunoprecipitation (RIP) with NF1 and LRPPRC antibodies, we have demonstrated that the two proteins do complex with 18S and 28S rRNA which is indicative of the presence of intact mRNA. Towards identifying the specific messages transported by the NF1-LRPPRC RNA granule complex we are performing RIP - microarray gene expression profiling (CHIP). The resultant candidate mRNAs will be further investigated to understand the importance of this novel interaction and novel mechanism towards some of the overlap of neurological and developmental manifestations between LSFC and NF1. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4023.

Modulation of PGC-1 Coactivator Pathways in Brown Fat Differentiation through LRP130

The PGC-1 coactivators are important regulators of oxidative metabolism. We previously demonstrated that LRP130 is a binding partner of PGC-1alpha, required for hepatic gluconeogenesis. LRP130 is the gene mutated in Leigh syndrome French Canadian variant, a rare neurodegenerative disease. The importance of LRP130 in other, non-hepatocyte biology remains obscure. To better understand PGC-1 coactivator function in brown fat development, we explored the metabolic role of LRP130 in brown adipocyte differentiation. We show that LRP130 is preferentially enriched in brown fat compared with white, and induced in a PGC-1-dependent manner during differentiation. Despite intact PGC-1 coactivator expression, brown fat cells deficient for LRP130 exhibit attenuated expression of several genes characteristic of brown fat, including uncoupling protein 1. Oxygen consumption studies support a specific defect in proton leak due to attenuated uncoupling protein 1 expression. Notably, brown fat cell development common to both PGC-1 coactivators is governed by LRP130. Conversely, the cAMP response controlled by PGC-1alpha is not regulated by LRP130. These data implicate LRP130 in brown fat cell development and differentiation.

Defects in energy homeostasis in Leigh syndrome French Canadian variant through PGC-1alpha/LRP130 complex.

Leigh syndrome French Canadian variant (LSFC) is an autosomal recessive neurodegenerative disorder due to mutation in the LRP130 (leucine-rich protein 130 kDa) gene. Unlike classic Leigh syndrome, the French Canadian variant spares the heart, skeletal muscle, and kidneys, but severely affects the liver. The precise role of LRP130 in cytochrome c oxidase deficiency and hepatic lactic acidosis that accompanies this disorder is unknown. We show here that LRP130 is a component of the PGC-1alpha (peroxisome proliferator-activated receptor coactivator 1-alpha) transcriptional coactivator holocomplex and regulates expression of PEPCK (phosphoenolpyruvate carboxykinase), G6P (glucose-6-phosphatase), and certain mitochondrial genes through PGC-1alpha. Reduction of LRP130 in fasted mice via adenoviral RNA interference (RNAi) vector blocks the induction of PEPCK and G6P, and blunts hepatic glucose output. LRP130 is also necessary for PGC-1alpha-dependent transcription of several mitochondrial genes in vivo. These data link LRP130 and PGC-1alpha to defective hepatic energy homeostasis in LSFC, and reveal a novel regulatory mechanism of glucose homeostasis.

The role of the LRPPRC (leucine-rich pentatricopeptide repeat cassette) gene in cytochrome oxidase assembly: mutation causes lowered levels of COX (cytochrome c oxidase) I and COX III mRNA.

Leigh syndrome French Canadian (LSFC) is a variant of cytochrome oxidase deficiency found in Québec and caused by mutations in the LRPPRC (leucine-rich pentatricopeptide repeat cassette) gene. Northern blots showed that the LRPPRC mRNA levels seen in skeletal muscle>heart>placenta>kidney>liver>lung=brain were proportionally almost opposite in strength to the severity of the enzymic cytochrome oxidase defect. The levels of COX (cytochrome c oxidase) I and COX III mRNA visible on Northern blots were reduced in LSFC patients due to the common (A354V, Ala354-->Val) founder mutation. The amount of LRPPRC protein found in both fibroblast and liver mitochondria from LSFC patients was consistently reduced to <30% of control levels. Import of [(35)S]methionine LRPPRC into rat liver mitochondria was slower for the mutant (A354V) protein. A titre of LRPPRC protein was also found in nuclear fractions that could not be easily accounted for by mitochondrial contamination. [35S]Methionine labelling of mitochondrial translation products showed that the translation of COX I, and perhaps COX III, was specifically reduced in the presence of the mutation. These results suggest that the gene product of LRPPRC, like PET 309p, has a role in the translation or stability of the mRNA for mitochondrially encoded COX subunits. A more diffuse distribution of LRPPRC in LSFC cells compared with controls was evident when viewed by immunofluorescence microscopy, with less LRPPRC present in peripheral mitochondria.