Effects of follicle-stimulating hormone on energy balance and tissue metabolic health after loss of ovarian function.

Loss of ovarian function imparts increased susceptibility to obesity and metabolic disease. These effects are largely attributed to decreased estradiol (E2), but the role of increased follicle-stimulating hormone (FSH) in modulating energy balance has not been fully investigated. Previous work that blocked FSH binding to its receptor in mice suggested this hormone may play a part in modulating body weight and energy expenditure after ovariectomy (OVX). We used an alternate approach to isolate the individual and combined contributions of FSH and E2 in mediating energy imbalance and changes in tissue-level metabolic health. Female Wistar rats were ovariectomized and given the gonadotropin releasing hormone (GnRH) antagonist degarelix to suppress FSH production. E2 and FSH were then added back individually and in combination for a period of 3 wk. Energy balance, body mass composition, and transcriptomic profiles of individual tissues were obtained. In contrast to previous studies, suppression and replacement of FSH in our paradigm had no effect on body weight, body composition, food intake, or energy expenditure. We did, however, observe organ-specific effects of FSH that produced unique transcriptomic signatures of FSH in retroperitoneal white adipose tissue. These included reductions in biological processes related to lipogenesis and carbohydrate transport. In addition, rats administered FSH had reduced liver triglyceride concentration (P < 0.001), which correlated with FSH-induced changes at the transcriptomic level. Although not appearing to modulate energy balance after loss of ovarian function in rats, FSH may still impart tissue-specific effects in the liver and white adipose tissue that might affect the metabolic health of those organs.NEW & NOTEWORTHY We find no effect of follicle-stimulating hormone (FSH) on energy balance using a novel model in which rats are ovariectomized, subjected to gonadotropin-releasing hormone antagonism, and systematically given back FSH by osmotic pump. However, tissue-specific effects of FSH on adipose tissue and liver were observed in this study. These include unique transcriptomic signatures induced by the hormone and a stark reduction in hepatic triglyceride accumulation.

Estrogen-Related Receptor Agonism Reverses Mitochondrial Dysfunction and Inflammation in the Aging Kidney.

A gradual decline in renal function occurs even in healthy aging individuals. In addition to aging, per se, concurrent metabolic syndrome and hypertension, which are common in the aging population, can induce mitochondrial dysfunction and inflammation, which collectively contribute to age-related kidney dysfunction and disease. This study examined the role of the nuclear hormone receptors, the estrogen-related receptors (ERRs), in regulation of age-related mitochondrial dysfunction and inflammation. The ERRs were decreased in both aging human and mouse kidneys and were preserved in aging mice with lifelong caloric restriction (CR). A pan-ERR agonist, SLU-PP-332, was used to treat 21-month-old mice for 8 weeks. In addition, 21-month-old mice were treated with a stimulator of interferon genes (STING) inhibitor, C-176, for 3 weeks. Remarkably, similar to CR, an 8-week treatment with a pan-ERR agonist reversed the age-related increases in albuminuria, podocyte loss, mitochondrial dysfunction, and inflammatory cytokines, via the cyclic GMP-AMP synthase-STING and STAT3 signaling pathways. A 3-week treatment of 21-month-old mice with a STING inhibitor reversed the increases in inflammatory cytokines and the senescence marker, p21/cyclin dependent kinase inhibitor 1A (Cdkn1a), but also unexpectedly reversed the age-related decreases in PPARG coactivator (PGC)-1α, ERRα, mitochondrial complexes, and medium chain acyl coenzyme A dehydrogenase (MCAD) expression. These studies identified ERRs as CR mimetics and as important modulators of age-related mitochondrial dysfunction and inflammation. These findings highlight novel druggable pathways that can be further evaluated to prevent progression of age-related kidney disease.

HERV1-env Induces Unfolded Protein Response Activation in Autoimmune Liver Disease: A Potential Mechanism for Regulatory T Cell Dysfunction.

