Loss of pex5 sensitizes zebrafish to fasting due to deregulated mitochondria, mTOR, and autophagy.

Animal models have been utilized to understand the pathogenesis of Zellweger spectrum disorders (ZSDs); however, the link between clinical manifestations and molecular pathways has not yet been clearly established. We generated peroxin 5 homozygous mutant zebrafish (pex5-/-) to gain insight into the molecular pathogenesis of peroxisome dysfunction. pex5-/- display hallmarks of ZSD in humans and die within one month after birth. Fasting rapidly depletes lipids and glycogen in pex5-/- livers and expedites their mortality. Mechanistically, deregulated mitochondria and mechanistic target of rapamycin (mTOR) signaling act together to induce metabolic alterations that deplete hepatic nutrients and accumulate damaged mitochondria. Accordingly, chemical interventions blocking either the mitochondrial function or mTOR complex 1 (mTORC1) or a combination of both improve the metabolic imbalance shown in the fasted pex5-/- livers and extend the survival of animals. In addition, the suppression of oxidative stress by N-acetyl L-cysteine (NAC) treatment rescued the apoptotic cell death and early mortality observed in pex5-/-. Furthermore, an autophagy activator effectively ameliorated the early mortality of fasted pex5-/-. These results suggest that fasting may be detrimental to patients with peroxisome dysfunction, and that modulating the mitochondria, mTORC1, autophagy activities, or oxidative stress may provide a therapeutic option to alleviate the symptoms of peroxisomal diseases associated with metabolic dysfunction.

Zebrafish: A Powerful Model for Genetics and Genomics.

Our understanding of fundamental biological mechanisms and the pathogenesis of human diseases has been greatly improved by studying the genetics and genomics of zebrafish [...].

Catalase-deficient mice induce aging faster through lysosomal dysfunction.

BACKGROUND: Lysosomes are a central hub for cellular metabolism and are involved in the regulation of cell homeostasis through the degradation or recycling of unwanted or dysfunctional organelles through the autophagy pathway. Catalase, a peroxisomal enzyme, plays an important role in cellular antioxidant defense by decomposing hydrogen peroxide into water and oxygen. In accordance with pleiotropic significance, both impaired lysosomes and catalase have been linked to many age-related pathologies with a decline in lifespan. Aging is characterized by progressive accumulation of macromolecular damage and the production of high levels of reactive oxygen species. Although lysosomes degrade the most long-lived proteins and organelles via the autophagic pathway, the role of lysosomes and their effect on catalase during aging is not known. The present study investigated the role of catalase and lysosomal function in catalase-knockout (KO) mice. METHODS: We performed experiments on WT and catalase KO younger (9 weeks) and mature adult (53 weeks) male mice and Mouse embryonic fibroblasts isolated from WT and KO mice from E13.5 embryos as in vivo and in ex-vivo respectively. Mouse phenotyping studies were performed with controls, and a minimum of two independent experiments were performed with more than five mice in each group. RESULTS: We found that at the age of 53 weeks (mature adult), catalase-KO mice exhibited an aging phenotype faster than wild-type (WT) mice. We also found that mature adult catalase-KO mice induced leaky lysosome by progressive accumulation of lysosomal content, such as cathespin D, into the cytosol. Leaky lysosomes inhibited autophagosome formation and triggered impaired autophagy. The dysregulation of autophagy triggered mTORC1 (mechanistic target of rapamycin complex 1) activation. However, the antioxidant N-acetyl-L-cysteine and mTORC1 inhibitor rapamycin rescued leaky lysosomes and aging phenotypes in catalase-deficient mature adult mice. CONCLUSIONS: This study unveils the new role of catalase and its role in lysosomal function during aging. Video abstract.

TMEM135 regulates primary ciliogenesis through modulation of intracellular cholesterol distribution.

