Mammalian cells remove misfolded proteins using various proteolytic systems, including the ubiquitin (Ub)-proteasome system (UPS), chaperone mediated autophagy (CMA) and macroautophagy. The majority ...of misfolded proteins are degraded by the UPS, in which Ub-conjugated substrates are deubiquitinated, unfolded and cleaved into small peptides when passing through the narrow chamber of the proteasome. The substrates that expose a specific degradation signal, the KFERQ sequence motif, can be delivered to and degraded in lysosomes via the CMA. Aggregation-prone substrates resistant to both the UPS and the CMA can be degraded by macroautophagy, in which cargoes are segregated into autophagosomes before degradation by lysosomal hydrolases. Although most misfolded and aggregated proteins in the human proteome can be degraded by cellular protein quality control, some native and mutant proteins prone to aggregation into β-sheet-enriched oligomers are resistant to all known proteolytic pathways and can thus grow into inclusion bodies or extracellular plaques. The accumulation of protease-resistant misfolded and aggregated proteins is a common mechanism underlying protein misfolding disorders, including neurodegenerative diseases such as Huntington's disease (HD), Alzheimer's disease (AD), Parkinson's disease (PD), prion diseases and Amyotrophic Lateral Sclerosis (ALS). In this review, we provide an overview of the proteolytic pathways in neurons, with an emphasis on the UPS, CMA and macroautophagy, and discuss the role of protein quality control in the degradation of pathogenic proteins in neurodegenerative diseases. Additionally, we examine existing putative therapeutic strategies to efficiently remove cytotoxic proteins from degenerating neurons.
The non-protein amino acid γ-aminobutyric acid (GABA) has been proposed to be an ancient messenger for cellular communication conserved across biological kingdoms. GABA has well-defined signalling ...roles in animals; however, whilst GABA accumulates in plants under stress it has not been determined if, how, where and when GABA acts as an endogenous plant signalling molecule. Here, we establish endogenous GABA as a bona fide plant signal, acting via a mechanism not found in animals. Using Arabidopsis thaliana, we show guard cell GABA production is necessary and sufficient to reduce stomatal opening and transpirational water loss, which improves water use efficiency and drought tolerance, via negative regulation of a stomatal guard cell tonoplast-localised anion transporter. We find GABA modulation of stomata occurs in multiple plants, including dicot and monocot crops. This study highlights a role for GABA metabolism in fine tuning physiology and opens alternative avenues for improving plant stress resilience.
Renal interstitial fibrosis is considered to be the typical manifestation of diabetic nephropathy (DN). Mangiferin has shown positive effect on the prevention or treatment of diabetes and its ...complications. The aim of this study was to explore the inhibitive effect and mechanism of mangiferin on renal interstitial fibrosis in diabetic mice. Streptozotocin- (STZ-) induced diabetic mice were treated with mangiferin (15, 30, and 60 mg/kg/d) for 4 weeks. The morphology of kidneys was observed by Masson’s trichrome staining, and the biochemical parameters (fasting blood glucose (FBG), triglyceride (TG), total cholesterol (TC), blood urea nitrogen (BUN), serum creatinine (SCr), and urine protein) were determined by kits. In addition, the levels of inflammatory cytokines (tumor necrosis factor-α (TNF-α), interleukin- (IL-) 6, and IL-1β), antioxidant enzymes (SOD, CAT, and GSH-Px), MDA, and ROS were assessed. Furthermore, the expressions of fibronectin (FN), collagen I (Col I), and α-SMA were measured by immunohistochemistry. Regulations of TGF-β1 and the PTEN/PI3K/Akt pathway were detected by Western blotting. Treatment with mangiferin significantly ameliorated renal dysfunction in diabetic mice, as evidenced by the increase in body weight and decreases in FBG, TG, TC, BUN, SCr, urine protein, and the kidney to body weight ratio (KW/BW). Furthermore, mangiferin treatment prevented renal interstitial fibrosis evidenced by decreases in the positive expression of FN, Col I, and α-SMA, in comparison with morphological changes in the renal tissue. Meanwhile, mangiferin increased antioxidant enzymes, reduced the TNF-α, IL-6, and IL-1β, as well as MDA and ROS. Additionally, mangiferin administration also downregulated TGF-β1, upregulated PTEN, and decreased the phosphorylation of both PI3K and Akt. These findings demonstrate that mangiferin may reduce inflammation and oxidative stress in DN, thereby inhibiting the renal interstitial fibrosis by reducing the TGF-β1-mediated elevation of Col I, FN, and α-SMA through the PTEN/PI3K/Akt pathway.
