No abstract

In diabetic neuropathy, activation of axonal and sensory neuronal degeneration pathways leads to distal axonopathy. The NAD+-dependent deacetylase enzyme, Sirtuin 1 (SIRT1), can prevent activation of these pathways. Chandrasekaran et al. show that increased expression of SIRT1 in sensory neurons prevents and reverses experimental diabetic neuropathy induced by a high-fat diet.

Nicotinamide adenine dinucleotide (NAD+) is a central signaling molecule and enzyme cofactor that is involved in a variety of fundamental biological processes. NAD+ levels decline with age, neurodegenerative conditions, acute brain injury, and in obesity or diabetes. Loss of NAD+ results in impaired mitochondrial and cellular functions. Administration of NAD+ precursor, nicotinamide mononucleotide (NMN), has shown to improve mitochondrial bioenergetics, reverse age‐associated physiological decline, and inhibit postischemic NAD+ degradation and cellular death. In this study, we identified a novel link between NAD+ metabolism and mitochondrial dynamics. A single dose (62.5 mg/kg) of NMN, administered to male mice, increases hippocampal mitochondria NAD+ pools for up to 24 hr posttreatment and drives a sirtuin 3 (SIRT3)‐mediated global decrease in mitochondrial protein acetylation. This results in a reduction of hippocampal reactive oxygen species levels via SIRT3‐driven deacetylation of mitochondrial manganese superoxide dismutase. Consequently, mitochondria in neurons become less fragmented due to lower interaction of phosphorylated fission protein, dynamin‐related protein 1 (pDrp1 [S616]), with mitochondria. In conclusion, manipulation of mitochondrial NAD+ levels by NMN results in metabolic changes that protect mitochondria against reactive oxygen species and excessive fragmentation, offering therapeutic approaches for pathophysiologic stress conditions.

Mitochondria are complex organelles that undergo constant fusion and fission in order to adapt to the ever-changing cellular environment. The fusion/fission proteins, localized in the inner and outer mitochondrial membrane, play critical roles under pathological conditions such as acute brain injury and neurodegenerative diseases. Post-translational modifications of these proteins tightly regulate their function and activity, ultimately impacting mitochondrial dynamics and their efficiency to generate ATP. The individual post-translational modifications that are known to affect mitochondrial dynamics include SUMOylation, ubiquitination, phosphorylation, S-nitrosylation, acetylation, O-linked N-acetyl-glucosamine glycosylation, ADP-ribosylation, and proteolytic cleavage. Under stress or pathologic conditions, several of these modifications are activated leading to a complex regulatory mechanism that shifts the state of the mitochondrial network. The main goal is to accommodate and adapt the cellular bioenergetics metabolism to the energetic demand of the new extra- and/or intracellular environment. Understanding the complex relationship between these modifications on fusion and fission proteins in particular pathologic stress or diseases can provide new promising therapeutic targets and treatment approaches. Here, we discuss the specific post-translational modifications of mitochondrial fusion/fission proteins under pathologic conditions and their impact on mitochondrial dynamics.