Recent evidence has linked the lysosomal cholesterol accumulation in Niemann-Pick type C1 with anomalies associated with primary ciliogenesis. Here, we report that perturbed intracellular cholesterol distribution imposed by lysosomal cholesterol accumulation during TMEM135 depletion is closely associated with impaired ciliogenesis. TMEM135 depletion does not affect the formation of the basal body and the ciliary transition zone. TMEM135 depletion severely blunts Rab8 trafficking to the centrioles without affecting the centriolar localization of Rab11 and Rabin8, the upstream regulators of Rab8 activation. Although TMEM135 depletion prevents enhanced IFT20 localization at the centrioles, ciliary vesicle formation is not affected. Furthermore, enhanced IFT20 localization at the centrioles is dependent on Rab8 activation. Supplementation of cholesterol in complex with cyclodextrin rescues Rab8 trafficking to the centrioles and Rab8 activation, thereby recovering primary ciliogenesis in TMEM135-depleted cells. Taken together, our data suggest that TMEM135 depletion prevents ciliary vesicle elongation, a characteristic of impaired Rab8 function. Our study thus reveals a previously uncharacterized effect of erroneous intracellular cholesterol distribution on impairing Rab8 function and primary ciliogenesis.

Disruption of Membrane Integrity as a Molecular Initiating Event Determines the Toxicity of Polyhexamethylene Guanidine Phosphate Depending on the Routes of Exposure.

Polyhexamethylene guanidine phosphate (PHMG-P), a cationic biocide, is widely used in household products due to its strong bactericidal activity and low toxicity. However, it causes fatal lung damage when inhaled. In this study, we investigated why PHMG-P causes fatal lung injury when inhaled, and demonstrated that the disruption of membrane integrity through ionic interaction-a molecular initiating event of PHMG-P-determines toxicity. Mice were injected intravenously with 0.9 or 7.2 mg/kg PHMG-P (IV group), or instilled intratracheally with 0.9 mg/kg PHMG-P (ITI group); they were euthanatized at 4 h and on days 1 and 7 after treatment. Increased total BAL cell count and proinflammatory cytokine production, along with fibrotic changes in the lungs, were detected in the ITI group only. Levels of hepatic enzymes and hepatic serum amyloid A mRNA expression were markedly upregulated in the 7.2 mg/kg IV and ITI groups at 4 h or day 1 after treatment, but returned to baseline. No pathological findings were detected in the heart, liver, or kidneys. To simulate the IV injection, A549, THP-1, and HepG2 cells were treated with PHMG-P in cell culture media supplemented with different serum concentrations. Increased serum concentration was associated with an increase in cell viability. These results support the idea that direct contact between PHMG-P and cell membranes is necessary for PHMG-induced toxicity.

Generation of a Novel Transgenic Zebrafish for Studying Adipocyte Development and Metabolic Control.

Zebrafish have become a popular animal model for studying various biological processes and human diseases. The metabolic pathways and players conserved among zebrafish and mammals facilitate the use of zebrafish to understand the pathological mechanisms underlying various metabolic disorders in humans. Adipocytes play an important role in metabolic homeostasis, and zebrafish adipocytes have been characterized. However, a versatile and reliable zebrafish model for long-term monitoring of adipose tissues has not been reported. In this study, we generated stable transgenic zebrafish expressing enhanced green fluorescent protein (EGFP) in adipocytes. The transgenic zebrafish harbored adipose tissues that could be detected using GFP fluorescence and the morphology of single adipocyte could be investigated in vivo. In addition, we demonstrated the applicability of this model to the long-term in vivo imaging of adipose tissue development and regulation based on nutrition. The transgenic zebrafish established in this study may serve as an excellent tool to advance the characterization of white adipose tissue in zebrafish, thereby aiding the development of therapeutic interventions to treat metabolic diseases in humans.

Slc25a17 acts as a peroxisomal coenzyme A transporter and regulates multiorgan development in zebrafish.