Uncoupling protein 1 (UCP1) is highly expressed in brown adipose tissue, where it generates heat by uncoupling electron transport from ATP production. UCP1 is also found outside classical brown ...adipose tissue depots, in adipocytes that are termed 'brite' (brown-in-white) or 'beige'. In humans, the presence of brite or beige (brite/beige) adipocytes is correlated with a lean, metabolically healthy phenotype, but whether a causal relationship exists is not clear. Here we report that human brite/beige adipocyte progenitors proliferate in response to pro-angiogenic factors, in association with expanding capillary networks. Adipocytes formed from these progenitors transform in response to adenylate cyclase activation from being UCP1 negative to being UCP1 positive, which is a defining feature of the beige/brite phenotype, while displaying uncoupled respiration. When implanted into normal chow-fed, or into high-fat diet (HFD)-fed, glucose-intolerant NOD-scid IL2rg(null) (NSG) mice, brite/beige adipocytes activated in vitro enhance systemic glucose tolerance. These adipocytes express neuroendocrine and secreted factors, including the pro-protein convertase PCSK1, which is strongly associated with human obesity. Pro-angiogenic conditions therefore drive the proliferation of human beige/brite adipocyte progenitors, and activated beige/brite adipocytes can affect systemic glucose homeostasis, potentially through a neuroendocrine mechanism.
BACKGROUNDReprogramming of host metabolism supports viral pathogenesis by fueling viral proliferation, by providing, for example, free amino acids and fatty acids as building blocks.METHODSTo ...investigate metabolic effects of SARS-CoV-2 infection, we evaluated serum metabolites of patients with COVID-19 (n = 33; diagnosed by nucleic acid testing), as compared with COVID-19-negative controls (n = 16).RESULTSTargeted and untargeted metabolomics analyses identified altered tryptophan metabolism into the kynurenine pathway, which regulates inflammation and immunity. Indeed, these changes in tryptophan metabolism correlated with interleukin-6 (IL-6) levels. Widespread dysregulation of nitrogen metabolism was also seen in infected patients, with altered levels of most amino acids, along with increased markers of oxidant stress (e.g., methionine sulfoxide, cystine), proteolysis, and renal dysfunction (e.g., creatine, creatinine, polyamines). Increased circulating levels of glucose and free fatty acids were also observed, consistent with altered carbon homeostasis. Interestingly, metabolite levels in these pathways correlated with clinical laboratory markers of inflammation (i.e., IL-6 and C-reactive protein) and renal function (i.e., blood urea nitrogen).CONCLUSIONIn conclusion, this initial observational study identified amino acid and fatty acid metabolism as correlates of COVID-19, providing mechanistic insights, potential markers of clinical severity, and potential therapeutic targets.FUNDINGBoettcher Foundation Webb-Waring Biomedical Research Award; National Institute of General and Medical Sciences, NIH; and National Heart, Lung, and Blood Institute, NIH.
While high-caloric diet impairs insulin response to cause hyperglycemia, whether and how counter-regulatory hormones are modulated by high-caloric diet is largely unknown. We find that enhanced ...response of Drosophila adipokinetic hormone (AKH, the glucagon homolog) in the fat body is essential for hyperglycemia associated with a chronic high-sugar diet. We show that the activin type I receptor Baboon (Babo) autonomously increases AKH signaling without affecting insulin signaling in the fat body via, at least, increase of Akh receptor (AkhR) expression. Further, we demonstrate that Activin-β (Actβ), an activin ligand predominantly produced in the enteroendocrine cells (EEs) of the midgut, is upregulated by chronic high-sugar diet and signals through Babo to promote AKH action in the fat body, leading to hyperglycemia. Importantly, activin signaling in mouse primary hepatocytes also increases glucagon response and glucagon-induced glucose production, indicating a conserved role for activin in enhancing AKH/glucagon signaling and glycemic control.
