AMPK-dependent and -independent coordination of mitochondrial function and muscle fiber type by FNIP1.

Mitochondria are essential for maintaining skeletal muscle metabolic homeostasis during adaptive response to a myriad of physiologic or pathophysiological stresses. The mechanisms by which mitochondrial function and contractile fiber type are concordantly regulated to ensure muscle function remain poorly understood. Evidence is emerging that the Folliculin interacting protein 1 (Fnip1) is involved in skeletal muscle fiber type specification, function, and disease. In this study, Fnip1 was specifically expressed in skeletal muscle in Fnip1-transgenic (Fnip1Tg) mice. Fnip1Tg mice were crossed with Fnip1-knockout (Fnip1KO) mice to generate Fnip1TgKO mice expressing Fnip1 only in skeletal muscle but not in other tissues. Our results indicate that, in addition to the known role in type I fiber program, FNIP1 exerts control upon muscle mitochondrial oxidative program through AMPK signaling. Indeed, basal levels of FNIP1 are sufficient to inhibit AMPK but not mTORC1 activity in skeletal muscle cells. Gain-of-function and loss-of-function strategies in mice, together with assessment of primary muscle cells, demonstrated that skeletal muscle mitochondrial program is suppressed via the inhibitory actions of FNIP1 on AMPK. Surprisingly, the FNIP1 actions on type I fiber program is independent of AMPK and its downstream PGC-1α. These studies provide a vital framework for understanding the intrinsic role of FNIP1 as a crucial factor in the concerted regulation of mitochondrial function and muscle fiber type that determine muscle fitness.

Coupling of COPII vesicle trafficking to nutrient availability by the IRE1α-XBP1s axis.

The cytoplasmic coat protein complex-II (COPII) is evolutionarily conserved machinery that is essential for efficient trafficking of protein and lipid cargos. How the COPII machinery is regulated to meet the metabolic demand in response to alterations of the nutritional state remains largely unexplored, however. Here, we show that dynamic changes of COPII vesicle trafficking parallel the activation of transcription factor X-box binding protein 1 (XBP1s), a critical transcription factor in handling cellular endoplasmic reticulum (ER) stress in both live cells and mouse livers upon physiological fluctuations of nutrient availability. Using live-cell imaging approaches, we demonstrate that XBP1s is sufficient to promote COPII-dependent trafficking, mediating the nutrient stimulatory effects. Chromatin immunoprecipitation (ChIP) coupled with high-throughput DNA sequencing (ChIP-seq) and RNA-sequencing analyses reveal that nutritional signals induce dynamic XBP1s occupancy of promoters of COPII traffic-related genes, thereby driving the COPII-mediated trafficking process. Liver-specific disruption of the inositol-requiring enzyme 1α (IRE1α)-XBP1s signaling branch results in diminished COPII vesicle trafficking. Reactivation of XBP1s in mice lacking hepatic IRE1α restores COPII-mediated lipoprotein secretion and reverses the fatty liver and hypolipidemia phenotypes. Thus, our results demonstrate a previously unappreciated mechanism in the metabolic control of liver protein and lipid trafficking: The IRE1α-XBP1s axis functions as a nutrient-sensing regulatory nexus that integrates nutritional states and the COPII vesicle trafficking.

Cataract formation in transgenic HO-1 G143H mutant mice: Involvement of oxidative stress and endoplasmic reticulum stress.

Oxidative stress and endoplasmic reticulum (ER) stress are the key contributing factors for cataract progression. In our previous studies, we demonstrated that the nuclear factor erythroid 2-like-2 (Nrf-2)/heme oxygenase-1 (HO-1)/carbon monoxide (CO) axis protects lens epithelial cells (LECs) against oxidants and ER stress. In the present study, transgenic FVB/N mice overexpressing the negative dominant mutant HO-1 G143H (TgHO-1 G143H) were generated to evaluate the crosstalk among HO-1, oxidative stress and ER stress in maintaining lens transparency. Slit-lamp examination revealed that nuclear cataracts occurred at 4 months in the TgHO-1 G143H mice, which was 5 months earlier than that of the control mice. The lenses of the transgenic mice showed an accumulation of malondialdehyde and protein carbonyl with a decrease in glutathione and protein sulfhydryl levels. Elevated concentrations of ER stress biomarkers (Bip, PERK, ATF6, IRE1, CHOP, caspase-12 and caspase-3) in the lenses of the TgHO-1 G143H mice were identified by western blotting. Furthermore, we confirmed that overexpressed HO-1 G143H in LECs resulted in oxidative insult and apoptosis in vitro. All of these data suggested that HO-1 enzymatic activity loss induces early-onset nuclear cataracts by activating oxidative stress and ER stress.

