Restoring SRSF3 in Kupffer cells attenuates obesity-related insulin resistance.

BACKGROUND AND AIMS: In obesity, depletion of KCs expressing CRIg (complement receptor of the Ig superfamily) leads to microbial DNA accumulation, which subsequently triggers tissue inflammation and insulin resistance. However, the mechanism underlying obesity-mediated changes in KC complement immune functions is largely unknown. APPROACH AND RESULTS: Using KC-specific deactivated Cas9 transgenic mice treated with guide RNA, we assessed the effects of restoring CRIg or the serine/arginine-rich splicing factor 3 (SRSF3) abundance on KC functions and metabolic phenotypes in obese mice. The impacts of weight loss on KC responses were evaluated in a diet switch mouse model. The role of SRSF3 in regulating KC functions was also evaluated using KC-specific SRSF3 knockout mice. Here, we report that overexpression of CRIg in KCs of obese mice protects against bacterial DNA accumulation in metabolic tissues. Mechanistically, SRSF3 regulates CRIg expression, which is essential for maintaining the CRIg+ KC population. During obesity, SRSF3 expression decreases, but it is restored with weight loss through a diet switch, normalizing CRIg+ KCs. KC SRSF3 is also repressed in obese human livers. Lack of SRSF3 in KCs in lean and obese mice decreases their CRIg+ population, impairing metabolic parameters. During the diet switch, the benefits of weight loss are compromised due to SRSF3 deficiency. Conversely, SRSF3 overexpression in obese mice preserves CRIg+ KCs and improves metabolic responses. CONCLUSIONS: Restoring SRSF3 abundance in KCs offers a strategy against obesity-associated tissue inflammation and insulin resistance by preventing bacterial DNA accumulation.

Oxidative stress in the medullary respiratory neurons contributes to respiratory dysfunction in the 6-OHDA model of Parkinson's disease.

KEY POINTS: Parkinson's disease (PD) is associated with respiratory dysfunction. In the 6-OHDA rat model of PD this is seen as a reduction in respiratory frequency and minute ventilation during normoxia and hypercapnia stimulus. Respiratory dysfunction is caused by neuronal death of medullary respiratory nuclei in the 6-OHDA model of PD. Oxidative stress can be considered a strong candidate for neurodegeneration via miR-34c downregulation and pro-apoptotic signalling in respiratory neurons, preceding the functional impairment observed in the 6-OHDA model of PD. ABSTRACT: Parkinson's disease (PD) is a neurodegenerative disease caused by dopaminergic neuron death in the substantia nigra (SN). New evidence has revealed that this neurodegeneration is the result of complex interactions between genetic abnormalities, environmental toxins, mitochondrial dysfunction and disruption of the blood-brain barrier (BBB) in the SN. In addition to classic symptoms, PD patients also exhibit respiratory failure. Here, we investigated whether oxidative stress was associated with neurodegeneration in a respiratory group (RG) of 6-OHDA-treated rats, which act as a model of PD. We analysed how oxidative stress affected apoptotic signalling in the RG 30 days after 6-OHDA treatment, shortly before commencement of breathing impairment (40 days). After 30 days, a dihydroethidium assay showed increased oxidative stress in the RG, anti-apoptotic signalling, as shown by an increase in p-Akt and BcL-2 and a decrease in Bax in the caudal aspect of the nucleus of the solitary tract (cNTS), and a decrease in p-p38 and Bax levels in the retrotrapezoid nucleus (RTN); pro-apoptotic signalling was indicated by a decrease in p-Akt and BcL-2 and an increase in Bax in the rostral ventral respiratory group (rVRG) and pre-Botzinger complex (preBotC). miR-34c, a known oxidative stress protector, was downregulated in 6-OHDA animals in the RC. After 40 days of 6-OHDA, the NTS, rVRG, preBotC and RTN exhibited reduced NeuN immunoreactivity, no BBB disruption and an increase in thiobarbituric acid reactivity. We conclude that in the 6-OHDA model of PD, oxidative stress contributes to neurodegeneration in medullary respiratory neurons.

Aerobic exercise training regulates serum extracellular vesicle miRNAs linked to obesity to promote their beneficial effects in mice.

There is a growing body of evidence that extracellular vesicles (EVs) and their cargo of RNA, DNA, and protein are released in the circulation with exercise and might mediate interorgan communication. C57BL6/J male mice were subjected to diet-induced obesity and aerobic training on a treadmill for 8 wk. The effect of aerobic training was evaluated in the liver, muscle, kidney, and white/brown adipose tissue. To provide new mechanistic insight, we profiled miRNA from serum EVs of obese and obese trained mice. We demonstrate that aerobic training changes the circulating EV miRNA profile of obese mice, including decreases in miR-122, miR-192, and miR-22 levels. Circulating miRNA levels were associated with miRNA levels in mouse liver white adipose tissue (WAT). In WAT, aerobically trained obese mice showed reduced adipocyte hypertrophy and increased the number of smaller adipocytes and the expression of Cebpa, Pparg, Fabp4 (adipogenesis markers), and ATP-citrate lyase enzyme activity. Importantly, miR-22 levels negatively correlated with the expression of adipogenesis and insulin sensitivity markers. In the liver, aerobic training reverted obesity-induced steatohepatitis, and steatosis score and Pparg expression were negatively correlated with miR-122 levels. The prometabolic effects of aerobic exercise in obesity possibly involve EV miRNAs, which might be involved in communication between liver and WAT. Our data provide significant evidence demonstrating that aerobic training exercise-induced EVs mediate the effect of exercise on adipose tissue metabolism.

Fenofibrate reverses changes induced by high-fat diet on metabolism in mice muscle and visceral adipocytes.

The effect of fenofibrate on the metabolism of skeletal muscle and visceral white adipose tissue of diet-induced obese (DIO) mice was investigated. C57BL/6J male mice were fed either a control or high-fat diet for 8 weeks. Fenofibrate (50 mg/Kg BW, daily) was administered by oral gavage during the last two weeks of the experimental period. Insulin-stimulated glucose metabolism in soleus muscles, glucose tolerance test, insulin tolerance test, indirect calorimetry, lipolysis of visceral white adipose tissue, expression of miR-103-3p in adipose tissue, and miR-1a, miR-133a/b, miR-206, let7b-5p, miR-23b-3p, miR-29-3p, miR-143-3p in soleus muscle, genes related to glucose and fatty acid metabolism in adipose tissue and soleus muscle, and proteins (phospho-AMPKα2, Pgc1α, Cpt1b), intramuscular lipid staining, and activities of fatty acid oxidation enzymes in skeletal muscle were investigated. In DIO mice, fenofibrate prevented weight gain induced by HFD feeding by increasing energy expenditure; improved whole body glucose homeostasis, and in skeletal muscle, increased insulin dependent glucose uptake, miR-1a levels, reduced intramuscular lipid accumulation, and phospho-AMPKα2 levels. In visceral adipose tissue of obese mice, fenofibrate decreased basal lipolysis rate and visceral adipocytes hypertrophy, and induced the expression of Glut-4, Irs1, and Cav-1 mRNA and miR-103-3p suggesting a higher insulin sensitivity of the adipocytes. The evidence is presented herein that beneficial effects of fenofibrate on body weight, glucose homeostasis, and muscle metabolism might be related to its action in adipose tissue. Moreover, fenofibrate regulates miR-1a-3p in soleus and miR-103-3p in adipose tissue, suggesting these microRNAs might contribute to fenofibrate beneficial effects on metabolism.