Cpt1a silencing in AgRP neurons improves cognitive and physical capacity and promotes healthy aging in male mice

Orexigenic neurons expressing agouti-related protein (AgRP) and neuropeptide Y in the arcuate nucleus (ARC) of the hypothalamus are activated in response to dynamic variations in the metabolic state, including exercise. We previously observed that carnitine palmitoyltransferase 1a (CPT1A), a rate-limiting enzyme of mitochondrial fatty acid oxidation, is a key factor in AgRP neurons, modulating whole-body energy balance and fluid homeostasis. However, the effect of CPT1A in AgRP neurons in aged mice and during exercise has not been explored yet. We have evaluated the physical and cognitive capacity of adult and aged mutant male mice lacking Cpt1a in AgRP neurons (Cpt1a KO). Adult Cpt1a KO male mice exhibited enhanced endurance performance, motor coordination, locomotion, and exploration compared with control mice. No changes were observed in anxiety-related behavior, cognition, and muscle strength. Adult Cpt1a KO mice showed a reduction in gastrocnemius and tibialis anterior muscle mass. The cross-sectional area (CSA) of these muscles were smaller than those of control mice displaying a myofiber remodeling from type II to type I fibers. In aged mice, changes in myofiber remodeling were maintained in Cpt1a KO mice, avoiding loss of physical capacity during aging progression. Additionally, aged Cpt1a KO mice revealed better cognitive skills, reduced inflammation, and oxidative stress in the hypothalamus and hippocampus. In conclusion, CPT1A in AgRP neurons appears to modulate health and protects against aging. Future studies are required to clarify whether CPT1A is a potential antiaging candidate for treating diseases affecting memory and physical activity.     

Group 1B phospholipase A₂ deficiency protects against diet-induced hyperlipidemia in mice

Excessive absorption of products of dietary fat digestion leads to type 2 diabetes and other obesity-related disorders. Mice deficient in the group 1B phospholipase A₂ (Pla2g1b), a gut digestive enzyme, are protected against diet-induced obesity and type 2 diabetes without displaying dietary lipid malabsorption. This study tested the hypothesis that inhibition of Pla2g1b protects against diet-induced hyperlipidemia. Results showed that the Pla2g1b^−/− mice had decreased plasma triglyceride and cholesterol levels compared with Pla2g1b^+/+ mice subsequent to feeding a high-fat, high-carbohydrate (hypercaloric) diet. These differences were evident before differences in body weight gains were observed. Injection of Poloxamer 407 to inhibit lipolysis revealed decreased VLDL production in Pla2g1b^−/− mice. Supplementation with lysophosphatidylcholine, the product of Pla2g1b hydrolysis, restored VLDL production rates in Pla2g1b^−/− mice and further elevated VLDL production in Pla2g1b^+/+ mice. The Pla2g1b^−/− mice also displayed decreased postprandial lipidemia compared with Pla2g1b^+/+ mice. These results show that, in addition to dietary fatty acids, gut-derived lysophospholipids derived from Pla2g1b hydrolysis of dietary and biliary phospholipids also promote hepatic VLDL production. Thus, the inhibition of lysophospholipid absorption via Pla2g1b inactivation may prove beneficial against diet-induced hyperlipidemia in addition to the protection against obesity and diabetes.     

Decreased Enterobacteriaceae translocation due to gut microbiota remodeling mediates the alleviation of premature aging by a high-fat diet

Aging-associated microbial dysbiosis exacerbates various disorders and dysfunctions, and is a major contributor to morbidity and mortality in the elderly, but the underlying cause of this aging-related syndrome is confusing. SIRT6 knockout (SIRT6 KO) mice undergo premature aging and succumb to death by 4 weeks, and are therefore useful as a premature aging research model. Here, fecal microbiota transplantation from SIRT6 KO mice into wild-type (WT) mice phenocopies the gut dysbiosis and premature aging observed in SIRT6 KO mice. Conversely, an expanded lifespan was observed in SIRT6 KO mice when transplanted with microbiota from WT mice. Antibiotic cocktail treatment attenuated inflammation and cell senescence in KO mice, directly suggesting that gut dysbiosis contributes to the premature aging of SIRT6 KO mice. Increased Enterobacteriaceae translocation, driven by the overgrowth of Escherichia coli, is the likely mechanism for the premature aging effects of microbiome dysregulation, which could be reversed by a high-fat diet. Our results provide a mechanism for the causal link between gut dysbiosis and aging, and support a beneficial effect of a high-fat diet for correcting gut dysbiosis and alleviating premature aging. This study provides a rationale for the integration of microbiome-based high-fat diets into therapeutic interventions against aging-associated diseases.     

