Dietary excess regulates absorption and surface of gut epithelium through intestinal PPARα.

Intestinal surface changes in size and function, but what propels these alterations and what are their metabolic consequences is unknown. Here we report that the food amount is a positive determinant of the gut surface area contributing to an increased absorptive function, reversible by reducing daily food. While several upregulated intestinal energetic pathways are dispensable, the intestinal PPARα is instead necessary for the genetic and environment overeating-induced increase of the gut absorptive capacity. In presence of dietary lipids, intestinal PPARα knock-out or its pharmacological antagonism suppress intestinal crypt expansion and shorten villi in mice and in human intestinal biopsies, diminishing the postprandial triglyceride transport and nutrient uptake. Intestinal PPARα ablation limits systemic lipid absorption and restricts lipid droplet expansion and PLIN2 levels, critical for droplet formation. This improves the lipid metabolism, and reduces body adiposity and liver steatosis, suggesting an alternative target for treating obesity.

NAAA inhibitor F96 attenuates BBB disruption and secondary injury after traumatic brain injury (TBI).

Traumatic brain injury (TBI) is a leading cause of death worldwide, for which there is currently no comprehensive treatment available. Preventing blood-brain barrier (BBB) disruption is crucial for TBI treatment. N-acylethanolamine acid amidase (NAAA)-regulated palmitoylethanolamide (PEA) signaling play an important role in the control of inflammation. However, the role of NAAA in BBB dysfunction following TBI remains unclear. In the present study, we found that TBI induces the increase of PEA levels in the injured cortex, which prevent the disruption of BBB after TBI. TBI also induces the infiltration of NAAA-contained neutrophils, increasing the contribution of NAAA to the PEA degradation. Neutrophil-derived NAAA weakens PEA/PPARα-mediated BBB protective effects after TBI, facilitates the accumulation of immune cells, leading to secondary expansion of tissue injury. Inactivation of NAAA increased PEA levels in injured site, prevents early BBB damage and improves secondary injury, thereby eliciting long-term functional improvements after TBI. This study identified a new role of NAAA in TBI, suggesting that NAAA is a new important target for BBB dysfunction related CNS diseases.

Fenofibrate reverses liver fibrosis in cholestatic mice induced by alpha-naphthylisothiocyanate.

Cholestatic liver fibrosis occurs in liver injuries accompanied by inflammation, which develops into cirrhosis if not effectively treated in early stage. The aim of the study is to explore the effect of fenofibrate on liver fibrosis in chronic cholestatic mice. In this study, wild-type (WT) and Pparα-null (KO) mice were dosed alpha-naphthylisothiocyanate (ANIT) diet to induce chronic cholestasis. Induced liver fibrosis was determined by pathological biomarkers. Then fenofibrate 25 mg/kg was orally administrated to mice twice/day for 14 days. Serum and liver samples were collected for analysis of biochemistry and fibrosis. In WT mice, cholestatic biomarkers were increased by 5-8-fold and the expression of tissue inhibitors of metalloproteinases 1 (TIMP-1), Monocyte chemoattractant protein 1 (MCP-1), Collagen protein I (Collagen I) was increased by more than 10-fold. Fenofibrate significantly downgraded the biochemical and fibrotic biomarkers. In Western blot analysis, levels of collagenI and alpha-smooth muscle actin (α-SMA) were strongly inhibited by fenofibrate. In KO mice, liver fibrosis was induced successfully, but no improvement after fenofibrate treatment was observed. These data showed low-dose fenofibrate reverses cholestatic liver fibrosis in WT mice but not in KO mice, suggesting the dependence of therapeutic action on peroxisome proliferator-activated receptor alpha (PPARα). The study offers an additional therapeutic strategy for cholestatic liver fibrosis in practice.

Adipose-Specific PPARα Knockout Mice Have Increased Lipogenesis by PASK-SREBP1 Signaling and a Polarity Shift to Inflammatory Macrophages in White Adipose Tissue.

