Molecular regulation of PPARγ/RXRα signaling by the novel cofactor ZFP407.

Cofactors interacting with PPARγ can regulate adipogenesis and adipocyte metabolism by modulating the transcriptional activity and selectivity of PPARγ signaling. ZFP407 was previously demonstrated to regulate PPARγ target genes such as GLUT4, and its overexpression improved glucose homeostasis in mice. Here, using a series of molecular assays, including protein-interaction studies, mutagenesis, and ChIP-seq, ZFP407 was found to interact with the PPARγ/RXRα protein complex in the nucleus of adipocytes. Consistent with this observation, ZFP407 ChIP-seq peaks significantly overlapped with PPARγ ChIP-seq peaks, with more than half of ZFP407 peaks overlapping with PPARγ peaks. Transcription factor binding motifs enriched in these overlapping sites included CTCF, RARα/RXRγ, TP73, and ELK1, which regulate cellular development and function within adipocytes. Site-directed mutagenesis of frequent PPARγ phosphorylation or SUMOylation sites did not prevent its regulation by ZFP407, while mutagenesis of ZFP407 domains potentially necessary for RXR and PPARγ binding abrogated any impact of ZFP407 on PPARγ activity. These data suggest that ZFP407 controls the activity of PPARγ, but does so independently of post-translational modifications, likely by direct binding, establishing ZFP407 as a newly identified PPARγ cofactor. In addition, ZFP407 ChIP-seq analyses identified regions that did not overlap with PPARγ peaks. These non-overlapping peaks were significantly enriched for the transcription factor binding motifs of TBX19, PAX8, HSF4, and ZKSCAN3, which may contribute to the PPARγ-independent functions of ZFP407 in adipocytes and other cell types.

Cell-state dependent regulation of PPAR γ signaling by ZBTB9 in adipocytes.

Adipocytes play a critical role in metabolic homeostasis. Peroxisome proliferator-activated receptor- γ (PPAR γ ) is a nuclear hormone receptor that is a master regulator of adipocyte differentiation and function. ZBTB9 was predicted to interact with PPAR γ based on large-scale protein interaction experiments. In addition, GWAS studies in the type 2 diabetes (T2D) Knowledge Portal revealed associations between Z btb9 and both BMI and T2D risk. Here we show that ZBTB9 positively regulates PPAR γ activity in mature adipocytes. Surprisingly Z btb9 knockdown (KD) also increased adipogenesis in 3T3-L1 cells and human preadipocytes. E2F activity was increased and E2F downstream target genes were upregulated in Zbtb9 -KD preadipocytes. Accordingly, RB phosphorylation, which regulates E2F activity, was enhanced in Zbtb9 -KD preadipocytes. Critically, an E2F1 inhibitor blocked the effects of Zbtb9 deficiency on adipogenic gene expression and lipid accumulation. Collectively, these results demonstrate that Zbtb9 inhibits adipogenesis as a negative regulator of Pparg expression via altered RB-E2F1 signaling. Our findings reveal complex cell-state dependent roles of ZBTB9 in adipocytes, identifying a new molecule that regulates adipogenesis and adipocyte biology as both a positive and negative regulator of PPAR γ signaling depending on the cellular context, and thus may be important in the pathogenesis and treatment of obesity and T2D.

Adipocyte-specific deletion of zinc finger protein 407 results in lipodystrophy and insulin resistance in mice.

PPARγ deficiency in humans and model organisms impairs the transcriptional control of adipogenesis and mature adipocyte function resulting in lipodystrophy and insulin resistance. Zinc finger protein 407 (ZFP407) positively regulates PPARγ target gene expression and insulin-stimulated glucose uptake in cultured adipocytes. The in vivo physiological role of ZFP407 in mature adipocytes, however, remains to be elucidated. Here we generated adipocyte-specific ZFP407 knockout (AZKO) mice and discovered a partial lipodystrophic phenotype with reduced fat mass, hypertrophic adipocytes in inguinal and brown adipose tissue, and reduced adipogenic gene expression. The lipodystrophy was further exacerbated in AZKO mice fed a high-fat diet. Glucose and insulin tolerance tests revealed decreased insulin sensitivity in AZKO mice compared to control littermates. Cell-based assays demonstrated that ZFP407 is also required for adipogenesis, which may also contribute to the lipodystrophic phenotype. These results demonstrate an essential in vivo role of ZFP407 in brown and white adipose tissue formation and organismal insulin sensitivity.