Deficiency of myotubularin-related protein 14 influences body weight,metabolism, and inflammation in an age-dependent manner

Background

Myotubularin-related protein 14 (MTMR14) is a novel phosphoinositide phosphatase with roles in the maintenance of normal muscle performance, autophagy, and aging in mice. Our initial pilot study demonstrated that MTMR14 knock out (KO) mice gain weight earlier than their wild-type (WT) littermates, which suggests that this gene may also be involved in metabolism regulation.

Results

The present study evaluated the role of MTMR14 in the development of aging-associated obesity. We found that aged MTMR14 KO mice fed a normal chow diet exhibited increased serum triglyceride, total cholesterol, and glucose levels compared to age-matched WT controls. Lipid accumulation was also increased in aged KO mice. Several inflammatory cytokines and adipokines were dramatically dysregulated in the metabolic tissues of aged MTMR14 KO mice compared to control mice. Circulating inflammatory cytokines were significantly elevated and plasma adipokine levels were abnormally regulated in aged MTMR14 KO mice. These data suggest that MTMR14 deficiency caused a late-onset inflammation and metabolic dysfunction. Further study demonstrated that this exacerbated metabolic dysfunction and inflammation may be regulated by the phosphoinositide 3 kinase/protein kinase B and extracellular signal-regulated protein kinase signaling pathways.

Conclusions

Our current research suggests that MTMR14 deletion induces overweight and adult obesity accompanied by chronic inflammation in an age-dependent manner.

     

Premature aging in vitamin D receptor mutant mice

Hypervitaminosis vitamin D₃ has been recently implicated in premature aging through the regulation of 1alpha hydroxylase expression by klotho and fibroblast growth factor-23 (Fgf-23). Here we examined whether the lack of hormonal function of vitamin D₃ in mice is linked to aging phenomena. For this, we used vitamin D₃ receptor (VDR) “Tokyo” knockout (KO) mice (fed with a special rescue diet) and analyzed their growth, skin and cerebellar morphology, as well as overall motor performance. We also studied the expression of aging-related genes, such as Fgf-23, nuclear factor kappaB (NF-kappaB), p53, insulin like growth factor 1 (IGF1) and IGF1 receptor (IGF1R), in liver, as well as klotho in liver, kidney and prostate tissues. Overall, VDR KO mice showed several aging related phenotypes, including poorer survival, early alopecia, thickened skin, enlarged sebaceous glands and development of epidermal cysts. There was no difference either in the structure of cerebellum or in the number of Purkinje cells. Unlike the wildtype controls, VDR KO mice lose their ability to swim after 6 months of age. Expression of all the genes was lower in old VDR KO mice, but only NF-kappaB, Fgf-23, p53 and IGF1R were significantly lower. Since the phenotype of aged VDR knockout mice is similar to mouse models with hypervitaminosis D₃, our study suggests that VDR genetic ablation promotes premature aging in mice, and that vitamin D₃ homeostasis regulates physiological aging.     

NLRP3 inflammasome suppression improves longevity and prevents cardiac aging in male mice

While NLRP3‐inflammasome has been implicated in cardiovascular diseases, its role in physiological cardiac aging is largely unknown. During aging, many alterations occur in the organism, which are associated with progressive impairment of metabolic pathways related to insulin resistance, autophagy dysfunction, and inflammation. Here, we investigated the molecular mechanisms through which NLRP3 inhibition may attenuate cardiac aging. Ablation of NLRP3‐inflammasome protected mice from age‐related increased insulin sensitivity, reduced IGF‐1 and leptin/adiponectin ratio levels, and reduced cardiac damage with protection of the prolongation of the age‐dependent PR interval, which is associated with atrial fibrillation by cardiovascular aging and reduced telomere shortening. Furthermore, old NLRP3 KO mice showed an inhibition of the PI3K/AKT/mTOR pathway and autophagy improvement, compared with old wild mice and preserved Nampt‐mediated NAD⁺ levels with increased SIRT1 protein expression. These findings suggest that suppression of NLRP3 prevented many age‐associated changes in the heart, preserved cardiac function of aged mice and increased lifespan.     

