The multifaceted role of sirtuins in inflammatory bowel diseases.

Inflammatory bowel diseases (IBDs), mainly involving the disease states of ulcerative colitis (UC) and Crohn's disease (CD), are characterized by chronic, relapsing inflammation of the gastrointestinal tract. IBD has an unclear etiology and likely develops from a complex interaction between the host's genetic predisposition, the gut microbiota, the immune system, and elements within the environment. In the United States alone, the estimated health care cost for IBD, according to a recent study, exceeds $25 billion. More than 200 genetic loci have been identified to be associated with IBD, highlighting its complex pathophysiology. Although existing treatments for IBD are generally supportive, they are not curative, underscoring the need to identify the causative agents that drive disease pathogenesis. Several studies have reported metabolic alterations in the pathogenesis of IBD. In all living cells, the central action of nicotinamide adenine dinucleotide (NAD) plays a pivotal role in the regulation of energy metabolism and cell signaling. Dysregulated NAD metabolism is reported in patients with IBD. Sirtuins, a protein family of posttranslational modifiers, need NAD as a cofactor to perform enzymatic reactions such as deacylation and ADP-ribosylation of not only histones, but also of various other key cellular proteins. Therefore, sirtuins play a vital and central role as stress-responsive metabolic sensors in cells. In this review, we address novel mechanisms by which sirtuins play a role in IBD pathogenesis, thus exposing a potential therapeutic role of this group of enzymes that might be useful in curtailing IBD and several other debilitating gastrointestinal inflammatory disorders.