The E3 Ligase TaSAP5 Alters Drought Stress Responses by Promoting the Degradation of DRIP Proteins.

In Arabidopsis (Arabidopsis thaliana) plants growing under normal conditions, DEHYDRATION-RESPONSIVE ELEMENT BINDING PROTEIN2A (DREB2A) is present at low levels because it is ubiquitinated and destabilized by DREB2A INTERACTING PROTEIN1 (DRIP1) and DRIP2 through 26S proteasome-mediated proteolysis. Drought stress counteracts the ubiquitination and proteolysis of DREB2A, thus allowing the accumulation of sufficient amounts of DREB2A protein to activate downstream gene expression. The mechanisms leading to drought stress-mediated DREB2A accumulation are still unclear. Here, we report that the wheat (Triticum aestivum) TaSAP5 protein, which contains an A20/AN1 domain, acts as an E3 ubiquitin ligase to mediate DRIP degradation and thus increase DREB2A protein levels. Drought induces TaSAP5 expression in wheat, and TaSAP5 overexpression in Arabidopsis and wheat seedlings increased their drought tolerance, as measured by survival rate and grain yield under severe drought stress. TaSAP5 can interact with and ubiquitinate TaDRIP, as well as AtDRIP1 and AtDRIP2, leading to their subsequent degradation through the 26S proteasome pathway. Consistent with this, TaSAP5 overexpression enhances DRIP degradation and increases the levels of DREB2A protein and its downstream targets. These results suggest that TaSAP5 acts to link drought with DREB2A accumulation and illustrate the molecular mechanisms involved in this process.

Acute high-altitude exposure shortens survival after uncontrolled hemorrhagic shock in rats.

BACKGROUND: Uncontrolled hemorrhage (UH) remains the most common cause of death on the battlefield. This study examined the pathophysiological characteristics of UH in rats acutely exposed to high altitude. MATERIAL AND METHODS: Rats raised at sea level were randomly divided into two groups. Rats in the high-altitude group were exposed to hypobaric hypoxia in a hypobaric chamber (simulating 4000 m above sea level) for 2 d and then were performed a hemorrhagic shock protocol in the hypobaric chamber. Rats that underwent the same hemorrhage procedure at sea level were used as control. Anesthetized rats were bled to maintain their mean arterial pressure at 45 mmHg for 1 h. The distal quarter of the tail was amputated to allow free blood loss. After 1 h, the tail cut was ligated to induce hemostasis. mean arterial pressure, acid-base balance, blood loss, and survival were recorded. Rats were killed, and tissues were obtained for histological analysis. RESULTS: Rats in the high-altitude group suffered less uncontrolled blood loss, more severe acidosis (lower pH and base excess), and inferior tissue oxygen supply (lower oxygen saturation and higher arterial lactate concentration) during the hemorrhage periods compared with the control group. Survival rates were significantly lower in the high-altitude group than those in the control group (P < 0.05), which was consistent with the results of pathological tissue injury. CONCLUSIONS: In this rat model of hemorrhagic shock, acute high-altitude exposure resulted in decreased UH but more serious hemorrhagic shock injuries than that at sea level.

C-type natriuretic peptide prevents kidney injury and attenuates oxidative and inflammatory responses in hemorrhagic shock.

Oxidative stress induced by hemorrhagic shock (HS) initiates a systemic inflammatory response, which leads to subsequent kidney injury. This study assessed the efficacy of c-type natriuretic peptide (CNP) in attenuating kidney injury in a rat model of hemorrhagic shock and resuscitation (HS/R). Sodium pentobarbital-anesthetized adult male Wistar rats underwent HS induced by the withdrawal of blood to a mean arterial pressure of 30-35 mmHg for 50 min. Then, the animals received CNP (25 µg/kg) or vehicle (saline) intravenously, followed byresuscitation with 1.5 times the shed blood volume in the form of normal saline. Mean arterial pressure was measured throughout the experiment, and acid-base status, oxidative stress, inflammation, tissue injury and kidney function were evaluated after resuscitation. CNP infusion reduced the malondialdehyde content, lowered the myeloperoxidase activity and decreased the expression of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1ß in the kidney. The histologic injury score and the plasma creatinine concentration were also significantly decreased after CNP treatment compared to the vehicle group. CNP treatment ameliorates oxidative stress, the inflammatory response, and consequently acute kidney injury after HS/R. Thus, CNP may represent a promising strategy to improve resuscitation for the treatment of HS and deserves further investigation.