Elevated COX2 expression and PGE2 production by downregulation of RXRα in senescent macrophages

Increased systemic level of inflammatory cytokines leads to numerous age-related diseases. In senescent macrophages, elevated prostaglandin E2 (PGE2) production contributes to the suppression of T cell function with aging, which increases the susceptibility to infections. However, the regulation of these inflammatory cytokines and PGE2 with aging still remains unclear. We have verified that cyclooxygenase (COX)-2 expression and PGE2 production are higher in LPS-stimulated macrophages from old mice than that from young mice. Downregulation of RXRα, a nuclear receptor that can suppress NF-κB activity, mediates the elevation of COX2 expression and PGE2 production in senescent macrophages. We also have found less induction of ABCA1 and ABCG1 by RXRα agonist in senescent macrophages, which partially accounts for high risk of atherosclerosis in aged population. Systemic treatment with RXRα antagonist HX531 in young mice increases COX2, TNF-α, and IL-6 expression in splenocytes. Our study not only has outlined a mechanism of elevated NF-κB activity and PGE2 production in senescent macrophages, but also provides RXRα as a potential therapeutic target for treating the age-related diseases.     

The protective effect of cycloastragenol on aging mouse circadian rhythmic disorder induced by d-galactose

Aging process in mammals is associated with a decline in amplitude and a long period of circadian behaviors which are regulated by a central circadian regulator in the suprachiasmatic nucleus (SCN) and local oscillators in peripheral tissues. It is unclear whether enhancing clock function can retard aging. Using fibroblasts expressing per2::lucSV and senescent cells, we revealed cycloastragenol (CAG), a natural aglycone derivative from astragaloside IV, as a clock amplitude enhancing small molecule. CAG could activate telomerase to antiaging, but no reports focused on its effects on circadian rhythm disorders in aging mice. Here we analyze the potential effects of CAG on d -galactose-induced aging mice on the circadian behavior and expression of clock genes. For this purpose, CAG (20 mg/kg orally), was administered daily to d -galactose (150 mg/kg, subcutaneous) mice model of aging for 6 weeks. An actogram analysis of free-running activity of these mice showed that CAG significantly enhances the locomotor activity. We further found that CAG increase expressions of per2 and bmal1 genes in liver and kidney of aging mouse. Furthermore, CAG enhanced clock protein BMAL1 and PER2 levels in aging mouse liver and SCN. Our results indicated that the CAG could restore the behavior of circadian rhythm in aging mice induced by d -galactose. These data of present study suggested that CAG could be used as a novel therapeutic strategy for the treatment of age-related circadian rhythm disruption.     

Age‐associated vascular inflammation promotes monocytosis during atherogenesis

Aging leads to a proinflammatory state within the vasculature without disease, yet whether this inflammatory state occurs during atherogenesis remains unclear. Here, we examined how aging impacts atherosclerosis using Ldlr^?/? mice, an established murine model of atherosclerosis. We found that aged atherosclerotic Ldlr^?/? mice exhibited enhanced atherogenesis within the aorta. Aging also led to increased LDL levels, elevated blood pressure on a low‐fat diet, and insulin resistance after a high‐fat diet (HFD). On a HFD, aging increased a monocytosis in the peripheral blood and enhanced macrophage accumulation within the aorta. When we conducted bone marrow transplant experiments, we found that stromal factors contributed to age‐enhanced atherosclerosis. To delineate these stromal factors, we determined that the vasculature exhibited an age‐enhanced inflammatory response consisting of elevated production of CCL‐2, osteopontin, and IL‐6 during atherogenesis. In addition, in vitro cultures showed that aging enhanced the production of osteopontin by vascular smooth muscle cells. Functionally, aged atherosclerotic aortas displayed higher monocyte chemotaxis than young aortas. Hence, our study has revealed that aging induces metabolic dysfunction and enhances vascular inflammation to promote a peripheral monocytosis and macrophage accumulation within the atherosclerotic aorta.     

Alteration in N-glycomics during mouse aging: a role for FUT8

We recently reported that N-glycosylation changes during human aging. To further investigate the molecular basis determining these alterations, the aging process in mice was studied. N-glycan profiling of mouse serum glycoproteins in different age groups of healthy C57BL/6 mice showed substantial age-related changes in three major N-glycan structures: under-galactosylated biantennary (NGA2F), biantennary (NA2), and core α-1,6-fucosylated -β-galactosylated biantennary structures (NA2F). Mice defective in klotho gene expression (kl/kl), which have a shortened lifespan, displayed a similar but accelerated trend. Interestingly, the opposite trend was observed in slow-aging Snell Dwarf mice (dw/dw) and in mice fed a calorically restricted diet. We also discovered that increased expression and activity of α-1,6-fucosyltransferase (FUT8) in the liver are strongly linked to the age-related changes in glycosylation and that this increased FUT8 and fucosylation influence IGF-1 signaling. These data demonstrate that the glycosylation machinery in liver cells is significantly affected during aging and that age-related increased FUT8 activity could influence the aging process by altering the sensitivity of the IGF-1R signaling pathway.     

