Zhenyuan Song, Ph.D. - US grants

[unreadable] DESCRIPTION (provided by applicant): Alcoholic liver disease (ALD) continues to be an important health problem in the United States. Abnormal hepatic methionine metabolism is an acquired metabolic abnormality in ALD and the effects of chronic alcohol intake on hepatic methionine metabolism are initially seemingly paradoxic. Whereas alcohol consumption causes hepatic deficiency of S-adenosylmethionie (SAMe), it elevates hepatic homocysteine levels, a product of SAMe metabolism. [unreadable] [unreadable] Decreased SAMe levels and elevated homocysteine levels may contribute to alcohol induced liver injury. The effect of alcohol on S-adenosylhomocysteine (SAH) levels, another metabolite in the methionine metabolism pathway, has received little investigative attention. It is our working hypothesis that tumor necrosis factor (TNF) in conjunction with certain metabolic abnormalities observed in ALD, such as altered intracellular methylation status due to abnormal methionine/SAMe/SAH metabolism play an etiologic role in the development of liver injury in ALD. We postulate that chronic alcohol abuse causes increased gut permeability and endotoxemia, generation of reactive oxygen intermediates, activation of Kupffer cell NFkB with increased TNF production, decreased hepatocyte MAT activity with subsequent SAMe deficiency, increased S-adenosylhomocysteine (SAH) concentrations, inhibition of transmethylation reactions, decreased hepatic methylation status, elevated expression/ activation/activity of proteins sensitive to intracellular methylation status such as caspase-8, mitochondrial dysfunction, increased susceptibility to hepatic TNF cytotoxicity, and subsequent liver injury. In this proposal, we will evaluate inhibition of hepatic transmethylation reactions by chronic alcohol exposure as a mechanism for hepatic sensitization to TNF-induced cytotoxicity in a relevant model of ALD. The specific objectives of this project are as follows: 1. Evaluate the effects of inhibition of hepatic transmethylation reactions on "sensitization" to TNF hepatotoxicity; 2. Investigate possible mechanisms by which inhibition of transmethylation reactions sensitizes hepatocytes to TNF hepatotoxicity; and 3. Evaluate the effects of chronic alcohol consumption (+/- SAMe supplementation) on hepatic methylation status and sensitization to TNF-hepatotoxicity in rats intragastrically fed alcohol. [unreadable] [unreadable] This research will be performed with structured mentoring support and a detailed training program designed to maximize my opportunity to become an independent NIH-funded investigator. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Chronic alcohol exposure causes the development and maintenance of fatty liver by interfering hepatic fat disposal. Adiponectin, an adipokine predominantly secreted by adipose tissue, plays a central role in the regulation of energy metabolism, lipid and carbohydrate metabolism. Accumulated evidence suggests that down- regulation of adiponectin production has patho-physiological importance in the process of alcoholic fatty liver disease;however, the underlying mechanisms are still elusive. Abnormal hepatic methionine/homocysteine metabolism and hyperhomocysteinemia induced by prolonged alcohol exposure has been reported both in clinical and experimental studies, however, the occurrence of this abnormality in adipose tissue, as well as its potential implication in the regulation of adipose tissue function, specifically adiponectin expression and secretion, has received very few attention. It is our hypothesis that chronic alcohol exposure induces abnormal methionine/homocysteine metabolism not only in the liver, but also in the adipose tissue. Furthermore, we hypothesize that increased accumulation of homocysteine in the adipocytes, either via alcohol-induced endogenous alteration in methionine/homocysteine metabolism or a cross-talk from the liver;contribute to the suppression of adiponectin gene expression and secretion in alcoholic liver disease (ALD). In this proposal, we will utilize both animal and cell culture models to evaluate excessive accumulation of homocysteine in the adipocytes by chronic alcohol feeding as a mechanism for decreased adiponectin gene expression, protein production and secretion. The specific objectives of this project are as follows: 1. Further document the effects of chronic alcohol consumption on methionine/homocysteine metabolism in adipose tissues and explore potential mechanisms involved in this process;2. Determine the effects of increased homocysteine accumulation in adipocytes on adiponectin production and its causal role in the inhibitory effects of chronic alcohol exposure on adiponectin production in ALD;3. Elucidate mechanisms whereby homocysteine modulates adiponectin production. The beneficial effects of nutritional intervention, specifically these being able to rectify abnormal methionine/homocysteine metabolism such as betaine and S-adenosylmethionine, have been well-accepted;thus, our approach is designed to not only more completely understand the mechanisms of ALD, but also to develop new therapeutic interventions. PHS 398/2590 (Rev. 09/04, Reissued 4/2006) Page Continuation Format Page PUBLIC HEALTH RELEVANCE: Alcoholic liver disease (ALD) remains an important health problem in the United States. Adiponectin is a soluble mediator predominantly secreted by adipose tissue and in possession of properties of anti-steatosis, anti-inflammation, and anti-fibrosis. Chronic alcohol exposure results in suppressed adiponectin production, which plays an important role in the pathogenesis of ALD. Based on our preliminary findings that chronic alcohol feeding caused elevation of homocysteine levels in the adipose tissue and homocysteine decreased adiponectin production by primary adipocytes, we propose here that altered methionine/homocysteine metabolism both in the liver and in the adipose tissue may play a mechanistic role in the suppression of adiponectin production in ALD. We will use the state-of-the-art technologies to investigate this clinically relevant process.