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•Enhanced fly AKH action is essential for high-sugar diet-induced hyperglycemia•Babo signaling directly promotes AKH response in the fat body•Midgut-derived Actβ signals to the fat body via Babo and modulates AKH action•Chronic high-sugar diet impairs midgut homeostasis and increases Actβ production
Song et al. reveal an insulin-independent mechanism driving hyperglycemia on a high-sugar diet and identify Activin-β as a gut hormone boosting AKH/glucagon signaling in the fly fat body, ultimately perturbing carbohydrate homeostasis. Activin signaling in mouse hepatocytes also increases glucagon-stimulated glucose production, indicating a conserved role in enhancing glucagon response.
Mucosal melanoma is a rare and poorly characterized subtype of human melanoma. Here we perform a cross-species analysis by sequencing tumor-germline pairs from 46 primary human muscosal, 65 primary ...canine oral and 28 primary equine melanoma cases from mucosal sites. Analysis of these data reveals recurrently mutated driver genes shared between species such as NRAS, FAT4, PTPRJ, TP53 and PTEN, and pathogenic germline alleles of BRCA1, BRCA2 and TP53. We identify a UV mutation signature in a small number of samples, including human cases from the lip and nasal mucosa. A cross-species comparative analysis of recurrent copy number alterations identifies several candidate drivers including MDM2, B2M, KNSTRN and BUB1B. Comparison of somatic mutations in recurrences and metastases to those in the primary tumor suggests pervasive intra-tumor heterogeneity. Collectively, these studies suggest a convergence of some genetic changes in mucosal melanomas between species but also distinctly different paths to tumorigenesis.
Diabetes is a major risk factor for atherosclerosis. Although atherosclerosis is initiated by deposition of cholesterol-rich lipoproteins in the artery wall, the entry of inflammatory leukocytes into ...lesions fuels disease progression and impairs resolution. We show that diabetic mice have increased numbers of circulating neutrophils and Ly6-Chi monocytes, reflecting hyperglycemia-induced proliferation and expansion of bone marrow myeloid progenitors and release of monocytes into the circulation. Increased neutrophil production of S100A8/S100A9, and its subsequent interaction with the receptor for advanced glycation end products on common myeloid progenitor cells, leads to enhanced myelopoiesis. Treatment of hyperglycemia reduces monocytosis, entry of monocytes into atherosclerotic lesions, and promotes regression. In patients with type 1 diabetes, plasma S100A8/S100A9 levels correlate with leukocyte counts and coronary artery disease. Thus, hyperglycemia drives myelopoiesis and promotes atherogenesis in diabetes.
