In our laboratory, we study mechanisms of innate immune activation in liver diseases and its role on modulation of liver parenchymal cells including hepatocytes and stellate cells.
We employ a broad range of preclinical murine liver injury models of alcoholic hepatitis, non-alcoholic steatohepatitis, liver fibrosis and drug-induced-liver injury and study their relevance to human disease based on patient samples. Our recent focus is on the role of microRNAs and extracellular vesicles in immunoregulation in the pathogenesis of liver diseases.
Check out the project overviews below or click on the project link at left for a more detailed description!
Alcohol and Monocyte Signaling
Macrophages (MØ), Kupffer cells (KC) and neutrophils mediate inflammation and play an important role in the pathogenesis of alcoholic liver disease (ALD).
Previous studies have demonstrated damaging effects of pro-inflammatory macrophages on alcoholic liver inflammation and high neutrophil infiltration in the liver predicted poor outcome in human alcoholic hepatitis.
Prior reports in humans and our preliminary data in mice show that both classically activated inflammatory, M1, and alternatively activated, M2, macrophages are present in the liver after chronic alcohol intake.
However, the significance of M1 and M2 type macrophage (MØ) polarization or therapeutic targeting of MØ polarization is yet to be explored in ALD. M2 “alternatively activated” macrophages have anti-inflammatory function and contribute to tissue repair.
M2 MØ phenotype is induced and modulated (regulated) by various factors including cytokines, microRNAs, transcription factors or phagocytosis of apoptotic neutrophils.
We found decreased phagocytic activity in alcohol exposed MØ and observed decreased apoptosis in neutrophils isolated from livers of chronic alcohol-fed mice.
Thus, we hypothesize that insufficient M2 polarization permits chronic inflammation and preferential M1 macrophage phenotype in the liver.
Innate Immune Signaling Pathways
The pathomechanism of alcoholic liver disease (ALD) involves cumulative events such as leaky gut, hepatocyte damage and inflammation that collectively contribute to the severity of disease.
Our studies have delineated the role of Toll-like receptor 4 (TLR4) signaling and identified a unique role for interferon regulatory factor 3 (IRF3) in alcohol-related inflammation and hepatocyte damage.
We reported that the endoplasmic reticulum (ER) adapter, stimulator of interferon genes (STING), is required for IRF3 phosphorylation and thatIRF3, through its BH3 domain, induces mitochondrial apoptosis in hepatocytes.
Double stranded DNAs are ligands for the cyclic GMP-AMP kinase (cGAS) that produces 2′3′-cGAMP (cGAMP) that can activate STING to trigger IRF3 activation and Type I IFN production.
We are exploring whether STING activation is at the crossroads of alcohol-induced liver pathology and in addition to ER stress, STING is also activated via cGAS-cGAMP in ALD.
Micro RNA’s in Alcoholic Liver Disease
Alcoholic liver disease affects millions of people worldwide and it remains to be a therapeutic challenge for clinicians.
Activation of the inflammatory cascade via gut-derived lipopolysaccharide (LPS) contributes to alcoholic liver disease via induction of pro-inflammatory cytokines induction in Kupffer cells.
Micro-RNA-155 (miR-155), small non-coding RNA molecule, is important in regulation of inflammation.
Our studies demonstrated that chronic alcohol up-regulates miR155 in macrophages in vitro as as as in vivo in the liver and in isolated Kupffer cells and this miR155 increase contributes to inflammation in alcoholic liver disease.
We recently reported that miR-155 deficient mice are partially provoked with alcohol induced liver damage and fibrosis.
Our studies on miR-155 revealed a critical role for reducing miR-155 in hepatocytes in the progression of alcoholic liver disease.
Danger signals and pathways of macrophage activation in NASH
Inflammatory cell activation drives diverse cellular programming in steatohepatitis.
Our studies revealed that activation of the multiprotein complex, inflammasome, contributes to non-alcoholic steatohepatitis (NASH) involving the NLRP3 and AIM2 inflammasomes both in hepatocytes and bone marrow-derived cells.
Activation of liver immune cells is triggered by damage-associated molecular patterns (DAMPs) released from hepatocytes and increased circulating endotoxin levels amplify this response in NASH.
In a high fat/cholesterol/sugar diet-induced metabolic syndrome and NASH in mice, accumulation of DAMPs paralleled the evolution of NASH from NAFLD suggesting the importance of DAMPs in disease progression.
This suggested that activation of multiple pattern recognition signaling pathways occurs in both hepatocytes and immune cells in the liver and crosstalk between hepatocytes and immune cells amplifies inflammation and fibrosis in NASH.
We identified that Hypoxia-inducible factor-1 (HIF-1α) upregulation in hepatocytes induces steatosis. Increased HIF-1α in hepatic macrophages and in NASH patients circulating monocytes is linked to impaired autophagy and this contributes to increased IL-1ß production in NASH.
Our results suggest that macrophage activation in NASH involves multiple signals and a complex interplay between HIF-1α and autophagy as these pathways promote proinflammatory overactivation in NASH.
Biomarkers in Liver Disease
We are exploring novel therapies and biomarker discoveries in AH.
Direct effects of alcohol on hepatocytes, increased intestinal permeability and activation of innate immune system (Kupffer cells) by gut-derived LPS are major factors in AH leading to over-activation of the pro-inflammatory cascade. Currently, there are no effective strategies in AH.
Our data in a mouse model demonstrated that deficiency of IL-1R or inhibition of IL-1R signaling by administration of IL-receptor antagonist significantly attenuated steatosis and inflammatory cytokine induction in alcoholic liver disease.
We also identified that microRNA-155 is an alcohol induced regulator of increased Kupffer cell activation TNF-alpha production in ALD. Furthermore, increased circulating levels of microRNAs correlated with liver injury and inflammation identifying them as potential biomarkers.
Extracellular Vesicles in Alcoholic Liver Disease: Basic and Pre-clinical Discovery
A salient feature of alcoholic liver disease is Kupffer cell activation and recruitment of inflammatory monocytes and macrophages.
These key cellular events of ALD pathogenesis may be mediated by extracellular vesicles (EV).
EVs transfer biomaterials, including proteins and microRNA's, and have recently emerged as important effectors of intercellular communications.
Our studies indicate a specific protein signature of ALD EVs and demonstrates a functional role of circulating EVs containing heat shock protein 90 in mediating Kupffer cell and macrophage activation in the liver.
Alcoholic Hepatitis Clinical and Translational Network Late Phase Clinical Trials and Observational Studies
Alcoholic liver disease (ALD) is a major cause of liver-related morbidity and mortality in the US.
Alcoholic hepatitis (AH) is a life-threatening form of ALD. Severe AH is associated with a mortality exceeding 30% at 3 months.
Despite its obvious public health and economic burden, there is a remarkable paucity of effective therapeutics for severe AH.
Corticosteroids have been the mainstay of therapy for AH, but are only modestly effective and increase the susceptibility to severe infections while pentoxifylline has recently been shown to be ineffective.
There is an urgent need to develop safe and effective targeted therapies for severe AH. Anakinra, an IL1β receptor antagonist, zinc, and granulocyte colony stimulating factor (G-CSF) have been evaluated and have potential therapeutic benefit.
Due to limitations in patient recruitment for clinical trials in general and AH in particular, there is a compelling need for an integrated national consortium for this deadly disease.
The use of the IL-1 receptor antagonist, anakinra, in this clinical trial is supported by preclinical studies in our group that demonstrated the role of NLRP3 inflammasome and the therapeutic benefit of anakinra in a mouse model of alcoholic liver disease.