Please cite this article as: M. Lukacs, J. Gilley, Y. Zhu, et al., Severe biallelic lossof-function mutations in nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) in two fetuses with fetal akinesia deformation sequence, Experimental Neurology,

Nicotinamide adenine dinucleotide (NAD +) is an essential biomolecule involved in many critical processes. Its role as both a driver of energy production and a signaling molecule underscores its importance in health and disease. NAD + signaling impacts multiple processes that are dysregulated in cancer, including DNA repair, cell proliferation, differentiation, redoxregulation, and oxidative stress. Distribution of NAD + is highly compartmentalized, with each subcellular NAD + pool differentially regulated and preferentially involved in distinct NAD +-dependent signaling or metabolic events. Emerging evidence suggests that targeting NAD + metabolism is likely to repress many specific mechanisms underlying tumor development and progression, including proliferation, survival, metabolic adaptations, invasive capabilities, heterotypic interactions with the tumor microenvironment, and stress response including notably DNA maintenance and repair. Here we provide a comprehensive overview of how compartmentalized NAD + metabolism in mitochondria, nucleus, cytosol, and extracellular space impacts cancer formation and progression, along with a discussion of the therapeutic potential of NAD +-targeting drugs in cancer.

Accumulative aggregation of mutant Huntingtin (Htt) is a primary neuropathological hallmark of Huntington’s disease (HD). Currently, mechanistic understanding of the cytotoxicity of mutant Htt aggregates remains limited, and neuroprotective strategies combating mutant Htt-induced neurodegeneration are lacking. Here, we show that in Drosophila models of HD, neuronal compartment-specific accumulation of mutant Htt aggregates causes neurodegenerative phenotypes. In addition to the increase in the number and size, we discovered an age-dependent acquisition of thioflavin S+, amyloid-like adhesive properties of mutant Htt aggregates and a concomitant progressive clustering of aggregates with mitochondria and synaptic proteins, indicating that the amyloid-like adhesive property underlies the neurotoxicity of mutant Htt aggregation. Importantly, nicotinamide mononucleotide adenylyltransferase (NMNAT), an evolutionarily conserved nicotinamide adenine dinucleotide (NAD+) synthase and neuroprotective factor, significantly mitigates mutant Htt-induced neurodegeneration by reducing mutant Htt aggregation through promoting autophagic clearance. Additionally, Nmnat overexpression reduces progressive accumulation of amyloid-like Htt aggregates, neutralizes adhesiveness, and inhibits the clustering of mutant Htt with mitochondria and synaptic proteins, thereby restoring neuronal function. Conversely, partial loss of endogenous Nmnat exacerbates mutant Htt-induced neurodegeneration through enhancing mutant Htt aggregation and adhesive property. Finally, conditional expression of Nmnat after the onset of degenerative phenotypes significantly delays the progression of neurodegeneration, revealing the therapeutic potential of Nmnat-mediated neuroprotection at advanced stages of HD. Our study uncovers essential mechanistic insights to the neurotoxicity of mutant Htt aggregation and describes the molecular basis of Nmnat-mediated neuroprotection in HD.

Traditionally, the use of genomic information for personalized medical decisions relies on prior discovery and validation of genotype–phenotype associations. This approach constrains care for patients presenting with undescribed problems. The National Institutes of Health (NIH) Undiagnosed Diseases Program (UDP) hypothesized that defining disease as maladaptation to an ecological niche allows delineation of a logical framework to diagnose and evaluate such patients. Herein, we present the philosophical bases, methodologies, and processes implemented by the NIH UDP. The NIH UDP incorporated use of the Human Phenotype Ontology, developed a genomic alignment strategy cognizant of parental genotypes, pursued agnostic biochemical analyses, implemented functional validation, and established virtual villages of global experts. This systematic approach provided a foundation for the diagnostic or non-diagnostic answers provided to patients and serves as a paradigm for scalable translational research.