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•Hyperglycemia causes myeloproliferation•Neutrophil S100A8/S100A9 interacts with RAGE to stimulate myelopoiesis•Glucose reduction improves atherosclerosis regression
Liver cirrhosis is a predominant risk factor for hepatocellular carcinoma (HCC). However, the mechanism underlying the progression from cirrhosis to HCC remains unclear. Herein we report the ...concurrent increase of liver progenitor cells (LPCs) and transforming growth factor‐β (TGF‐β) in diethylnitrosamine (DEN)‐induced rat hepatocarcinogenesis and cirrhotic livers of HCC patients. Using several experimental approaches, including 2‐acetylaminofluorene/partial hepatectomy (2‐AAF/PHx) and 3,5‐diethoxycarbonyl‐1,4‐dihydrocollidine (DDC)‐elicited murine liver regeneration, we found that activation of LPCs in the absence of TGF‐β induction was insufficient to trigger hepatocarcinogenesis. Moreover, a small fraction of LPCs was detected to coexpress tumor initiating cell (T‐IC) markers during rat hepatocarcinogenesis and in human HCCs, and TGF‐β levels were positively correlated with T‐IC marker expression, which indicates a role of TGF‐β in T‐IC generation. Rat pluripotent LPC‐like WB‐F344 cells were exposed to low doses of TGF‐β for 18 weeks imitating the enhanced TGF‐β expression in cirrhotic liver. Interestingly, long‐term treatment of TGF‐β on WB‐F344 cells impaired their LPC potential but granted them T‐IC properties including expression of T‐IC markers, increased self‐renewal capacity, stronger chemoresistance, and tumorigenicity in NOD‐SCID mice. Hyperactivation of Akt but not Notch, signal transducer and activator of transcription 3 (STAT3), or mammalian target of rapamycin (mTOR) was detected in TGF‐β‐treated WB‐F344 cells. Introduction of the dominant‐negative mutant of Akt significantly attenuated T‐IC properties of those transformed WB‐F344 cells, indicating Akt was required in TGF‐β‐mediated‐generation of hepatic T‐ICs. We further demonstrate that TGF‐β‐induced Akt activation and LPC transformation was mediated by microRNA‐216a‐modulated phosphatase and tensin homolog deleted on chromosome 10 (PTEN) suppression. Conclusion: Hepatoma‐initiating cells may derive from hepatic progenitor cells exposed to chronic and constant TGF‐β stimulation in cirrhotic liver, and pharmaceutical inhibition of microRNA‐216a/PTEN/Akt signaling could be a novel strategy for HCC prevention and therapy targeting hepatic T‐ICs. (HEPATOLOGY 2012;56:2255–2267)
Myocardial metabolic impairment is a major feature in chronic heart failure. As the major coenzyme in fuel oxidation and oxidative phosphorylation and a substrate for enzymes signaling energy stress ...and oxidative stress response, nicotinamide adenine dinucleotide (NAD
) is emerging as a metabolic target in a number of diseases including heart failure. Little is known on the mechanisms regulating homeostasis of NAD
in the failing heart.
To explore possible alterations of NAD
homeostasis in the failing heart, we quantified the expression of NAD
biosynthetic enzymes in the human failing heart and in the heart of a mouse model of dilated cardiomyopathy (DCM) triggered by Serum Response Factor transcription factor depletion in the heart (SRF
) or of cardiac hypertrophy triggered by transverse aorta constriction. We studied the impact of NAD
precursor supplementation on cardiac function in both mouse models.
We observed a 30% loss in levels of NAD
in the murine failing heart of both DCM and transverse aorta constriction mice that was accompanied by a decrease in expression of the nicotinamide phosphoribosyltransferase enzyme that recycles the nicotinamide precursor, whereas the nicotinamide riboside kinase 2 (NMRK2) that phosphorylates the nicotinamide riboside precursor is increased, to a higher level in the DCM (40-fold) than in transverse aorta constriction (4-fold). This shift was also observed in human failing heart biopsies in comparison with nonfailing controls. We show that the
gene is an AMP-activated protein kinase and peroxisome proliferator-activated receptor α responsive gene that is activated by energy stress and NAD
depletion in isolated rat cardiomyocytes. Nicotinamide riboside efficiently rescues NAD
synthesis in response to FK866-mediated inhibition of nicotinamide phosphoribosyltransferase and stimulates glycolysis in cardiomyocytes. Accordingly, we show that nicotinamide riboside supplementation in food attenuates the development of heart failure in mice, more robustly in DCM, and partially after transverse aorta constriction, by stabilizing myocardial NAD
levels in the failing heart. Nicotinamide riboside treatment also robustly increases the myocardial levels of 3 metabolites, nicotinic acid adenine dinucleotide, methylnicotinamide, and N1-methyl-4-pyridone-5-carboxamide, that can be used as validation biomarkers for the treatment.
The data show that nicotinamide riboside, the most energy-efficient among NAD precursors, could be useful for treatment of heart failure, notably in the context of DCM, a disease with few therapeutic options.
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