Extracellular glucose triggers metabolic reprogramming of cultured human bronchial epithelial cells and indirect fibroblast activation.

Glucose is essential for energy metabolism, and its usage can determine other cellular functions, depending on the cell type. In some pathological conditions, cells are exposed to high concentrations of glucose for extended periods. In this study, we investigated metabolic, oxidative stress, and cellular senescence pathways in human bronchial epithelial cells (HBECs) cultured in media with physiologically low (5 mm) and high (12.5 mm) glucose concentrations. HBECs exposed to 12.5 mm glucose showed increased glucose routing toward the pentose phosphate pathway, lactate synthesis, and glycogen, but not triglyceride synthesis. These metabolic shifts were not associated with changes in cell proliferation rates, oxidative stress, or cellular senescence pathways. Since hyperglycemia is associated with fibrosis in the lung, we asked whether HBECS could activate fibroblasts. Primary human lung fibroblasts cultured in media conditioned by 12.5 mm glucose-exposed HBECs showed a 1.3-fold increase in the gene expression of COL1A1 and COL1A2, along with twofold increased protein levels of smooth muscle cell actin and 2.4-fold of COL1A1. Consistently, HBECs cultured with 12.5 mm glucose secreted proteins associated with inflammation and fibrosis, such as interleukins IL-1ß, IL-10, and IL-13, CC chemokine ligands CCL2 and CCL24, and with extracellular matrix remodeling, such as metalloproteinases (MMP)-1, MMP-3, MMP-9, and MMP-13 and tissue inhibitors of MMPs (TIMP)-1 and -2. This study shows that HBECs undergo metabolic reprogramming and increase the secretion of profibrotic mediators following exposure to high concentrations of glucose, and it contributes to the understanding of the metabolic crosstalk of neighboring cells in diabetes-associated pulmonary fibrosis.

Type 1 diabetes contributes to combined pulmonary fibrosis and emphysema in male alpha 1 antitrypsin deficient mice.

Type 1 diabetes (T1D) is a metabolic disease characterized by hyperglycemia and can affect multiple organs, leading to life-threatening complications. Increased prevalence of pulmonary disease is observed in T1D patients, and diabetes is a leading cause of comorbidity in several lung pathologies. A deficiency of alpha-1 antitrypsin (AAT) can lead to the development of emphysema. Decreased AAT plasma concentrations and anti-protease activity are documented in T1D patients. The objective of this study was to determine whether T1D exacerbates the progression of lung damage in AAT deficiency. First, pulmonary function testing (PFT) and histopathological changes in the lungs of C57BL/6J streptozotocin (STZ)-induced T1D mice were investigated 3 and 6 months after the onset of hyperglycemia. PFT demonstrated a restrictive pulmonary pattern in the lungs of STZ-injected mice, along with upregulation of mRNA expression of pro-fibrotic markers Acta2, Ccn2, and Fn1. Increased collagen deposition was observed 6 months after the onset of hyperglycemia. To study the effect of T1D on the progression of lung damage in AAT deficiency background, C57BL/6J AAT knockout (KO) mice were used. Control and STZ-challenged AAT KO mice did not show significant changes in lung function 3 months after the onset of hyperglycemia. However, histological examination of the lung demonstrated increased collagen accumulation and alveolar space enlargement in STZ-induced AAT KO mice. AAT pretreatment on TGF-ß-stimulated primary lung fibroblasts reduced mRNA expression of pro-fibrotic markers ACTA2, CCN2, and FN1. Induction of T1D in AAT deficiency leads to a combined pulmonary fibrosis and emphysema (CPFE) phenotype in male mice.

Mechanisms Linking COPD to Type 1 and 2 Diabetes Mellitus: Is There a Relationship between Diabetes and COPD?

