Effects of a high-phosphate diet on vascular calcification and abdominal aortic aneurysm in mice.

AIM: Vascular aging is an important risk factor for cardiovascular diseases, including abdominal aortic aneurysm (AAA) and pathological aortic dilatation, playing a critical role in the morbidity and mortality of older adults. Vascular calcification, a phenotype of vascular aging, is frequently associated with AAA. However, this association remains unclear owing to the lack of animal models. This study investigated the effects of a high-phosphate diet (HPD), a prominent trigger of vascular calcification in AAA. METHODS: Eight-week-old male mice were fed either a normal diet (ND; Ca 1.18%/P 1.07% = 1.10) or an HPD (Ca 1.23%/P 1.65% = 0.75) for 4 weeks. Subsequently, AAA was induced using CaCl2 application and angiotensin II (AngII) infusion for 4 weeks. RESULTS: The HPD resulted in more pronounced AAA formation than did the ND. Importantly, vascular calcification was observed only in the aorta of the HPD mice. Enhanced Runt-related transcription factor 2 expression and apoptosis (downregulation of growth arrest-specific gene 6/pAkt survival pathway), two major mechanisms of vascular calcification, were also observed. Furthermore, increased IL-6 and F4/80 expression was observed in the aorta of HPD mice. In RAW264.7 cells, inorganic phosphate enhanced IL-6 and IL-1ß expression under AngII priming. Ferric citrate, a phosphate binder, significantly inhibited HPD-induced AAA formation. CONCLUSIONS: These findings suggest that HPD induces vascular calcification and AAA formation, possibly through inflammation. This murine model suggests that vascular calcification induced by phosphate burden may be a therapeutic target for vascular diseases, including AAA. Geriatr Gerontol Int 2024; ••: ••-••.

An NAD+-dependent metabolic checkpoint regulates hematopoietic stem cell activation and aging.

How hematopoietic stem cells (HSCs) maintain metabolic homeostasis to support tissue repair and regeneration throughout the lifespan is elusive. Here, we show that CD38, an NAD+-dependent metabolic enzyme, promotes HSC proliferation by inducing mitochondrial Ca2+ influx and mitochondrial metabolism in young mice. Conversely, aberrant CD38 upregulation during aging is a driver of HSC deterioration in aged mice due to dysregulated NAD+ metabolism and compromised mitochondrial stress management. The mitochondrial calcium uniporter, a mediator of mitochondrial Ca2+ influx, also supports HSC proliferation in young mice yet drives HSC decline in aged mice. Pharmacological inactivation of CD38 reverses HSC aging and the pathophysiological changes of the aging hematopoietic system in aged mice. Together, our study highlights an NAD+ metabolic checkpoint that balances mitochondrial activation to support HSC proliferation and mitochondrial stress management to enhance HSC self-renewal throughout the lifespan, and links aberrant Ca2+ signaling to HSC aging.

TET3 plays a critical role in white adipose development and diet-induced remodeling.

Maintaining healthy adipose tissue is crucial for metabolic health, requiring a deeper understanding of adipocyte development and response to high-calorie diets. This study highlights the importance of TET3 during white adipose tissue (WAT) development and expansion. Selective depletion of Tet3 in adipose precursor cells (APCs) reduces adipogenesis, protects against diet-induced adipose expansion, and enhances whole-body metabolism. Transcriptomic analysis of wild-type and Tet3 knockout (KO) APCs unveiled TET3 target genes, including Pparg and several genes linked to the extracellular matrix, pivotal for adipogenesis and remodeling. DNA methylation profiling and functional studies underscore the importance of DNA demethylation in gene regulation. Remarkably, targeted DNA demethylation at the Pparg promoter restored its transcription. In conclusion, TET3 significantly governs adipogenesis and diet-induced adipose expansion by regulating key target genes in APCs.

The mitochondrial unfolded protein response regulates hippocampal neural stem cell aging.

