BACKGROUND:Alterations in circulating amino acid profiles have been observed in ischemic stroke patients; however, whether cerebral ischemia disrupts amino acid metabolism within brain tissue and whether this disruption contributes to cellular stress and cerebral injury remain unknown. This hypothesis-testing study investigates disrupted BCAA (branched-chain amino acid) catabolism as a key mechanism of ischemic brain damage and evaluates BCKDK (branched-chain α-keto acid dehydrogenase kinase) as a novel therapeutic target. METHODS:Mouse primary cortical neurons subjected to oxygen-glucose deprivation and brain tissue from a mouse acute ischemic stroke model were used as experimental systems. Untargeted metabolomics and metabolic flux analysis were used to characterize BCAA metabolism in both models. In vivo pharmacological inhibition or in vitro knockdown of BCKDK was performed using BT2 (3,6-dichlorobenzo[b]thiophene-2-carboxylic acid) treatment or RNA interference. Primary outcome variables included infarct volume, BCKDH (branched-chain α-keto acid dehydrogenase) enzyme activity, neuronal viability, and markers of energy metabolism and glutamate excitotoxicity. Between-group differences were evaluated using 1-way ANOVA; data are presented as mean ± SD with 95% CIs and corresponding P values. RESULTS:Metabolomics analysis of oxygen-glucose deprivation-exposed primary neurons revealed impaired BCAA catabolism and significant BCAA accumulation compared with normoxic controls. In ischemic mouse brain tissue, BCKDH activity was significantly suppressed, and BCKDK expression was markedly upregulated relative to sham-operated animals. Both pharmacological and genetic suppression of BCKDK substantially reduced cerebral ischemic injury, as evidenced by decreased infarct volume and improved neuronal survival (95% CI and P values per comparison). Mechanistically, ischemia-induced BCKDK expression via HIF-1α (hypoxia-inducible factor 1α)-mediated transcriptional activation, which inhibited BCAA conversion to tricarboxylic acid cycle substrates, thereby potentiating energy deficiency and glutamate excitotoxicity. CONCLUSIONS:These data identify BCKDK as a novel hypoxia-responsive factor whose upregulation drives disrupted BCAA catabolism as a key mechanism of ischemic neuronal injury. BCKDK represents a promising therapeutic target for cerebral ischemia, directly supported by both in vitro and in vivo experimental evidence presented here.

Introduction: Ischemic stroke is an acute metabolic and cerebrovascular disease that leads to high mortality and disability rate in the world. Database analysis in patients and rodents suggest Syndecan-4 (Sdc4) may play a potential role in ischemic stroke, but the underlying mechanisms remain unclear. As a kind of transmembrane core protein, Sdc4 may initiate intracellular signaling via either its protein core ectodomain or cytoplasmic domain. Therefore, it is of great significance to investigate the specific function of Sdc4 and its potential as a novel therapeutic target in ischemic stroke. Methods: The serum level of shed Sdc4 extracellular domain in patients with ischemic stroke and mice with transient middle cerebral artery occlusion (MCAO) was determined. Sdc4 global knockout mice (GKO) and their wildtype (WT) littermates were generated and subjected to MCAO to investigate whether Sdc4 deficiency alters functional outcome following ischemic stroke and its underlying mechanisms. Infarct volume, neurological deficits, neuroinflammation, and blood-brain barrier (BBB) integrity were assessed. Results: Shed Sdc4 level in the serum of both patients with ischemic stroke and mice with MCAO was decreased acutely at 24 hours after disease onset, while cerebral Sdc4 expression was significantly increased in the ipsilateral brain hemisphere of mice. Infiltrated macrophages were identified as the major cerebral source of Sdc4. Sdc4 deficiency reduced the infarct volume in mice subjected to MCAO, compared to that of the WT controls. Neurological deficit and neuroinflammation were also attenuated in Sdc4 GKO mice following MCAO. Furthermore, Sdc4 GKO mice showed an improved BBB integrity. Conclusions: These results reveal that altered serum and cerebral Sdc4 level are implicated in the pathogenesis of ischemic stroke. Genetic deletion of Sdc4 significantly prevents brain injury in mice at 24 hours following MCAO. Further investigation is warranted to explore underlying mechanisms of Sdc4 mediated brain injury in ischemic stroke.

