Compromised mitochondrial quality control triggers lipin1-related rhabdomyolysis.

LPIN1 mutations are responsible for inherited recurrent rhabdomyolysis, a life-threatening condition with no efficient therapeutic intervention. Here, we conduct a bedside-to-bench-and-back investigation to study the pathophysiology of lipin1 deficiency. We find that lipin1-deficient myoblasts exhibit a reduction in phosphatidylinositol-3-phosphate close to autophagosomes and late endosomes that prevents the recruitment of the GTPase Armus, locks Rab7 in the active state, inhibits vesicle clearance by fusion with lysosomes, and alters their positioning and function. Oxidized mitochondrial DNA accumulates in late endosomes, where it activates Toll-like receptor 9 (TLR9) and triggers inflammatory signaling and caspase-dependent myolysis. Hydroxychloroquine blocks TLR9 activation by mitochondrial DNA in vitro and may attenuate flares of rhabdomyolysis in 6 patients treated. We suggest a critical role for defective clearance of oxidized mitochondrial DNA that activates TLR9-restricted inflammation in lipin1-related rhabdomyolysis. Interventions blocking TLR9 activation or inflammation can improve patient care in vivo.

Lipin 1 deficiency causes adult-onset myasthenia with motor neuron dysfunction in humans and neuromuscular junction defects in zebrafish.

Lipin 1 is an intracellular protein acting as a phosphatidic acid phosphohydrolase enzyme controlling lipid metabolism. Human recessive mutations in LPIN1 cause recurrent, early-onset myoglobinuria, a condition normally associated with muscle pain and weakness. Whether and how lipin 1 deficiency in humans leads to peripheral neuropathy is yet unclear. Herein, two novel compound heterozygous mutations in LPIN1 with neurological disorders, but no myoglobinuria were identified in an adult-onset syndromic myasthenia family. The present study sought to explore the pathogenic mechanism of LPIN1 in muscular and neural development. Methods: The clinical diagnosis of the proband was compared to the known 48 cases of LPIN1 recessive homozygous mutations. Whole-exome sequencing was carried out on the syndromic myasthenia family to identify the causative gene. The pathogenesis of lipin 1 deficiency during somitogenesis and neurogenesis was investigated using the zebrafish model. Whole-mount in situ hybridization, immunohistochemistry, birefringence analysis, touch-evoke escape response and locomotion assays were performed to observe in vivo the changes in muscles and neurons. The conservatism of the molecular pathways regulated by lipin 1 was evaluated in human primary glioblastoma and mouse myoblast cells by siRNA knockdown, drug treatment, qRT-PCR and Western blotting analysis. Results: The patient exhibited adult-onset myasthenia accompanied by muscle fiber atrophy and nerve demyelination without myoglobinuria. Two novel heterozygous mutations, c.2047A>C (p.I683L) and c.2201G>A (p.R734Q) in LPIN1, were identified in the family and predicted to alter the tertiary structure of LPIN1 protein. Lipin 1 deficiency in zebrafish embryos generated by lpin1 morpholino knockdown or human LPIN1 mutant mRNA injections reproduced the myotomes defects, a reduction both in primary motor neurons and secondary motor neurons projections, morphological changes of post-synaptic clusters of acetylcholine receptors, and myelination defects, which led to reduced touch-evoked response and abnormalities of swimming behaviors. Loss of lipin 1 function in zebrafish and mammalian cells also exhibited altered expression levels of muscle and neuron markers, as well as abnormally enhanced Notch signaling, which was partially rescued by the specific Notch pathway inhibitor DAPT. Conclusions: These findings pointed out that the compound heterozygous mutations in human LPIN1 caused adult-onset syndromic myasthenia with peripheral neuropathy. Moreover, zebrafish could be used to model the neuromuscular phenotypes due to the lipin 1 deficiency, where a novel pathological role of over-activated Notch signaling was discovered and further confirmed in mammalian cell lines.

Loss of membrane integrity drives myofiber death in lipin1-deficient skeletal muscle.