Aging differentially alters the expression of angiogenic genes in a tissue-dependent manner

Organ functions are altered and impaired during aging, thereby resulting in increased morbidity of age-related diseases such as Alzheimer’s disease, diabetes, and heart failure in the elderly. Angiogenesis plays a crucial role in the maintenance of tissue homeostasis, and aging is known to reduce the angiogenic capacity in many tissues. Here, we report the differential effects of aging on the expression of angiogenic factors in different tissues, representing a potentially causes for age-related metabolic disorders. PCR-array analysis revealed that many of angiogenic genes were down-regulated in the white adipose tissue (WAT) of aged mice, whereas they were largely up-regulated in the skeletal muscle (SM) of aged mice compared to that in young mice. Consistently, blood vessel density was substantially reduced and hypoxia was exacerbated in WAT of aged mice compared to that in young mice. In contrast, blood vessel density in SM of aged mice was well preserved and was not different from that in young mice. Moreover, we identified that endoplasmic reticulum (ER) stress was strongly induced in both WAT and SM during aging in vivo. We also found that ER stress significantly reduced the expression of angiogenic genes in 3T3-L1 adipocytes, whereas it increased their expression in C2C12 myotubes in vitro. These results collectively indicate that aging differentially affects the expression of angiogenic genes in different tissues, and that aging-associated down-regulation of angiogenic genes in WAT, at least in part through ER stress, is potentially involved in the age-related adipose tissue dysfunction.     

Glutaredoxin 2 (Grx2) Gene Deletion Induces Early Onset of Age-dependent Cataracts in Mice

Glutaredoxin 2 (Grx2) is an isozyme of glutaredoxin1 (thioltransferase) present in the mitochondria and nucleus with disulfide reductase and peroxidase activities, and it controls thiol/disulfide balance in cells. In this study, we investigated whether Grx2 gene deletion could induce faster age-related cataract formation and elucidated the biochemical changes effected by Grx2 gene deletion that may contribute to lens opacity. Slit lamp was used to examine the lenses in Grx2 knock-out (KO) mice and age-matched wild-type (WT) mice ages 1 to 16 months. In the Grx2 null mice, the lens nuclear opacity began at 5 months, 3 months sooner than that of the control mice, and the progression of cataracts was also much faster than the age-matched controls. Lenses of KO mice contained lower levels of protein thiols and GSH with a significant accumulation of S-glutathionylated proteins. Actin, αA-crystallin, and βB2-crystallin were identified by Western blot and mass spectroscopy as the major S-glutathionylated proteins in the lenses of 16-month-old Grx2 KO mice. Compared with the WT control, the lens of Grx2 KO mice had only 50% of the activity in complex I and complex IV and less than 10% of the ATP pool. It was concluded that Grx2 gene deletion altered the function of lens structural proteins through S-glutathionylation and also caused severe disturbance in mitochondrial function. These combined alterations affected lens transparency.     

Osbpl8 Deficiency in Mouse Causes an Elevation of High-Density Lipoproteins and Gender-Specific Alterations of Lipid Metabolism