Dysregulation of adipose tissue (AT) homeostasis in obesity contributes to metabolic stress and disorders. Here, we identified that Coiled-coil-helix-coiled-coil-helix domain containing 10 (Chchd10) is a novel regulator of AT remodeling upon excess energy intake. Chchd10 is significantly reduced in the white adipose tissue (WAT) of mice in response to high-fat diet (HFD) feeding. AT-Chchd10 deficiency accelerates adipogenesis predominantly in subcutaneous AT of mice to store excess energy in response to short-term HFD feeding while upregulates glutathione S-transferase A4 (GSTA4) to facilitate 4-HNE clearance mainly in visceral AT to prevent protein carbonylation-induced cell dysfunction after long-term HFD feeding. Hence, Chchd10 deficiency attenuates diet-induced obesity and related metabolic disorders in mice. Mechanistically, Chchd10 deficiency enhances adipogenesis and GSTA4 expression by activating TDP43/Raptor/p62/Keap1/NRF2 axis. Notably, the beneficial effect of Chchd10 deficiency is eliminated in hypertrophic adipocytes, where p62 is strikingly reduced. Collectively, Chchd10 is a metabolic sensor maintaining AT homeostasis, and the loss of p62 in adipose tissue under obese conditions impairs Chchd10-mediated AT remodeling.

The blood-brain barrier (BBB) is a critical interface that maintains the central nervous system homeostasis by controlling the exchange of substances between the blood and the brain. Disruption of the BBB plays a vital role in the development of neuroinflammation and neurological dysfunction in sepsis, but the mechanisms by which the BBB becomes disrupted during sepsis are not well understood. Here, we induced endotoxemia, a major type of sepsis, in mice by intraperitoneal injection of lipopolysaccharide (LPS). LPS acutely increased BBB permeability, activated microglia, and heightened inflammatory responses in brain endothelium and parenchyma. Concurrently, LPS or proinflammatory cytokines activated the NF-κB pathway, inhibiting Wnt/β-catenin signaling in brain endothelial cells in vitro and in vivo. Cell culture study revealed that NF-κB p65 directly interacted with β-catenin to suppress Wnt/β-catenin signaling. Pharmacological NF-κB pathway inhibition restored brain endothelial Wnt/β-catenin signaling activity and mitigated BBB disruption and neuroinflammation in septic mice. Furthermore, genetic or pharmacological activation of brain endothelial Wnt/β-catenin signaling substantially alleviated LPS-induced BBB leakage and neuroinflammation, while endothelial conditional ablation of the Wnt7a/7b co-receptor Gpr124 exacerbated the BBB leakage caused by LPS. Mechanistically, Wnt/β-catenin signaling activation rectified the reduced expression levels of tight junction protein ZO-1 and transcytosis suppressor Mfsd2a in brain endothelial cells of mice with endotoxemia, inhibiting both paracellular and transcellular permeability of the BBB. Our findings demonstrate that endotoxemia-associated systemic inflammation decreases endothelial Wnt/β-catenin signaling through activating NF-κB pathway, resulting in acute BBB disruption and neuroinflammation. Targeting the endothelial Wnt/β-catenin signaling may offer a promising therapeutic strategy for preserving BBB integrity and treating neurological dysfunction in sepsis.

Background and PurposeAdipocyte fatty acid-binding protein (A-FABP) exacerbates cerebral ischaemia injury by disrupting the blood-brain barrier (BBB) through inducing expression of MMP-9. Circulating A-FABP levels positively correlate with infarct size in stroke patients. We hypothesized that targeting circulating A-FABP by a neutralizing antibody would alleviate ischaemic stroke outcome.Experimental ApproachMonoclonal antibodies (mAbs) against A-FABP were generated using mouse hybridoma techniques. Binding affinities of a generated mAb named 6H2 towards various FABPs were determined using Biacore. Molecular docking studies were performed to characterize the 6H2-A-FABP complex structure and epitope. The therapeutic potential and safety of 6H2 were evaluated in mice with transient middle cerebral artery occlusion (MCAO) and healthy mice, respectively.Key ResultsReplenishment of recombinant A-FABP exaggerated the stroke outcome in A-FABP-deficient mice. 6H2 exhibited nanomolar to picomolar affinities to human and mouse A-FABP, respectively, with minimal cross-reactivities with heart and epidermal FABPs. 6H2 effectively neutralized JNK/c-Jun activation elicited by A-FABP and reduced MMP-9 production in macrophages. Molecular docking suggested that 6H2 interacts with the "lid" of the fatty acid binding pocket of A-FABP, thus likely hindering the binding of its substrates. In mice with transient MCAO, 6H2 significantly attenuated BBB disruption, cerebral oedema, infarction, neurological deficits, and decreased mortality associated with reduced cytokine and MMP-9 production. Chronic 6H2 treatment showed no obvious adverse effects in healthy mice.Conclusion and ImplicationsThese results establish circulating A-FABP as a viable therapeutic target for ischaemic stroke, and provide a highly promising antibody drug candidate with high affinity and specificity.