Abstract Alcoholic liver disease (ALD) remains an important health problem in the United States. It ranks among the major causes of morbidity and mortality in the world, and affects millions of patients worldwide each year. The disease process is characterized by early steatosis, steatohepatitis, with some individuals ultimately progressing to fibrosis. Currently, there is no accepted therapy available to halt or reverse this process in humans. Nicotinamide N-methyltransferase (NNMT) catalyzes nicotinamide degradation via a SAM-dependent methylation reaction. Emerging evidence supports that NNMT is a novel regulator of metabolism. The very recent studies in our laboratory demonstrated for the first time that chronic alcohol exposure increases hepatic NNMT expression. Using both animal models and in vitro cell culture system, we identified NNMT as a pivotal regulator of cellular and mitochondrial NAD+ homeostasis and mitochondrial function. Specifically, we found that NNMT overexpression in hepatocytes decreased NAD content in both cytosol and mitochondrial and impair mitophagy induction, a protective mechanism in ALD. In this proposal, we will explore the mechanistic implication of NNMT in the pathogenesis of ALD. Successful performance of the studies proposed in this proposal will not only shed new light on the pathogenesis of this disease, but also pave the way for novel therapeutic interventions for ALD. The aims are: AIM 1: AIM 1: To determine the pathological role of NNMT upregulation in ALD and explore therapeutic potential of targeting NNMT for the treatment of the disease. We hypothesize that NNMT inhibition, via either genetic (shRNA administration) or pharmacological (1-MNA, a potent NNMT inhibitor) approach, can prevent and even reverse ALD development/progression. AIM 2: To delineate mechanisms involved in NNMT-induced cellular dysfunction in ALD. Both in vivo (alcohol feeding vs. NAD+ precursor supplementation) and in vitro (NNMT overexpression) experiments will be conducted to test our hypothesis that alcohol-induced NNMT overexpression contribute to ALD via decreasing cellular and mitochondrial NAD+ levels in both the liver and adipose tissue. AIM 3: To elucidate mechanisms underlying alcohol-induced NNMT overexpression. Hif-1alpha knockout mice will be employed to test our hypothesis that Hif-1alpha activation contributes to NNMT upregulation in both the liver and adipose tissue in response to chronic alcohol consumption.

Abstract Alcoholic liver disease (ALD) remains an important health problem in the United States. It ranks among the major causes of morbidity and mortality in the world, and affects millions of patients worldwide each year. The disease process is characterized by early steatosis, steatohepatitis, with some individuals ultimately progressing to fibrosis/cirrhosis and liver failure. Currently, there is no accepted therapy available to halt or reverse this process in humans. Adipose tissue dysfunction plays a critical role in the pathogenesis of ALD; however, the exact mechanisms underlying the detrimental effect of alcohol on adipocyte function remain elusive. In mammals, adipose tissues comprise white adipose tissue (WAT) and brown adipose tissue (BAT), which is further categorized into ?classical? BAT and ?inducible? beige fat. The adipocytes in beige fat are Ucp1-expressing thermogenic adipocytes and can be induced to manifest the phenotypes of classical brown adipocytes via a process called ?browning?. Sympathetic nervous system (SNS) is the primary initiator of both lipolysis and browning process through releasing norepinephrine (NE) at target adipose tissues. Physiologically, a tightly-regulated ?coupling? between lipolytic and thermogenic machinery activation must be maintained to assure that most fatty acids released from adipose tissue by lipolysis can be ultimately utilized for thermogenesis process/heat production. The promotive effect of chronic alcohol consumption on lipolysis activation has been well- documented, in contrast, its effect on adipose tissue browning/thermogenic process, as well as its potential involvement in the pathogenesis of ALD development, remain unknown. Furthermore, although the profound effect of alcohol on central nervous system (CNS) has been widely reported, whether and how CNS contributes to these processes remain ambiguous. The data obtained recently in my laboratory revealed that ALD development was associated with adipose tissue cAMP/PKA pathway activation. Nevertheless, chronic alcohol exposure inhibited adipose tissue ?browning?, implying a ?dissociation? between the two physiologically coupled processes in response to increased SNS tone in response to alcohol drinking. Based on our Preliminary Studies, we hypothesize that chronic alcohol consumption activates SNS, however, it ?dissociates? the coupling between lipolysis and browning/thermogenesis in adipose tissues, leading to uncontrolled FFAs release and resultant fatty liver and liver damage. This hypothesis will be tested in the following Specific Aims: AIM 1: To determine the critical role of SNS activation in adipose tissue lipolysis and liver pathologies in response to chronic alcohol exposure; AIM 2: To determine the pathological role of impaired browning/thermogenesis process in ALD and mechanism(s) underlying alcohol-triggered uncoupling between lipolysis and browning/thermogenesis; and AIM 3: To elucidate the mechanism(s) underlying alcohol-induced sympathetic activation.