Chronic obstructive pulmonary disease (COPD) patients frequently suffer from multiple comorbidities, resulting in poor outcomes for these patients. Diabetes is observed at a higher frequency in COPD patients than in the general population. Both type 1 and 2 diabetes mellitus are associated with pulmonary complications, and similar therapeutic strategies are proposed to treat these conditions. Epidemiological studies and disease models have increased our knowledge of these clinical associations. Several recent genome-wide association studies have identified positive genetic correlations between lung function and obesity, possibly due to alterations in genes linked to cell proliferation; embryo, skeletal, and tissue development; and regulation of gene expression. These studies suggest that genetic predisposition, in addition to weight gain, can influence lung function. Cigarette smoke exposure can also influence the differential methylation of CpG sites in genes linked to diabetes and COPD, and smoke-related single nucleotide polymorphisms are associated with resting heart rate and coronary artery disease. Despite the vast literature on clinical disease association, little direct mechanistic evidence is currently available demonstrating that either disease influences the progression of the other, but common pharmacological approaches could slow the progression of these diseases. Here, we review the clinical and scientific literature to discuss whether mechanisms beyond preexisting conditions, lifestyle, and weight gain contribute to the development of COPD associated with diabetes. Specifically, we outline environmental and genetic confounders linked with these diseases.

LRP1 loss in airway epithelium exacerbates smoke-induced oxidative damage and airway remodeling.

The LDL receptor-related protein 1 (LRP1) partakes in metabolic and signaling events regulated in a tissue-specific manner. The function of LRP1 in airways has not been studied. We aimed to study the function of LRP1 in smoke-induced disease. We found that bronchial epithelium of patients with chronic obstructive pulmonary disease and airway epithelium of mice exposed to smoke had increased LRP1 expression. We then knocked out LRP1 in human bronchial epithelial cells in vitro and in airway epithelial club cells in mice. In vitro, LRP1 knockdown decreased cell migration and increased transforming growth factor ß activation. Tamoxifen-inducible airway-specific LRP1 knockout mice (club Lrp1-/-) induced after complete lung development had increased inflammation in the bronchoalveolar space and lung parenchyma at baseline. After 6 months of smoke exposure, club Lrp1-/- mice showed a combined restrictive and obstructive phenotype, with lower compliance, inspiratory capacity, and forced expiratory volume0.05/forced vital capacity than WT smoke-exposed mice. This was associated with increased values of Ashcroft fibrotic index. Proteomic analysis of room air exposed-club Lrp1-/- mice showed significantly decreased levels of proteins involved in cytoskeleton signaling and xenobiotic detoxification as well as decreased levels of glutathione. The proteome fingerprint created by smoke eclipsed many of the original differences, but club Lrp1-/- mice continued to have decreased lung glutathione levels and increased protein oxidative damage and airway cell proliferation. Therefore, LRP1 deficiency leads to greater lung inflammation and damage and exacerbates smoke-induced lung disease.

Therapeutic Potential of Alpha-1 Antitrypsin in Type 1 and Type 2 Diabetes Mellitus.

Alpha-1 antitrypsin (AAT) has established anti-inflammatory and immunomodulatory effects in chronic obstructive pulmonary disease but there is increasing evidence of its role in other inflammatory and immune-mediated conditions, like diabetes mellitus (DM). AAT activity is altered in both developing and established type 1 diabetes mellitus (T1DM) as well in established type 2 DM (T2DM). Augmentation therapy with AAT appears to favorably impact T1DM development in mice models and to affect ß-cell function and inflammation in humans with T1DM. The role of AAT in T2DM is less clear, but AAT activity appears to be reduced in T2DM. This article reviews these associations and emerging therapeutic strategies using AAT to treat DM.

Alveolar lipids in pulmonary disease. A review.

Lung lipid metabolism participates both in infant and adult pulmonary disease. The lung is composed by multiple cell types with specialized functions and coordinately acting to meet specific physiologic requirements. The alveoli are the niche of the most active lipid metabolic cell in the lung, the type 2 cell (T2C). T2C synthesize surfactant lipids that are an absolute requirement for respiration, including dipalmitoylphosphatidylcholine. After its synthesis and secretion into the alveoli, surfactant is recycled by the T2C or degraded by the alveolar macrophages (AM). Surfactant biosynthesis and recycling is tightly regulated, and dysregulation of this pathway occurs in many pulmonary disease processes. Alveolar lipids can participate in the development of pulmonary disease from their extracellular location in the lumen of the alveoli, and from their intracellular location in T2C or AM. External insults like smoke and pollution can disturb surfactant homeostasis and result in either surfactant insufficiency or accumulation. But disruption of surfactant homeostasis is also observed in many chronic adult diseases, including chronic obstructive pulmonary disease (COPD), and others. Sustained damage to the T2C is one of the postulated causes of idiopathic pulmonary fibrosis (IPF), and surfactant homeostasis is disrupted during fibrotic conditions. Similarly, surfactant homeostasis is impacted during acute respiratory distress syndrome (ARDS) and infections. Bioactive lipids like eicosanoids and sphingolipids also participate in chronic lung disease and in respiratory infections. We review the most recent knowledge on alveolar lipids and their essential metabolic and signaling functions during homeostasis and during some of the most commonly observed pulmonary diseases.

