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ATP-sensitive potassium (K ATP ) gain-of-function (GOF) mutations cause neonatal diabetes, with some individuals exhibiting developmental delay, epilepsy, and neonatal diabetes (DEND) syndrome. Mice expressing K ATP -GOF mutations pan-neuronally (nK ATP -GOF) demonstrated sensorimotor and cognitive deficits, whereas hippocampus-specific hK ATP -GOF mice exhibited mostly learning and memory deficiencies. Both nK ATP -GOF and hK ATP -GOF mice showed altered neuronal excitability and reduced hippocampal long-term potentiation (LTP). Sulfonylurea therapy, which inhibits K ATP , mildly improved sensorimotor but not cognitive deficits in K ATP -GOF mice. Mice expressing K ATP -GOF mutations in pancreatic β-cells developed severe diabetes but did not show learning and memory deficits, suggesting neuronal K ATP -GOF as promoting these features. These findings suggest a possible origin of cognitive dysfunction in DEND and the need for novel drugs to treat neurological features induced by neuronal K ATP -GOF., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)

Nicotinamide adenine dinucleotide (NAD(+)) is an enzyme cofactor or cosubstrate in many essential biological pathways. To date, the primary source of neuronal NAD(+) has been unclear. NAD(+) can be synthesized from several different precursors, among which nicotinamide is the substrate predominantly used in mammals. The rate-limiting step in the NAD(+) biosynthetic pathway from nicotinamide is performed by nicotinamide phosphoribosyltransferase (Nampt). Here, we tested the hypothesis that neurons use intracellular Nampt-mediated NAD(+) biosynthesis by generating and evaluating mice lacking Nampt in forebrain excitatory neurons (CaMKIIαNampt(-/-) mice). CaMKIIαNampt(-/-) mice showed hippocampal and cortical atrophy, astrogliosis, microgliosis, and abnormal CA1 dendritic morphology by 2-3 months of age. Importantly, these histological changes occurred with altered intrahippocampal connectivity and abnormal behavior; including hyperactivity, some defects in motor skills, memory impairment, and reduced anxiety, but in the absence of impaired sensory processes or long-term potentiation of the Schaffer collateral pathway. These results clearly demonstrate that forebrain excitatory neurons mainly use intracellular Nampt-mediated NAD(+) biosynthesis to mediate their survival and function. Studying this particular NAD(+) biosynthetic pathway in these neurons provides critical insight into their vulnerability to pathophysiological stimuli and the development of therapeutic and preventive interventions for their preservation.

Genetic ablation of calcium-independent phospholipase A(2)gamma (iPLA(2)gamma) results in profound alterations in hippocampal phospholipid metabolism and mitochondrial phospholipid homeostasis resulting in enlarged and degenerating mitochondria leading to autophagy and cognitive dysfunction. Shotgun lipidomics demonstrated multiple alterations in hippocampal lipid metabolism in iPLA(2)gamma(-/-) mice including: 1) a markedly elevated hippocampal cardiolipin content with an altered molecular species composition characterized by a shift to shorter chain length molecular species; 2) alterations in both choline and ethanolamine glycerophospholipids, including a decreased plasmenylethanolamine content; 3) increased oxidized phosphatidylethanolamine molecular species; and 4) an increased content of ceramides. Electron microscopic examination demonstrated the presence of enlarged heteromorphic lamellar structures undergoing degeneration accompanied by the presence of ubiquitin positive spheroid inclusion bodies. Purification of these enlarged heteromorphic lamellar structures by buoyant density centrifugation and subsequent SDS-PAGE and proteomics identified them as degenerating mitochondria. Collectively, these results identify the obligatory role of iPLA(2)gamma in neuronal mitochondrial lipid metabolism and membrane structure demonstrating that iPLA(2)gamma loss of function results in a mitochondrial neurodegenerative disorder characterized by degenerating mitochondria, autophagy, and cognitive dysfunction.

PDAPP transgenic mice overexpress a mutant form of human amyloid precursor protein under control of the platelet-derived growth factor promoter in CNS neurons that causes early onset, familial Alzheimer's disease in humans. These mice, on a mixed genetic background, have been shown to have substantial learning impairments from early ages, as well as an age-dependent decline in learning ability that has been hypothesized to be caused by amyloid-beta (Abeta) accumulation. The goals of this study were to determine: (1) whether PDAPP mice on a pure C57BL/6 background develop more severe age-dependent learning deficits than wild-type mice; (2) if so, whether Abeta accumulation accounts for the excessive decline in learning ability; and (3) whether the learning deficits are reversible, even after significant Abeta deposition. At 4-6, 10-12, or 17-19 months of age, PDAPP and littermate wild-type mice on a C57BL/6 background were tested on a 5 week water maze protocol in which the location of the escape platform changed weekly, requiring the mice to repeatedly learn new information. PDAPP mice exhibited impaired spatial learning as early as 4 months (pre-Abeta deposition), and the performance of both wild-type and PDAPP mice declined with age. However, PDAPP mice exhibited significantly greater deterioration with age. Direct evidence for the role of Abeta accumulation in the age-related worsening in PDAPP mice was provided by the observation that systemic treatment over several weeks with the anti-Abeta antibody 10D5 reduced plaque deposition, increased plasma Abeta, improved hippocampal long-term potentiation, and improved behavioral performance in aged PDAPP mice with substantial Abeta burden.

Brain cholesterol metabolic products include neurosteroids and oxysterols, which play important roles in cellular physiology. In neurons, the cholesterol oxidation product, 24S-hydroxycholesterol (24S-HC), is a regulator of signaling and transcription. Here, we examined the behavioral effects of 24S-HC loss, using global and cell-selective genetic deletion of the synthetic enzyme CYP46A1. Mice that are globally deficient in CYP46A1 exhibited hypoactivity at young ages and unexpected increases in conditioned fear memory. Despite strong reductions in hippocampal 24S-HC in mice with selective loss of CYP46A1 in VGLUT1-positive cells, behavioral effects were not recapitulated in these conditional knockout mice. Global knockout produced strong, developmentally dependent transcriptional effects on select cholesterol metabolism genes. These included paradoxical changes in Liver X Receptor targets. Again, conditional knockout was insufficient to recapitulate most changes. Overall, our results highlight the complex effects of 24S-HC in an in vivo setting that are not fully predicted by known mechanisms. The results also demonstrate that the complete inhibition of enzymatic activity may be needed for a detectable, therapeutically relevant impact on gene expression and behavior. [ABSTRACT FROM AUTHOR]