When Hexokinase Gets that NAG-ing Feeling…

Pattern-Recognition Receptors and Immunometabolic Reprogramming: What We Know and What to Explore

BACKGROUND

Evolutionarily, immune response is a complex mechanism that protects the host from internal and external threats. Pattern-recognition receptors (PRRs) recognize MAMPs, PAMPs, and DAMPs to initiate a protective pro-inflammatory immune response. PRRs are expressed on the cell membranes by TLR1, 2, 4, and 6 and in the cytosolic organelles by TLR3, 7, 8, and 9, NLRs, ALRs, and cGLRs. We know their downstream signaling pathways controlling immunoregulatory and pro-inflammatory immune response. However, the impact of PRRs on metabolic control of immune cells to control their pro- and anti-inflammatory activity has not been discussed extensively.

SUMMARY

Immune cell metabolism or immunometabolism critically determines immune cells' pro-inflammatory phenotype and function. The current article discusses immunometabolic reprogramming (IR) upon activation of different PRRs, such as TLRs, NLRs, cGLRs, and RLRs. The duration and type of PRR activated, species studied, and location of immune cells to specific organ are critical factors to determine the IR-induced immune response.

KEY MESSAGE

The work herein describes IR upon TLR, NLR, cGLR, and RLR activation. Understanding IR upon activating different PRRs is critical for designing better immune cell-specific immunotherapeutics and immunomodulators targeting inflammation and inflammatory diseases.

Sirtuin-dependent metabolic and epigenetic regulation of macrophages during tuberculosis

Macrophages are the preeminent phagocytic cells which control multiple infections. Tuberculosis a leading cause of death in mankind and the causative organism Mycobacterium tuberculosis (MTB) infects and persists in macrophages. Macrophages use reactive oxygen and nitrogen species (ROS/RNS) and autophagy to kill and degrade microbes including MTB. Glucose metabolism regulates the macrophage-mediated antimicrobial mechanisms. Whereas glucose is essential for the growth of cells in immune cells, glucose metabolism and its downsteam metabolic pathways generate key mediators which are essential co-substrates for post-translational modifications of histone proteins, which in turn, epigenetically regulate gene expression. Herein, we describe the role of sirtuins which are NAD+-dependent histone histone/protein deacetylases during the epigenetic regulation of autophagy, the production of ROS/RNS, acetyl-CoA, NAD+, and S-adenosine methionine (SAM), and illustrate the cross-talk between immunometabolism and epigenetics on macrophage activation. We highlight sirtuins as emerging therapeutic targets for modifying immunometabolism to alter macrophage phenotype and antimicrobial function.

α-Synuclein fibrillation products trigger the release of hexokinase I from mitochondria: Protection by curcumin, and possible role in pathogenesis of Parkinson's disease

Extensive research has shown that assembling of α-synuclein amyloid aggregates on mitochondria is an important mechanistic feature of Parkinson's disease (PD) and other Lewy body disorders. However, the molecular mechanism(s) of its neuronal toxicity remain unclear. Type 1 Hexokinase (HKI), a key enzyme in the control of brain glucose metabolism, plays an important role in protecting against mitochondrially-regulated apoptosis through reducing generation of reactive oxygen species (ROS). The release of mitochondrially-bound HKI causes a significant decrease in enzyme activity and triggers oxidative stress. Here, we have investigated the potency of amyloid fibrillation products arising from α-synuclein and hen egg white lysozyme (HEWL) for the release of HKI and ROS content enhancement in mitochondria isolated from rat brain. Results clearly indicate the capacity of the fibrillation products of α-synuclein, and not HEWL, to trigger release of HKI from the Type A binding site of mitochondria for the enzyme and to induce mitochondrial ROS enhancement in a dose-dependent manner. Moreover, we found that curcumin was very effective in preventing mitochondrial HKI release and ROS enhancement induced by α-synuclein fibrillation products. The pathophysiological significance of mitochondrial HKI activity and localization in pathogenesis of neurodegenerative disorders including PD are discussed. Taken together, these results may offer insight into a possible mechanism by which disease-related peptides and proteins may exert their neuronal toxicity.

Biochemistry of proinflammatory macrophage activation

In the last decade, metabolism has been recognized as a major determinant of immunological processes. During an inflammatory response, macrophages undergo striking changes in their metabolism. This metabolic reprogramming is governed by a complex interplay between metabolic enzymes and metabolites of different pathways and represents the basis for proper macrophage function. It is now evident that these changes go far beyond the well-known Warburg effect and the perturbation of metabolic targets is being investigated as a means to treat infections and auto-immune diseases. In the present review, we will aim to provide an overview of the metabolic responses during proinflammatory macrophage activation and show how these changes modulate the immune response.