Regulatory T cells (Tregs) are not terminally differentiated but can acquire effector properties. Here we report an increased expression of human endogenous retrovirus 1 (HERV1-env) proteins in Tregs of patients with de novo autoimmune hepatitis and autoimmune hepatitis, which induces endoplasmic reticulum (ER) stress. HERV1-env-triggered ER stress activates all three branches (IRE1, ATF6, and PERK) of the unfolded protein response (UPR). Our coimmunoprecipitation studies show an interaction between HERV1-env proteins and the ATF6 branch of the UPR. The activated form of ATF6α activates the expression of RORC and STAT3 by binding to promoter sequences and induces IL-17A production. Silencing of HERV1-env results in recovery of Treg suppressive function. These findings identify ER stress and UPR activation as key factors driving Treg plasticity (species: human).

The role of FXR and TGR5 in reversing and preventing progression of Western diet-induced hepatic steatosis, inflammation, and fibrosis in mice.

Nonalcoholic steatohepatitis (NASH) is the most common chronic liver disease in the US, partly due to the increasing incidence of metabolic syndrome, obesity, and type 2 diabetes. The roles of bile acids and their receptors, such as the nuclear receptor farnesoid X receptor (FXR) and the G protein-coupled receptor TGR5, on the development of NASH are not fully clear. C57BL/6J male mice fed a Western diet (WD) develop characteristics of NASH, allowing determination of the effects of FXR and TGR5 agonists on this disease. Here we show that the FXR-TGR5 dual agonist INT-767 prevents progression of WD-induced hepatic steatosis, inflammation, and fibrosis, as determined by histological and biochemical assays and novel label-free microscopy imaging techniques, including third harmonic generation, second harmonic generation, and fluorescence lifetime imaging microscopy. Furthermore, we show INT-767 decreases liver fatty acid synthesis and fatty acid and cholesterol uptake, as well as liver inflammation. INT-767 markedly changed bile acid composition in the liver and intestine, leading to notable decreases in the hydrophobicity index of bile acids, known to limit cholesterol and lipid absorption. In addition, INT-767 upregulated expression of liver p-AMPK, SIRT1, PGC-1α, and SIRT3, which are master regulators of mitochondrial function. Finally, we found INT-767 treatment reduced WD-induced dysbiosis of gut microbiota. Interestingly, the effects of INT-767 in attenuating NASH were absent in FXR-null mice, but still present in TGR5-null mice. Our findings support treatment and prevention protocols with the dual FXR-TGR5 agonist INT-767 arrest progression of WD-induced NASH in mice mediated by FXR-dependent, TGR5-independent mechanisms.

Perilipin-2 promotes lipid droplet-plasma membrane interactions that facilitate apocrine lipid secretion in secretory epithelial cells of the mouse mammary gland.

Secretory epithelial cells (sMEC) in mammary glands of lactating animals secrete lipids by a novel apocrine mechanism in which cytoplasmic lipid droplets (LD) contact and are enveloped by elements of the apical plasma membrane (APM) before being released into the lumen of the gland as membrane bound structures. The molecular properties of LD-APM contacts and the mechanisms regulating LD membrane envelopment and secretion are not fully understood. Perilipin-2 (Plin2) is a constitutive LD protein that has been proposed to tether LD to the APM through formation of a complex with the transmembrane protein, butyrophilin1a1 (BTN) and the redox enzyme, xanthine oxidoreductase (XOR). Using mice lacking Plin2 and physiological inhibition of apocrine lipid secretion, we demonstrate that LD-APM contact and envelopment are mechanistically distinct steps that they are differentially regulated by Plin2 and independent of LD secretion. We find that Plin2 is not required for formation of LD-APM contacts. However, it increases the percentage of LD that contact the APM and mediates enlargement of the LD-APM contact zone as LD undergo membrane envelopment. The effects of Plin2 LD-APM interactions are associated with increased abundances of BTN, XOR and Cidea, which are implicated as mediators of LD-APM contact formation, on membranes surrounding secreted LD, and with promotion of glycocalyx remodeling at LD-APM contact sites. We propose that Plin2 does not directly mediate contact between LD and the APM but acts by enhancing molecular interactions that stabilize LD-APM contacts and govern membrane envelopment of LD during apocrine lipid secretion. Plin2 does not appear to significantly affect the lipid content of milk in fully lactating animals, but it does increase lipid secretion at the onset of lactation in primaparous dams, which suggest a role in facilitating apocrine lipid secretion in sMEC during their initial transition to a secretory phenotype.