OSBP-related protein 8 (ORP8) encoded by Osbpl8 is an endoplasmic reticulum sterol sensor implicated in cellular lipid metabolism. We generated an Osbpl8^−/− (KO) C57Bl/6 mouse strain. Wild-type and Osbpl8KO animals at the age of 13-weeks were fed for 5 weeks either chow or high-fat diet, and their plasma lipids/lipoproteins and hepatic lipids were analyzed. The chow-fed Osbpl8KO male mice showed a marked elevation of high-density lipoprotein (HDL) cholesterol (+79%) and phospholipids (+35%), while only minor increase of apolipoprotein A-I (apoA-I) was detected. In chow-fed female KO mice a less prominent increase of HDL cholesterol (+27%) was observed, while on western diet the HDL increment was prominent in both genders. The HDL increase was accompanied by an elevated level of HDL-associated apolipoprotein E in male, but not female KO animals. No differences between genotypes were observed in lecithin:cholesterol acyltransferase (LCAT) or hepatic lipase (HL) activity, or in the fractional catabolic rate of fluorescently labeled mouse HDL injected in chow-diet fed animals. The Osbpl8KO mice of both genders displayed reduced phospholipid transfer protein (PLTP) activity, but only on chow diet. These findings are consistent with a model in which Osbpl8 deficiency results in altered biosynthesis of HDL. Consistent with this hypothesis, ORP8 depleted mouse hepatocytes secreted an increased amount of nascent HDL into the culture medium. In addition to the HDL phenotype, distinct gender-specific alterations in lipid metabolism were detected: Female KO animals on chow diet showed reduced lipoprotein lipase (LPL) activity and increased plasma triglycerides, while the male KO mice displayed elevated plasma cholesterol biosynthetic markers cholestenol, desmosterol, and lathosterol. Moreover, modest gender-specific alterations in the hepatic expression of lipid homeostatic genes were observed. In conclusion, we report the first viable OsbplKO mouse model, demonstrating a HDL elevating effect of Osbpl8 knock-out and additional gender- and/or diet-dependent impacts on lipid metabolism.     

Mitochondrial DNA heteroplasmy rises in substantial nigra of aged PINK1 KO mice

Mutations in PINK1 and Parkin result in early-onset autosomal recessive Parkinson’s disease (PD). PINK1/Parkin pathway maintain mitochondrial function by mediating the clearance of damaged mitochondria. However, the role of PINK1/Parkin in maintaining the balance of mtDNA heteroplasmy is still unknown. Here, we isolated mitochondrial DNA (mtDNA) from cortex, striatum and substantia nigra of wildtype (WT), PINK1 knockout (PINK1 KO) and Parkin knockout (Parkin KO) mice to analyze mtDNA heteroplasmy induced by PINK1/Parkin deficiency or aging. Our results showed that the Single Nucleotide Variants (SNVs) of late-onset somatic variants mainly increased with aging. Conversely, the early-onset somatic variants exhibited significant increase in the cortex and substantia nigra of PINK1 KO mice than WT mice of the same age. Increased average variant allele frequency was observed in aged PINK1 KO mice and in substantial nigra of aged Parkin KO mice than in WT mice. Cumulative variant allele frequency in the substantia nigra of PINK1 KO mice was significantly higher than that in WT mice, further supporting the pivotal role of PINK1 in mtDNA maintenance.This study presented a new evidence for PINK1 and Parkin in participating in mitochondrial quality control and provided clues for further revealing the role of PINK1 and Parkin in the pathogenesis of PD.     

Quantitative identification of senescent cells in aging and disease

Senescent cells are present in premalignant lesions and sites of tissue damage and accumulate in tissues with age. In vivo identification, quantification and characterization of senescent cells are challenging tasks that limit our understanding of the role of senescent cells in diseases and aging. Here, we present a new way to precisely quantify and identify senescent cells in tissues on a single‐cell basis. The method combines a senescence‐associated beta‐galactosidase assay with staining of molecular markers for cellular senescence and of cellular identity. By utilizing technology that combines flow cytometry with high‐content image analysis, we were able to quantify senescent cells in tumors, fibrotic tissues, and tissues of aged mice. Our approach also yielded the finding that senescent cells in tissues of aged mice are larger than nonsenescent cells. Thus, this method provides a basis for quantitative assessment of senescent cells and it offers proof of principle for combination of different markers of senescence. It paves the way for screening of senescent cells for identification of new senescence biomarkers, genes that bypass senescence or senolytic compounds that eliminate senescent cells, thus enabling a deeper understanding of the senescent state in vivo.     