Mutations in lipin1 are suggested to be a common cause of massive rhabdomyolysis episodes in children; however, the molecular mechanisms involved in the regulation of myofiber death caused by the absence of lipin1 are not fully understood. Loss of membrane integrity is considered as an effective inducer of cell death in muscular dystrophy. In this study, we utilized a mouse line with selective homozygous lipin1 deficiency in the skeletal muscle (Lipin1Myf5cKO ) to determine the role of compromised membrane integrity in the myofiber death in lipin1-deficient muscles. We found that Lipin1Myf5cKO muscles had significantly elevated proapoptotic factors (Bax, Bak, and cleaved caspase-9) and necroptotic proteins such as RIPK1, RIPK3, and MLKL compared with WT mice. Moreover, Lipin1Myf5cKO muscle had significantly higher membrane disruptions, as evidenced by increased IgG staining and elevated uptake of Evans Blue Dye (EBD) and increased serum creatine kinase activity in Lipin1Myf5cKO muscle fibers. EBD-positive fibers were strongly colocalized with apoptotic or necroptotic myofibers, suggesting an association between compromised plasma membrane integrity and cell death pathways. We further show that the absence of lipin1 leads to a significant decrease in the absolute and specific muscle force (normalized to muscle mass). Our work indicates that apoptosis and necroptosis are associated with a loss of membrane integrity in Lipin1Myf5cKO muscle and that myofiber death and dysfunction may cause a decrease in contractile force.

A rare case of adult onset LPIN1 associated rhabdomyolysis.

Pathogenic variants in LPIN1 are a recognised cause of severe and often fatal rhabdomyolysis in childhood. We present a rare case of adult onset recurrent rhabdomyolysis due to compound heterozygous variants in LPIN1. Despite first presenting with rhabdomyolysis in his twenties and having undergone extensive investigations, the patient did not receive a diagnosis until he was 46 years of age. DNA sequencing revealed a pathogenic deletion involving exon 18 of LPIN1 in conjunction with a c.2410G>A missense variant in exon 19. Whilst LPIN1 variants are a noteworthy cause of severe recurrent rhabdomyolysis in childhood, this is the first detailed description and only the second reported case of adult onset rhabdomyolysis. Variants in LPIN1 should be considered as a cause of recurrent severe rhabdomyolysis in adults when other more common causes have been excluded.

Lipin1 mediates cognitive impairment in fld mice via PKD-ERK pathway.

Lipin1 is important in lipid synthesis because of its phosphatidate phosphatase activity, and it also functions as transcriptional coactivators to regulate the expression of genes involved in lipid metabolism. We found that fld mice exhibit cognitive impairment, and it is related to the DAG-PKD-ERK pathway. We used fld mice to explore the relationship between lipin1 and cognitive function. Our results confirmed the presence of cognitive impairment in the hippocampus of lipin1-deficient mice. As shown in behavioral test, the spatial learning and memory ability of fld mice was much worse than that of wild-type mice. Electron microscopy results showed that the number of synapses in hippocampus of fld mice was significantly reduced. BDNF,SYP, PSD95 were significantly reduced. These results suggest that lipin1 impairs synaptic plasticity. Hence,a deficiency of lipin1 leads to decreased DAG levels and inhibits PKD activation, thereby affecting the phosphorylation of ERK and the CREB.

Fat oxidation is impaired during exercise in lipin-1 deficiency.

OBJECTIVE: To investigate substrate metabolism during exercise in an adult with lipin-1 deficiency, an inherited defect in lipid homeostasis, and to study the effect of glucose supplementation on his exercise tolerance. METHODS: We studied a 48-year-old man with lipin-1 deficiency and 2 healthy men. The patient has exercise intolerance and monthly episodes of rhabdomyolysis. All participants performed a submaximal exercise test while total fatty acid oxidation (FAO) and palmitate oxidation rate were assessed by stable isotope technique and indirect calorimetry. On another day, the patient was infused with 10% glucose (410 mL/h) and repeated the exercise. On the third and fourth visits, he was randomized in a double-blind manner to drink a supplement of glucose (soft drink 2% concentration) or placebo (soft drink: aspartame, acesulfame-K) before and during exercise. RESULTS: Mean FAO and palmitate oxidation rate during exercise were lower in the patient vs controls: 431 vs 1,271 and 1912 µmol/min and 122 vs 191 and 212 µmol/min. Plasma fatty acid concentration was lower in the patient during exercise than in controls: 477 vs 643 and 630 µmol/L. The patient's exercise duration increased from 36 to 60 minutes with IV glucose and 46 minutes with oral glucose, and his rating of exertion dropped from 15 to 9 on average (Borg scale). CONCLUSION: In this adult lipin-1-deficient patient, FAO was reduced, which was associated with no increase in plasma free fatty acids during submaximal exercise, and his exercise capacity improved with continuous ingestion of high-dose glucose. CLINICALTRIALSGOV IDENTIFIER: NCT02635269.