Oral N-acetylcysteine decreases IFN-γ production and ameliorates ischemia-reperfusion injury in steatotic livers.

Type 1 Natural Killer T-cells (NKT1 cells) play a critical role in mediating hepatic ischemia-reperfusion injury (IRI). Although hepatic steatosis is a major risk factor for preservation type injury, how NKT cells impact this is understudied. Given NKT1 cell activation by phospholipid ligands recognized presented by CD1d, we hypothesized that NKT1 cells are key modulators of hepatic IRI because of the increased frequency of activating ligands in the setting of hepatic steatosis. We first demonstrate that IRI is exacerbated by a high-fat diet (HFD) in experimental murine models of warm partial ischemia. This is evident in the evaluation of ALT levels and Phasor-Fluorescence Lifetime (Phasor-FLIM) Imaging for glycolytic stress. Polychromatic flow cytometry identified pronounced increases in CD45+CD3+NK1.1+NKT1 cells in HFD fed mice when compared to mice fed a normal diet (ND). This observation is further extended to IRI, measuring ex vivo cytokine expression in the HFD and ND. Much higher interferon-gamma (IFN-γ) expression is noted in the HFD mice after IRI. We further tested our hypothesis by performing a lipidomic analysis of hepatic tissue and compared this to Phasor-FLIM imaging using "long lifetime species", a byproduct of lipid oxidation. There are higher levels of triacylglycerols and phospholipids in HFD mice. Since N-acetylcysteine (NAC) is able to limit hepatic steatosis, we tested how oral NAC supplementation in HFD mice impacted IRI. Interestingly, oral NAC supplementation in HFD mice results in improved hepatic enhancement using contrast-enhanced magnetic resonance imaging (MRI) compared to HFD control mice and normalization of glycolysis demonstrated by Phasor-FLIM imaging. This correlated with improved biochemical serum levels and a decrease in IFN-γ expression at a tissue level and from CD45+CD3+CD1d+ cells. Lipidomic evaluation of tissue in the HFD+NAC mice demonstrated a drastic decrease in triacylglycerol, suggesting downregulation of the PPAR-γ pathway.

Exploring Visceral and Subcutaneous Adipose Tissue Secretomes in Human Obesity: Implications for Metabolic Disease.

Adipose tissue secretions are depot-specific and vary based on anatomical location. Considerable attention has been focused on visceral (VAT) and subcutaneous (SAT) adipose tissue with regard to metabolic disease, yet our knowledge of the secretome from these depots is incomplete. We conducted a comprehensive analysis of VAT and SAT secretomes in the context of metabolic function. Conditioned media generated using SAT and VAT explants from individuals with obesity were analyzed using proteomics, mass spectrometry, and multiplex assays. Conditioned media were administered in vitro to rat hepatocytes and myotubes to assess the functional impact of adipose tissue signaling on insulin responsiveness. VAT secreted more cytokines (IL-12p70, IL-13, TNF-α, IL-6, and IL-8), adipokines (matrix metalloproteinase-1, PAI-1), and prostanoids (TBX2, PGE2) compared with SAT. Secretome proteomics revealed differences in immune/inflammatory response and extracellular matrix components. In vitro, VAT-conditioned media decreased hepatocyte and myotube insulin sensitivity, hepatocyte glucose handling, and increased basal activation of inflammatory signaling in myotubes compared with SAT. Depot-specific differences in adipose tissue secretome composition alter paracrine and endocrine signaling. The unique secretome of VAT has distinct and negative impact on hepatocyte and muscle insulin action.