Coordinated transcriptional control of adipocyte triglyceride lipase (Atgl) by transcription factors Sp1 and peroxisome proliferator-activated receptor γ (PPARγ) during adipocyte differentiation.

The breakdown of stored fat deposits into its components is a highly regulated process that maintains plasma levels of free fatty acids to supply energy to cells. Insulin-mediated transcription of Atgl, the enzyme that mediates the rate-limiting step in lipolysis, is a key point of this regulation. Under conditions such as obesity or insulin resistance, Atgl transcription is often misregulated, which can contribute to overall disease progression. The mechanisms by which Atgl is induced during adipogenesis are not fully understood. We utilized computational approaches to identify putative transcriptional regulatory elements in Atgl and then tested the effect of these elements and the transcription factors that bind to them in cultured preadipocytes and mature adipocytes. Here we report that Atgl is down-regulated by the basal transcription factor Sp1 in preadipocytes and that the magnitude of down-regulation depends on interactions between Sp1 and peroxisome proliferator-activated receptor γ (PPARγ). In mature adipocytes, when PPARγ is abundant, PPARγ abrogated transcriptional repression by Sp1 at the Atgl promoter and up-regulated Atgl mRNA expression. Targeting the PPARγ-Sp1 interaction could be a potential therapeutic strategy to restore insulin sensitivity by modulating Atgl levels in adipocytes.

Zinc finger protein 407 overexpression upregulates PPAR target gene expression and improves glucose homeostasis in mice.

The peroxisome proliferator-activated receptor (PPAR) family of nuclear receptors is central to the pathophysiology and treatment of metabolic disease through the receptors' ability to regulate the expression of genes involved in glucose homeostasis, adipogenesis, and lipid metabolism. However, the mechanism by which PPAR is regulated remains incompletely understood. We generated a transgenic mouse strain (ZFP-TG) that overexpressed Zfp407 primarily in muscle and heart. Transcriptome analysis by RNA-Seq identified 1,300 differentially expressed genes in the muscle of ZFP-TG mice, among which PPAR target genes were significantly enriched. Among the physiologically important PPARγ target genes, Glucose transporter (Glut)-4 mRNA and protein levels were increased in heart and muscle. The increase in Glut4 and other transcriptional effects of Zfp407 overexpression together decreased body weight and lowered plasma glucose, insulin, and HOMA-IR scores relative to control littermates. When placed on high-fat diet, ZFP-TG mice remained more glucose tolerant than their wild-type counterparts. Cell-based assays demonstrated that Zfp407 synergistically increased the transcriptional activity of all PPAR subtypes, PPARα, PPARγ, and PPARδ. The increased PPAR activity was not associated with increased PPAR mRNA or protein levels, suggesting that Zfp407 posttranslationally regulates PPAR activity. Collectively, these results demonstrate that Zfp407 overexpression improved glucose homeostasis. Thus, Zfp407 represents a new drug target for treating metabolic disease.

Suppression of fibrogenic signaling in hepatic stellate cells by Twist1-dependent microRNA-214 expression: Role of exosomes in horizontal transfer of Twist1.

A hallmark of liver fibrosis is the activation of hepatic stellate cells (HSC), which results in their production of fibrotic molecules, a process that is largely regulated by connective tissue growth factor (CCN2). CCN2 is increasingly expressed during HSC activation because of diminished expression of microRNA-214 (miR-214), a product of dynamin 3 opposite strand (DNM3os) that directly suppresses CCN2 mRNA. We show that an E-box in the miR-214 promoter binds the basic helix-loop-helix transcription factor, Twist1, which drives miR-214 expression and results in CCN2 suppression. Twist1 expression was suppressed in HSC of fibrotic livers or in cultured HSC undergoing activation in vitro or after treatment with ethanol. Furthermore, Twist1 decreasingly interacted with DNM3os as HSC underwent activation in vitro. Nanovesicular exosomes secreted by quiescent but not activated HSC contained high levels of Twist1, thus reflecting the suppression of cellular Twist1 during HSC activation. Exosomal Twist1 was intercellularly shuttled between HSC and stimulated expression of miR-214 in the recipient cells, causing expression of CCN2 and its downstream effectors to be suppressed. Additionally, the miR-214 E-box in HSC was also regulated by hepatocyte-derived exosomes, showing that functional transfer of exosomal Twist1 occurs between different cell types. Finally, the levels of Twist1, miR-214, or CCN2 in circulating exosomes from fibrotic mice reflected fibrosis-induced changes in the liver itself, highlighting the potential utility of these and other constituents in serum exosomes as novel circulating biomarkers for liver fibrosis. These findings reveal a unique function for cellular or exosomal Twist1 in CCN2-dependent fibrogenesis.