A Healthy Toddler With Fever and Lethargy.

A 21-month-old previously healthy girl presented to the emergency department initially with fever, rhinorrhea, and poor oral intake. She was subsequently discharged from the hospital on amoxicillin for treatment of acute otitis media but presented hours later on the same day with continued poor oral intake, decreased urine output, and lethargy. The patient was afebrile on examination without a focal source of infection or evidence of meningismus, but she was lethargic and minimally responsive to pain and had reduced strength in the upper and lower extremities. Initial laboratory analysis revealed leukocytosis with a neutrophil predominance and bandemia, hyponatremia, mild hyperkalemia, hyperglycemia, elevated transaminases, a mild metabolic acidosis, glucosuria, ketonuria, and hematuria. Follow-up tests, based on the history and results of the initial tests, were sent and led to a surprising diagnosis.

Phenotypic Modulation of Skeletal Muscle Fibers in LPIN1-Deficient Lipodystrophic ( fld) Mice.

Lipin-1 ( Lpin1)-deficient lipodystrophic mice have scant and immature adipocytes and develop transient fatty liver early in life. Unlike normal mice, these mice cannot rely on stored triglycerides to generate adenosine triphosphate (ATP) from the ß-oxidation of fatty acids during periods of fasting. To compensate, these mice store much higher amounts of glycogen in skeletal muscle and liver than wild-type mice in order to support energy needs during periods of fasting. Our studies demonstrated that there are phenotypic changes in skeletal muscle fibers that reflect an adaptation to this unique metabolic situation. The phenotype of skeletal muscle (soleus, gastrocnemius, plantaris, and extensor digitorum longus [EDL]) from Lpin1-/- was evaluated using various methods including immunohistochemistry for myosin heavy chains (Myh) 1, 2, 2a, 2b, and 2x; enzyme histochemistry for myosin ATPase, cytochrome-c oxidase (COX), and succinyl dehydrogenase (SDH); periodic acid-Schiff; and transmission electron microscopy. Fiber-type changes in the soleus muscle of Lpin1-/- mice were prominent and included decreased Myh1 expression with concomitant increases in Myh2 expression and myosin-ATPase activity; this change was associated with an increase in the presence of Myh1/2a or Myh1/2x hybrid fibers. Alterations in mitochondrial enzyme activity (COX and SDH) were apparent in the myofibers in the soleus, gastrocnemius, plantaris, and EDL muscles. Electron microscopy revealed increases in the subsarcolemmal mitochondrial mass in the muscles of Lpin1-/- mice. These data demonstrate that lipin-1 deficiency results in phenotypic fiber-specific modulation of skeletal muscle necessary for compensatory fuel utilization adaptations in lipodystrophy.

Volatile anesthesia for a child with LPIN1 gene mutation and recurrent rhabdomyolysis.

We report the case of a boy with LPIN1 gene mutation presenting for adenotonsillectomy who was successfully managed with preoperative saline and glucose infusion followed by balanced anesthesia including sevoflurane. The anesthetic planning is described as there is no modern literature to guide the perioperative management of these children.

Lipid phosphate phosphatase 3 regulates adipocyte sphingolipid synthesis, but not developmental adipogenesis or diet-induced obesity in mice.