The nuclear receptor PPARα is associated with reducing adiposity, especially in the liver, where it transactivates genes for ß-oxidation. Contrarily, the function of PPARα in extrahepatic tissues is less known. Therefore, we established the first adipose-specific PPARα knockout (PparaFatKO) mice to determine the signaling position of PPARα in adipose tissue expansion that occurs during the development of obesity. To assess the function of PPARα in adiposity, female and male mice were placed on a high-fat diet (HFD) or normal chow for 30 weeks. Only the male PparaFatKO animals had significantly more adiposity in the inguinal white adipose tissue (iWAT) and brown adipose tissue (BAT) with HFD, compared to control littermates. No changes in adiposity were observed in female mice compared to control littermates. In the males, the loss of PPARα signaling in adipocytes caused significantly higher cholesterol esters, activation of the transcription factor sterol regulatory element-binding protein-1 (SREBP-1), and a shift in macrophage polarity from M2 to M1 macrophages. We found that the loss of adipocyte PPARα caused significantly higher expression of the Per-Arnt-Sim kinase (PASK), a kinase that activates SREBP-1. The hyperactivity of the PASK-SREBP-1 axis significantly increased the lipogenesis proteins fatty acid synthase (FAS) and stearoyl-Coenzyme A desaturase 1 (SCD1) and raised the expression of genes for cholesterol metabolism (Scarb1, Abcg1, and Abca1). The loss of adipocyte PPARα increased Nos2 in the males, an M1 macrophage marker indicating that the population of macrophages had changed to proinflammatory. Our results demonstrate the first adipose-specific actions for PPARα in protecting against lipogenesis, inflammation, and cholesterol ester accumulation that leads to adipocyte tissue expansion in obesity.

Hepatocyte-specific deletion of Pparα promotes NAFLD in the context of obesity.

Peroxisome proliferator activated receptor α (PPARα) acts as a fatty acid sensor to orchestrate the transcription of genes coding for rate-limiting enzymes required for lipid oxidation in hepatocytes. Mice only lacking Pparα in hepatocytes spontaneously develop steatosis without obesity in aging. Steatosis can develop into non alcoholic steatohepatitis (NASH), which may progress to irreversible damage, such as fibrosis and hepatocarcinoma. While NASH appears as a major public health concern worldwide, it remains an unmet medical need. In the current study, we investigated the role of hepatocyte PPARα in a preclinical model of steatosis. For this, we used High Fat Diet (HFD) feeding as a model of obesity in C57BL/6 J male Wild-Type mice (WT), in whole-body Pparα- deficient mice (Pparα-/-) and in mice lacking Pparα only in hepatocytes (Pparαhep-/-). We provide evidence that Pparα deletion in hepatocytes promotes NAFLD and liver inflammation in mice fed a HFD. This enhanced NAFLD susceptibility occurs without development of glucose intolerance. Moreover, our data reveal that non-hepatocytic PPARα activity predominantly contributes to the metabolic response to HFD. Taken together, our data support hepatocyte PPARα as being essential to the prevention of NAFLD and that extra-hepatocyte PPARα activity contributes to whole-body lipid homeostasis.

Sleep profile during fasting in PPAR-alpha knockout mice.

Peroxisome proliferator-activated receptor alpha (PPARα) is a transcription factor that belongs to the nuclear receptor family and plays an important role in regulating gene expression associated with lipid metabolism. PPARα promotes hepatic fatty acid oxidation and ketogenesis in response to fasting. Because energy metabolism is known to affect sleep regulation, manipulations that change PPARα are likely to affect sleep and other physiological phenotypes. In this study, we examined the role of PPARα in sleep/wake regulation using PPARα knockout (KO) mice. Sleep, body temperature (BT), locomotor activity, arterial pressure (AP) and heart rate (HR) were recorded in KO mice and wild-type (WT) controls under ad libitum-fed conditions and 24-hour food deprivation (FD). KO and WT mice were identical in basal sleep amount, BT, mean AP and HR, although KO mice showed enhanced sleepiness (enhanced EEG slow-wave activity). In response to FD, KO mice showed a large drop in wakefulness and locomotor activity at the end of the dark phase, whereas WT mice did not. Similarly, AP and HR, which were suppressed by FD, decreased more in KO than in WT mice. Compared to WT mice, KO mice showed a reduced concentration of plasma ketone bodies and decreased mRNA expression of the ketogenic enzyme gene Hmgcs2 in the liver and brain under FD conditions. These results suggest that PPARα and/or lipid metabolism is involved in the maintenance of wakefulness and locomotor activity during fasting in mice.

