Non-Necroptotic Roles of MLKL in Diet-Induced Obesity, Liver Pathology, and Insulin Sensitivity: Insights from a High-Fat, High-Fructose, High-Cholesterol Diet Mouse Model.

Chronic inflammation is a key player in metabolic dysfunction-associated fatty liver disease (MAFLD) progression. Necroptosis, an inflammatory cell death pathway, is elevated in MAFLD patients and mouse models, yet its role is unclear due to the diverse mouse models and inhibition strategies. In our study, we inhibited necroptosis by targeting mixed lineage kinase domain-like pseudokinase (MLKL), the terminal effector of necroptosis, in a high-fat, high-fructose, high-cholesterol (HFHFrHC) mouse model of diet-induced MAFLD.

MLKL overexpression leads to Ca and metabolic dyshomeostasis in a neuronal cell model.

The necroptotic effector molecule MLKL accumulates in neurons over the lifespan of mice, and its downregulation has the potential to improve cognition through neuroinflammation, and changes in the abundance of synaptic proteins and enzymes in the central nervous system. Notwithstanding, direct evidence of cell-autonomous effects of MLKL expression on neuronal physiology and metabolism are lacking. Here, we tested whether the overexpression of MLKL in the absence of cell death in the neuronal cell line Neuro-2a recapitulates some of the hallmarks of aging at the cellular level.

Non-Necroptotic Roles of MLKL in Diet-Induced Obesity, Liver Pathology, and Insulin Sensitivity: Insights from a High Fat, High Fructose, High Cholesterol Diet Mouse Model.

Chronic inflammation is a key player in metabolic dysfunction-associated fatty liver disease (MAFLD) progression. Necroptosis, an inflammatory cell death pathway, is elevated in MAFLD patients and mouse models, yet its role is unclear due to diverse mouse models and inhibition strategies. In our study, we inhibited necroptosis by targeting mixed lineage kinase domain like pseudokinase (MLKL), the terminal effector of necroptosis, in a high-fat, high-fructose, high-cholesterol (HFHFrHC) mouse model of diet-induced MAFLD mouse model.

Intracellular iron accumulation facilitates mycobacterial infection in old mouse macrophages.

Aging has a significant impact on the immune system, leading to a gradual decline in immune function and changes in the body's ability to respond to bacterial infections. Non-tuberculous mycobacteria (NTM), also known as atypical mycobacteria or environmental mycobacteria, are commonly found in soil, water, and various environmental sources. While many NTM species are considered opportunistic pathogens, some can cause significant infections, particularly in individuals with compromised immune systems, such as older individuals.

Characterization of novel mouse models to study the role of necroptosis in aging and age-related diseases.

To study the impact of necroptosis-induced chronic inflammation on age-related diseases and aging, two knockin mouse models (Ripk3-KI and Mlkl-KI) were generated that overexpress two genes involved in necroptosis (Ripk3 or Mlkl) when crossed to Cre transgenic mice. Crossing Ripk3-KI or Mlkl-KI mice to albumin-Cre transgenic mice produced hepatocyte specific hRipk3-KI or hMlkl-KI mice, which express the two transgenes only in the liver. Ripk3 and Mlkl proteins were overexpressed 10- and fourfold, respectively, in the livers of the hRipk3-KI or hMlkl-KI mice.

Absence of Either Ripk3 or Mlkl Reduces Incidence of Hepatocellular Carcinoma Independent of Liver Fibrosis.

Unlabelled: Nonalcoholic fatty liver disease (NAFLD) is one of the etiologies that contribute to hepatocellular carcinoma (HCC), and chronic inflammation is one of the proposed mediators of HCC. Because necroptosis is a cell death pathway that induces inflammation, we tested whether necroptosis-induced inflammation contributes to the progression of NAFLD to HCC in a mouse model of diet-induced HCC. Male and female wild-type (WT) mice and mouse models where necroptosis is blocked (Ripk3-/- or Mlkl-/- mice) were fed either a control diet, choline-deficient low-fat diet or choline-deficient high-fat diet.

Neuronal deletion of MnSOD in mice leads to demyelination, inflammation and progressive paralysis that mimics phenotypes associated with progressive multiple sclerosis.

Neuronal oxidative stress has been implicated in aging and neurodegenerative disease. Here we investigated the impact of elevated oxidative stress induced in mouse spinal cord by deletion of Mn-Superoxide dismutase (MnSOD) using a neuron specific Cre recombinase in Sod2 floxed mice (i-mn-Sod2 KO). Sod2 deletion in spinal cord neurons was associated with mitochondrial alterations and peroxide generation.