Zinc finger protein 407 (ZFP407) regulates insulin-stimulated glucose uptake and glucose transporter 4 (Glut4) mRNA.

The glucose transporter GLUT4 facilitates insulin-stimulated glucose uptake in peripheral tissues including adipose, muscle, and heart. GLUT4 function is impaired in obesity and type 2 diabetes leading to hyperglycemia and an increased risk of cardiovascular disease and neuropathy. To better understand the regulation of GLUT4 function, a targeted siRNA screen was performed and led to the discovery that ZFP407 regulates insulin-stimulated glucose uptake in adipocytes. The decrease in insulin-stimulated glucose uptake due to ZFP407 deficiency was attributed to a reduction in GLUT4 mRNA and protein levels. The decrease in GLUT4 was due to both decreased transcription of Glut4 mRNA and decreased efficiency of Glut4 pre-mRNA splicing. Interestingly, ZFP407 coordinately regulated this decrease in transcription with an increase in the stability of Glut4 mRNA, resulting in opposing effects on steady-state Glut4 mRNA levels. More broadly, transcriptome analysis revealed that ZFP407 regulates many peroxisome proliferator-activated receptor (PPAR) γ target genes beyond Glut4. ZFP407 was required for the PPARγ agonist rosiglitazone to increase Glut4 expression, but was not sufficient to increase expression of a PPARγ target gene reporter construct. However, ZFP407 and PPARγ co-overexpression synergistically activated a PPARγ reporter construct beyond the level of PPARγ alone. Thus, ZFP407 may represent a new modulator of the PPARγ signaling pathway.

Exosomes mediate intercellular transfer of pro-fibrogenic connective tissue growth factor (CCN2) between hepatic stellate cells, the principal fibrotic cells in the liver.

BACKGROUND: Fibrogenic pathways in the liver are principally regulated by hepatic stellate cells (HSC), which produce and respond to fibrotic mediators such as connective tissue growth factor (CCN2). The aim of this study was to determine whether CCN2 is shuttled between HSC in membranous nanovesicles, or "exosomes." METHODS: Exosomes were incubated with HSC after isolation from conditioned medium of control or CCN2-green fluorescent protein (GFP)-transfected primary mouse HSC or human LX-2 HSC. Some exosomes were stained fluorescently with PKH26. HSC co-culture experiments were performed in the presence of GW4869 exosome inhibitor. CCN2 or CCN2-GFP were evaluated by quantitative real-time polymerase chain reaction or Western blot. RESULTS: HSC-derived exosomes contained CCN2 or CCN2 mRNA, each of which increased in concentration during HSC activation or after transfection of HSC with CCN2-GFP. Exosomes, stained with either PKH26 or purified from CCN2-GFP-transfected cells, were taken up by activated or quiescent HSC resulting in CCN2-GFP delivery, as shown by their direct addition to recipient cells or by the GW4869-dependency of donor HSC. CONCLUSION: CCN2 is packaged into secreted, nano-sized exosomes that mediate its intercellular transfer between HSC. Exosomal CCN2 may amplify or fine tune fibrogenic signaling and, in conjunction with other exosome constituents, may have utility as a noninvasive biomarker to assess hepatic fibrosis.

Regulation of pancreatic inflammation by connective tissue growth factor (CTGF/CCN2).