Type 1 diabetes (T1D) is a chronic disease characterized by self-destruction of insulin-producing pancreatic β cells by cytotoxic T cell activity. However, the pathogenic mechanism of T cell infiltration remains obscure. Recently, tissue-resident memory T (TRM) cells have been shown to contribute to cytotoxic T cell recruitment. TRM cells are found present in human pancreas and are suggested to modulate immune homeostasis. Here, the role of TRM cells in the development of T1D is investigated. The presence of TRM cells in pancreatic islets is observed in non-obese diabetic (NOD) mice before T1D onset. Mechanistically, elevated fatty acid-binding protein 4 (FABP4) potentiates the survival and alarming function of TRM cells by promoting fatty acid utilization and C-X-C motif chemokine 10 (CXCL10) secretion, respectively. In NOD mice, genetic deletion of FABP4 or depletion of TRM cells using CD69 neutralizing antibodies resulted in a similar reduction of pancreatic cytotoxic T cell recruitment, a delay in diabetic incidence, and a suppression of CXCL10 production. Thus, targeting FABP4 may represent a promising therapeutic strategy for T1D.

Reperfusion therapy is currently the most effective treatment for acute ischemic stroke, but often results in secondary brain injury. Adipocyte fatty acid-binding protein (A-FABP, FABP4, or aP2) was shown to critically mediate cerebral ischemia/reperfusion (I/R) injury by exacerbating blood-brain barrier (BBB) disruption. However, no A-FABP inhibitors have been approved for clinical use due to safety issues. Here, we identified the therapeutic effect of levofloxacin, a widely used antibiotic displaying A-FABP inhibitory activity in vitro, on cerebral I/R injury and determined its target specificity and action mechanism in vivo. Using molecular docking and site-directed mutagenesis, we showed that levofloxacin inhibited A-FABP activity through interacting with the amino acid residue Asp76, Gln95, Arg126 of A-FABP. Accordingly, levofloxacin significantly inhibited A-FABP-induced JNK phosphorylation and expressions of proinflammatory factors and matrix metalloproteinase 9 (MMP-9) in mouse primary macrophages. In wild-type mice with transient middle cerebral artery occlusion, levofloxacin substantially mitigated BBB disruption and neuroinflammation, leading to reduced cerebral infarction, alleviated neurological outcomes, and improved survival. Mechanistically, levofloxacin decreased MMP-9 expression and activity, and thus reduced degradation of extracellular matrix and endothelial tight junction proteins. Importantly, the BBB- and neuro-protective effects of levofloxacin were abolished in A-FABP or MMP-9 knockout mice, suggesting that the therapeutic effects of levofloxacin highly depended on specific targeting of the A-FABP-MMP-9 axis. Overall, our study demonstrates that levofloxacin alleviates A-FABP-induced BBB disruption and neural tissue injury following cerebral I/R, and unveils its therapeutic potential for the treatment of ischemic stroke.

Background. The COVID-19 pandemic caused by the SARS-CoV-2 virus has resulted in a global health crisis with significant morbidity and mortality. While effective vaccinations have been developed, drug treatments for the disease are still required, particularly for different stages of the disease and to combat evolving variants. Identifying reliable biomarkers and potential therapeutic targets for the different stages of COVID-19 is crucial. Methods. Mendelian randomization using the largest publicly available datasets was conducted to identify potential causal plasma proteins for severe COVID-19, hospitalized COVID-19, and SARS-CoV-2 infection. Independent, and strongly associated cis- or pan-pQTLs were used as instrumental variables for each protein. The FDR q-value was used to correct for multiple testing followed by sensitivity analyses, reverse MR and genetic colocalization to ensure the robustness of the results. Results. We identified proteins with strong evidence of causal association with different stages of COVID-19. Some of these proteins were identified previously, such as BGAT and BCAT2, but we also identified the novel proteins, such as KLC1, MRVI1, CACO2, and PCNP. Conclusion. These proteins provide valuable insights into the underlying mechanisms of COVID-19. The identification of these proteins offers new opportunities for developing potential therapeutic targets or biomarkers for the treatment and prevention of COVID-19.