Slc25a17 is known as a peroxisomal solute carrier, but the in vivo role of the protein has not been demonstrated. We found that the zebrafish genome contains two slc25a17 genes that function redundantly, but additively. Notably, peroxisome function in slc25a17 knockdown embryos is severely compromised, resulting in an altered lipid composition. Along the defects found in peroxisome-associated phenotypic presentations, we highlighted that development of the swim bladder is also highly dependent on Slc25a17 function. As Slc25a17 showed substrate specificity towards coenzyme A (CoA), injecting CoA, but not NAD+ , rescued the defective swim bladder induced by slc25a17 knockdown. These results indicated that Slc25a17 acts as a CoA transporter, involved in the maintenance of functional peroxisomes that are essential for the development of multiple organs during zebrafish embryogenesis. Given high homology in protein sequences, the role of zebrafish Slc25a17 may also be applicable to the mammalian system.

Loss of abcd4 in zebrafish leads to vitamin B12-deficiency anemia.

ABCD4, a member of the ATP-binding cassette transporter superfamily, is associated with the transport of vitamin B12 which is crucial for the development of red blood cells (RBCs) and may also be involved in its metabolism. However, the molecular function of ABCD4 during RBC development in zebrafish is mostly unknown. Using a morpholino-based knockdown approach, we found that abcd4-knockdown resulted in abnormal RBCs of irregular shapes and various sizes. o-Dianisidine staining, as an indicator of hemoglobin in RBCs, further confirmed that abcd4 morphants possessed fewer hemoglobinized cells and impaired blood circulation. Multiple protein sequence alignment revealed that the amino acid sequence for residues 13-292, which is the domain of vitamin B12 transport, of the zebrafish Abcd4 was highly conserved compared to that of other species. Accordingly, the abcd4 morphants can be rescued with human ABCD4, demonstrating a conserved role of ABCD4 in vertebrates. Notably, the vitamin B12-deficient phenotype in abcd4 morphants, which causes anemia, was recapitulated in the newly-established abcd4 mutant, indicating the possibility that the abcd4 mutant could be used as a disease model of vitamin B12-deficiency anemia. Our study provides an insight that the analysis of the newly-established abcd4 mutant may contribute to understanding its roles in ABCD4-related vitamin B12-deficiency anemia and the associated pathogeneses in humans.

Augmentation of NAD+ levels by enzymatic action of NAD(P)H quinone oxidoreductase 1 attenuates adriamycin-induced cardiac dysfunction in mice.

BACKGROUND: Adriamycin (ADR) is a powerful chemotherapeutic agent extensively used to treat various human neoplasms. However, its clinical utility is hampered due to severe adverse side effects i.e. cardiotoxicity and heart failure. ADR-induced cardiomyopathy (AIC) has been reported to be caused by myocardial damage and dysfunction through oxidative stress, DNA damage, and inflammatory responses. Nonetheless, the remedies for AIC are even not established. Therefore, we illustrate the role of NAD+/NADH modulation by NAD(P)H quinone oxidoreductase 1 (NQO1) enzymatic action on AIC. METHODS AND RESULTS: AIC was established by intraperitoneal injection of ADR in C57BL/6 wild-type (WT) and NQO1 knockout (NQO1-/-) mice. All Mice were orally administered dunnione (named NQO1 substrate) before and after exposure to ADR. Cardiac biomarker levels in the plasma, cardiac dysfunction, oxidative biomarkers, and mRNA and protein levels of pro-inflammatory mediators were determined compared the cardiac toxicity of each experimental group. All biomarkers of Cardiac damage and oxidative stress, and mRNA levels of pro-inflammatory cytokines including cardiac dysfunction were increased in ADR-treated both WT and NQO1-/- mice. However, this increase was significantly reduced by dunnione in WT, but not in NQO1-/- mice. In addition, a decrease in SIRT1 activity due to a reduction in the NAD+/NADH ratio by PARP-1 hyperactivation was associated with AIC through increased nuclear factor (NF)-κB p65 and p53 acetylation in both WT and NQO1-/- mice. While an elevation in NAD+/NADH ratio via NQO1 enzymatic action using dunnione recovered SIRT1 activity and subsequently deacetylated NF-κB p65 and p53, however not in NQO1-/- mice, thereby attenuating AIC. CONCLUSION: Thus, modulation of NAD+/NADH by NQO1 may be a novel therapeutic approach to prevent chemotherapy-associated heart failure, including AIC.