Pancreatitis is caused by long-term heavy alcohol consumption, which results in injury and death of pancreatic acinar cells (PAC). The PAC play a pivotal role in mediating early inflammatory responses but the underlying mechanisms remain poorly understood. Treatment of C57BL/6 mice with ethanol and cerulein resulted in increased staining for acinar interleukin- 1b (IL-1b), chemokine (C-C motif) ligand 3 (CCL3), or connective tissue growth factor (CTGF/CCN2) by Day 16 and this was associated with increased infiltration of F4/80-positive macrophages and increased expression of pancreatic CTGF/CCN2 mRNA. Compared with wild-type Swiss Webster mice, ethanol treatment of pan-green fluorescent protein (GFP)-CTGF/CCN2 transgenic mice caused enhanced acinar staining for GFP or CTGF/CCN2 and a significant increase in pancreatic infiltration of F4/80-positive macrophages or NIMP-R14-positive neutrophils. Treatment of primary mouse PAC or the rat AR42J PAC line with ethanol or CTGF/CCN2 resulted in enhanced expression of IL-1b or CCL3. Conditioned medium from CTGF/CCN2-treated AR42J cells induced chemotaxis in NR8383 macrophages and this response was abrogated in a dose dependent manner by addition of BX471, an inhibitor of chemokine (C-C motif) receptor 1. These results reveal that acinar CTGF/CCN2 plays a novel role in alcohol-induced inflammatory processes in the pancreas by increasing infiltration of macrophages and neutrophils and increasing acinar production of inflammatory mediators such as IL-1b or CCL3. The early production of CTGF/CCN2 by PAC to drive inflammation is distinct from its previously reported production by pancreatic stellate cells to drive fibrosis at later stages of pancreatic injury.

Connective tissue growth factor (CCN2) and microRNA-21 are components of a positive feedback loop in pancreatic stellate cells (PSC) during chronic pancreatitis and are exported in PSC-derived exosomes.

Pancreatitis is an inflammatory condition of the pancreas which, in its chronic form, involves tissue destruction, exocrine and endocrine insufficiency, increased risk of pancreatic cancer, and an extensive fibrotic pathology which is due to unrelenting collagen deposition by pancreatic stellate cells (PSC). In response to noxious agents such as alcohol-excessive consumption of which is a major cause of pancreatitis in the West-normally quiescent PSC undergo a phenotypic and functional transition to activated myofibroblasts which produce and deposit collagen at high levels. This process is regulated by connective tissue growth factor (CCN2), expression of which is highly up-regulated in activated PSC. We show that CCN2 production by activated PSC is associated with enhanced expression of microRNA-21 (miR-21) which was detected at high levels in activated PSC in a murine model of alcoholic chronic pancreatitis. A positive feedback loop between CCN2 and miR-21 was identified that resulted in enhancement of their respective expression as well as that of collagen α1(I). Both miR-21 and CCN2 mRNA were present in PSC-derived exosomes, which were characterized as 50-150 nm CD9-positive nano-vesicles. Exosomes from CCN2-GFP- or miR-21-GFP-transfected PSC were taken up by other PSC cultures, as shown by direct fluorescence or qRT-PCR for GFP. Collectively these studies establish miR-21 and CCN2 as participants in a positive feedback loop during PSC activation and as components of the molecular payload in PSC-derived exosomes that can be delivered to other PSC. Thus interactions between cellular or exosomal miR-21 and CCN2 represent novel aspects of fibrogenic regulation in PSC. Summary Chronic injury in the pancreas is associated with fibrotic pathology which is driven in large part by CCN2-dependent collagen production in pancreatic stellate cells. This study shows that CCN2 up-regulation in PSC is associated with increased expression of miR-21 which, in turn, is able to stimulate CCN2 expression further via a positive feedback loop. Additionally miR-21 and CCN2 were identified in PSC-derived exosomes which effected their delivery to other PSC. The cellular and exosomal miR-21-CCN2 axis is a novel component in PSC fibrogenic signaling.

Epigenetic regulation of connective tissue growth factor by MicroRNA-214 delivery in exosomes from mouse or human hepatic stellate cells.