Introduction: High baseline circulating thrombospondin-2 (TSP2) level was recently found to associate with both the development and progression of liver fibrosis in patients with co-existing nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes. Here, we investigated whether circulating TSP2 levels changed with improvement in liver fibrosis. Methods: Serum TSP2 levels were measured in all participants of the DISTINCTION study (NCT 03959501), a randomized 1:1 open-label intervention study, at baseline and after treatment with either 10mg dapagliflozin (N=30) or 100mg sitagliptin daily (N=30) for 24 weeks. Liver stiffness (LS) and controlled attenuation parameter (CAP) were measured using vibration-controlled transient elastography for evaluation of hepatic fibrosis and steatosis, respectively. Results: Among these 60 participants with similar clinical characteristics at baseline (mean HbA1c 8.9%, CAP 289 dB/m and LS 5.9 kPa), despite similar HbA1c lowering, treatment with dapagliflozin, but not sitagliptin, led to significant improvements in body weight (BW) (p=0.012), CAP (p=0.015) and LS (p=0.011) after 24 weeks. Serum TSP2 level significantly decreased from 3.07 to 2.90 ng/mL (p=0.012), whereas no significant change in TSP2 was observed with sitagliptin. In Pearson correlation analysis, change in serum TSP2 levels positively correlated with change in LS in the dapagliflozin group (r=0.388, p=0.034), but not with changes in BW, CAP or HbA1c after dapagliflozin treatment. Conclusion: Serum TSP2 level decreased with LS after dapagliflozin treatment, and was independent of improvements in BW, glycemic control and liver steatosis, further supporting the potential of serum TSP2 level as a novel liver fibrosis biomarker in type 2 diabetes. Disclosure J.H.C. Mak: None. H. Fong: None. Y. Wong: None. K.C. Tan: None. S. Lam: None. C. Lee: None.

Supplementary Figures 7-10, Table 1 from Adiponectin Modulates the Glycogen Synthase Kinase-3β/β-Catenin Signaling Pathway and Attenuates Mammary Tumorigenesis of MDA-MB-231 Cells in Nude Mice

Lymph nodes (LNs) are always embedded in the metabolically-active white adipose tissue (WAT), whereas their functional relationship remains obscure. Here, we identify fibroblastic reticular cells (FRCs) in inguinal LNs (iLNs) as a major source of IL-33 in mediating cold-induced beiging and thermogenesis of subcutaneous WAT (scWAT). Depletion of iLNs in male mice results in defective cold-induced beiging of scWAT. Mechanistically, cold-enhanced sympathetic outflow to iLNs activates β1- and β2-adrenergic receptor (AR) signaling in FRCs to facilitate IL-33 release into iLN-surrounding scWAT, where IL-33 activates type 2 immune response to potentiate biogenesis of beige adipocytes. Cold-induced beiging of scWAT is abrogated by selective ablation of IL-33 or β1- and β2-AR in FRCs, or sympathetic denervation of iLNs, whereas replenishment of IL-33 reverses the impaired cold-induced beiging in iLN-deficient mice. Taken together, our study uncovers an unexpected role of FRCs in iLNs in mediating neuro-immune interaction to maintain energy homeostasis.

Rapid upregulation of matrix metalloproteinase 9 (MMP-9) leads to blood-brain barrier (BBB) breakdown following stroke, but no MMP-9 inhibitors have been approved in clinic largely due to their low specificities and side effects. Here, we explored the therapeutic potential of a human IgG monoclonal antibody (mAb), L13, which was recently developed with exclusive neutralizing specificity to MMP-9, nanomolar potency, and biological function, using mouse stroke models and stroke patient samples. We found that L13 treatment at the onset of reperfusion following cerebral ischemia or after intracranial hemorrhage (ICH) significantly reduced brain tissue injury and improved the neurological outcomes of mice. Compared to control IgG, L13 substantially attenuated BBB breakdown in both types of stroke model by inhibiting MMP-9 activity-mediated degradations of basement membrane and endothelial tight junction proteins. Importantly, these BBB-protective and neuroprotective effects of L13 in wild-type mice were comparable to Mmp9 genetic deletion and fully abolished in Mmp9 knockout mice, highlighting the in vivo target specificity of L13. Meanwhile, ex vivo co-incubation with L13 significantly neutralized the enzymatic activities of human MMP-9 in the sera of ischemic and hemorrhagic stroke patients, or in the peri-hematoma brain tissues from hemorrhagic stroke patients. Overall, we demonstrated that MMP-9 exclusive neutralizing mAbs constitute a potential feasible therapeutic approach for both ischemic and hemorrhagic stroke.