Loss of hepatic PPARα promotes inflammation and serum hyperlipidemia in diet-induced obesity.

Agonists for PPARα are used clinically to reduce triglycerides and improve high-density lipoprotein (HDL) cholesterol levels in patients with hyperlipidemia. Whether the mechanism of PPARα activation to lower serum lipids occurs in the liver or other tissues is unknown. To determine the function of hepatic PPARα on lipid profiles in diet-induced obese mice, we placed hepatocyte-specific peroxisome proliferator-activated receptor-α (PPARα) knockout (PparaHepKO) and wild-type (Pparafl/fl) mice on high-fat diet (HFD) or normal fat diet (NFD) for 12 wk. There was no significant difference in weight gain, percent body fat mass, or percent body lean mass between the groups of mice in response to HFD or NFD. Interestingly, the PparaHepKO mice on HFD had worsened hepatic inflammation and a significant shift in the proinflammatory M1 macrophage population. These changes were associated with higher hepatic fat mass and decreased hepatic lean mass in the PparαHepKO on HFD but not in NFD as measured by Oil Red O and noninvasive EchoMRI analysis (31.1 ± 2.8 vs. 20.2 ± 1.5, 66.6 ± 2.5 vs. 76.4 ± 1.5%, P < 0.05). We did find that this was related to significantly reduced peroxisomal gene function and lower plasma ß-hydroxybutyrate in the PparaHepKO on HFD, indicative of reduced metabolism of fats in the liver. Together, these provoked higher plasma triglyceride and apolipoprotein B100 levels in the PparaHepKO mice compared with Pparafl/fl on HFD. These data indicate that hepatic PPARα functions to control inflammation and liver triglyceride accumulation that prevent hyperlipidemia.

Dietary Intake Regulates the Circulating Inflammatory Monocyte Pool.

Caloric restriction is known to improve inflammatory and autoimmune diseases. However, the mechanisms by which reduced caloric intake modulates inflammation are poorly understood. Here we show that short-term fasting reduced monocyte metabolic and inflammatory activity and drastically reduced the number of circulating monocytes. Regulation of peripheral monocyte numbers was dependent on dietary glucose and protein levels. Specifically, we found that activation of the low-energy sensor 5'-AMP-activated protein kinase (AMPK) in hepatocytes and suppression of systemic CCL2 production by peroxisome proliferator-activator receptor alpha (PPARα) reduced monocyte mobilization from the bone marrow. Importantly, we show that fasting improves chronic inflammatory diseases without compromising monocyte emergency mobilization during acute infectious inflammation and tissue repair. These results reveal that caloric intake and liver energy sensors dictate the blood and tissue immune tone and link dietary habits to inflammatory disease outcome.

Chronic oleoylethanolamide treatment attenuates diabetes-induced mice encephalopathy by triggering peroxisome proliferator-activated receptor alpha in the hippocampus.