UNLABELLED: Connective tissue growth factor (CCN2) drives fibrogenesis in hepatic stellate cells (HSC). Here we show that CCN2 up-regulation in fibrotic or steatotic livers, or in culture-activated or ethanol-treated primary mouse HSC, is associated with a reciprocal down-regulation of microRNA-214 (miR-214). By using protector or reporter assays to investigate the 3'-untranslated region (UTR) of CCN2 mRNA, we found that induction of CCN2 expression in HSC by fibrosis-inducing stimuli was due to reduced expression of miR-214, which otherwise inhibited CCN2 expression by directly binding to the CCN2 3'-UTR. Additionally, miR-214 was present in HSC exosomes, which were bi-membrane vesicles, 50-150 nm in diameter, negatively charged (-26 mV), and positive for CD9. MiR-214 levels in exosomes but not in cell lysates were reduced by pretreatment of the cells with the exosome inhibitor, GW4869. Coculture of either quiescent HSC or miR-214-transfected activated HSC with CCN2 3'-UTR luciferase reporter-transfected recipient HSC resulted in miR-214- and exosome-dependent regulation of a wild-type CCN2 3'-UTR reporter but not of a mutant CCN2 3'-UTR reporter lacking the miR-214 binding site. Exosomes from HSC were a conduit for uptake of miR-214 by primary mouse hepatocytes. Down-regulation of CCN2 expression by miR-214 also occurred in human LX-2 HSC, consistent with a conserved miR-214 binding site in the human CCN2 3'-UTR. MiR-214 in LX-2 cells was shuttled by way of exosomes to recipient LX-2 cells or human HepG2 hepatocytes, resulting in suppression of CCN2 3'-UTR activity or expression of CCN2 downstream targets, including alpha smooth muscle actin or collagen. Experimental fibrosis in mice was associated with reduced circulating miR-214 levels. CONCLUSION: Exosomal transfer of miR-214 is a paradigm for the regulation of CCN2-dependent fibrogenesis and identifies fibrotic pathways as targets of intercellular regulation by exosomal miRs.

Regulation of pancreatic function by connective tissue growth factor (CTGF, CCN2).

Connective tissue growth factor (CTGF/CCN2) is a cysteine-rich matricellular secreted protein that regulates diverse cell functions including adhesion, migration, proliferation, differentiation, survival, senescence and apoptosis. In the pancreas, CTGF/CCN2 regulates critical functions including ß cell replication during embryogenesis, stimulation of fibrogenic pathways in pancreatic stellate cells during pancreatitis, and regulation of the epithelial and stromal components in pancreatic ductal adenocarcinoma. This article reviews the evidence establishing CTGF/CCN2 as an important player in pancreatic physiology and pathology, highlighting the specific cell types that are involved in each process and the importance of CTGF/CCN2 as a component of autocrine or paracrine signaling within or between these various cells. Translational applications, including the potential for CTGF/CCN2-based therapies in diabetes, fibrosis, or cancer, are discussed.

Ethanol-stimulated differentiated functions of human or mouse hepatic stellate cells are mediated by connective tissue growth factor.

BACKGROUND & AIMS: Connective tissue growth factor (CTGF) expression is intimately associated with hepatic fibrotic pathophysiology. In this study, CTGF production and action was investigated in ethanol-treated mouse primary hepatic stellate cells (HSC) or human LX-2 cells. METHODS: CTGF, transforming growth factor-beta1 (TGF-ß1), alpha-smooth muscle actin (α-SMA) or collagen α1(I) mRNA were quantified by real-time PCR after treatment of HSC with ethanol or acetaldehyde. CTGF protein production was assessed by immunoprecipitation or ELISA. Ethanol-stimulated CTGF transcription was investigated using CTGF promoter reporter constructs. The TGF-ß1- or CTGF-dependency of ethanol-induced CTGF, α-SMA, or collagen α1(I) was determined using small interfering RNA (siRNA) to TGF-ß1 or CTGF. RESULTS: In human steatohepatitis, CTGF was produced by presumptive activated HSC. In cultured human or mouse HSC, production of CTGF, α-SMA and/or collagen was increased by ethanol treatment, an effect mimicked by acetaldehyde and blocked by 4-methylpyrazole (4-MP) or N-acetylcysteine (NAC). CTGF promoter activity was stimulated in a sustained fashion by ethanol or TGF-ß1. Mutation of the Smad site or basal control element (BCE-1) in the CTGF promoter caused a 5-fold reduction in ethanol-stimulated CTGF promoter activity. Administration of TGF-ß1 siRNA or CTGF siRNA significantly decreased ethanol- or acetaldehyde-stimulated mRNA or protein levels of CTGF, α-SMA or collagen I in LX-2 cells. In mouse HSC, TGF-ß1- or ethanol-stimulated CTGF, α-SMA or collagen I were significantly attenuated by CTGF siRNA. CONCLUSIONS: Ethanol-induced α-SMA or collagen α1(I) in HSC are mediated via TGF-ß-dependent CTGF production, highlighting potential therapeutic benefits of targeting CTGF in alcoholic liver disease.

Connective tissue growth factor production by activated pancreatic stellate cells in mouse alcoholic chronic pancreatitis.