Discovery of JND003 as a New Selective Estrogen-Related Receptor α Agonist Alleviating Nonalcoholic Fatty Liver Disease and Insulin Resistance.

Nonalcoholic fatty liver disease (NAFLD) is one of the most prevalent forms of chronic liver diseases and is causally linked to hepatic insulin resistance and reduced fatty acid oxidation. Therapeutic treatments targeting both hepatic insulin resistance and lipid oxidative metabolism are considered as feasible strategies to alleviate this disease. Emerging evidence suggests Estrogen-Related Receptor alpha (ERRα), the first orphan nuclear receptor identified, as a master regulator in energy homeostasis by controlling glucose and lipid metabolism. Small molecules improving the functions of ERRα may provide a new option for management of NAFLD. In the present study, by using liver-specific Errα knockout mouse (Errα-LKO), we showed that liver-specific deletion of ERRα exacerbated diet-evoked fatty liver, hepatic and systemic insulin resistance in mice. A potent and selective ERRα agonist JND003 (7) was also discovered. In vitro and in vivo investigation demonstrated that the compound enhanced the transactivation of ERRα downstream target genes, which was accompanied by improved insulin sensitivity and fatty liver symptoms. Furthermore, the therapeutic effects were completely abolished in Errα-LKO mice, indicative of its on-target efficacy. Our study thus suggests that hepatic ERRα is a viable target for NAFLD and that ERRα agonist may serve as an intriguing pharmacological option for management of metabolic diseases.

Hematopoietic Stem Cell-Derived Adipocytes Modulate Adipose Tissue Cellularity, Leptin Production and Insulin Responsiveness in Female Mice.

A subpopulation of adipocytes in the major adipose depots of mice is produced from hematopoietic stem cells rather than mesenchymal progenitors that are the source of conventional white and brown/beige adipocytes. To analyze the impact of hematopoietic stem cell-derived adipocytes (HSCDAs) in the adipose niche we transplanted HSCs in which expression of a diphtheria toxin gene was under the control of the adipocyte-specific adiponectin gene promoter into irradiated wild type recipients. Thus, only adipocytes produced from HSC would be ablated while conventional white and brown adipocytes produced from mesenchymal progenitor cells would be spared. Wild type mice transplanted with HSCs from mice containing a reporter gene, but not the diphtheria toxin gene, regulated by the adiponectin gene promoter served as controls. In mice in which HSCDA production was suppressed, adipocyte size declined while adipose depot weights were unchanged and the number of conventional adipocyte progenitors significantly increased. We also measured a paradoxical increase in circulating leptin levels while physical activity was significantly decreased in the HSCDA depleted mice. Finally, insulin sensitivity was significantly reduced in HSCDA depleted mice. In contrast, loss of HSCDA production had no effect on body weight, components of energy balance, or levels of several circulating adipokines and tissue-resident inflammatory cells. These data indicate that ablation of this low-abundance subpopulation of adipocytes is associated with changes in circulating leptin levels and leptin-regulated endpoints associated with adipose tissue function. How they do so remains a mystery, but our results highlight the need for additional studies to explore the role of HSCDAs in other physiologic contexts such as obesity, metabolic dysfunction or loss of sex hormone production.

Empagliflozin Treatment Attenuates Hepatic Steatosis by Promoting White Adipose Expansion in Obese TallyHo Mice.