Senolytic treatment reduces cell senescence and necroptosis in Sod1 knockout mice that is associated with reduced inflammation and hepatocellular carcinoma.

The goal of this study was to test the role cellular senescence plays in the increased inflammation, chronic liver disease, and hepatocellular carcinoma seen in mice null for Cu/Zn-Superoxide dismutase (Sod1KO). To inhibit senescence, wildtype (WT) and Sod1KO mice were given the senolytics, dasatinib, and quercetin (D + Q) at 6 months of age when the Sod1KO mice begin exhibiting signs of accelerated aging. Seven months of D + Q treatment reduced the expression of p16 in the livers of Sod1KO mice to WT levels and the expression of several senescence-associated secretory phenotype factors (IL-6, IL-1β, CXCL-1, and GDF-15).

Necroptosis contributes to chronic inflammation and fibrosis in aging liver.

Inflammaging, characterized by an increase in low-grade chronic inflammation with age, is a hallmark of aging and is strongly associated with various age-related diseases, including chronic liver disease (CLD) and hepatocellular carcinoma (HCC). Because necroptosis is a cell death pathway that induces inflammation through the release of DAMPs, we tested the hypothesis that age-associated increase in necroptosis contributes to chronic inflammation in aging liver. Phosphorylation of MLKL and MLKL oligomers, markers of necroptosis, as well as phosphorylation of RIPK3 and RIPK1 were significantly upregulated in the livers of old mice relative to young mice and this increase occurred in the later half of life (i.

Necroptosis increases with age in the brain and contributes to age-related neuroinflammation.

Chronic inflammation of the central nervous system (CNS), termed neuroinflammation, is a hallmark of aging and a proposed mediator of cognitive decline associated with aging. Neuroinflammation is characterized by the persistent activation of microglia, the innate immune cells of the CNS, with damage-associated molecular patterns (DAMPs) being one of the well-known activators of microglia. Because necroptosis is a cell death pathway that induces inflammation through the release of DAMPs, we hypothesized that an age-associated increase in necroptosis contributes to increased neuroinflammation with age.

Role of necroptosis in chronic hepatic inflammation and fibrosis in a mouse model of increased oxidative stress.

Mice deficient in the antioxidant enzyme Cu/Zn-superoxide dismutase (Sod1 or Sod1KO mice) have increased oxidative stress, show accelerated aging and develop spontaneous hepatocellular carcinoma (HCC) with age. Similar to humans, HCC development in Sod1KO mice progresses from non-alcoholic fatty liver disease (NAFLD) to non-alcoholic steatohepatitis (NASH) with fibrosis, which eventually progresses to HCC. Oxidative stress plays a role in NAFLD to NASH progression, and liver inflammation is the main mechanism that drives the disease progression from NASH to fibrosis.

The potential role of necroptosis in inflammaging and aging.

An age-associated increase in chronic, low-grade sterile inflammation termed "inflammaging" is a characteristic feature of mammalian aging that shows a strong association with occurrence of various age-associated diseases. However, the mechanism(s) responsible for inflammaging and its causal role in aging and age-related diseases are not well understood. Age-associated accumulation of damage-associated molecular patterns (DAMPs) is an important trigger in inflammation and has been proposed as a potential driver of inflammaging.

Accelerated decline in cognition in a mouse model of increased oxidative stress.

Mice deficient in the antioxidant enzyme Cu/Zn-superoxide dismutase (Sod1KO mice) have a significant reduction in lifespan, exhibit many phenotypes of accelerated aging, and have high levels of oxidative stress in various tissues. Age-associated cognitive decline is a hallmark of aging and the increase in oxidative stress/damage with age is one of the mechanisms proposed for cognitive decline with age. Therefore, the goal of this study was to determine if Sod1KO mice exhibit an accelerated loss in cognitive function similar to that observed in aged animals.

Accelerated sarcopenia in Cu/Zn superoxide dismutase knockout mice.

Mice lacking Cu/Zn-superoxide dismutase (Sod1 or Sod1KO mice) show high levels of oxidative stress/damage and a 30% decrease in lifespan. The Sod1KO mice also show many phenotypes of accelerated aging with the loss of muscle mass and function being one of the most prominent aging phenotypes. Using various genetic models targeting the expression of Cu/Zn-superoxide dismutase to specific tissues, we evaluated the role of motor neurons and skeletal muscle in the accelerated loss of muscle mass and function in Sod1KO mice.

Lifelong reduction in complex IV induces tissue-specific metabolic effects but does not reduce lifespan or healthspan in mice.