Brain is a site of diabetic end-organ damage. Diabetes-associated cognitive dysfunction, referred as "diabetic encephalopathy" (DE) has been coined for the patients with type 2 diabetes mellitus showing decline in their cognitive function, especially weak episodic memory, cognitive inflexibility and poor psychomotor performance leading towards Alzheimer's disease. Current evidence supported that aberrant synapses, energy metabolism imbalance, advanced glycation end products (AGEs) accumulation and Tau hyperphosphorylation are associated with cognition deficits induced by diabetes. Oleoylethanolamide (OEA), an endogenous peroxisome proliferator-activated receptor alpha (PPARα) agonist, has anti-hyperlipidemia, anti-inflammatory and neuroprotective activities. However, the effect of OEA on DE is unknown. Therefore, we tested its influence against cognitive dysfunction in high fat diet and streptozotocin (HFD + STZ)-induced diabetic C57BL/6J and PPARα--/- mice using Morris water maze (MWM) test. Neuron staining, dementia markers and neuroplasticity in the hippocampus were assessed to evaluate the neuropathological changes. The results showed that chronic OEA treatment significantly lowered hyperglycemia, recovered cognitive performance, reduced dementia markers, and inhibited hippocampal neuron loss and neuroplasticity impairments in diabetic mice. In contrast, the changes in MWM performance and neuron loss were not observed in PPARα knockout mice via OEA administration. These results indicated that OEA may provide a potential alternative therapeutic for DE by activating PPARα signaling.

Intestinal PPARα Protects Against Colon Carcinogenesis via Regulation of Methyltransferases DNMT1 and PRMT6.

BACKGROUND & AIMS: Many genetic and environmental factors, including family history, dietary fat, and inflammation, increase risk for colon cancer development. Peroxisome proliferator-activated receptor alpha (PPARα) is a nuclear receptor that regulates systemic lipid homeostasis. We explored the role of intestinal PPARα in colon carcinogenesis. METHODS: Colon cancer was induced in mice with intestine-specific disruption of Ppara (PparaΔIE), Pparafl/fl (control), and mice with disruption of Ppara that express human PPARA (human PPARA transgenic mice), by administration of azoxymethane with or without dextran sulfate sodium (DSS). Colons were collected from mice and analyzed by immunoblots, quantitative polymerase chain reaction, and histopathology. Liquid chromatography coupled with mass spectrometry-based metabolomic analyses were performed on urine and colons. We used molecular biology and biochemical approaches to study mechanisms in mouse colons, primary intestinal epithelial cells, and colon cancer cell lines. Gene expression data and clinical features of patients with colorectal tumors were obtained from Oncomine, and human colorectal-tumor specimens and adjacent normal tissues were collected and analyzed by immunohistochemistry. RESULTS: Levels of Ppara messenger RNA were reduced in colon tumors from mice. PparaΔIE mice developed more and larger colon tumors than control mice following administration of azoxymethane, with or without DSS. Metabolomic analyses revealed increases in methylation-related metabolites in urine and colons from PparaΔIE mice, compared with control mice, following administration of azoxymethane, with or without DSS. Levels of DNA methyltransferase 1 (DNMT1) and protein arginine methyltransferase 6 (PRMT6) were increased in colon tumors from PparaΔIE mice, compared with colon tumors from control mice. Depletion of PPARα reduced the expression of retinoblastoma protein, resulting in increased expression of DNMT1 and PRMT6. DNMT1 and PRMT6 decreased expression of the tumor suppressor genes Cdkn1a (P21) and Cdkn1b (p27) via DNA methylation and histone H3R2 dimethylation-mediated repression of transcription, respectively. Fenofibrate protected human PPARA transgenic mice from azoxymethane and DSS-induced colon cancer. Human colon adenocarcinoma specimens had lower levels of PPARA and retinoblastoma protein and higher levels of DNMT1 and PRMT6 than normal colon tissues. CONCLUSIONS: Loss of PPARα from the intestine promotes colon carcinogenesis by increasing DNMT1-mediated methylation of P21 and PRMT6-mediated methylation of p27 in mice. Human colorectal tumors have lower levels of PPARA messenger RNA and protein than nontumor tissues. Agents that activate PPARα might be developed for chemoprevention or treatment of colon cancer.

PPARα contributes to protection against metabolic and inflammatory derangements associated with acute kidney injury in experimental sepsis.