Dephosphorylation of phosphatidic acid (PA) is the penultimate step in triglyceride synthesis. Adipocytes express soluble intracellular PA-specific phosphatases (Lipins) and broader specificity membrane-associated lipid phosphate phosphatases (LPPs) that can also dephosphorylate PA. Inactivation of lipin1 causes lipodystrophy in mice due to defective developmental adipogenesis. Triglyceride synthesis is diminished but not ablated by inactivation of lipin1 in differentiated adipocytes implicating other PA phosphatases in this process. To investigate the possible role of LPPs in adipocyte lipid metabolism and signaling we made mice with adipocyte-targeted inactivation of LPP3 encoded by the Plpp3(Ppap2b) gene. Adipocyte LPP3 deficiency resulted in blunted ceramide and sphingomyelin accumulation during diet-induced adipose tissue expansion, accumulation of the LPP3 substrate sphingosine 1- phosphate, and reduced expression of serine palmitoyl transferase. However, adiposity was unaffected by LPP3 deficiency on standard, high fat diet or Western diets, although Western diet-fed mice with adipocyte LPP3 deficiency exhibited improved glucose tolerance. Our results demonstrate functional compartmentalization of lipid phosphatase activity in adipocytes and identify an unexpected role for LPP3 in the regulation of diet-dependent sphingolipid synthesis that may impact on insulin signaling.

Cardiac function and exercise adaptation in 8 children with LPIN1 mutations.

INTRODUCTION: Lipin-1 deficiency is a major cause of rhabdomyolysis that are precipitated by febrile illness. The prognosis is poor, with one-third of patients dying from cardiac arrest during a crisis episode. Apart from acute rhabdomyolysis, most patients are healthy, showing normal clinical and cardiac ultrasound parameters. PATIENTS AND METHODS: We report cardiac and exercise examinations of 8 children carrying two LPIN1 mutations. The examinations were performed outside of a myolysis episode, but one patient presented with fever during one examination. RESULTS: All but one patient displayed normal resting cardiac function, as determined by echocardiography. One patient exhibited slight left ventricular dysfunction at rest and a lack of increased stroke volume during cycle ramp exercise. During exercise, peripheral muscle adaptation was impaired in 2 patients compared to healthy controls: they presented an abnormal increase in cardiac output relative to oxygen uptake: dQ/dVO2=8.2 and 9.5 (>2DS of controls population). One patient underwent 2 exercise tests; during one test, the patient was febrile, leading to acute rhabdomyolysis in the following hours. He exhibited changes in recovery muscle reoxygenation parameters and an increased dQ/dVO2 during exercise compared with that under normothermia (7.9 vs 6), which did not lead to acute rhabdomyolysis. The four patients assessed by cardiac 1H-magnetic resonance spectroscopy exhibited signs of intracardiac steatosis. CONCLUSION: We observed abnormal haemodynamic profiles during exercise in 3/8 patients with lipin-1 deficiency, suggesting impaired muscle oxidative phosphorylation during exercise. Fever appeared to be an aggravating factor. One patient exhibited moderate cardiac dysfunction, which was possibly related to intracardiac stored lipid toxicity.

Macrophage-Associated Lipin-1 Enzymatic Activity Contributes to Modified Low-Density Lipoprotein-Induced Proinflammatory Signaling and Atherosclerosis.

OBJECTIVE: Macrophage proinflammatory responses induced by modified low-density lipoproteins (modLDL) contribute to atherosclerotic progression. How modLDL causes macrophages to become proinflammatory is still enigmatic. Macrophage foam cell formation induced by modLDL requires glycerolipid synthesis. Lipin-1, a key enzyme in the glycerolipid synthesis pathway, contributes to modLDL-elicited macrophage proinflammatory responses in vitro. The objective of this study was to determine whether macrophage-associated lipin-1 contributes to atherogenesis and to assess its role in modLDL-mediated signaling in macrophages. APPROACH AND RESULTS: We developed mice lacking lipin-1 in myeloid-derived cells and used adeno-associated viral vector 8 expressing the gain-of-function mutation of mouse proprotein convertase subtilisin/kexin type 9 (adeno-associated viral vector 8-proprotein convertase subtilisin/kexin type 9) to induce hypercholesterolemia and plaque formation. Mice lacking myeloid-associated lipin-1 had reduced atherosclerotic burden compared with control mice despite similar plasma lipid levels. Stimulation of bone marrow-derived macrophages with modLDL activated a persistent protein kinase Cα/ßII-extracellular receptor kinase1/2-jun proto-oncogene signaling cascade that contributed to macrophage proinflammatory responses that was dependent on lipin-1 enzymatic activity. CONCLUSIONS: Our data demonstrate that macrophage-associated lipin-1 is atherogenic, likely through persistent activation of a protein kinase Cα/ßII-extracellular receptor kinase1/2-jun proto-oncogene signaling cascade that contributes to foam cell proinflammatory responses. Taken together, these results suggest that modLDL-induced foam cell formation and modLDL-induced macrophage proinflammatory responses are not independent consequences of modLDL stimulation but rather are both directly influenced by enhanced lipid synthesis.