Catalase inhibition induces pexophagy through ROS accumulation.

Peroxisomes are dynamic and multifunctional organelles involved in various cellular metabolic processes, and their numbers are tightly regulated by pexophagy, a selective degradation of peroxisomes through autophagy to maintain peroxisome homeostasis in cells. Catalase, a major peroxisome protein, plays a critical role in removing peroxisome-generated reactive oxygen species (ROS) produced by peroxisome enzymes, but the contribution of catalase to pexophagy has not been reported. Here, we investigated the role of catalase in peroxisome degradation during nutrient deprivation. Both short interfering RNA-mediated silencing of catalase and pharmacological inhibition by 3-aminotriazole (3AT) decreased the number of peroxisomes and resulted in the downregulation of peroxisomal proteins, such as PMP70 and PEX14 under serum starvation. In addition, treatment with 3AT induced NBR1-dependent autophagy and PEX5 ubiquitination in the absence of serum, which was accompanied by accumulation of ROS. Co-treatment with antioxidant agent N-acetyl-l-cysteine (NAC) prevented ROS accumulation and pexophagy by modulating peroxisome protein levels and the association of NBR1, a pexophagy receptor with peroxisomes. Taken together, these findings demonstrate that catalase plays an important role in pexophagy during nutrient deprivation.

Suppression of ABCD2 dysregulates lipid metabolism via dysregulation of miR-141:ACSL4 in human osteoarthritis.

Even though increasing evidence indicates the importance of peroxisomal lipid metabolism in regulating biological and pathological events, its involvement in cartilage development has not been well studied. Here, we identified the importance of peroxisomal function, particularly the functional integrity of ABCD2, in the pathogenesis of osteoarthritis (OA). Knockdown of ABCD2 in OA chondrocytes induced the accumulation of very long chain fatty acids (VLCFAs) and apoptotic cell death. Moreover, knockdown of ABCD2 altered profiles of miRNAs that affect the expression level of ACSL4, a known direct regulator of lipid metabolism. Suppression of ACSL4 in human chondrocytes-induced VLCFA accumulation, MMP-13 expression, and apoptotic cell death. In vivo morph-down of the ACSL4 homologue in zebrafish resulted in significant defects in cartilage development and in vivo knockdown of ACSL4 in cartilage tissue of an OA model mice promoted severe cartilage degradation. In summary, to the best of our knowledge, this is the first report suggesting that the regulatory network among peroxisomal ABCD2:ACSL4:VLCFA serves as a novel regulator of cartilage homeostasis, and these data may provide novel insights into the role of peroxisomal fatty acid metabolism in pathogenesis of human OA. SIGNIFICANCE OF THE STUDY: Our study indicates that peroxisomal dysfunction is closely related to OA pathogenesis. Particularly, the functional integrity of ABCD2 may play an important role in OA pathogenesis via the accumulation of VLCFAs and stimulation of apoptotic death through altering profiles of miRNAs that target ACSL4. Our findings suggest that targeting the regulatory network among the peroxisomal ABCD2:ACSL4:VLCFA axis may provide a new potential therapeutic strategy for OA pathogenesis.

Tetrabromobisphenol-A induces apoptotic death of auditory cells and hearing loss.

Phenolic tetrabromobisphenol-A (TBBPA) and its derivatives are commonly used flame-retardants, in spite of reported toxic effects including neurotoxicity, immunotoxicity, nephrotoxicity, and hepatotoxicity. However, the effects of TBBPA on ototoxicity have not yet been reported. In this study, we investigated the effect of TBBPA on hearing function in vivo and in vitro. Auditory Brainstem Response (ABR) threshold was markedly increased in mice after oral administration of TBBPA, indicating that TBBPA causes hearing loss. In addition, TBBPA induced the loss of both zebrafish neuromasts and hair cells in the rat cochlea in a dose-dependent manner. Mechanistically, hearing loss is largely attributed to apoptotic cell death, as TBBPA increased the expression of pro-apoptotic genes but decreased the expression of anti-apoptotic genes. We also found that TBBPA induced oxidative stress, and importantly, pretreatment with NAC, an anti-oxidant reagent, reduced TBBPA-induced reactive oxygen species (ROS) generation and partially prevented cell death. Our results show that TBBPA-mediated ROS generation induces ototoxicity and hearing loss. These findings implicate TBBPA as a potential environmental ototoxin by exerting its hazardous effects on the auditory system.

