Cysteine depletion triggers adipose tissue thermogenesis and weight-loss.

Dietary interventions such as caloric restriction (CR) 1 and methionine restriction 2 that prolong lifespan induce the 'browning' of white adipose tissue (WAT), an adaptive metabolic response that increases heat production to maintain health 3,4 . However, how diet influences adipose browning and metabolic health is unclear. Here, we identified that weight-loss induced by CR in humans 5 reduces cysteine concentration in WAT suggesting depletion of this amino-acid may be involved in metabolic benefits of CR. To investigate the role of cysteine on organismal metabolism, we created a cysteine-deficiency mouse model in which dietary cysteine was eliminated and cystathionine γ-lyase (CTH) 6 , the enzyme that synthesizes cysteine was conditionally deleted. Using this animal model, we found that systemic cysteine-depletion causes drastic weight-loss with increased fat utilization and browning of adipose tissue. The restoration of dietary cysteine in cysteine-deficient mice rescued weight loss together with reversal of adipose browning and increased food-intake in an on-demand fashion. Mechanistically, cysteine deficiency induced browning and weight loss is dependent on sympathetic nervous system derived noradrenaline signaling via ß3-adrenergic-receptors and does not require UCP1. Therapeutically, in high-fat diet fed obese mice, one week of cysteine-deficiency caused 30% weight-loss and reversed inflammation. These findings thus establish that cysteine is essential for organismal metabolism as removal of cysteine in the host triggers adipose browning and rapid weight loss.

[WITHDRAWN] Activation of transsulfuration pathway to maintain cysteine is a thermogenic checkpoint for the conservation of energy.

The authors have requested that this preprint be removed from Research Square.

Innate immune cell-intrinsic ketogenesis is dispensable for organismal metabolism and age-related inflammation.

Aging is accompanied by chronic low-grade inflammation, but the mechanisms that allow this to persist are not well understood. Ketone bodies are alternative fuels produced when glucose is limited and improve indicators of healthspan in aging mouse models. Moreover, the most abundant ketone body, ß-hydroxybutyrate, inhibits the NLRP3 inflammasome in myeloid cells, a key potentiator of age-related inflammation. Given that myeloid cells express ketogenic machinery, we hypothesized this pathway may serve as a metabolic checkpoint of inflammation. To test this hypothesis, we conditionally ablated ketogenesis by disrupting expression of the terminal enzyme required for ketogenesis, 3-Hydroxy-3-Methylglutaryl-CoA Lyase (HMGCL). By deleting HMGCL in the liver, we validated the functional targeting and establish that the liver is the only organ that can produce the life-sustaining quantities of ketone bodies required for survival during fasting or ketogenic diet feeding. Conditional ablation of HMGCL in neutrophils and macrophages had modest effects on body weight and glucose tolerance in aging but worsened glucose homeostasis in myeloid cell-specific Hmgcl-deficient mice fed a high-fat diet. Our results suggest that during aging, liver-derived circulating ketone bodies might be more important for deactivating the NLRP3 inflammasome and controlling organismal metabolism.

IL-33 causes thermogenic failure in aging by expanding dysfunctional adipose ILC2.

Aging impairs the integrated immunometabolic responses, which have evolved to maintain core body temperature in homeotherms to survive cold stress, infections, and dietary restriction. Adipose tissue inflammation regulates the thermogenic stress response, but how adipose tissue-resident cells instigate thermogenic failure in the aged are unknown. Here, we define alterations in the adipose-resident immune system and identify that type 2 innate lymphoid cells (ILC2s) are lost in aging. Restoration of ILC2 numbers in aged mice to levels seen in adults through IL-33 supplementation failed to rescue old mice from metabolic impairment and increased cold-induced lethality. Transcriptomic analyses revealed intrinsic defects in aged ILC2, and adoptive transfer of adult ILC2s are sufficient to protect old mice against cold. Thus, the functional defects in adipose ILC2s during aging drive thermogenic failure.

Ketogenic diet restrains aging-induced exacerbation of coronavirus infection in mice.