Sepsis-associated acute kidney injury (AKI) is a significant problem in critically ill children and adults resulting in increased morbidity and mortality. Fundamental mechanisms contributing to sepsis-associated AKI are poorly understood. Previous research has demonstrated that peroxisome proliferator-activated receptor α (PPARα) expression is associated with reduced organ system failure in sepsis. Using an experimental model of polymicrobial sepsis, we demonstrate that mice deficient in PPARα have worse kidney function, which is likely related to reduced fatty acid oxidation and increased inflammation. Ultrastructural evaluation with electron microscopy reveals that the proximal convoluted tubule is specifically injured in septic PPARα deficient mice. In this experimental group, serum metabolomic analysis reveals unanticipated metabolic derangements in tryptophan-kynurenine-NAD+ and pantothenate pathways. We also show that a subgroup of children with sepsis whose genome-wide expression profiles are characterized by repression of the PPARα signaling pathway has increased incidence of severe AKI. These findings point toward interesting associations between sepsis-associated AKI and PPARα-driven fatty acid metabolism that merit further investigation.

Hepatic carboxylesterases are differentially regulated in PPARα-null mice treated with perfluorooctanoic acid.

Hepatic carboxylesterases (Ces) catalyze the metabolism of drugs, environmental toxicants, and endogenous lipids and are known to be regulated by multiple nuclear receptors. Perfluorooctanoic acid (PFOA) is a synthetic fluorochemical that has been associated with dyslipidemia in exposed populations. In liver, PFOA can activate nuclear receptors such as PPARα, and alter the metabolism and excretion of chemicals. Here, we sought to test the ability of PFOA to modulate Ces expression and activity in the presence and absence of the PPARα receptor. For this purpose, male C57BL/6 NCrl mice were administered PFOA (1 or 3 mg/kg, po, 7 days) and livers collected for assessment of Ces expression and activity. PFOA increased Ces1 and 2 protein and activity. Notably, PFOA increased Ces1d, 1e, 1f, 1 g, 2c, and 2e mRNAs between 1.5- and 2.5-fold, while it decreased Ces1c and 2b. Activation of PPARα by PFOA was confirmed by up-regulation of Cyp4a14 mRNA. In a separate study of PFOA-treated wild-type (WT) and PPARα-null mice, induction of Ces 1e and 1f mRNA and in turn, Ces1 protein, was PPARα-dependent. Interestingly, in PPARα-null mice, Ces1c, 1d, 1 g, 2a, 2b, and 2e mRNAs and Ces2 protein were up-regulated by PFOA which contributed to sustained up-regulation of Ces activity, although to a lower extent than observed in WT mice. Activation of the CAR and PXR receptors likely accounted for up-regulation of select Ces1 and 2 subtypes in PPARα-null mice. In conclusion, the environmental contaminant PFOA modulates the expression and function of hepatic Ces enzymes, in part through PPARα.

Cinnamic Acid Protects the Nigrostriatum in a Mouse Model of Parkinson's Disease via Peroxisome Proliferator-Activated Receptorα.

Parkinson's disease (PD) is the second most common devastating human neurodegenerative disorder and despite intense investigation, no effective therapy is available for PD. Cinnamic acid, a naturally occurring aromatic fatty acid of low toxicity, is a precursor for the synthesis of a huge number of plant substances. This study highlights the neuroprotective effect of cinnamic acid in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. Oral administration of cinnamic acid protected tyrosine hydroxylase (TH)-positive dopaminergic neurons in the substantia nigra pars compacta (SNpc) and TH fibers in the striatum of MPTP-insulted mice. Accordingly, oral cinnamic acid also normalized striatal neurotransmitters and improved locomotor activities in MPTP-intoxicated mice. While investigating mechanisms, we found that cinnamic acid induced the activation of peroxisome proliferator-activated receptor α (PPARα), but not PPARß, in primary mouse astrocytes. Cinnamic acid mediated protection of the nigrostriatal system and locomotor activities in WT and PPARß (-/-), but not PPARα (-/-) mice from MPTP intoxication suggests that cinnamic acid requires the involvement of PPARα in protecting dopaminergic neurons in this model of PD. This study delineates a new function of cinnamic acid in protecting dopaminergic neurons via PPARα that could be beneficial for PD.