2,2'-dipyridyl induces pexophagy.

Pexophagy is the selective degradation of peroxisomes for maintaining peroxisome homeostasis within cells. Peroxisome dynamics and pexophagy are important events required to maintain the quality control of peroxisomes, thereby preventing peroxisome-associated diseases. To identify novel pexophagy modulators, we developed a cell-based screening system and selected 2,2'-dipyridyl (2,2-DP) as a candidate molecule. 2,2-DP treatment induced peroxisome degradation as evidenced by an increased number of low-pH autolysosomes originating from peroxisomes and a decrease in the expression of peroxisomal proteins such as catalase, Pex14, and PMP70. The phenotype was defined as pexophagy, because 2,2-DP induced autophagy and inhibition of autophagy significantly reduced the degree of peroxisome degradation. Mechanistically, 2,2-DP-dependent pexophagy seemed to be mediated by iron chelation, since another iron chelator displayed a similar effect on pexophagy, but a copper chelator did not. Notably, iron replenishment prevented 2,2-DP-mediated pexophagy. Taken together, our results suggest that 2,2-DP treatment disrupts peroxisome dynamics and promotes pexophagy through iron depletion.

3-Aminotriazole protects from CoCl2-induced ototoxicity by inhibiting the generation of reactive oxygen species and proinflammatory cytokines in mice.

Cobalt is an essential heavy metal that is necessary for the formation of vitamin B12 (hydroxocobalamin). However, exposure to excess cobalt for a prolonged period can harm the human body, causing pulmonary fibrosis, blindness, deafness, and peripheral neuropathy. 3-Aminotriazole (3-AT) is a catalase inhibitor that is often used to investigate the physiological effects of catalase. The present study found that injection of 3-AT in mice significantly reduced CoCl2-induced hearing impairment. In cultured organ of Corti explants from rats, 3-AT treatment protected hair cells from CoCl2-induced cytotoxicity. To determine the mechanism by which 3-AT protected from CoCl2-induced ototoxicity, we used the HEI-OC1 auditory cell line. Pretreatment with 10 mM 3-AT attenuated CoCl2-induced accumulation of ROS and induction of proinflammatory cytokine expression. Interestingly, these protective effects of 3-AT did not require catalase activity, as demonstrated by a series of experiments using RNA interference-mediated catalase knockdown in HEI-OC1 cells and using catalase-deficient mouse embryonic fibroblasts. Our results demonstrated the mechanisms of CoCl2-induced ototoxicity that may provide better ways to prevent the ototoxic effect of cobalt exposure.

Proteasome inhibitors induce auditory hair cell death through peroxisome dysfunction.

Even though bortezomib, a proteasome inhibitor, is a powerful chemotherapeutic agent used to treat multiple myeloma (MM) and other lymphoma cells, recent clinical reports suggest that the proteasome inhibitor therapy may be associated with severe bilateral hearing loss. We herein investigated the adverse effect of proteasome inhibitor on auditory hair cells. Treatment of a proteasome inhibitor destroys stereocilia bundles of hair cells resulting in the disarray of stereocilia in the organ of Corti explants. Since proteasome activity may be potentially important for biogenesis and function of the peroxisome, we tested whether proteasome activity is necessary for maintaining functional peroxisomes. Our results showed that treatment of a proteasome inhibitor significantly decreases both the number of peroxisomes and expression of peroxisomal proteins such as PMP70 and Catalase. In addition, we also found that proteasome inhibitor impairs the import pathway of PTS1-peroxisome matrix proteins. Taken together, our findings support recent clinical reports of hearing loss associated with proteasome inhibition. Mechanistically, peroxisome dysfunction may contribute to hair cell damage and hearing loss in response to the treatment of a proteasome inhibitor.

