Pharmacological NAD-Boosting Strategies Improve Mitochondrial Homeostasis in Human Complex I–Mutant Fibroblasts

Abstract

Mitochondrial disorders are devastating genetic diseases for which efficacious therapies are still an unmet need. Recent studies report that increased availability of intracellular NAD obtained by inhibition of the NAD-consuming enzyme poly(ADP-ribose) polymerase (PARP)-1 or supplementation with the NAD-precursor nicotinamide riboside (NR) ameliorates energetic derangement and symptoms in mouse models of mitochondrial disorders. Whether these pharmacological approaches also improve bioenergetics of human cells harboring mitochondrial defects is unknown. It is also unclear whether the same signaling cascade is prompted by PARP-1 inhibitors and NR supplementation to improve mitochondrial homeostasis. Here, we show that human fibroblasts mutant for the NADH dehydrogenase (ubiquinone) Fe-S protein 1 (NDUFS1) subunit of respiratory complex I have similar ATP, NAD, and mitochondrial content compared with control cells, but show reduced mitochondrial membrane potential. Interestingly, mutant cells also show increased transcript levels of mitochondrial DNA but not nuclear DNA respiratory complex subunits, suggesting activation of a compensatory response. At variance with prior work in mice, however, NR supplementation, but not PARP-1 inhibition, increased intracellular NAD content in NDUFS1 mutant human fibroblasts. Conversely, PARP-1 inhibitors, but not NR supplementation, increased transcription of mitochondrial transcription factor A and mitochondrial DNA-encoded respiratory complexes constitutively induced in mutant cells. Still, both NR and PARP-1 inhibitors restored mitochondrial membrane potential and increased organelle content as well as oxidative activity of NDUFS1-deficient fibroblasts. Overall, data provide the first evidence that in human cells harboring a mitochondrial respiratory defect exposure to NR or PARP-1, inhibitors activate different signaling pathways that are not invariantly prompted by NAD increases, but equally able to improve energetic derangement.

Mitochondrial dysfunction in cardiac aging

“…NA helped decrease the amount of ROS in the worms system and it was suggested that the NA increased NAD + pools which can help maintain Sirt3 acetylation patterns. Nicotinamide riboside can also increase the NAD + pool without activating Sirt3, but providing comparable benefits [222]. PARP-1inhibitors, Phe and PJ34, demonstrated improved mitochondrial content and membrane potential in Complex I mutant human fibroblasts [222].…”

“…Nicotinamide riboside can also increase the NAD + pool without activating Sirt3, but providing comparable benefits [222]. PARP-1inhibitors, Phe and PJ34, demonstrated improved mitochondrial content and membrane potential in Complex I mutant human fibroblasts [222]. Both inhibitors increase the transcription of mitochondrially encoded respiratory complexes, relaying a better survival of the cells.…”

Sirtuin activation as a therapeutic approach against inborn errors of metabolism

“…The only clinical result so far comes from the NAD + precursor acipimox, which improves muscle mitochondrial function and glucose homeostasis in type 2 diabetes patients (van de Weijer et al 2015). In the field of IEM, NR was shown to restore mitochondrial homeostasis in fibroblasts from patients with a mitochondrial respiratory chain defect (Felici et al 2015). Furthermore, NR induces mitochondrial biogenesis in skeletal muscle of mice that suffer from mitochondrial myopathy (Khan et al 2014) and induces OXPHOS-related gene expression and improves motor performance in mice that suffer from cytochrome c oxidase deficiency (Cerutti et al 2014).…”

Nicotinamide Riboside Delivery Generates Nad+ Reserves to Protect Vascular Cells Against Oxidative Damage

“…Additionally, NR was reported to elevate NAD + levels and protect against two distinct models of mitochondrial disease in mice (235,236). These studies have recently been expanded to human cells; NR delivery and PARP inhibition were reported to restore mitochondrial membrane potential and oxidative activity in human fibroblasts (237). Mitochondrial dysfunction is a hallmark of aging and effective energy metabolism is essential to support repair responses during oxidative insults.…”

“…NR delivery is an emerging intervention to combat this NAD + deficiency. Current literature has reported that NR will elevate NAD + levels to promote mitochondrial health and protect against metabolic disease (233)(234)(235)(236)(237). Some reports have indirectly linked NR to oxidative stress response and DNA damage repair pathways in diseased mouse models (238,239).…”