Normal human adipose tissue functions and differentiation in patients with biallelic LPIN1 inactivating mutations.

Lipin-1 is a Mg2+-dependent phosphatidic acid phosphatase (PAP) that in mice is necessary for normal glycerolipid biosynthesis, controlling adipocyte metabolism, and adipogenic differentiation. Mice carrying inactivating mutations in the Lpin1 gene display the characteristic features of human familial lipodystrophy. Very little is known about the roles of lipin-1 in human adipocyte physiology. Apparently, fat distribution and weight is normal in humans carrying LPIN1 inactivating mutations, but a detailed analysis of adipose tissue appearance and functions in these patients has not been available so far. In this study, we performed a systematic histopathological, biochemical, and gene expression analysis of adipose tissue biopsies from human patients harboring LPIN1 biallelic inactivating mutations and affected by recurrent episodes of severe rhabdomyolysis. We also explored the adipogenic differentiation potential of human mesenchymal cell populations derived from lipin-1 defective patients. White adipose tissue from human LPIN1 mutant patients displayed a dramatic decrease in lipin-1 protein levels and PAP activity, with a concomitant moderate reduction of adipocyte size. Nevertheless, the adipose tissue develops without obvious histological signs of lipodystrophy and with normal qualitative composition of storage lipids. The increased expression of key adipogenic determinants such as SREBP1, PPARG, and PGC1A shows that specific compensatory phenomena can be activated in vivo in human adipocytes with deficiency of functional lipin-1.

Myeloid Cell-Specific Lipin-1 Deficiency Stimulates Endocrine Adiponectin-FGF15 Axis and Ameliorates Ethanol-Induced Liver Injury in Mice.

Lipin-1 is a phosphatidate phosphohydrolase (PAP) required for the generation of diacylglycerol during glycerolipid synthesis, and exhibits dual functions in the regulation of lipid metabolism. Lipin-1 has been implicated in the pathogenesis of alcoholic liver disease (ALD). In the present study, we assessed lipin-1 function in myeloid cells in ALD using a myeloid cell-specific lipin-1 knockout (mLipin-1KO) mouse model. Utilizing the Gao-binge ethanol feeding protocol, matched mLipin-1KO mice and littermate loxP control (WT) mice were pair-fed with either an ethanol-containing diet or an ethanol-free diet (control). Surprisingly, deletion of lipin-1 in myeloid cells dramatically attenuated liver inflammatory responses and ameliorated liver injury that would normally occur following the ethanol feeding protocol, but slightly exacerbated the ethanol-induced steatosis in mice. Mechanistically, myeloid cell-specific lipin-1 deficiency concomitantly increased the fat-derived adiponectin and ileum-derived fibroblast growth factor (FGF) 15. In concordance with concerted elevation of circulating adiponectin and FGF15, myeloid cell-specific lipin-1 deficiency diminished hepatic nuclear factor kappa B (NF-κB) activity, limited liver inflammatory responses, normalized serum levels of bile acids, and protected mice from liver damage after ethanol challenge. Our novel data demonstrate that myeloid cell-specific deletion of lipin-1 ameliorated inflammation and alcoholic hepatitis in mice via activation of endocrine adiponectin-FGF15 signaling.