Dunnione ameliorates cisplatin-induced small intestinal damage by modulating NAD(+) metabolism.

Although cisplatin is a widely used anticancer drug for the treatment of a variety of tumors, its use is critically limited because of adverse effects such as ototoxicity, nephrotoxicity, neuropathy, and gastrointestinal damage. Cisplatin treatment increases oxidative stress biomarkers in the small intestine, which may induce apoptosis of epithelial cells and thereby elicit damage to the small intestine. Nicotinamide adenine dinucleotide (NAD(+)) is a cofactor for various enzymes associated with cellular homeostasis. In the present study, we demonstrated that the hyper-activation of poly(ADP-ribose) polymerase-1 (PARP-1) is closely associated with the depletion of NAD(+) in the small intestine after cisplatin treatment, which results in downregulation of sirtuin1 (SIRT1) activity. Furthermore, a decrease in SIRT1 activity was found to play an important role in cisplatin-mediated small intestinal damage through nuclear factor (NF)-κB p65 activation, facilitated by its acetylation increase. However, use of dunnione as a strong substrate for the NADH:quinone oxidoreductase 1 (NQO1) enzyme led to an increase in intracellular NAD(+) levels and prevented the cisplatin-induced small intestinal damage correlating with the modulation of PARP-1, SIRT1, and NF-κB. These results suggest that direct modulation of cellular NAD(+) levels by pharmacological NQO1 substrates could be a promising therapeutic approach for protecting against cisplatin-induced small intestinal damage.

Erdosteine protects HEI-OC1 auditory cells from cisplatin toxicity through suppression of inflammatory cytokines and induction of Nrf2 target proteins.

Cisplatin has many adverse effects, which are a major limitation to its use, including ototoxicity, neurotoxicity, and nephrotoxicity. This study aims to elucidate the protective mechanisms of erdosteine against cisplatin in HEI-OC1 cells. Pretreatment with erdosteine protects HEI-OC1 cells from cisplatin-medicated apoptosis, which is characterized by increase in nuclear fragmentation, DNA laddering, sub-G0/G1 phase, H2AX phosphorylation, PARP cleavage, and caspase-3 activity. Erdosteine significantly suppressed the production of reactive nitrogen/oxygen species and pro-inflammatory cytokines such as tumor necrosis factor-α, interleukin (IL)-1ß, and IL-6 in cisplatin-treated cells. Studies using pharmacologic inhibitors demonstrated that phosphatidylinositol-3-kinases (PI3K) and protein kinase B (Akt) have protective roles in the action of erdosteine against cisplatin in HEI-OC1 cells. In addition, pretreatment with erdosteine clearly suppressed the phosphorylation of p53 (Ser15) and expression of p53-upregulated modulator of apoptosis. Erdosteine markedly induces expression of NF-E2-related factor 2 (Nrf2), which may contribute to the increase in expression of glutathione redox genes γ-l-glutamate-l-cysteine-ligase catalytic and γ-l-glutamate-l-cysteine-ligase modifier subunits, as well as in the antioxidant genes HO-1 and SOD2 in cisplatin-treated HEI-OC1 cells. Furthermore, the increase in expression of phosphorylated p53 induced by cisplatin is markedly attenuated by pretreatment with erdosteine in the mitochondrial fraction. This increased expression may inhibit the cytosolic expression of the apoptosis-inducing factor, cytochrome c, and Bax/Bcl-xL ratio. Thus, our results suggest that treatment with erdosteine is significantly attenuated cisplatin-induced damage through the activation of Nrf2-dependent antioxidant genes, inhibition of pro-inflammatory cytokines, activation of the PI3K/Akt signaling, and mitochondrial-related inhibition of pro-apoptotic protein expression in HEI-OC1 auditory cells.

Pharmacological activation of NQO1 increases NAD⁺ levels and attenuates cisplatin-mediated acute kidney injury in mice.

