Sterol regulatory element-binding protein-1c orchestrates metabolic remodeling of white adipose tissue by caloric restriction

Caloric restriction (CR) can delay onset of several age‐related pathophysiologies and extend lifespan in various species, including rodents. CR also induces metabolic remodeling involved in activation of lipid metabolism, enhancement of mitochondrial biogenesis, and reduction of oxidative stress in white adipose tissue (WAT). In studies using genetically modified mice with extended lifespans, WAT characteristics influenced mammalian lifespans. However, molecular mechanisms underlying CR‐associated metabolic remodeling of WAT remain unclear. Sterol regulatory element‐binding protein‐1c (Srebp‐1c), a master transcription factor of fatty acid (FA) biosynthesis, is responsible for the pathogenesis of fatty liver (steatosis). Our study showed that, under CR conditions, Srebp‐1c enhanced mitochondrial biogenesis via increased expression of peroxisome proliferator‐activated receptor gamma coactivator‐1α (Pgc‐1α) and upregulated expression of proteins involved in FA biosynthesis within WAT. However, via Srebp‐1c, most of these CR‐associated metabolic alterations were not observed in other tissues, including the liver. Moreover, our data indicated that Srebp‐1c may be an important factor both for CR‐associated suppression of oxidative stress, through increased synthesis of glutathione in WAT, and for the prolongevity action of CR. Our results strongly suggested that Srebp‐1c, the primary FA biosynthesis‐promoting transcriptional factor implicated in fatty liver disease, is also the food shortage‐responsive factor in WAT. This indicated that Srebp‐1c is a key regulator of metabolic remodeling leading to the beneficial effects of CR.

Impact of Ramadan Diurnal Intermittent Fasting on Hypoglycemic Events in Patients With Type 2 Diabetes: A Systematic Review of Randomized Controlled Trials and Observational Studies

Ramadan is the 9th month of the lunar calendar during which Muslims abstain from food and drink between dawn and sunset for 30 consecutive days. Ramadan fasting is observed by all healthy Muslim adults, as well many Muslims with type 2 diabetes (T2DM). Hypoglycemic events (HE) are a serious complication associated with diabetes management and are associated with increased cardiovascular disease risk. Conflicting results have been reported concerning the incidence of HE among people with T2DM observing Ramadan fasting. This review summarizes available scientific evidence on the occurrence of HE and the effects of different moderators on the incidence of HE among patients with T2DM during Ramadan. We conducted a systematic review of available observational studies and randomized controlled trials (RCTs) for patients with T2DM who fasted during Ramadan, with HE as the primary outcome. Ten databases were searched for relevant studies from inception until October 31, 2020. In total, 68 studies (35 RCTs and 33 observational studies) met the inclusion criteria. Non-sulfonylureas hypoglycemic medications showed superior effects in lowering the incidence of HE over sulfonylureas hypoglycemic medications. Variable moderators were associated with experiencing HE during Ramadan in both observational studies and RCTs, including sex, geographical location, body anthropometric indicators, season, dietary behaviors, fasting duration, time since diagnosis, and pre-fasting education. This comprehensive systematic review covered the largest number of observational and clinical studies investigating the impact of Ramadan on HE among patients with T2DM. The study highlights the significance of different moderators that influence the effect of Ramadan fasting on HE, including dietary behaviors, fasting time duration, sex, season, country, pre-fasting education, age, and time since diagnosis. The study also highlighted the impact of different hypoglycemic medications on HE and noted the superiority of non-sulfonylureas over sulfonylureas hypoglycemic medications in lowering the risk for hypoglycemia in people with T2DM during Ramadan fasting.

Modulation of Atg genes expression in aged rat liver, brain, and kidney by caloric restriction analyzed via single-nucleus/cell RNA sequencing

Dysregulation of macroautophagy/autophagy has been closely implicated in aging. Caloric restriction (CR) is an effective intervention of aging partially via activation of autophagy. Recently, a high-throughput single-cell RNA-seq technique has been employed to detect the comprehensive transcriptomes of individual cells. However, the transcriptional networks of ATG (autophagy related) genes in the aging process and the modulation of ATG genes expression by CR at the single-cell level have not been elucidated. Here, by performing data analysis of single nucleus/cells RNA sequencing in rats undergoing aging and the modulation by CR, we demonstrate that the transcription patterns of Atg genes in different cell types of rat liver, brain, and kidney are highly heterogeneous. Importantly, CR reversed aging-induced changes of multiple Atg genes across different cell types in the brain, liver, and kidney. In summary, our results, for the first time, provide comprehensive information on Atg gene expression in specific cell types of different organs in a mammal during aging and give novel insight into the protective role of autophagy and CR in aging at the single-cell resolution.Abbreviations: ATG genes: autophagy-related genes; Atg5: autophagy related 5; Atg7: autophagy related 7; CR: caloric restriction; DEATG: differentially expressed autophagy-related; NAFLD: nonalcoholic fatty liver disease; ScRNA-seq: single-cell RNA sequencing.