27The three nicotinamide mononucleotide adenylyltransferase (NMNAT) family members 28 synthesize the electron carrier nicotinamide adenine dinucleotide (NAD + ) and are essential for 29 cellular metabolism. In mammalian axons, NMNAT activity appears to be required for axon 30 survival and is predominantly provided by NMNAT2. NMNAT2 has recently been shown to also 31 function as a chaperone to aid in the refolding of misfolded proteins. Nmnat2 deficiency in 32 mice, or in its ortholog dNmnat in Drosophila, results in axon outgrowth and survival defects. 33Peripheral nerve axons in NMNAT2-deficient mice fail to extend and innervate targets, and 34 skeletal muscle is severely underdeveloped. In addition, removing NMNAT2 from established 35 axons initiates axon death by Wallerian degeneration. We report here on two stillborn siblings 36 with fetal akinesia deformation sequence (FADS), severely reduced skeletal muscle mass and 37 hydrops fetalis. Clinical exome sequencing identified compound heterozygous NMNAT2 38 variant alleles in both cases. Both protein variants are incapable of supporting axon survival in 39 mouse primary neuron cultures when overexpressed. In vitro assays demonstrate altered 40 protein stability and/or defects in NAD + synthesis and chaperone functions. Thus, both patient 41 NMNAT2 alleles are null or severely hypo-morphic. These data indicate a previously unknown 42 role for NMNAT2 in human neurological development and provide the first direct molecular 43 evidence to support the involvement of Wallerian degeneration in a human axonal disorder. 44 45 46 47 Fetal Akinesia Deformation Sequence (FADS) defines a broad range of disorders unified by 51 absent fetal movement resulting in secondary defects often leading to stillbirth or limited 52 postnatal survival 1; 2 . These secondary features include edema, hydrops fetalis, craniofacial 53 anomalies including micrognathia, lung hypoplasia, rocker bottom feet, intrauterine growth 54 restriction, and decreased muscle mass 3 . Through previous experimental models of fetal 55 paralysis, the secondary findings have been shown to be primarily caused by a lack of fetal 56 movement 1; 4 . FADS has both genetic and environmental causes that can affect any aspect of 57 the motor system including the central nervous system (CNS), peripheral nervous system 58 (PNS), neuromuscular junction (NMJ), and/or skeletal muscle. Although most cases of FADS 59 do not have a genetic diagnosis, multiple monogenic causes of FADS affecting PNS 60 innervation development have been identified to date including RAPSN, DOK7, MUSK 5-7 . 61 62Through whole exome sequencing and subsequent Sanger sequencing of a family with two 63 fetuses with FADS, we identified compound heterozygous mutations in a gene previously 64 unlinked to FADS, nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2). NMNAT 65 family members were first shown to play a role in axon degeneration with the discovery of the 66 slow Wallerian Degeneration (Wld S ) mutant mouse that showed delayed axon degenera...

SummaryUnderstanding endogenous regulation of stress resistance and homeostasis maintenance is critical to developing neuroprotective therapies. Nicotinamide mononucleotide adenylyltransferase (NMNAT) is a conserved essential enzyme that confers extraordinary protection and stress resistance in many neurodegenerative disease models. Drosophila Nmnat is alternatively spliced to two mRNA variants, RA and RB. RB translates to protein isoform PD with robust protective activity and is upregulated upon stress to confer enhanced neuroprotection. The mechanisms regulating the alternative splicing and stress response of NMNAT remain unclear. We have discovered a Drosophila microRNA, dme-miR-1002, which promotes the splicing of NMNAT pre-mRNA to RB by disrupting a pre-mRNA stem-loop structure. NMNAT pre-mRNA is preferentially spliced to RA in basal conditions, whereas miR-1002 enhances NMNAT PD-mediated stress protection by binding via RISC component Argonaute1 to the pre-mRNA, facilitating the splicing switch to RB. These results outline a new process for microRNAs in regulating alternative splicing and modulating stress resistance.

Proper development and plasticity of hippocampal neurons require specific RNA isoforms to be expressed in the right place at the right time. Precise spatiotemporal transcript regulation requires the incorporation of essential regulatory RNA sequences into expressed isoforms. In this review, we describe several RNA processing strategies utilized by hippocampal neurons to regulate the spatiotemporal expression of genes critical to development and plasticity. The works described here demonstrate how the hippocampus is an ideal investigative model for uncovering alternate isoform-specific mechanisms that restrict the expression of transcripts in space and time.

Understanding endogenous regulation of stress resistance and homeostasis maintenance is critical to developing neuroprotective therapies. Nicotinamide mononucleotide adenylyltransferase (NMNAT) is a conserved essential enzyme that confers extraordinary protection and stress resistance in many neurodegenerative disease models. Drosophila Nmnat is alternatively spliced to two mRNA variants, RA and RB. RB translates to protein isoform PD with robust protective activity and is upregulated upon stress to confer enhanced neuroprotection. The mechanisms regulating alternative splicing and stress response of NMNAT remain unclear. We have discovered a Drosophila microRNA, dme-miR-1002, which promotes the splicing of NMNAT pre-mRNA to RB by disrupting a pre-mRNA stemloop structure. While NMNAT pre-mRNA is preferentially spliced to RA in basal conditions, miR-1002 enhances NMNAT PD-mediated stress protection by binding via RISC component Argonaute1 to the pre-mRNA, facilitating the splicing switch to RB. These results outline a new process for microRNAs in regulating alternative splicing and modulating stress resistance.