Effects of myostatin deletion in aging mice

Inhibitors of myostatin, a negative regulator of skeletal muscle mass, are being developed to mitigate aging-related muscle loss. Knock-out (KO) mouse studies suggest myostatin also affects adiposity, glucose handling and cardiac growth. However, the cardiac consequences of inhibiting myostatin remain unclear. Myostatin inhibition can potentiate cardiac growth in specific settings ( Morissette et al., 2006) , a concern because of cardiac hypertrophy is associated with adverse clinical outcomes. Therefore, we examined the systemic and cardiac effects of myostatin deletion in aged mice (27–30 months old). Heart mass increased comparably in both wild-type (WT) and KO mice. Aged KO mice maintained twice as much quadriceps mass as aged WT; however, both groups lost the same percentage (36%) of adult muscle mass. Dual-energy X-ray absorptiometry revealed increased bone density, mineral content, and area in aged KO vs. aged WT mice. Serum insulin and glucose levels were lower in KO mice. Echocardiography showed preserved cardiac function with better fractional shortening (58.1% vs. 49.4%, P  = 0.002) and smaller left ventricular diastolic diameters (3.41 vs. 2.71, P  = 0.012) in KO vs. WT mice. Phospholamban phosphorylation was increased 3.3-fold in KO hearts ( P  < 0.05), without changes in total phospholamban, sarco(endo)plasmic reticulum calcium ATPase 2a or calsequestrin. Aged KO hearts showed less fibrosis by Masson's Trichrome staining. Thus, myostatin deletion does not affect aging-related increases in cardiac mass and appears beneficial for bone density, insulin sensitivity and heart function in senescent mice. These results suggest that clinical interventions designed to inhibit skeletal muscle mass loss with aging could have beneficial effects on other organ systems as well.     

Longitudinal in vivo developmental changes of metabolites in the hippocampus of Fmr1 knockout mice

Fragile X syndrome (FXS) is the most common form of inherited mental retardation and is studied in the Fmr1 knockout (KO) mouse, which models both the anatomical and behavioral changes observed in FXS patients. In vitro studies have shown many alterations in synaptic plasticity and increased density of immature dendritic spines in the hippocampus, a region involved in learning and memory. In this study, magnetic resonance imaging (MRI) and ¹H magnetic resonance spectroscopy (MRS) were used to determine in vivo longitudinal changes in volume and metabolites in the hippocampus during the critical period of early myelination and synaptogenesis at post‐natal days (PND) 18, 21, and 30 in Fmr1 KO mice compared with wild‐type (WT) controls. MRI demonstrated an increase in volume of the hippocampus in the Fmr1 KO mouse compared with controls. MRS revealed significant developmental changes in the ratios of hippocampal metabolites N‐acetylaspartate (NAA), myo‐inositol (Ins), and taurine to total creatine (tCr) in Fmr1 KO mice compared with WT controls. Ins was decreased at PND 30, and taurine was increased at all ages studied in Fmr1 KO mice compared with controls. An imbalance of brain metabolites in the hippocampus of Fmr1 KO mice during the critical developmental period of synaptogenesis and early myelination could have long‐lasting effects that adversely affect brain development and contribute to ongoing alterations in brain function.     

Nupr1 deficiency downregulates HtrA1, enhances SMAD1 signaling,and suppresses age-related bone loss in male mice

Nuclear protein 1 (NUPR1) is a stress-induced protein activated by various stresses, such as inflammation and oxidative stress. We previously reported that Nupr1 deficiency increased bone volume by enhancing bone formation in 11-week-old mice. Analysis of differentially expressed genes between wild-type (WT) and Nupr1-knockout (Nupr1-KO) osteocytes revealed that high temperature requirement A 1 (HTRA1), a serine protease implicated in osteogenesis and transforming growth factor-β signaling was markedly downregulated in Nupr1-KO osteocytes. Nupr1 deficiency also markedly reduced HtrA1 expression, but enhanced SMAD1 signaling in in vitro-cultured primary osteoblasts. In contrast, Nupr1 overexpression enhanced HtrA1 expression in osteoblasts, suggesting that Nupr1 regulates HtrA1 expression, thereby suppressing osteoblastogenesis. Since HtrA1 is also involved in cellular senescence and age-related diseases, we analyzed aging-related bone loss in Nupr1-KO mice. Significant spine trabecular bone loss was noted in WT male and female mice during 6−19 months of age, whereas aging-related trabecular bone loss was attenuated, especially in Nupr1-KO male mice. Moreover, cellular senescence-related markers were upregulated in the osteocytes of 6−19-month-old WT male mice but markedly downregulated in the osteocytes of 19-month-old Nupr1-KO male mice. Oxidative stress-induced cellular senescence stimulated Nupr1 and HtrA1 expression in in vitro-cultured primary osteoblasts, and Nupr1 overexpression enhanced p16^ink4a expression in osteoblasts. Finally, NUPR1 expression in osteocytes isolated from the bones of patients with osteoarthritis was correlated with age. Collectively, these results indicate that Nupr1 regulates HtrA1-mediated osteoblast differentiation and senescence. Our findings unveil a novel Nupr1/HtrA1 axis, which may play pivotal roles in bone formation and age-related bone loss.