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

BACKGROUND & AIMS: The prevalence of nonalcoholic fatty liver disease (NAFLD) has reached epidemic proportions globally as a result of the rapid increase in obesity. However, there is no Food and Drug Administration-approved pharmacotherapy available for NAFLD. This study investigated the role of autotaxin, a secreted enzyme that hydrolyzes lysophosphatidylcholine to produce lysophosphatidic acid (LPA), in the pathogenesis of NAFLD and to explore whether genetic or pharmacologic interventions targeting autotaxin ameliorate NAFLD. METHODS: The clinical association of autotaxin with the severity of NAFLD was analyzed in 125 liver biopsy-proven NAFLD patients. C57BL/6N mice or fibroblast growth factor 21 (FGF21)-null mice were fed a high-fat diet or a choline-deficient diet to investigate the role of the autotaxin-FGF21 axis in NAFLD development by hepatic knockdown and antibody neutralization. Huh7 cells were used to investigate the autocrine effects of autotaxin. RESULTS: Serum autotaxin levels were associated positively with histologic scores and NAFLD severity. Hepatocytes, but not adipocytes, were the major contributor to increased circulating autotaxin in both patients and mouse models with NAFLD. In mice, knocking-down hepatic autotaxin or treatment with a neutralizing antibody against autotaxin significantly reduced high-fat diet-induced NAFLD and high fat- and choline-deficient diet-induced nonalcoholic steatohepatitis and fibrosis, accompanied by a marked increase of serum FGF21. Mechanistically, autotaxin inhibited the transcriptional activity of peroxisome proliferator-activated receptor a through LPA-induced activation of extracellular signal-regulated kinas, thereby leading to suppression of hepatic FGF21 production. The therapeutic benefit of anti-autotaxin neutralizing antibody against NAFLD was abrogated in FGF21-null mice. CONCLUSIONS: Liver-secreted autotaxin acts in an autocrine manner to exacerbate NAFLD through LPA-induced suppression of the peroxisome proliferator-activated receptor alpha-FGF21 axis and is a promising therapeutic target for NAFLD.

Dysfunctional triglyceride-very low-density lipoprotein (TG-VLDL) metabolism is linked to metabolic-associated fatty liver disease (MAFLD); however, the underlying cause remains unclear. The study shows that hepatic E3 ubiquitin ligase murine double minute 2 (MDM2) controls MAFLD by blocking TG-VLDL secretion. A remarkable upregulation of MDM2 is observed in the livers of human and mouse models with different levels of severity of MAFLD. Hepatocyte-specific deletion of MDM2 protects against high-fat high-cholesterol diet-induced hepatic steatosis and inflammation, accompanied by a significant elevation in TG-VLDL secretion. As an E3 ubiquitin ligase, MDM2 targets apolipoprotein B (ApoB) for proteasomal degradation through direct protein-protein interaction, which leads to reduced TG-VLDL secretion in hepatocytes. Pharmacological blockage of the MDM2-ApoB interaction alleviates dietary-induced hepatic steatohepatitis and fibrosis by inducing hepatic ApoB expression and subsequent TG-VLDL secretion. The effect of MDM2 on VLDL metabolism is p53-independent. Collectively, these findings suggest that MDM2 acts as a negative regulator of hepatic ApoB levels and TG-VLDL secretion in MAFLD. Inhibition of the MDM2-ApoB interaction may represent a potential therapeutic approach for MAFLD treatment.