Increasing age is the strongest predictor of risk of COVID-19 severity and mortality. Immunometabolic switch from glycolysis to ketolysis protects against inflammatory damage and influenza infection in adults. To investigate how age compromises defense against coronavirus infection, and whether a pro-longevity ketogenic diet (KD) impacts immune surveillance, we developed an aging model of natural murine beta coronavirus (mCoV) infection with mouse hepatitis virus strain-A59 (MHV-A59). When inoculated intranasally, mCoV is pneumotropic and recapitulates several clinical hallmarks of COVID-19 infection. Aged mCoV-A59-infected mice have increased mortality and higher systemic inflammation in the heart, adipose tissue, and hypothalamus, including neutrophilia and loss of γδ T cells in lungs. Activation of ketogenesis in aged mice expands tissue protective γδ T cells, deactivates the NLRP3 inflammasome, and decreases pathogenic monocytes in lungs of infected aged mice. These data establish harnessing of the ketogenic immunometabolic checkpoint as a potential treatment against coronavirus infection in the aged.

Ketogenesis restrains aging-induced exacerbation of COVID in a mouse model.

Increasing age is the strongest predictor of risk of COVID-19 severity. Unregulated cytokine storm together with impaired immunometabolic response leads to highest mortality in elderly infected with SARS-CoV-2. To investigate how aging compromises defense against COVID-19, we developed a model of natural murine beta coronavirus (mCoV) infection with mouse hepatitis virus strain MHV-A59 (mCoV-A59) that recapitulated majority of clinical hallmarks of COVID-19. Aged mCoV-A59-infected mice have increased mortality and higher systemic inflammation in the heart, adipose tissue and hypothalamus, including neutrophilia and loss of γδ T cells in lungs. Ketogenic diet increases beta-hydroxybutyrate, expands tissue protective γδ T cells, deactivates the inflammasome and decreases pathogenic monocytes in lungs of infected aged mice. These data underscore the value of mCoV-A59 model to test mechanism and establishes harnessing of the ketogenic immunometabolic checkpoint as a potential treatment against COVID-19 in the elderly. HIGHLIGHTS: - Natural MHV-A59 mouse coronavirus infection mimics COVID-19 in elderly.- Aged infected mice have systemic inflammation and inflammasome activation.- Murine beta coronavirus (mCoV) infection results in loss of pulmonary γδ T cells.- Ketones protect aged mice from infection by reducing inflammation. ETOC BLURB: Elderly have the greatest risk of death from COVID-19. Here, Ryu et al report an aging mouse model of coronavirus infection that recapitulates clinical hallmarks of COVID-19 seen in elderly. The increased severity of infection in aged animals involved increased inflammasome activation and loss of γδ T cells that was corrected by ketogenic diet.

GPR119 Agonism Increases Glucagon Secretion During Insulin-Induced Hypoglycemia.

Insulin-induced hypoglycemia in diabetes is associated with impaired glucagon secretion. In this study, we tested whether stimulation of GPR119, a G-protein-coupled receptor expressed in pancreatic islet as well as enteroendocrine cells and previously shown to stimulate insulin and incretin secretion, might enhance glucagon secretion during hypoglycemia. In the study, GPR119 agonists were applied to isolated islets or perfused pancreata to assess insulin and glucagon secretion during hypoglycemic or hyperglycemic conditions. Insulin infusion hypoglycemic clamps were performed with or without GPR119 agonist pretreatment to assess glucagon counterregulation in healthy and streptozotocin (STZ)-induced diabetic rats, including those exposed to recurrent bouts of insulin-induced hypoglycemia that leads to suppression of hypoglycemia-induced glucagon release. Hypoglycemic clamp studies were also conducted in GPR119 knockout (KO) mice to evaluate whether the pharmacological stimulatory actions of GPR119 agonists on glucagon secretion during hypoglycemia were an on-target effect. The results revealed that GPR119 agonist-treated pancreata or cultured islets had increased glucagon secretion during low glucose perfusion. In vivo, GPR119 agonists also significantly increased glucagon secretion during hypoglycemia in healthy and STZ-diabetic rats, a response that was absent in GPR119 KO mice. In addition, impaired glucagon counterregulatory responses were restored by a GPR119 agonist in STZ-diabetic rats that were exposed to antecedent bouts of hypoglycemia. Thus, GPR119 agonists have the ability to pharmacologically augment glucagon secretion, specifically in response to hypoglycemia in diabetic rodents. Whether this effect might serve to diminish the occurrence and severity of iatrogenic hypoglycemia during intensive insulin therapy in patients with diabetes remains to be established.