Non-alcoholic fatty liver disease (NAFLD) affects 1 in 3 Americans and is a significant risk factor for type II diabetes mellitus, insulin resistance and hepatic carcinoma. Characterized by excessive hepatic triglyceride accumulation, the incidence of NAFLD is increasing exponentially - in line with the growing obesity epidemic. There is mounting evidence that endoplasmic reticulum (ER) stress-induced transcription factor activation is involved in the generation and maintenance of NAFLD. While mechanisms at the peripheral level are important, changes in the autonomic nervous system are poorly understood yet crucial in the acute and long- term regulation of liver metabolism. Our preliminary data have identified novel targets, mechanisms of action and neuronal populations that play an essential role in NAFLD during diet-induced obesity in mice, including within forebrain and hypothalamic regions, involving ER stress and activation of the transcription factor activator protein-1 (AP-1). We also provide key evidence that elevations in sympathetic nervous system outflow to the liver is an underlying component driving NAFLD. Using a combination of innovative imaging, molecular, neuroanatomical and integrative physiological approaches, we will address the central hypothesis that hepatic sympathetic overactivity due to ER stress-induced AP-1 activation in forebrain-hypothalamic circuits is critical in driving the development of NAFLD. Our novel preliminary findings highlight ER stress in the forebrain subfornical organ and hypothalamic paraventricular nucleus as a mediator of NAFLD during diet- induced obesity in mice, and point to elevations in hepatic sympathetic nerve activity as a cause. Building upon these findings, in Aim 1 we will comprehensively evaluate the role of forebrain and hypothalamic ER stress in distinct neuronal populations in obesity-induced hepatic sympathetic overactivity and NAFLD development. Long-lasting alterations in CNS function, including chronic activation of the sympathetic nervous system, require changes in gene expression through regulation of inducible transcription factors. In line with this, in Aim 2, we will examine the role of ER stress in the activation of AP-1 in hypothalamic neurons during the development of NAFLD. The functional role of brain AP-1 activation in the pathology of NAFLD will also be examined. Dissecting the links between CNS ER stress and transcription factor activation in the control of hepatic sympathetic outflow and NAFLD development has the potential to identify new therapeutic targets for the treatment and prevention of this condition. Moreover, the combination of live animal molecular imaging, brain site- and neuron subtype- specific manipulations, direct recording of central sympathetic outflow to the liver, and comprehensive histological and molecular hepatic analysis provides a novel and integrative approach to gain insight into NAFLD development.
Non-alcoholic fatty liver disease (NAFLD) is a major global health challenge and is directly associated with the development of obesity. The role of the central nervous system in this growing epidemic remains unclear. Understanding the molecular mechanisms in the brain, including endoplasmic reticulum stress and transcription factor activation, will greatly advance our understanding of the underlying contributors to NAFLD.