Enhancement of fear learning in PPARα knockout mice.

Peroxisome proliferator-activated receptor alpha (PPARα) is a member of the nuclear receptor superfamily and regulates fatty acid oxidation. Although PPARα is expressed not only in the peripheral tissues but also in the brain, its role in higher brain function is unclear. In this study, we investigated the role of PPARα in the control of behavior, including memory/learning and mood change, using PPARα knockout (KO) mice. A significant difference between wild-type (WT) and KO mice was seen in the passive avoidance test, demonstrating that KO mice showed enhanced fear leaning. In the amygdala of KO mice, the levels of dopamine and its metabolites were increased, and the mRNA expression of dopamine degrading enzyme was decreased. When dopamine D1 receptor antagonist was administered, the enhanced fear learning observed in KO mice was attenuated. These results suggest that PPARα is involved in the regulation of emotional memory via the dopamine pathway in the amygdala.

Pparα deficiency inhibits the proliferation of neuronal and glial precursors in the zebrafish central nervous system.

BACKGROUND: Many molecules and signaling pathways involved in neural development play a role in neurodegenerative diseases and brain tumor progression. Peroxisome proliferator-activated receptor (PPAR) proteins regulate the differentiation of tissues and the progression of many diseases. However, the role of these proteins in neural development is unclear. RESULTS: We examined the function of Pparα in the neural development of zebrafish. Two duplicate paralogs for mammalian PPARA/Ppara, namely pparaa and pparab, are present in the zebrafish genome. Both pparaa and pparab are expressed in the developing central nervous system in zebrafish embryos. Inhibiting the function of Pparα by using either the PPARα/Pparα antagonist GW6471 or pparaa or pparab truncated constructs produced identical phenotypes, which were sufficient to reduce the proliferation of neuronal and glial precursor cells without affecting the formation of neural progenitors. CONCLUSIONS: We demonstrated that both Pparαa and Pparαb proteins are essential regulators of the proliferation of neuronal and glial precursors. This study provides a better understanding of the functions of PPARα/Pparα in neural development and further expands our knowledge of the potential role of PPARα/Pparα in neurological disorders and brain tumors. Developmental Dynamics 247:1264-1275, 2018. © 2018 Wiley Periodicals, Inc.

Ciliogenesis is reciprocally regulated by PPARA and NR1H4/FXR through controlling autophagy in vitro and in vivo.

The primary cilia are evolutionarily conserved microtubule-based cellular organelles that perceive metabolic status and thus link the sensory system to cellular signaling pathways. Therefore, ciliogenesis is thought to be tightly linked to autophagy, which is also regulated by nutrient-sensing transcription factors, such as PPARA (peroxisome proliferator activated receptor alpha) and NR1H4/FXR (nuclear receptor subfamily 1, group H, member 4). However, the relationship between these factors and ciliogenesis has not been clearly demonstrated. Here, we present direct evidence for the involvement of macroautophagic/autophagic regulators in controlling ciliogenesis. We showed that activation of PPARA facilitated ciliogenesis independently of cellular nutritional states. Importantly, PPARA-induced ciliogenesis was mediated by controlling autophagy, since either pharmacological or genetic inactivation of autophagy significantly repressed ciliogenesis. Moreover, we showed that pharmacological activator of autophagy, rapamycin, recovered repressed ciliogenesis in ppara-/- cells. Conversely, activation of NR1H4 repressed cilia formation, while knockdown of NR1H4 enhanced ciliogenesis by inducing autophagy. The reciprocal activities of PPARA and NR1H4 in regulating ciliogenesis were highlighted in a condition where de-repressed ciliogenesis by NR1H4 knockdown was further enhanced by PPARA activation. The in vivo roles of PPARA and NR1H4 in regulating ciliogenesis were examined in greater detail in ppara-/- mice. In response to starvation, ciliogenesis was facilitated in wild-type mice via enhanced autophagy in kidney, while ppara-/- mice displayed impaired autophagy and kidney damage resembling ciliopathy. Furthermore, an NR1H4 agonist exacerbated kidney damage associated with starvation in ppara-/- mice. These findings indicate a previously unknown role for PPARA and NR1H4 in regulating the autophagy-ciliogenesis axis in vivo.

