Yu and Richardson et al. find that restriction of dietary isoleucine or valine promotes metabolic health in mice and that restriction of dietary isoleucine is required for the metabolic benefits of a low-protein diet. Furthermore, higher dietary isoleucine levels are associated with increased BMI in humans.

Calorie restriction (CR) promotes healthy aging in diverse species. Recently, it has been shown that fasting for a portion of each day has metabolic benefits and promotes lifespan. These findings complicate the interpretation of rodent CR studies, in which animals typically eat only once per day and rapidly consume their food, which collaterally imposes fasting. Here, we show that a prolonged fast is necessary for key metabolic, molecular and geroprotective effects of a CR diet. Using a series of feeding regimens, we dissect the effects of calories and fasting, and proceed to demonstrate that fasting alone recapitulates many of the physiological and molecular effects of CR. Our results shed new light on how both when and how much we eat regulate metabolic health and longevity, and demonstrate that daily prolonged fasting, and not solely reduced calorie intake, is likely responsible for the metabolic and geroprotective benefits of a CR diet.

Induction of protective mucosal T cell memory remains a formidable challenge to vaccinologists. Using a combination adjuvant strategy that elicits potent CD8 and CD4 T cell responses, we define the tenets of vaccine-induced pulmonary T cell immunity. An acrylic-acid-based adjuvant (ADJ), in combination with Toll-like receptor (TLR) agonists glucopyranosyl lipid adjuvant (GLA) or CpG, promotes mucosal imprinting but engages distinct transcription programs to drive different degrees of terminal differentiation and disparate polarization of T H 1/T C 1/T H 17/T C 17 effector/memory T cells. Combination of ADJ with GLA, but not CpG, dampens T cell receptor (TCR) signaling, mitigates terminal differentiation of effectors, and enhances the development of CD4 and CD8 T RM cells that protect against H1N1 and H5N1 influenza viruses. Mechanistically, vaccine-elicited CD4 T cells play a vital role in optimal programming of CD8 T RM and viral control. Taken together, these findings provide further insights into vaccine-induced multifaceted mucosal T cell immunity with implications in the development of vaccines against respiratorypathogens, including influenza virus and SARS-CoV-2.

The increasing prevalence of obesity is a serious threat to global health. Low protein (LP) diets are associated with a decreased risk of diabetes in humans, and a low protein diet promotes leanness and glycemic control in both rodents and humans. The effects of a LP diet on glycemic control are mediated by reduced dietary levels of the branched-chain amino acids (BCAAs). However, we have observed that reducing dietary levels of the other six essential amino acids leads to changes in body composition. Here, we find that dietary histidine plays a key role in the response to a LP diet. Specifically reducing dietary levels of histidine by 67% reduces weight gain of young, lean C57BL/6J mice, reducing both adipose and lean mass gain, without altering glucose metabolism. Specifically reducing dietary histidine rapidly reverses diet-induced obesity and hepatic steatosis in diet-induced obese mice, increasing insulin sensitivity; this normalization of metabolic health was associated not with caloric restriction or increased activity, but with increased energy expenditure that surprisingly did not require Fgf21. Histidine restriction started in mid-life promoted leanness and glucose tolerance in aged males, but did not affect frailty or lifespan in either sex. Finally, we demonstrate that variation in dietary histidine levels helps to explain body mass index differences in humans. Overall, our findings demonstrate that dietary histidine is a key regulator of weight and body composition in both mice and humans, and suggest that reducing dietary levels of histidine may be a highly translatable option for the treatment of obesity.

Low protein (LP) diets promote health and longevity in diverse species. Although the precise components of an LP diet that mediate its beneficial effects have not been defined, reducing dietary levels of the three branched-chain amino acids (BCAAs) leucine, isoleucine and valine promotes metabolic health in both sexes, and increases lifespan while reducing frailty in male, but not female, C57BL/6J mice. Each BCAA has unique metabolic effects, and we recently showed that restriction of isoleucine is both sufficient to promote metabolic health and required for the metabolic benefits of an LP diet in male C57BL/6J mice. Here, we tested the hypothesis that specifically restricting isoleucine could promote healthy aging in genetically heterogenous UM-HET3 mice. We find that a reduced isoleucine diet improves the metabolic health of both young and old HET3 mice, promoting leanness and glycemic control. Restriction of isoleucine starting in adult, 6 month old HET3 mice reprograms hepatic metabolism in a way distinct from an LP diet. Finally, we find that a reduced isoleucine diet reduces frailty and extends the lifespan of both male and female HET3 mice, but to a much greater degree in males. Our results demonstrate that restricting dietary isoleucine can increase health span and longevity in a genetically diverse population of mice, and suggests that reducing dietary levels of isoleucine may have great potential as a geroprotective intervention.