Development of liver fibrosis results in drastic changes in the liver microenvironment, which in turn accelerates disease progression. Although the pathological function of various hepatic cells in fibrogenesis is identified, the crosstalk between them remains obscure. The present study demonstrates that hepatic expression of adipocyte fatty acid binding protein (A-FABP) is induced especially in the liver sinusoidal endothelial cells (LSECs) in mice after bile duct ligation (BDL). Genetic ablation and pharmacological inhibition of A-FABP attenuate BDL- or carbon tetrachloride-induced liver fibrosis in mice associating with reduced collagen accumulation, LSEC capillarization, and hepatic stellate cell (HSC) activation. Mechanistically, elevated A-FABP promotes LSEC capillarization by activating Hedgehog signaling, thus impairs the gatekeeper function of LSEC on HSC activation. LSEC-derived A-FABP also acts on HSCs in paracrine manner to potentiate the transactivation of transforming growth factor β1 (TGFβ1) by activating c-Jun N-terminal kinase (JNK)/c-Jun signaling. Elevated TGFβ1 subsequently exaggerates liver fibrosis. These findings uncover a novel pathological mechanism of liver fibrosis in which LSEC-derived A-FABP is a key regulator modulating the onset and progression of the disease. Targeting A-FABP may represent a potential approach against liver fibrosis.

Although mitophagy is known to restrict NLRP3 inflammasome activation, the underlying regulatory mechanism remains poorly characterized. Here we describe a type of early endosome-dependent mitophagy that limits NLRP3 inflammasome activation. Deletion of the endosomal adaptor protein APPL1 impairs mitophagy, leading to accumulation of damaged mitochondria producing reactive oxygen species (ROS) and oxidized cytosolic mitochondrial DNA, which in turn trigger NLRP3 inflammasome overactivation in macrophages. NLRP3 agonist causes APPL1 to translocate from early endosomes to mitochondria, where it interacts with Rab5 to facilitate endosomal-mediated mitophagy. Mice deficient for APPL1 specifically in hematopoietic cell are more sensitive to endotoxin-induced sepsis, obesity-induced inflammation and glucose dysregulation. These are associated with increased expression of systemic interleukin-1β, a major product of NLRP3 inflammasome activation. Our findings indicate that the early endosomal machinery is essential to repress NLRP3 inflammasome hyperactivation by promoting mitophagy in macrophages.

Amauroderma rugosum (AR) is a dietary mushroom in the Ganodermataceae family whose pharmacological activity and medicinal value have rarely been reported. In this study, the antioxidant capacity and neuroprotective effects of AR were investigated. The aqueous extract of AR was confirmed to contain phenolic compounds, polysaccharides, and triterpenes. The results of 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) and total antioxidant capacity assays revealed that AR extract scavenged reactive oxygen species. Moreover, AR extract decreased the cytotoxicity, oxidative stress, mitochondrial dysfunction, and apoptosis of PC12 cells induced by 6-hydroxydopamine (6-OHDA). In addition, 6-OHDA upregulated the expressions of proapoptotic proteins and downregulated the Akt (protein kinase B)/mTOR- (mammalian target of rapamycin-) and MEK (mitogen-activated protein kinase kinase)/ERK- (extracellular signal-regulated kinases-) dependent signaling pathways. These effects of 6-OHDA were abolished or partially reversed by AR extract. Furthermore, the neuroprotective effects of AR in 6-OHDA-treated PC12 cells were significantly abolished by Akt and MEK inhibitor. Thus, AR extract possesses neuroprotective effects, probably through its antioxidant and antiapoptotic effects. These findings suggest the potential application of AR in the prevention or treatment of oxidative stress-related neurodegenerative diseases such as Parkinson's disease.

Both innate and adaptive immune cells are critical players in autoimmune destruction of insulin-producing β cells in type 1 diabetes. However, the early pathogenic events triggering the recruitment and activation of innate immune cells in islets remain obscure. Here we show that circulating fatty acid binding protein 4 (FABP4) level was significantly elevated in patients with type 1 diabetes and their first-degree relatives and positively correlated with the titers of several islet autoantibodies. In nonobese diabetic (NOD) mice, increased FABP4 expression in islet macrophages started from the neonatal period, well before the occurrence of overt diabetes. Furthermore, the spontaneous development of autoimmune diabetes in NOD mice was markedly reduced by pharmacological inhibition or genetic ablation of FABP4 or adoptive transfer of FABP4-deficient bone marrow cells. Mechanistically, FABP4 activated innate immune responses in islets by enhancing the infiltration and polarization of macrophages to proinflammatory M1 subtype, thus creating an inflammatory milieu required for activation of diabetogenic CD8+ T cells and shift of CD4+ helper T cells toward Th1 subtypes. These findings demonstrate FABP4 as a possible early mediator for β cell autoimmunity by facilitating crosstalk between innate and adaptive immune cells, suggesting that pharmacological inhibition of FABP4 may represent a promising therapeutic strategy for autoimmune diabetes.