Altered hepatic metabolic landscape and insulin sensitivity in response to pulmonary tuberculosis.

Chronic inflammation triggers development of metabolic disease, and pulmonary tuberculosis (TB) generates chronic systemic inflammation. Whether TB induced-inflammation impacts metabolic organs and leads to metabolic disorder is ill defined. The liver is the master regulator of metabolism and to determine the impact of pulmonary TB on this organ we undertook an unbiased mRNA and protein analyses of the liver in mice with TB and reanalysed published data on human disease. Pulmonary TB led to upregulation of genes in the liver related to immune signalling and downregulation of genes encoding metabolic processes. In liver, IFN signalling pathway genes were upregulated and this was reflected in increased biochemical evidence of IFN signalling, including nuclear location of phosphorylated Stat-1 in hepatocytes. The liver also exhibited reduced expression of genes encoding the gluconeogenesis rate-limiting enzymes Pck1 and G6pc. Phosphorylation of CREB, a transcription factor controlling gluconeogenesis was drastically reduced in the livers of mice with pulmonary TB as was phosphorylation of other glucose metabolism-related kinases, including GSK3a, AMPK, and p42. In support of the upregulated IFN signalling being linked to the downregulated metabolic functions in the liver, we found suppression of gluconeogenic gene expression and reduced CREB phosphorylation in hepatocyte cell lines treated with interferons. The impact of reduced gluconeogenic gene expression in the liver was seen when infected mice were less able to convert pyruvate, a gluconeogenesis substrate, to the same extent as uninfected mice. Infected mice also showed evidence of reduced systemic and hepatic insulin sensitivity. Similarly, in humans with TB, we found that changes in a metabolite-based signature of insulin resistance correlates temporally with successful treatment of active TB and with progression to active TB following exposure. These data support the hypothesis that TB drives interferon-mediated alteration of hepatic metabolism resulting in reduced gluconeogenesis and drives systemic reduction of insulin sensitivity. Author summary: Tuberculosis (TB) is a worldwide disease with a substantial proportion of undiagnosed cases. Control of TB is mediated by a protective cellular immune response which is also chronic, inflammatory and systemic. Chronic inflammation can disrupt metabolism and compromise the organs key to maintaining health–such as the liver. The extent to which pulmonary TB can disrupt the metabolic function of the liver is ill defined. We have used a mouse model of pulmonary TB to examine the changes occurring in the liver when immunity is first being expressed in the lung. We found that pulmonary TB leads to upregulation of immune-related signalling pathways in liver cells and that TB infected mice have altered glucose metabolism. Reanalysing published metabolic data from humans, we find that a metabolic signature associated with insulin resistance separates those with TB from healthy subjects and alters with time to progression and resolution of TB, thereby indicating glucose metabolism disruption occurs during TB in humans. These data are important because we show that TB disrupts liver glucose metabolism, and this is critical to understanding the interplay between TB and metabolic disease. [ABSTRACT FROM AUTHOR]

Copyright of PLoS Pathogens is the property of Public Library of Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)