Decreased surfactant lipids correlate with lung function in chronic obstructive pulmonary disease (COPD).

Smoke exposure is known to decrease total pulmonary surfactant and alter its composition, but the role of surfactant in chronic obstructive pulmonary disease (COPD) remains unknown. We aimed to analyze the compositional changes in the surfactant lipidome in COPD and identify specific lipids associated with pulmonary function decline. Bronchoalveolar lavage (BAL) fluid was obtained from 12 former smokers with COPD and 5 non-smoking, non-asthmatic healthy control volunteers. Lipids were extracted and analyzed by liquid chromatography and mass spectrometry. Pulmonary function data were obtained by spirometry, and correlations of lung function with lipid species were determined. Wild-type C57BL/6 mice were exposed to 6 months of second-hand smoke in a full-body chamber. Surfactant lipids were decreased by 60% in subjects with COPD. All phospholipid classes were dramatically decreased, including ether phospholipids, which have not been studied in pulmonary surfactant. Availability of phospholipid, cholesterol, and sphingomyelin in BAL strongly correlated with pulmonary function and this was attributable to specific lipid species of phosphatidylcholine with surface tension reducing properties, and of phosphatidylglycerol with antimicrobial roles, as well as to other less studied lipid species. Mice exposed to smoke for six months recapitulated surfactant lipidomic changes observed in human subjects with COPD. In summary, we show that the surfactant lipidome is substantially altered in subjects with COPD, and decreased availability of phospholipids correlated with decreased pulmonary function. Further investigation of surfactant alterations in COPD would improve our understanding of its physiopathology and reveal new potential therapeutic targets.

Molecular and cellular insights into the role of SND1 in lipid metabolism.

Staphylococcal nuclease and Tudor domain containing 1 (SND1) is an evolutionarily conserved protein present in eukaryotic cells from protozoa to mammals. SND1 has gained importance because it is overexpressed in aggressive cancer cells and diverse primary tumors. Indeed, it is regarded as a marker of cancer malignity. A broad range of molecular functions and the participation in many cellular processes have been attributed to SND1, mostly related to the regulation of gene expression. An increasing body of evidence points to a relevant relationship between SND1 and lipid metabolism. In this review, we summarize the knowledge about SND1 and its molecular and functional relationship with lipid metabolism. We highlight that SND1 plays a direct role in the regulation of cholesterol metabolism by affecting the activation of sterol response element-binding protein 2 (SREBP2) and we propose that that might have implications in the response of lipid homeostasis to stress situations.

Lipoprotein Lipase Deficiency Impairs Bone Marrow Myelopoiesis and Reduces Circulating Monocyte Levels.

OBJECTIVE: Tissue macrophages induce and perpetuate proinflammatory responses, thereby promoting metabolic and cardiovascular disease. Lipoprotein lipase (LpL), the rate-limiting enzyme in blood triglyceride catabolism, is expressed by macrophages in atherosclerotic plaques. We questioned whether LpL, which is also expressed in the bone marrow (BM), affects circulating white blood cells and BM proliferation and modulates macrophage retention within the artery. APPROACH AND RESULTS: We characterized blood and tissue leukocytes and inflammatory molecules in transgenic LpL knockout mice rescued from lethal hypertriglyceridemia within 18 hours of life by muscle-specific LpL expression (MCKL0 mice). LpL-deficient mice had ≈40% reduction in blood white blood cell, neutrophils, and total and inflammatory monocytes (Ly6C/Ghi). LpL deficiency also significantly decreased expression of BM macrophage-associated markers (F4/80 and TNF-α [tumor necrosis factor α]), master transcription factors (PU.1 and C/EBPα), and colony-stimulating factors (CSFs) and their receptors, which are required for monocyte and monocyte precursor proliferation and differentiation. As a result, differentiation of macrophages from BM-derived monocyte progenitors and monocytes was decreased in MCKL0 mice. Furthermore, although LpL deficiency was associated with reduced BM uptake and accumulation of triglyceride-rich particles and macrophage CSF-macrophage CSF receptor binding, triglyceride lipolysis products (eg, linoleic acid) stimulated expression of macrophage CSF and macrophage CSF receptor in BM-derived macrophage precursor cells. Arterial macrophage numbers decreased after heparin-mediated LpL cell dissociation and by genetic knockout of arterial LpL. Reconstitution of LpL-expressing BM replenished aortic macrophage density. CONCLUSIONS: LpL regulates peripheral leukocyte levels and affects BM monocyte progenitor differentiation and aortic macrophage accumulation.