Sodium-glucose co-transporters (SGLTs) serve to reabsorb glucose in the kidney. Recently, these transporters, mainly SGLT2, have emerged as new therapeutic targets for patients with diabetes and kidney disease; by inhibiting glucose reabsorption, they promote glycosuria, weight loss, and improve glucose tolerance. They have also been linked to cardiac protection and mitigation of liver injury. However, to date, the mechanism(s) by which SGLT2 inhibition promotes systemic improvements is not fully appreciated. Using an obese TallyHo mouse model which recapitulates the human condition of diabetes and nonalcoholic fatty liver disease (NAFLD), we sought to determine how modulation of renal glucose handling impacts liver structure and function. Apart from an attenuation of hyperglycemia, Empagliflozin was found to decrease circulating triglycerides and lipid accumulation in the liver in male TallyHo mice. This correlated with lowered hepatic cholesterol esters. Using in vivo MRI analysis, we further determined that the reduction in hepatic steatosis in male TallyHo mice was associated with an increase in nuchal white fat indicative of "healthy adipose expansion". Notably, this whitening of the adipose came at the expense of brown adipose tissue. Collectively, these data indicate that the modulation of renal glucose handling has systemic effects and may be useful as a treatment option for NAFLD and steatohepatitis.

Advances in fluorescence microscopy techniques to study kidney function.

Fluorescence microscopy, in particular immunofluorescence microscopy, has been used extensively for the assessment of kidney function and pathology for both research and diagnostic purposes. The development of confocal microscopy in the 1950s enabled imaging of live cells and intravital imaging of the kidney; however, confocal microscopy is limited by its maximal spatial resolution and depth. More recent advances in fluorescence microscopy techniques have enabled increasingly detailed assessment of kidney structure and provided extraordinary insights into kidney function. For example, nanoscale precise imaging by rapid beam oscillation (nSPIRO) is a super-resolution microscopy technique that was originally developed for functional imaging of kidney microvilli and enables detection of dynamic physiological events in the kidney. A variety of techniques such as fluorescence recovery after photobleaching (FRAP), fluorescence correlation spectroscopy (FCS) and Förster resonance energy transfer (FRET) enable assessment of interaction between proteins. The emergence of other super-resolution techniques, including super-resolution stimulated emission depletion (STED), photoactivated localization microscopy (PALM), stochastic optical reconstruction microscopy (STORM) and structured illumination microscopy (SIM), has enabled functional imaging of cellular and subcellular organelles at ≤50 nm resolution. The deep imaging via emission recovery (DIVER) detector allows deep, label-free and high-sensitivity imaging of second harmonics, enabling assessment of processes such as fibrosis, whereas fluorescence lifetime imaging microscopy (FLIM) enables assessment of metabolic processes.

Nuclear receptors in the kidney during health and disease.

Over the last 30 years, nuclear receptors (NRs) have been increasingly recognized as key modulators of systemic homeostasis and as contributing factors in many diseases. In the kidney, NRs play numerous important roles in maintaining homeostasis-many of which continue to be unraveled. As "master regulators", these important transcription factors integrate and coordinate many renal processes such as circadian responses, lipid metabolism, fatty acid oxidation, glucose handling, and inflammatory responses. The use of recently-developed genetic tools and small molecule modulators have allowed for detailed studies of how renal NRs contribute to kidney homeostasis. Importantly, while NRs are intimately involved in proper kidney function, they are also implicated in a variety of renal diseases such as diabetes, acute kidney injury, and other conditions such as aging. In the last 10 years, our understanding of renal disease etiology and progression has been greatly shaped by knowledge regarding how NRs are dysregulated in these conditions. Importantly, NRs have also become attractive therapeutic targets for attenuation of renal diseases, and their modulation for this purpose has been the subject of intense investigation. Here, we review the role in health and disease of six key renal NRs including the peroxisome proliferator-activated receptors (PPAR), estrogen-related receptors (ERR), the farnesoid X receptors (FXR), estrogen receptors (ER), liver X receptors (LXR), and vitamin D receptors (VDR) with an emphasis on recent findings over the last decade. These NRs have generated a wealth of data over the last 10 years that demonstrate their crucial role in maintaining normal renal homeostasis as well as their capacity to modulate disease progression.

Neuronal Lipoprotein Lipase Deficiency Alters Neuronal Function and Hepatic Metabolism.