Histamine-deficient mice do not respond to the antidepressant-like effects of oleoylethanolamide.

It has been suggested that the bioactive lipid mediator oleoylethanolamide (OEA), a potent agonist of the peroxisome proliferator-activated receptor-alpha (PPAR-α) possesses anti-depressant-like effects in several preclinical models. We recently demonstrated that several of OEA's behavioural actions require the integrity of the brain histaminergic system, and that an intact histaminergic neurotransmission is specifically required for selective serotonin re-uptake inhibitors to exert their anti-depressant-like effect. The purpose of our study was to test if OEA requires the integrity of the histaminergic neurotransmission to exert its antidepressant-like effects. Immobility time in the tail suspension test was measured to assess OEA's potential (10 mg/kg i.p.) as an antidepressant drug in histidine decarboxylase null (HDC-/-) mice and HDC+/+ littermates, as well as in PPAR-α+/+ and PPAR-α-/- mice. CREB phosphorylation was evaluated using Western blot analysis in hippocampal and cortical homogenates, as pCREB is considered partially responsible for the efficacy of antidepressants. Serotonin release from ventral hippocampi of HDC+/+ and HDC-/- mice was measured with in-vivo microdialysis, following OEA administration. OEA decreased immobility time and increased brain pCREB levels in HDC+/+ mice, whereas it was ineffective in HDC-/- mice. Comparable results were obtained in PPAR-α+/+ and PPAR-α-/- mice. Microdialysis revealed a dysregulation of serotonin release induced by OEA in HDC-/- mice. Our observations corroborate our hypothesis that brain histamine and signals transmitted by OEA interact to elaborate appropriate behaviours and may be the basis for the efficacy of OEA as an antidepressant-like compound.

HIV-1 Tat-induced diarrhea is improved by the PPARalpha agonist, palmitoylethanolamide, by suppressing the activation of enteric glia.

BACKGROUND: Diarrhea is a severe complication in HIV-1-infected patients with Trans-activator of transcription (HIV-1 Tat) protein being recognized as a major underlying cause. Beside its direct enterotoxic effects, Tat protein has been recently shown to affect enteric glial cell (EGC) activity. EGCs regulate intestinal inflammatory responses by secreting pro-inflammatory molecules; nonetheless, they might also release immune-regulatory factors, as palmytoilethanolamide (PEA), which exerts anti-inflammatory effects by activating PPARα receptors. We aimed at clarifying whether EGCs are involved in HIV-1 Tat-induced diarrhea and if PEA exerts antidiarrheal activity. METHODS: Diarrhea was induced by intracolonic administration of HIV-1 Tat protein in rats at day 1. PEA alone or in the presence of peroxisome proliferator-activated receptor (PPAR) antagonists was given intraperitoneally from day 2 to day 7. S100B, iNOS, NF-kappaB, TLR4 and GFAP expression were evaluated in submucosal plexi, while S100B and NO levels were measured in EGC submucosal plexi lysates, respectively. To verify whether PEA effects were PPARα-mediated, PPARα-/- mice were also used. After 7 days from diarrhea induction, endogenous PEA levels were measured in submucosal plexi homogenates deriving from rats and PPARα-/- mice. RESULTS: HIV-1 Tat protein induced rapid onset diarrhea alongside with a significant activation of EGCs. Tat administration significantly increased all hallmarks of neuroinflammation by triggering TLR4 and NF-kappaB activation and S100B and iNOS expression. Endogenous PEA levels were increased following HIV-1 Tat exposure in both wildtype and knockout animals. In PPARα-/- mice, PEA displayed no effects. In wildtype rats, PEA, via PPARα-dependent mechanism, resulted in a significant antidiarrheal activity in parallel with marked reduction of EGC-sustained neuroinflammation. CONCLUSIONS: EGCs mediate HIV-1 Tat-induced diarrhea by sustaining the intestinal neuroinflammatory response. These effects are regulated by PEA through a selective PPARα-dependent mechanism. PEA might be considered as an adjuvant therapy in HIV-1-induced diarrhea.