Endothelial lipid phosphate phosphatase-3 deficiency that disrupts the endothelial barrier function is a modifier of cardiovascular development.

AIMS: Lipid phosphate phosphatase-3 (LPP3) is expressed at high levels in endothelial cells (ECs). Although LPP3 is known to hydrolyse the phosphate group from lysolipids such as spingosine-1-phosphate and its structural homologues, the function of Lpp3 in ECs is not completely understood. In this study, we investigated how tyrosine-protein kinase receptor (TEK or Tie2) promoter-dependent deletion of Lpp3 alters EC activities. METHODS AND RESULTS: Lpp3(fl/fl) mice were crossed with the tg.Tie2(Cre) transgenic line. Vasculogenesis occurred normally in embryos with Tie2(Cre)-mediated deletion of Lpp3 (called Lpp3(ECKO)), but embryonic lethality occurred in two waves, the first wave between E8.5 and E10.5, while the second between E11.5 and E13.5. Lethality in Lpp3(ECKO) embryos after E11.5 was accompanied by vascular leakage and haemorrhage, which likely resulted in insufficient cardiovascular development. Analyses of haematoxylin- and eosin-stained heart sections from E11.5 Lpp3(ECKO) embryos showed insufficient heart growth associated with decreased trabeculation, reduced growth of the compact wall, and absence of cardiac cushions. Staining followed by microscopic analyses of Lpp3(ECKO) embryos revealed the presence of apoptotic ECs. Furthermore, Lpp3-deficient ECs showed decreased gene expression and protein levels of Cyclin-D1, VE-cadherin, Fibronectin, Klf2, and Klf4. To determine the underlying mechanisms of vascular leakage and barrier disruption, we performed knockdown and rescue experiments in cultured ECs. LPP3 knockdown decreased transendothelial electrical resistance and increased permeability. Re-expression of ß-catenin cDNA in LPP3-knockdown ECs partially restored the effect of the LPP3 loss, whereas re-expression of p120ctn cDNA did not. CONCLUSION: These findings demonstrate the essential roles of LPP3 in the maturation of EC barrier integrity and normal cardiovascular development.

Lipin-1 expression is critical for keratinocyte differentiation.

Lipin-1 is an Mg(2+)-dependent phosphatidate phosphatase that facilitates the dephosphorylation of phosphatidic acid to generate diacylglycerol. Little is known about the expression and function of lipin-1 in normal human epidermal keratinocytes (NHEKs). Here, we demonstrate that lipin-1 is present in basal and spinous layers of the normal human epidermis, and lipin-1 expression is gradually downregulated during NHEK differentiation. Interestingly, lipin-1 knockdown (KD) inhibited keratinocyte differentiation and caused G1 arrest by upregulating p21 expression. Cell cycle arrest by p21 is required for commitment of keratinocytes to differentiation, but must be downregulated for the progress of keratinocyte differentiation. Therefore, reduced keratinocyte differentiation results from sustained upregulation of p21 by lipin-1 KD. Lipin-1 KD also decreased the phosphorylation/activation of protein kinase C (PKC)α, whereas lipin-1 overexpression increased PKCα phosphorylation. Treatment with PKCα inhibitors, like lipin-1 KD, stimulated p21 expression, while lipin-1 overexpression reduced p21 expression, implicating PKCα in lipin-1-induced regulation of p21 expression. Taken together, these results suggest that lipin-1-mediated downregulation of p21 is critical for the progress of keratinocyte differentiation after the initial commitment of keratinocytes to differentiation induced by p21, and that PKCα is involved in p21 expression regulation by lipin-1.

Liver-specific loss of lipin-1-mediated phosphatidic acid phosphatase activity does not mitigate intrahepatic TG accumulation in mice.