Chronic electronic cigarette exposure in mice induces features of COPD in a nicotine-dependent manner.

BACKGROUND: The use of electronic (e)-cigarettes is increasing rapidly, but their lung health effects are not established. Clinical studies examining the potential long-term impact of e-cigarette use on lung health will take decades. To address this gap in knowledge, this study investigated the effects of exposure to aerosolised nicotine-free and nicotine-containing e-cigarette fluid on mouse lungs and normal human airway epithelial cells. METHODS: Mice were exposed to aerosolised phosphate-buffered saline, nicotine-free or nicotine-containing e-cigarette solution, 1-hour daily for 4 months. Normal human bronchial epithelial (NHBE) cells cultured at an air-liquid interface were exposed to e-cigarette vapours or nicotine solutions using a Vitrocell smoke exposure robot. RESULTS: Inhalation of nicotine-containing e-cigarettes increased airway hyper-reactivity, distal airspace enlargement, mucin production, cytokine and protease expression. Exposure to nicotine-free e-cigarettes did not affect these lung parameters. NHBE cells exposed to nicotine-containing e-cigarette vapour showed impaired ciliary beat frequency, airway surface liquid volume, cystic fibrosis transmembrane regulator and ATP-stimulated K+ ion conductance and decreased expression of FOXJ1 and KCNMA1. Exposure of NHBE cells to nicotine for 5 days increased interleukin (IL)-6 and IL-8 secretion. CONCLUSIONS: Exposure to inhaled nicotine-containing e-cigarette fluids triggered effects normally associated with the development of COPD including cytokine expression, airway hyper-reactivity and lung tissue destruction. These effects were nicotine-dependent both in the mouse lung and in human airway cells, suggesting that inhaled nicotine contributes to airway and lung disease in addition to its addictive properties. Thus, these findings highlight the potential dangers of nicotine inhalation during e-cigarette use.

Synaptotagmin 11 interacts with components of the RNA-induced silencing complex RISC in clonal pancreatic ß-cells.

Synaptotagmins are two C2 domain-containing transmembrane proteins. The function of calcium-sensitive members in the regulation of post-Golgi traffic has been well established whereas little is known about the calcium-insensitive isoforms constituting half of the protein family. Novel binding partners of synaptotagmin 11 were identified in ß-cells. A number of them had been assigned previously to ER/Golgi derived-vesicles or linked to RNA synthesis, translation and processing. Whereas the C2A domain interacted with the Q-SNARE Vti1a, the C2B domain of syt11 interacted with the SND1, Ago2 and FMRP, components of the RNA-induced silencing complex (RISC). Binding to SND was direct via its N-terminal tandem repeats. Our data indicate that syt11 may provide a link between gene regulation by microRNAs and membrane traffic.

Cathepsin G degradation of phospholipid transfer protein (PLTP) augments pulmonary inflammation.

Phospholipid transfer protein (PLTP) regulates phospholipid transport in the circulation and is highly expressed within the lung epithelium, where it is secreted into the alveolar space. Since PLTP expression is increased in chronic obstructive pulmonary disease (COPD), this study aimed to determine how PLTP affects lung signaling and inflammation. Despite its increased expression, PLTP activity decreased by 80% in COPD bronchoalveolar lavage fluid (BALF) due to serine protease cleavage, primarily by cathepsin G. Likewise, PLTP BALF activity levels decreased by 20 and 40% in smoke-exposed mice and in the media of smoke-treated small airway epithelial (SAE) cells, respectively. To assess how PLTP affected inflammatory responses in a lung injury model, PLTP siRNA or recombinant protein was administered to the lungs of mice prior to LPS challenge. Silencing PLTP at baseline caused a 68% increase in inflammatory cell infiltration, a 120 and 340% increase in ERK and NF-κB activation, and increased MMP-9, IL1ß, and IFN-γ levels after LPS treatment by 39, 140, and 190%, respectively. Conversely, PLTP protein administration countered these effects in this model. Thus, these findings establish a novel anti-inflammatory function of PLTP in the lung and suggest that proteolytic cleavage of PLTP by cathepsin G may enhance the injurious inflammatory responses that occur in COPD.