Impairment of PPARα and the Fatty Acid Oxidation Pathway Aggravates Renal Fibrosis during Aging.

Defects in the renal fatty acid oxidation (FAO) pathway have been implicated in the development of renal fibrosis. Although, compared with young kidneys, aged kidneys show significantly increased fibrosis with impaired kidney function, the mechanisms underlying the effects of aging on renal fibrosis have not been investigated. In this study, we investigated peroxisome proliferator-activated receptor α (PPARα) and the FAO pathway as regulators of age-associated renal fibrosis. The expression of PPARα and the FAO pathway-associated proteins significantly decreased with the accumulation of lipids in the renal tubular epithelial region during aging in rats. In particular, decreased PPARα protein expression associated with increased expression of PPARα-targeting microRNAs. Among the microRNAs with increased expression during aging, miR-21 efficiently decreased PPARα expression and impaired FAO when ectopically expressed in renal epithelial cells. In cells pretreated with oleic acid to induce lipid stress, miR-21 treatment further enhanced lipid accumulation. Furthermore, treatment with miR-21 significantly exacerbated the TGF-ß-induced fibroblast phenotype of epithelial cells. We verified the physiologic importance of our findings in a calorie restriction model. Calorie restriction rescued the impaired FAO pathway during aging and slowed fibrosis development. Finally, compared with kidneys of aged littermate controls, kidneys of aged PPARα-/- mice showed exaggerated lipid accumulation, with decreased activity of the FAO pathway and a severe fibrosis phenotype. Our results suggest that impaired renal PPARα signaling during aging aggravates renal fibrosis development, and targeting PPARα is useful for preventing age-associated CKD.

Effect of an acute moderate-exercise session on metabolic and inflammatory profile of PPAR-α knockout mice.

Peroxisome proliferator-activated receptors (PPARs) play a major role in metabolism and inflammatory control. Exercise can modulate PPAR expression in skeletal muscle, adipose tissue, and macrophages. Little is known about the effects of PPAR-α in metabolic profile and cytokine secretion after acute exercise in macrophages. In this context, the aim of this study was to understand the influence of PPAR-α on exercise-mediated immune metabolic parameters in peritoneal macrophages. Mice C57BL/6 (WT) and PPAR-α knockout (KO) were examined in non-exercising control (n = 4) or 24 hours after acute moderate exercise (n = 8). Metabolic parameters (glucose, non-esterified fatty acids, total cholesterol [TC], and triacylglycerol [TG]) were assessed in serum. Cytokine concentrations (IL-1ß, IL-6, IL-10, TNF-α, and MCP-1) were measured from peritoneal macrophages cultured or not with LPS (2.5 µg/mL) and Rosiglitazone (1 µM). Exercised KO mice exhibited low glucose concentration and higher TC and TG in serum. At baseline, no difference in cytokine production between the genotypes was observed. However, IL-1ß was significantly higher in KO mice after LPS stimulus. IL-6 and IL-1ß had increased concentrations in KO compared with WT, even after exercise. MCP-1 was not restored in exercised KO LPS group. Rosiglitazone was not able to reduce proinflammatory cytokine production in KO mice at baseline level or associated with exercise. Acute exercise did not alter mRNA expression in WT mice. CONCLUSION: PPAR-α seems to be needed for metabolic glucose homeostasis and anti-inflammatory effect of acute exercise. Its absence may induce over-expression of pro-inflammatory cytokines in LPS stimulus. Moreover, moderate exercise or PPAR-γ agonist did not reverse this response.