The autonomic regulation of hepatic metabolism offers a novel target for the treatment of non-alcoholic fatty liver disease (NAFLD). However, the molecular characteristics of neurons that regulate the brain-liver axis remain unclear. Since mice lacking neuronal lipoprotein lipase (LPL) develop perturbations in neuronal lipid-sensing and systemic energy balance, we reasoned that LPL might be a component of pre-autonomic neurons involved in the regulation of hepatic metabolism. Here, we show that, despite obesity, mice with reduced neuronal LPL (NEXCreLPLflox (LPL KD)) show improved glucose tolerance and reduced hepatic lipid accumulation with aging compared to wilt type (WT) controls (LPLflox). To determine the effect of LPL deficiency on neuronal physiology, liver-related neurons were identified in the paraventricular nucleus (PVN) of the hypothalamus using the transsynaptic retrograde tracer PRV-152. Patch-clamp studies revealed reduced inhibitory post-synaptic currents in liver-related neurons of LPL KD mice. Fluorescence lifetime imaging microscopy (FLIM) was used to visualize metabolic changes in LPL-depleted neurons. Quantification of free vs. bound nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) revealed increased glucose utilization and TCA cycle flux in LPL-depleted neurons compared to controls. Global metabolomics from hypothalamic cell lines either deficient in or over-expressing LPL recapitulated these findings. Our data suggest that LPL is a novel feature of liver-related preautonomic neurons in the PVN. Moreover, LPL loss is sufficient to cause changes in neuronal substrate utilization and function, which may precede changes in hepatic metabolism.

Learning the ABCs of ATP release.

ATP plays important roles outside the cell, but the mechanism by which it is arrives in the extracellular environment is not clear. Dunn et al now show that decreases in cellular cholesterol levels mediated by the ABCG1 transporter increase ATP release by volume-regulated anion channels under hypotonic conditions. Importantly, these results may imply that cells that handle cholesterol differently might experience differential extracellular ATP release during hypotonicity.

Bile acid sequestration reverses liver injury and prevents progression of nonalcoholic steatohepatitis in Western diet-fed mice.

Nonalcoholic fatty liver disease is a rapidly rising problem in the 21st century and is a leading cause of chronic liver disease that can lead to end-stage liver diseases, including cirrhosis and hepatocellular cancer. Despite this rising epidemic, no pharmacological treatment has yet been established to treat this disease. The rapidly increasing prevalence of nonalcoholic fatty liver disease and its aggressive form, nonalcoholic steatohepatitis (NASH), requires novel therapeutic approaches to prevent disease progression. Alterations in microbiome dynamics and dysbiosis play an important role in liver disease and may represent targetable pathways to treat liver disorders. Improving microbiome properties or restoring normal bile acid metabolism may prevent or slow the progression of liver diseases such as NASH. Importantly, aberrant systemic circulation of bile acids can greatly disrupt metabolic homeostasis. Bile acid sequestrants are orally administered polymers that bind bile acids in the intestine, forming nonabsorbable complexes. Bile acid sequestrants interrupt intestinal reabsorption of bile acids, decreasing their circulating levels. We determined that treatment with the bile acid sequestrant sevelamer reversed the liver injury and prevented the progression of NASH, including steatosis, inflammation, and fibrosis in a Western diet-induced NASH mouse model. Metabolomics and microbiome analysis revealed that this beneficial effect is associated with changes in the microbiota population and bile acid composition, including reversing microbiota complexity in cecum by increasing Lactobacillus and decreased Desulfovibrio The net effect of these changes was improvement in liver function and markers of liver injury and the positive effects of reversal of insulin resistance.

Perilipin-2 promotes obesity and progressive fatty liver disease in mice through mechanistically distinct hepatocyte and extra-hepatocyte actions.