Alcoholic chronic pancreatitis (ACP) is characterized by pancreatic necrosis, inflammation, and scarring, the latter of which is due to excessive collagen deposition by activated pancreatic stellate cells (PSC). The aim of this study was to establish a model of ACP in mice, a species that is usually resistant to the toxic effects of alcohol, and to identify the cell type(s) responsible for production of connective tissue growth factor (CTGF), a pro-fibrotic molecule. C57Bl/6 male mice received intraperitoneal ethanol injections for 3 weeks against a background of cerulein-induced acute pancreatitis. Peak blood alcohol levels remained consistently high in ethanol-treated mice as compared with control mice. In mice receiving ethanol plus cerulein, there was increased collagen deposition as compared with other treatment groups as well as increased frequency of alpha-smooth muscle actin and desmin-positive PSC, which also showed significantly enhanced CTGF protein production. Expression of mRNA for collagen alpha1(I), alpha-smooth muscle actin or CTGF were all increased and co-localized exclusively to activated PSC in ACP. Pancreatic expression of mRNA for key profibrotic markers were all increased in ACP. In conclusion, a mouse model of ACP has been developed that mimics key pathophysiological features of the disease in humans and which shows that activated PSC are the principal producers of collagen and CTGF. PSC-derived CTGF is thus a candidate therapeutic target in anti-fibrotic strategies for ACP.

Ethanol-mediated expression of connective tissue growth factor (CCN2) in mouse pancreatic stellate cells.

Activated pancreatic stellate cells (PSC) play a central role in the pathogenesis of pancreatic fibrosis, a common feature of chronic pancreatitis which is often caused by excessive alcohol consumption. In view of the central role of connective tissue growth factor (CCN2) in fibrosis, we investigated the mechanisms by which CCN2 is regulated in PSC following their exposure to ethanol or acetaldehyde. Primary cultures of PSC from Balb/c mice were treated with 0-50 mM ethanol or 0-200 microM acetaldehyde in the presence or absence of 4-methylpyrazole (4MP; an inhibitor of alcohol dehydrogenase), diallyl sulfide (DAS; an inhibitor of cytochrome P4502E1) or anti-oxidant catalase or vitamin D. CCN2 production, assessed by reverse-transcriptase polymerase chain reaction to measure CCN2 mRNA levels or by fluorescence activated cell sorting to assess CCN2 protein, was enhanced in a dose-dependent manner by ethanol or acetaldehyde. In the presence of 4MP, DAS, or the anti-oxidants vitamin D or catalase, there was a substantial decrease in the ability of ethanol to stimulate CCN2 mRNA expression and a concomitant decrease in CCN2-positive PSC. Accumulation of reactive oxygen species in PSC after exposure to ethanol was verified by loading the cells with dichlorofluorescin diacetate and showing that there was a stimulation of its oxidized fluorescent product, the latter of which was diminished in the presence of catalase or vitamin D. These results show the production of acetaldehyde and oxidant stress in mouse PSC are the cause of increased CCN2 mRNA and protein production after exposure of the cells to ethanol. The potential therapeutic effects of inhibitors of ethanol metabolism or anti-oxidants in alcoholic pancreatitis may arise in part through their ability to attenuate CCN2 production by PSC.

Innate and adaptive immune activation in the brain of MPS IIIB mouse model.

Mucopolysaccharidosis (MPS) IIIB is a lysosomal storage disease with severe neurological manifestations due to alpha-N-acetylglucosaminidase (NaGlu) deficiency. The mechanism of neuropathology in MPS IIIB is unclear. This study investigates the role of immune responses in neurological disease of MPS IIIB in mice. By means of gene expression microarrays and real-time quantitative reverse transcriptase-polymerase chain reaction, we demonstrated significant up-regulation of numerous immune-related genes in MPS IIIB mouse brain involving a broad range of immune cells and molecules, including T cells, B cells, microglia/macrophages, complement, major histocompatibility complex class I, immunoglobulin, Toll-like receptors, and molecules essential for antigen presentation. The significantly enlarged spleen and lymph nodes in MPS IIIB mice were due to an increase in splenocytes/lymphocytes, and functional assays indicated that the T cells were activated. An autoimmune component to the disease was further suggested by the presence of putative autoantigen or autoantigens in brain extracts that reacted specifically with serum IgG from MPS IIIB mice. We also demonstrated for the first time that immunosuppression with prednisolone alone can significantly slow the central nervous system disease progression. Our data indicate that immune responses contribute greatly to the neuropathology of MPS IIIB and should be considered as an adjunct treatment in future therapeutic developments for optimal therapeutic effect.