Lower intake of dietary protein is associated with improved metabolic health and reduced rates of age-associated diseases in humans, while low protein (LP) diets improve fitness and extend the lifespan of diverse animal species. Paradoxically, many athletes and bodybuilders consume high protein (HP) diets and protein or branched-chain amino acid supplements, yet remain fit and metabolically healthy. Here, we examine the effect of weight pulling, a validated progressive resistance exercise training regimen in mice fed either a LP diet or an isocaloric HP diet. We find that sedentary HP-fed male C57BL/6J mice gain significantly more fat mass than sedentary mice fed a LP diet, despite not consuming more calories. Resistance exercise was protective against this effect, blocking excess fat gain overall and in specific fat depots in HP-fed mice, but did not alter fat mass gain or distribution in LP-fed mice. In accordance with the widespread belief that high protein diets help promote muscle mass gain, the HP diet augmented the hypertrophy of the soleus, flexor digitorum longus (FDL) and the forearm flexor complex that occurred in response to exercise. While strength increased more rapidly in HP-fed mice, the maximum strength pulled by LP and HP-fed mice after 12 weeks was indistinguishable. Our results confirm the widespread belief that HP diets can augment muscle hypertrophy and strength gain induced by resistance exercise without negative metabolic consequences, while demonstrating that LP diets may be relatively advantageous in the sedentary. The results here highlight the need to consider both dietary composition and activity levels, not simply calories, when taking a precision nutrition approach to health.

Induction of protective mucosal T-cell memory remains a formidable challenge to vaccinologists. Using a novel adjuvant strategy that elicits unusually potent CD8 and CD4 T-cell responses, we have defined the tenets of vaccine-induced pulmonary T-cell immunity. An acrylic acid-based adjuvant (ADJ), in combination with TLR agonists glucopyranosyl lipid adjuvant (GLA) or CpG promoted mucosal imprinting but engaged distinct transcription programs to drive different degrees of terminal differentiation and disparate polarization of TH1/TC1/TH17/TC17 effector/memory T cells. Combination of ADJ with GLA, but not CpG, dampened TCR signaling, mitigated terminal differentiation of effectors and enhanced the development of CD4 and CD8 TRM that protected against H1N1 and H5N1 influenza viruses. Mechanistically, vaccine-elicited CD4 T cells played a vital role in optimal programming of CD8 TRM and anti-viral immunity. Taken together, these findings provide new insights into vaccine-induced multi-faceted mucosal T-cell immunity with significant implications in the development of vaccines against respiratory pathogens.

Calorie restriction (CR) promotes healthspan and extends the lifespan of diverse organisms, including mice, and there is intense interest in understanding the molecular mechanisms by which CR functions. Some studies have demonstrated that CR induces fibroblast growth factor 21 (FGF21), a hormone that regulates energy balance and that when overexpressed, promotes metabolic health and longevity in mice, but the role of FGF21 in the response to CR has not been investigated. We directly examined the role of FGF21 in the physiological and metabolic response to a CR diet by feeding Fgf21-/- and wild-type control mice either ad libitum (AL) diet or a 30% CR diet. Here, we find that FGF21 is largely dispensable for CR-induced improvements in body composition and energy balance, but that lack of Fgf21 blunts CR-induced changes in glucose tolerance and insulin sensitivity in females. Surprisingly, despite not affecting CR-induced changes in energy expenditure, loss of Fgf21 significantly blunts CR-induced beiging of white adipose tissue in male but not female mice. Our results shed new light on the molecular mechanisms involved in the beneficial effects of a CR diet, clarify that FGF21 is largely dispensable for the metabolic effects of a CR diet, and highlight a sex-dependent role for FGF21 in the molecular adaptation of white adipose tissue to CR.