KEY POINTS: Wild-type mice and mice with hepatocyte-specific or whole-body deletions of perilipin-2 (Plin2) were used to define hepatocyte and extra-hepatocyte effects of altered cellular lipid storage on obesity and non-alcoholic fatty liver disease (NAFLD) pathophysiology in a Western-diet (WD) model of these disorders. Extra-hepatocyte actions of Plin2 are responsible for obesity, adipose inflammation and glucose clearance abnormalities in WD-fed mice. Hepatocyte and extra-hepatic actions of Plin2 mediate fatty liver formation in WD-fed mice through distinct mechanisms. Hepatocyte-specific actions of Plin2 are primary mediators of immune cell infiltration and fibrotic injury in livers of obese mice. ABSTRACT: Non-alcoholic fatty liver disease (NAFLD) is an obesity- and insulin resistance-related metabolic disorder with progressive pathology. Perilipin-2 (Plin2), a ubiquitously expressed cytoplasmic lipid droplet scaffolding protein, is hypothesized to contribute to NAFLD in humans and rodent models through effects on cellular lipid metabolism. In this study, we delineate hepatocyte-specific and extra-hepatocyte Plin2 mechanisms regulating the effects of obesity and insulin resistance on NAFLD pathophysiology in mice fed an obesogenic Western-style diet (WD). Total Plin2 deletion (Plin2-Null) fully protected WD-fed mice from obesity, insulin resistance, adipose inflammation, steatohepatitis (NASH) and liver fibrosis found in WT animals. Hepatocyte-specific Plin2 deletion (Plin2-HepKO) largely protected against NASH and fibrosis and partially protected against steatosis in WD-fed animals, but it did not protect against obesity, insulin resistance, or adipose inflammation. Significantly, total or hepatocyte-specific Plin2 deletion impaired WD-induced monocyte recruitment and pro-inflammatory macrophage polarization found in livers of WT mice. Analyses of the molecular and cellular processes mediating steatosis, inflammation and fibrosis identified differences in total and hepatocyte-specific actions of Plin2 on the mechanisms promoting NAFLD pathophysiology. Our results demonstrate that hepatocyte-specific actions of Plin2 are central to the initiation and pathological progression of NAFLD in obese and insulin-resistant mice through effects on immune cell recruitment and fibrogenesis. Conversely, extra-hepatocyte Plin2 actions promote NAFLD pathophysiology through effects on obesity, inflammation and insulin resistance. Our findings provide new insight into hepatocyte and extra-hepatocyte mechanisms underlying NAFLD development and progression.

Perilipin-2 deletion promotes carbohydrate-mediated browning of white adipose tissue at ambient temperature.

Mice lacking perilipin-2 (Plin2-null) are resistant to obesity, insulin resistance, and fatty liver induced by Western or high-fat diets. In the current study, we found that, compared with WT mice on Western diet, Plin2-null adipose tissue was more insulin sensitive and inguinal subcutaneous white adipose tissue (iWAT) exhibited profound browning and robust induction of thermogenic and carbohydrate-responsive genetic programs at room temperature. Surprisingly, these Plin2-null responses correlated with the content of simple carbohydrates, rather than fat, in the diet, and were independent of adipose Plin2 expression. To define Plin2 and sugar effects on adipose browning, WT and Plin2-null mice were placed on chow diets containing 20% sucrose in their drinking water for 6 weeks. Compared with WT mice, iWAT of Plin2-null mice exhibited pronounced browning and striking increases in the expression of thermogenic and insulin-responsive genes on this diet. Significantly, Plin2-null iWAT browning was associated with reduced sucrose intake and elevated serum fibroblast growth factor (FGF)21 levels, which correlated with greatly enhanced hepatic FGF21 production. These data identify Plin2 actions as novel mediators of sugar-induced adipose browning through indirect effects of hepatic FGF21 expression, and suggest that adipose browning mechanisms may contribute to Plin2-null resistance to obesity.

Maternal obesity during lactation may protect offspring from high fat diet-induced metabolic dysfunction.