Aging results in a decline in neural stem cells (NSCs), neurogenesis, and cognitive function, and evidence is emerging to demonstrate disrupted adult neurogenesis in the hippocampus of patients with several neurodegenerative disorders. Here, single-cell RNA sequencing of the dentate gyrus of young and old mice shows that the mitochondrial protein folding stress is prominent in activated NSCs/neural progenitors (NPCs) among the neurogenic niche, and it increases with aging accompanying dysregulated cell cycle and mitochondrial activity in activated NSCs/NPCs in the dentate gyrus. Increasing mitochondrial protein folding stress results in compromised NSC maintenance and reduced neurogenesis in the dentate gyrus, neural hyperactivity, and impaired cognitive function. Reducing mitochondrial protein folding stress in the dentate gyrus of old mice improves neurogenesis and cognitive function. These results establish the mitochondrial protein folding stress as a driver of NSC aging and suggest approaches to improve aging-associated cognitive decline.

The hepatic integrated stress response suppresses the somatotroph axis to control liver damage in nonalcoholic fatty liver disease.

Nonalcoholic fatty liver disease (NAFLD) can be ameliorated by calorie restriction, which leads to the suppressed somatotroph axis. Paradoxically, the suppressed somatotroph axis is associated with patients with NAFLD and is correlated with the severity of fibrosis. How the somatotroph axis becomes dysregulated and whether the repressed somatotroph axis impacts liver damage during the progression of NAFLD are unclear. Here, we identify a regulatory branch of the hepatic integrated stress response (ISR), which represses the somatotroph axis in hepatocytes through ATF3, resulting in enhanced cell survival and reduced cell proliferation. In mouse models of NAFLD, the ISR represses the somatotroph axis, leading to reduced apoptosis and inflammation but decreased hepatocyte proliferation and exacerbated fibrosis in the liver. NAD+ repletion reduces the ISR, rescues the dysregulated somatotroph axis, and alleviates NAFLD. These results establish that the hepatic ISR suppresses the somatotroph axis to control cell fate decisions and liver damage in NAFLD.

The therapeutic promises of NAD+ boosters.

Numerous preclinical studies implicate the decline in NAD+ signaling in developing aging- and obesity-associated metabolic disorders. Yoshino et al. (2021) now provide the clinical evidence that an NAD+ booster increases muscle insulin sensitivity in postmenopausal prediabetic women, validating the therapeutic promises of NAD+ boosters in humans.

Open-Ended Video Question Answering via Multi-Modal Conditional Adversarial Networks.

As a challenging task in visual information retrieval, open-ended long-form video question answering automatically generates the natural language answer from the referenced video content according to the given question. However, the existing video question answering works mainly focus on the short-form video, which may be ineffectively applied for long-form video question answering directly, due to the insufficiency of modeling the semantic representation of long-form video content. In this paper, we study the problem of open-ended long-form video question answering from the viewpoint of hierarchical multimodal conditional adversarial network learning. We propose the hierarchical attentional encoder network to learn the joint representation of long-form video content and given question with adaptive video segmentation. We then devise the reinforced decoder network to generate the natural language answer for openended video question answering with multi-modal conditional adversarial network learning. We construct three large-scale open-ended video question answering datasets. The extensive experiments validate the effectiveness of our method.

Stem Cell Metabolism and Diet.

PURPOSE OF REVIEW: Diet has profound impacts on health and longevity. Evidence is emerging to suggest that diet impinges upon the metabolic pathways in tissue-specific stem cells to influence health and disease. Here, we review the similarities and differences in the metabolism of stem cells from several tissues, and highlight the mitochondrial metabolic checkpoint in stem cell maintenance and aging. We discuss how diet engages the nutrient sensing metabolic pathways and impacts stem cell maintenance. Finally, we explore the therapeutic implications of dietary and metabolic regulation of stem cells. RECENT FINDINGS: Stem Cell transition from quiescence to proliferation is associated with a metabolic switch from glycolysis to mitochondrial OXPHOS and the mitochondrial metabolic checkpoint is critically controlled by the nutrient sensors SIRT2, SIRT3, and SIRT7 in hematopoietic stem cells. Intestine stem cell homeostasis during aging and in response to diet is critically dependent on fatty acid metabolism and ketone bodies and is influenced by the niche mediated by the nutrient sensor mTOR. SUMMARY: Nutrient sensing metabolic pathways critically regulate stem cell maintenance during aging and in response to diet. Elucidating the molecular mechanisms underlying dietary and metabolic regulation of stem cells provides novel insights for stem cell biology and may be targeted therapeutically to reverse stem cell aging and tissue degeneration.