Loss of SURF1, a Complex IV assembly protein, was reported to increase lifespan in mice despite dramatically lower cytochrome oxidase (COX) activity. Consistent with this, our previous studies found advantageous changes in metabolism (reduced adiposity, increased insulin sensitivity, and mitochondrial biogenesis) in Surf1 mice. The lack of deleterious phenotypes in Surf1 mice is contrary to the hypothesis that mitochondrial dysfunction contributes to aging.

Necroptosis increases with age and is reduced by dietary restriction.

Necroptosis is a newly identified programmed cell death pathway that is highly proinflammatory due to the release of cellular components that promote inflammation. To determine whether necroptosis might play a role in inflammaging, we studied the effect of age and dietary restriction (DR) on necroptosis in the epididymal white adipose tissue (eWAT), a major source of proinflammatory cytokines. Phosphorylated MLKL and RIPK3, markers of necroptosis, were increased 2.

The Geropathology Grading Platform demonstrates that mice null for Cu/Zn-superoxide dismutase show accelerated biological aging.

The Geropathology Grading Platform (GGP) that is being developed by the Geropathology Research Network provides a grading system that allows investigators to assess biological aging in mice by measuring the pathological status of a wide range of tissues in a standardized scoring system. The GGP is a grading system that generates a numerical score for the total lesions in each tissue, which when averaged over the mice in the cohort provides a composite lesion score (CLS) for each tissue and mouse. In this study, we tested ability of the GGP to predict accelerated aging in mice null for Cu/Zn-superoxide dismutase (Sod1KO mice), which have been shown to have reduced lifespan and healthspan.

The effect of different levels of dietary restriction on glucose homeostasis and metabolic memory.

Over the past 50 years, dietary restriction (DR) has been shown to extend the life span of a wide variety of organisms. A hallmark feature of DR is improved glucose homeostasis resulting in increased glucose tolerance and insulin sensitivity of animals ranging from rodents to humans. In this study, we demonstrate the early effects of varying levels of DR on glucose tolerance.

Loss of mitochondrial protease ClpP protects mice from diet-induced obesity and insulin resistance.

Caseinolytic peptidase P (ClpP) is a mammalian quality control protease that is proposed to play an important role in the initiation of the mitochondrial unfolded protein response (UPR), a retrograde signaling response that helps to maintain mitochondrial protein homeostasis. Mitochondrial dysfunction is associated with the development of metabolic disorders, and to understand the effect of a defective UPR on metabolism, ClpP knockout () mice were analyzed. mice fed have reduced adiposity and paradoxically improved insulin sensitivity.

A fish oil diet induces mitochondrial uncoupling and mitochondrial unfolded protein response in epididymal white adipose tissue of mice.

White adipose tissue (WAT) mitochondrial dysfunction is linked to the pathogenesis of obesity driven insulin resistance. Dietary conditions that alter fat mass are known to affect white adipocyte mitochondrial function, however, the impact of high calorie diets on white adipocyte mitochondria is not fully understood. The aim of this study is to assess the effect of a diet rich in saturated or polyunsaturated fat on mitochondrial unfolded protein response (UPR), a retrograde signaling response that maintains mitochondrial homeostasis, in epididymal WAT (eWAT).

Sco2 deficient mice develop increased adiposity and insulin resistance.

Cytochrome c oxidase (COX) is an essential transmembrane protein complex (Complex IV) in the mitochondrial respiratory electron chain. Mutations in genes responsible for the assembly of COX are associated with Leigh syndrome, cardiomyopathy, spinal muscular atrophy and other fatal metabolic disorders in humans. Previous studies have shown that mice lacking the COX assembly protein Surf1 (Surf1 mice) paradoxically show a number of beneficial metabolic phenotypes including increased insulin sensitivity, upregulation of mitochondrial biogenesis, induction of stress response pathways and increased lifespan.

A new mouse model of frailty: the Cu/Zn superoxide dismutase knockout mouse.

Frailty is a geriatric syndrome that is an important public health problem for the older adults living in the USA. Although several methods have been developed to measure frailty in humans, we have very little understanding of its etiology. Because the molecular basis of frailty is poorly understood, mouse models would be of great value in determining which pathways contribute to the development of frailty.

A new role for oxidative stress in aging: The accelerated aging phenotype in Sod1 mice is correlated to increased cellular senescence.

In contrast to other mouse models that are deficient in antioxidant enzymes, mice null for Cu/Zn-superoxide dismutase (Sod1 mice) show a major decrease in lifespan and several accelerated aging phenotypes. The goal of this study was to determine if cell senescence might be a contributing factor in the accelerated aging phenotype observed in the Sod1 mice. We focused on kidney because it is a tissue that has been shown to a significant increase in senescent cells with age.