[Metabolic Alteration in Aging Process: Metabolic Remodeling in White Adipose Tissue by Caloric Restriction]

Caloric restriction (CR) improves whole-body metabolism, suppresses various age-related pathophysiological changes, and extends lifespan. The beneficial actions of CR are regulated in growth hormone (GH)/insulin-like growth factor-1 (IGF-1) signal-dependent and -independent manners. To clarify the GH/IGF-1-independent mechanism, we compared gene expression profiles in white adipose tissue (WAT) between CR and GH/IGF-1 suppression, and found that CR upregulated sterol regulatory element-binding protein 1c (SREBP-1c) regulatory gene expression. To validate the impact of SREBP-1c as a beneficial mediator of CR, we compared the responses to CR between wild-type and SREBP-1c knockout (KO) mice. CR extended lifespan, upregulated gene expression involved in FA biosynthesis, activated mitochondrial biogenesis, and suppressed oxidative stress predominantly in WAT. In contrast, most of these findings were not observed in KO mice. Furthermore, SREBP-1c was implicated in CR-associated mitochondrial activation through upregulation of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), a master regulator of mitochondrial biogenesis. Sirtuin-3 (SIRT3) regulates mitochondrial quality and is also involved in the beneficial actions of CR. We observed that CR upregulated the mature form of SIRT3 protein and mitochondrial intermediate peptidase (MIPEP), a mitochondrial signal peptidase (MtSPase), in WAT. MIPEP cleaved precursor form of SIRT3 to mature form, and activated certain mitochondrial matrix proteins, suggesting that MIPEP might contribute to maintenance of mitochondrial quality during CR via SIRT3 activation. Taken together, CR induces SREBP-1c-dependent metabolic remodeling, including enhancement of FA biosynthesis and mitochondrial activation, via PGC-1α, and improvement of mitochondria quality via Mipep in WAT, resulting in beneficial actions.

The effects of popular diets on bone health in the past decade: a narrative review

Bone health encompasses not only bone mineral density but also bone architecture and mechanical properties that can impact bone strength. While specific dietary interventions have been proposed to treat various diseases such as obesity and diabetes, their effects on bone health remain unclear. The aim of this review is to examine literature published in the past decade, summarize the effects of currently popular diets on bone health, elucidate underlying mechanisms, and provide solutions to neutralize the side effects. The diets discussed in this review include a ketogenic diet (KD), a Mediterranean diet (MD), caloric restriction (CR), a high-protein diet (HP), and intermittent fasting (IF). Although detrimental effects on bone health have been noticed in the KD and CR diets, it is still controversial, while the MD and HP diets have shown protective effects, and the effects of IF diets are still uncertain. The mechanism of these effects and the attenuation methods have gained attention and have been discussed in recent years: the KD diet interrupts energy balance and calcium metabolism, which reduces bone quality. Ginsenoside-Rb2, metformin, and simvastatin have been shown to attenuate bone loss during KD. The CR diet influences energy imbalance, glucocorticoid levels, and adipose tissue, causing bone loss. Adequate vitamin D and calcium supplementation and exercise training can attenuate these effects. The olive oil in the MD may be an effective component that protects bone health. HP diets also have components that protect bone health, but their mechanism requires further investigation. In IF, animal studies have shown detrimental effects on bone health, while human studies have not. Therefore, the effects of diets on bone health vary accordingly.