STAT3 modulates cigarette smoke-induced inflammation and protease expression.

Signal transducer and activator of transcription-3 (STAT3) regulates inflammation, apoptosis, and protease expression, which are critical processes associated with airway injury and lung tissue destruction. However, the precise role of STAT3 in the development of airway diseases such as chronic obstructive pulmonary disease (COPD) has not been established. This study shows that cigarette smoke activates STAT3 in the lungs of mice. Since cigarette smoke activated STAT3 in the lung, we then evaluated how the loss of STAT3 would impact on smoke-mediated lung inflammation, protease expression, and apoptosis. STAT3(+/+) and STAT3(-/-) mice were exposed to 8 days of cigarette smoke. Compared to the STAT3(+/+) mice bronchoalveolar lavage fluid (BALF) cellularity was significantly elevated in the STAT3(-/-) mice both before and after cigarette smoke exposure, with the increase in cells primarily macrophages. In addition, smoke exposure induced significantly higher BALF protein levels of Interleukin-1α (IL-1α), and monocyte chemotactic protein-1 (MCP-1) and higher tissue expression of keratinocyte chemoattractant (KC) in the STAT3(-/-) mice. Lung mRNA expression of MMP-12 was increased in STAT3(-/-) at baseline. However, the smoke-induced increase in MMP-10 expression seen in the STAT3(+/+) mice was not observed in the STAT3(-/-) mice. Moreover, lung protein levels of the anti-inflammatory proteins SOCS3 and IL-10 were markedly lower in the STAT3(-/-) mice compared to the STAT3(+/+) mice. Lastly, apoptosis, as determined by caspase 3/7 activity assay, was increased in the STAT3(-/-) at baseline to levels comparable to those observed in the smoke-exposed STAT3(+/+) mice. Together, these results indicate that the smoke-mediated induction of lung STAT3 activity may play a critical role in maintaining normal lung homeostasis and function.

Involvement of lipid droplets in hepatic responses to lipopolysaccharide treatment in mice.

Infection and inflammation induce important changes in lipid metabolism, which result in increased free fatty acids and triacylglycerol in plasma and altered high density lipoprotein (HDL) metabolism. Our aim was to elucidate whether hepatic lipid droplets (LDs) are involved in the adaptations of lipid metabolism to endotoxemia. We characterized the lipid content and several enzymatic activities in subcellular fractions and subpopulations of LDs from livers of mice 24h after lipopolysaccharide (LPS) treatment and analyzed the expression of key genes involved in lipid management. Endotoxemic mice showed lower lipid content in LDs with decreased molar fraction of cholesteryl ester and higher diacylglycerol/triacylglycerol ratio as compared to their controls. They also showed a decrease in cytosolic triacylglycerol hydrolase activity, specifically in dense LDs, and in microsomal and cytosolic diacylglycerol hydrolase activity; concomitantly neutral lipid biosynthetic capacity and triacylglycerol levels in plasma lipoproteins increased. Together with the overexpression of genes involved in lipogenesis and HDL formation our results suggest that altered hepatic management of LD lipids in LPS-treated mice might be related to the channeled mobilization of triacylglycerol for very low density lipoprotein assembly and to the induction of cholesterol export.

Infection of primary hepatocytes with adenoviral vectors alters biliary lipid metabolism.

In the context of a study of the involvement of SND1 (also known as coactivator p100) in biliary lipid secretion by primary rat hepatocytes, first-generation adenoviral vectors were used to promote the overexpression and underexpression of the protein SND1. Although differential expression of SND1 did not result in significant changes in the processes studied, some effects of the adenoviral infection itself were observed. In particular, infected hepatocytes showed a higher intracellular taurocholate accumulation capacity. Additionally, small heterodimer partner (SHP) and farnesoid X receptor (FXR), which are nuclear receptors essential for the regulation of bile salt metabolism and transport, were underregulated at the mRNA level. Our results suggest that adenoviral vectors could be altering some important control mechanism and indicate that adenoviral vectors should be used with caution as transfection vectors for hepatocytes when biliary lipid metabolism is to be studied.