BACKGROUND/OBJECTIVES: The current obesity epidemic has spurred exploration of the developmental origin of adult heath and disease. A mother's dietary choices and health can affect both the early wellbeing and lifelong disease-risk of the offspring. SUBJECTS/METHODS: To determine if changes in the mother's diet and adiposity have long-term effects on the baby's metabolism, independently from a prenatal insult, we utilized a mouse model of diet-induced-obesity and cross-fostering. All pups were born to lean dams fed a low fat diet but were fostered onto lean or obese dams fed a high fat diet. This study design allowed us to discern the effects of a poor diet from those of mother's adiposity and metabolism. The weaned offspring were placed on a high fat diet to test their metabolic function. RESULTS: In this feeding challenge, all male (but not female) offspring developed metabolic dysfunction. We saw increased weight gain in the pups nursed on an obesity-resistant dam fed a high fat diet, and increased pathogenesis including liver steatosis and adipose tissue inflammation, when compared to pups nursed on either obesity-prone dams on a high fat diet or lean dams on a low fat diet. CONCLUSION: Exposure to maternal over-nutrition, through the milk, is sufficient to shape offspring health outcomes in a sex- and organ-specific manner, and milk from a mother who is obesity-prone may partially protect the offspring from the insult of a poor diet.

Striated muscle gene therapy for the treatment of lipoprotein lipase deficiency.

Excessive circulating triglycerides due to reduction or loss of lipoprotein lipase activity contribute to hypertriglyceridemia and increased risk for pancreatitis. The only gene therapy treatment for lipoprotein lipase deficiency decreases pancreatitis but minimally reduces hypertriglyceridemia. Synthesized in multiple tissues including striated muscle and adipose tissue, lipoprotein lipase is trafficked to blood vessel endothelial cells where it is anchored at the plasma membrane and hydrolyzes triglycerides into free fatty acids. We conditionally knocked out lipoprotein lipase in differentiated striated muscle tissue lowering striated muscle lipoprotein lipase activity causing hypertriglyceridemia. We then crossed lipoprotein lipase striated muscle knockout mice with mice possessing a conditional avian retroviral receptor gene and injected mice with either a human lipoprotein lipase retrovirus or an mCherry control retrovirus. Post-heparin plasma lipoprotein lipase activity increased for three weeks following human lipoprotein lipase retroviral infection compared to mCherry infected mice. Human lipoprotein lipase infected mice had significantly lower blood triglycerides compared to mCherry controls and were comparable to wild-type blood triglyceride levels. Thus, targeted delivery of human lipoprotein lipase into striated muscle tissue identifies a potential therapeutic target for lipoprotein lipase deficiency.

Perilipin-2 Deletion Impairs Hepatic Lipid Accumulation by Interfering with Sterol Regulatory Element-binding Protein (SREBP) Activation and Altering the Hepatic Lipidome.

Perilipin-2 (PLIN2) is a constitutively associated cytoplasmic lipid droplet coat protein that has been implicated in fatty liver formation in non-alcoholic fatty liver disease. Mice with or without whole-body deletion of perilipin-2 (Plin2-null) were fed either Western or control diets for 30 weeks. Perilipin-2 deletion prevents obesity and insulin resistance in Western diet-fed mice and dramatically reduces hepatic triglyceride and cholesterol levels in mice fed Western or control diets. Gene and protein expression studies reveal that PLIN2 deletion suppressed SREBP-1 and SREBP-2 target genes involved in de novo lipogenesis and cholesterol biosynthetic pathways in livers of mice on either diet. GC-MS lipidomics demonstrate that this reduction correlated with profound alterations in the hepatic lipidome with significant reductions in both desaturation and elongation of hepatic neutral lipid species. To examine the possibility that lipidomic actions of PLIN2 deletion contribute to suppression of SREBP activation, we isolated endoplasmic reticulum membrane fractions from long-term Western diet-fed wild type (WT) and Plin2-null mice. Lipidomic analyses reveal that endoplasmic reticulum membranes from Plin2-null mice are markedly enriched in ω-3 and ω-6 long-chain polyunsaturated fatty acids, which others have shown inhibit SREBP activation and de novo lipogenesis. Our results identify PLIN2 as a determinant of global changes in the hepatic lipidome and suggest the hypothesis that these actions contribute to SREBP-regulated de novo lipogenesis involved in non-alcoholic fatty liver disease.