Lipin proteins (lipin 1, 2, and 3) regulate glycerolipid homeostasis by acting as phosphatidic acid phosphohydrolase (PAP) enzymes in the TG synthesis pathway and by regulating DNA-bound transcription factors to control gene transcription. Hepatic PAP activity could contribute to hepatic fat accumulation in response to physiological and pathophysiological stimuli. To examine the role of lipin 1 in regulating hepatic lipid metabolism, we generated mice that are deficient in lipin-1-encoded PAP activity in a liver-specific manner (Alb-Lpin1(-/-) mice). This allele of lipin 1 was still able to transcriptionally regulate the expression of its target genes encoding fatty acid oxidation enzymes, and the expression of these genes was not affected in Alb-Lpin1(-/-) mouse liver. Hepatic PAP activity was significantly reduced in mice with liver-specific lipin 1 deficiency. However, hepatocytes from Alb-Lpin1(-/-) mice had normal rates of TG synthesis, and steady-state hepatic TG levels were unaffected under fed and fasted conditions. Furthermore, Alb-Lpin1(-/-) mice were not protected from intrahepatic accumulation of diacylglycerol and TG after chronic feeding of a diet rich in fat and fructose. Collectively, these data demonstrate that marked deficits in hepatic PAP activity do not impair TG synthesis and accumulation under acute or chronic conditions of lipid overload.

Lipin-1 integrates lipid synthesis with proinflammatory responses during TLR activation in macrophages.

Lipin-1 is a Mg(2+)-dependent phosphatidic acid phosphatase involved in the de novo synthesis of phospholipids and triglycerides. Using macrophages from lipin-1-deficient animals and human macrophages deficient in the enzyme, we show in this work that this phosphatase acts as a proinflammatory mediator during TLR signaling and during the development of in vivo inflammatory processes. After TLR4 stimulation lipin-1-deficient macrophages showed a decreased production of diacylglycerol and activation of MAPKs and AP-1. Consequently, the generation of proinflammatory cytokines like IL-6, IL-12, IL-23, or enzymes like inducible NO synthase and cyclooxygenase 2, was reduced. In addition, animals lacking lipin-1 had a faster recovery from endotoxin administration concomitant with a reduced production of harmful molecules in spleen and liver. These findings demonstrate an unanticipated role for lipin-1 as a mediator of macrophage proinflammatory activation and support a critical link between lipid biosynthesis and systemic inflammatory responses.

Lipin-1 regulates autophagy clearance and intersects with statin drug effects in skeletal muscle.

LPIN1 encodes lipin-1, a phosphatidic acid phosphatase (PAP) enzyme that catalyzes the dephosphorylation of phosphatidic acid to form diacylglycerol. Homozygous LPIN1 gene mutations cause severe rhabdomyolysis, and heterozygous LPIN1 missense mutations may promote statin-induced myopathy. We demonstrate that lipin-1-related myopathy in the mouse is associated with a blockade in autophagic flux and accumulation of aberrant mitochondria. Lipin-1 PAP activity is required for maturation of autolysosomes, through its activation of the protein kinase D (PKD)-Vps34 phosphatidylinositol 3-kinase signaling cascade. Statin treatment also reduces PKD activation and autophagic flux, which are compounded by diminished mammalian target of rapamycin (mTOR) abundance in lipin-1-haploinsufficent and -deficient muscle. Lipin-1 restoration in skeletal muscle prevents myonecrosis and statin toxicity in vivo, and activated PKD rescues autophagic flux in lipin-1-deficient cells. Our findings identify lipin-1 PAP activity as a component of the macroautophagy pathway and define the basis for lipin-1-related myopathies.

Arguing the case for the autotaxin-lysophosphatidic acid-lipid phosphate phosphatase 3-signaling nexus in the development and complications of atherosclerosis.

The structurally simple glycero- and sphingo-phospholipids, lysophosphatidic acid (LPA) and sphingosine-1-phosphate, serve as important receptor-active mediators that influence blood and vascular cell function and are positioned to influence the events that contribute to the progression and complications of atherosclerosis. Growing evidence from preclinical animal models has implicated LPA, LPA receptors, and key enzymes involved in LPA metabolism in pathophysiologic events that may underlie atherosclerotic vascular disease. These observations are supported by genetic analysis in humans implicating a lipid phosphate phosphatase as a novel risk factor for coronary artery disease. In this review, we summarize current understanding of LPA production, metabolism, and signaling as may be relevant for atherosclerotic and other vascular disease.