Adipose-specific lipoprotein lipase deficiency more profoundly affects brown than white fat biology.

Adipose fat storage is thought to require uptake of circulating triglyceride (TG)-derived fatty acids via lipoprotein lipase (LpL). To determine how LpL affects the biology of adipose tissue, we created adipose-specific LpL knock-out (ATLO) mice, and we compared them with whole body LpL knock-out mice rescued with muscle LpL expression (MCK/L0) and wild type (WT) mice. ATLO LpL mRNA and activity were reduced, respectively, 75 and 70% in gonadal adipose tissue (GAT), 90 and 80% in subcutaneous tissue, and 84 and 85% in brown adipose tissue (BAT). ATLO mice had increased plasma TG levels associated with reduced chylomicron TG uptake into BAT and lung. ATLO BAT, but not GAT, had altered TG composition. GAT from MCK/L0 was smaller and contained less polyunsaturated fatty acids in TG, although GAT from ATLO was normal unless LpL was overexpressed in muscle. High fat diet feeding led to less adipose in MCK/L0 mice but TG acyl composition in subcutaneous tissue and BAT reverted to that of WT. Therefore, adipocyte LpL in BAT modulates plasma lipoprotein clearance, and the greater metabolic activity of this depot makes its lipid composition more dependent on LpL-mediated uptake. Loss of adipose LpL reduces fat accumulation only if accompanied by greater LpL activity in muscle. These data support the role of LpL as the "gatekeeper" for tissue lipid distribution.

Lipid analysis reveals quiescent and regenerating liver-specific populations of lipid droplets.

The mammalian liver, a key organ in lipid homeostasis, can accumulate increased amounts of lipids in certain physiological conditions including liver regeneration. Lipid droplets (LD), the lipid storage organelles in the cytoplasm, are composed of a core of neutral lipids (mainly triacylglycerols and cholesteryl esters) surrounded by a monolayer of phospholipids and cholesterol with associated proteins. It is recognized that LD lipid composition is cell- and environment-specific and enables LD to carry out specific functions, but few descriptive studies aiming to interpret such differences have been published. We characterized eight density fractions of LD isolated from quiescent (control) and regenerating liver after partial hepatectomy, and grouped populations according to their lipid composition. LD from quiescent liver resembled the cholesteryl ester storage LD found in steroidogenic tissues, whereas in the regenerating tissue they were similar to adipocyte LD. Specifically, there were large, light LD with increased triacylglycerol content, the hallmark of liver regeneration. The apparent volume of the dense LD was, however, lower than in the quiescent density-matched populations, concomitant with increased phosphatidylcholine and phosphatidylethanolamine and decreased neutral lipid content. Analysis of the lipid profile of LD populations from quiescent and regenerating tissue leads us to define four physiological LD phenotypes for rat liver.

Age-related subproteomic analysis of mouse liver and kidney peroxisomes.

BACKGROUND: Despite major recent advances in the understanding of peroxisomal functions and how peroxisomes arise, only scant information is available regarding this organelle in cellular aging. The aim of this study was to characterize the changes in the protein expression profile of aged versus young liver and kidney peroxisome-enriched fractions from mouse and to suggest possible mechanisms underlying peroxisomal aging. Peroxisome-enriched fractions from 10 weeks, 18 months and 24 months C57bl/6J mice were analyzed by quantitative proteomics. RESULTS: Peroxisomal proteins were enriched by differential and density gradient centrifugation and proteins were separated by two-dimensional electrophoresis (2-DE), quantified and identified by mass spectrometry (MS). In total, sixty-five proteins were identified in both tissues. Among them, 14 proteins were differentially expressed in liver and 21 proteins in kidney. The eight proteins differentially expressed in both tissues were involved in beta-oxidation, alpha-oxidation, isoprenoid biosynthesis, amino acid metabolism, and stress response. Quantitative proteomics, clustering methods, and prediction of transcription factors, all indicated that there is a decline in protein expression at 18 months and a recovery at 24 months. CONCLUSION: These results indicate that some peroxisomal proteins show a tissue-specific functional response to aging. This response is probably dependent on their differential regeneration capacity. The differentially expressed proteins could lead several cellular effects: such as alteration of fatty acid metabolism that could alert membrane protein functions, increase of the oxidative stress and contribute to decline in bile salt synthesis. The ability to detect age-related variations in the peroxisomal proteome can help in the search for reliable and valid aging biomarkers.