Sulfur Amino Acid Supplementation Abrogates Protective Effects of Caloric Restriction for Enhancing Bone Marrow Regrowth Following Ionizing Radiation

Radiation therapy damages and depletes total bone marrow (BM) cellularity, compromising safety and limiting effective dosing. Aging also strains total BM and BM hematopoietic stem and progenitor cell (HSPC) renewal and function, resulting in multi-system defects. Interventions that preserve BM and BM HSPC homeostasis thus have potential clinical significance. Here, we report that 50% calorie restriction (CR) for 7-days or fasting for 3-days prior to irradiation improved mouse BM regrowth in the days and weeks post irradiation. Specifically, one week of 50% CR ameliorated loss of total BM cellularity post irradiation compared to ad libitum-fed controls. CR-mediated BM protection was abrogated by dietary sulfur amino acid (i.e., cysteine, methionine) supplementation or pharmacological inhibition of sulfur amino acid metabolizing and hydrogen sulfide (H₂S) producing enzymes. Up to 2-fold increased proliferative capacity of ex vivo-irradiated BM isolated from food restricted mice relative to control mice indicates cell autonomy of the protective effect. Pretreatment with H₂S in vitro was sufficient to preserve proliferative capacity by over 50% compared to non-treated cells in ex vivo-irradiated BM and BM HSPCs. The exogenous addition of H₂S inhibited Ten eleven translocation 2 (TET2) activity in vitro, thus providing a potential mechanism of action. Short-term CR or fasting therefore offers BM radioprotection and promotes regrowth in part via altered sulfur amino acid metabolism and H₂S generation, with translational implications for radiation treatment and aging.

Deficiency of glucocorticoid receptor in bone marrow adipocytes has mild effects on bone and hematopoiesis but does not influence expansion of marrow adiposity with caloric restriction

Introduction

Unlike white adipose tissue depots, bone marrow adipose tissue (BMAT) expands during caloric restriction (CR). Although mechanisms for BMAT expansion remain unclear, prior research suggested an intermediary role for increased circulating glucocorticoids.

Methods

In this study, we utilized a recently described mouse model (BMAd-Cre) to exclusively target bone marrow adipocytes (BMAds) for elimination of the glucocorticoid receptor (GR) (i.e. Nr3c1) whilst maintaining GR expression in other adipose depots.

Results

Mice lacking GR in BMAds (BMAd-Nr3c1 -/-) and control mice (BMAd-Nr3c1 +/+) were fed ad libitum or placed on a 30% CR diet for six weeks. On a normal chow diet, tibiae of female BMAd-Nr3c1-/- mice had slightly elevated proximal trabecular metaphyseal bone volume fraction and thickness. Both control and BMAd-Nr3c1-/- mice had increased circulating glucocorticoids and elevated numbers of BMAds in the proximal tibia following CR. However, no significant differences in trabecular and cortical bone were observed, and quantification with osmium tetroxide and μCT revealed no difference in BMAT accumulation between control or BMAd-Nr3c1 -/- mice. Differences in BMAd size were not observed between BMAd-Nr3c1-/- and control mice. Interestingly, BMAd-Nr3c1-/- mice had decreased circulating white blood cell counts 4 h into the light cycle.

Discussion

In conclusion, our data suggest that eliminating GR from BMAd has minor effects on bone and hematopoiesis, and does not impair BMAT accumulation during CR.

Caloric restriction delays age-related muscle atrophy by inhibiting 11β-HSD1 to promote the differentiation of muscle stem cells

Introduction

Calorie restriction (CR) is an important direction for the delay of sarcopenia in elderly individuals. However, the specific mechanisms of CR against aging are still unclear.

Methods

In this study, we used a CR model of elderly mice with muscle-specific 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) knockout mice and 11β-HSD1 overexpression mice to confirm that CR can delay muscle aging by inhibiting 11β-HSD1 which can transform inactive GC(cortisone) into active GC(cortisol). The ability of self-proliferation and differentiation into muscle fibers of these mouse muscle stem cells (MuSCs) was observed in vitro. Additionally, the mitochondrial function and mitochondrial ATP production capacity of MuSCs were measured by mitochondrial oxygen consumption.

Results

It was found that the 11β-HSD1 expression level was increased in age-related muscle atrophy. Overexpression of 11β-HSD1 led to muscle atrophy in young mice, and 11β-HSD1 knockout rescued age-related muscle atrophy. Moreover, CR in aged mice reduced the local effective concentration of glucocorticoid (GC) through 11β-HSD1, thereby promoting the mitochondrial function and differentiation ability of MuSCs.

Conclusions

Together, our findings highlight promising sarcopenia protection with 40% CR in older ages. Furthermore, we speculated that targeting an 11β-HSD1-dependent metabolic pathway may represent a novel strategy for developing therapeutics against age-related muscle atrophy.