Cisplatin is a widely used chemotherapeutic agent for the treatment of various tumors. In addition to its antitumor activity, cisplatin affects normal cells and may induce adverse effects, such as ototoxicity, nephrotoxicity, and neuropathy. Various mechanisms, such as DNA adduct formation, mitochondrial dysfunction, oxidative stress, and inflammatory responses, are critically involved in cisplatin-induced adverse effects. As NAD(+) is a cofactor for various enzymes associated with cellular homeostasis, we studied the effects of increased NAD(+) levels by means of NAD(P)H: quinone oxidoreductase 1 (NQO1) activation using a known pharmacological activator (ß-lapachone) in wild-type and NQO1(-/-) mice on cisplatin-induced renal dysfunction in vivo. The intracellular NAD(+)/NADH ratio in renal tissues was significantly increased in wild-type mice co-treated with cisplatin and ß-lapachone compared with the ratio in mice treated with cisplatin alone. Inflammatory cytokines and biochemical markers for renal damage were significantly attenuated by ß-lapachone co-treatment compared with those in the cisplatin alone group. Notably, the protective effects of ß-lapachone in wild-type mice were completely abrogated in NQO1(-/-) mice. Moreover, ß-lapachone enhanced the tumoricidal action of cisplatin in a xenograft tumor model. Thus, intracellular regulation of NAD(+) levels through NQO1 activation might be a promising therapeutic target for the protection of cisplatin-induced acute kidney injury.

Mitochondrial Fission Is Involved in Heat Resistance in Zebrafish.

Global warming and extreme weather events pose a significant threat to global biodiversity, with rising water temperatures exerting a profound influence on fish conservation and fishery development. In this study, we used zebrafish as a model organism to explore the impact of a heat acclimation period on their survival rates. The results demonstrated that a 2-month heat acclimation period almost completely mitigated heat stress-induced mortality in zebrafish. Subsequent analysis of the surviving zebrafish revealed a predominance of hepatic mitochondria in a fission state. Remarkably, a short-term fasting regimen, which induced hepatic mitochondrial fission, mirrored the outcomes of the protective effect of heat acclimation and augmented animal survival under heat stress. Conversely, treatment with a mitochondrial fission inhibitor within the fasting group attenuated the elevated survival rate. Furthermore, zebrafish embryos subjected to brief heat acclimation also exhibited increased heat resistance, a trait diminished by a chemical intervention inhibiting mitochondrial fission. This suggests a shared mechanism for heat resistance between embryos and adult zebrafish. These findings underscore the potential use of inducing mitochondrial fission to enhance heat resistance in zebrafish, offering promise for fish biodiversity conservation in the face of global warming.

Moderating AKT signaling with baicalein protects against weight loss by preventing muscle atrophy in a cachexia model caused by CT26 colon cancer.

Cancer cachexia is a type of energy-wasting syndrome characterized by fatigue, anorexia, muscle weakness, fat loss, and systemic inflammation. Baicalein, a flavonoid with bioactive properties, has demonstrated the ability to mitigate cardiac and skeletal muscle atrophy in different experimental settings. This effect is achieved through the inhibition of muscle proteolysis, suggesting its potential in preserving skeletal muscle homeostasis. In this study, we investigated the anti-cancer cachexia effects of baicalein in the regulation of muscle and fat wasting, both in vivo and in vitro. Baicalein attenuated body weight loss, including skeletal muscle and white adipose tissue (WAT), in CT26-induced cachectic mice. Moreover, baicalein increased muscle fiber thickness and suppressed the muscle-specific ubiquitin-protease system, including F-box only protein 32 and muscle RING-finger protein-1, by activating AKT phosphorylation both in vivo and in vitro. The use of LY294002, a particular inhibitor of AKT, eliminated the observed impact of baicalein on the improvement of muscle atrophy. In conclusion, baicalein inhibits muscle proteolysis and enhances AKT phosphorylation, indicating its potential role in cancer cachexia-associated muscle atrophy.