Early resuscitation with exendin-4 alleviates acute lung injury after hemorrhagic shock in rats.

BACKGROUND: Oxidative stress induced by hemorrhagic shock (HS) is known to initiate a systemic inflammatory response, which leads to subsequent acute lung injury. This study is aimed to assess the efficacy of exendin-4 (Ex-4) in attenuating lung injury in a rat model of HS and resuscitation (HS/R). METHODS: HS was induced in sodium pentobarbital-anesthetized adult male Wistar rats by withdrawing blood to maintain a mean arterial pressure of 30-35 mm Hg for 50 min. Then, the animals received Ex-4 (5 µg/kg) or vehicle (saline) intravenously and were resuscitated with a volume of normal saline 1.5 times that of the shed blood volume. Mean arterial pressure was measured throughout the experiment, and acid-base status, oxidative stress, inflammation, and lung injury were evaluated at 2 h after resuscitation. RESULTS: Ex-4 infusion reduced the methemoglobin content, the malondialdehyde content, the myeloperoxidase activity, and the expression of tumor necrosis factor-α and interleukin-6 in the lungs. The histologic injury was also markedly decreased in the Ex-4 group compared with the vehicle group. CONCLUSIONS: Ex-4 ameliorates the oxidative stress, inflammatory response, and subsequent acute lung injury occurring after HS/R. Although future studies are required to elucidate the underlying mechanism, our results indicate that Ex-4 infusion may be a promising strategy for improving lung injury in the treatment of HS.

Addition of Sodium Pyruvate to Stored Red Blood Cells Attenuates Liver Injury in a Murine Transfusion Model.

RBCs undergo numerous changes during storage and stored RBCs may induce adverse effects, ultimately resulting in organ injury in transfusion recipients. We tested the hypothesis that the addition of SP to stored RBCs would improve the quality of the stored RBCs and mitigate liver injury after transfusion in a murine model. RBCs were harvested from C57BL/6J mice and stored for 14 days in CPDA-1 containing either a solution of SP in saline or saline alone. Haemolysis, the 24-hour posttransfusion recovery, the oxygen-carrying capacity, and the SOD activity of stored RBCs were evaluated. The plasma biochemistry, hepatic MDA level, MPO activity, IL-6, TNF-α concentrations, and histopathology were measured two hours after the transfusion of stored RBCs. Compared with RBCs stored in CPDA-1 and saline, the addition of SP to stored RBCs restored their oxygen-carrying capacity and SOD activity, reduced the AST activity, BUN concentrations, and LDH activity in the plasma, and decreased the MDA level, MPO activity, and concentrations of IL-6 and TNF-α in the liver. These data indicate that the addition of SP to RBCs during storage has a beneficial effect on storage lesions in vitro and subsequently alleviates liver injury after the transfusion of stored RBCs in vivo.

Impaired erythrocyte deformability in transgenic HO-1G143H mutant mice.

To investigate the potential effects of variation of HO-1 activity on hemorheology, this study compared the hemorheological properties between transgenic HO-1G143H mutant mice and wild-type (WT) control mice. Fresh blood samples were obtained from mice via the ocular venous sinus. The whole blood viscosity was measured using a cone-plate viscometer. Erythrocyte deformability and aggregation was measured using ektacytometry. The elongation index was significantly reduced in the HO-1G143H mutant mice compared to the WT mice at the shear rates of 600, 800, and 1,000 s(-1). The integrated elongation index was decreased in the HO-1G143H mutant mice compared to the WT mice. There was no statistically significant difference between the HO-1G143H mutant mice and the WT mice in terms of whole blood viscosity, aggregation index, amplitude of aggregation, and aggregation half time. The present study demonstrated that a reduction in HO-1 activity results in an impaired erythrocyte deformability. Although the mechanism underlying this effect remains unclear, our study brings to light the participation of HO-1 in the variations of hemorheology.

Gradually Increased Oxygen Administration Improved Oxygenation and Mitigated Oxidative Stress after Resuscitation from Severe Hemorrhagic Shock.

BACKGROUND: The optimal oxygen administration strategy during resuscitation from hemorrhagic shock (HS) is still controversial. Improving oxygenation and mitigating oxidative stress simultaneously seem to be contradictory goals. To maximize oxygen delivery while minimizing oxidative damage, the authors proposed the notion of gradually increased oxygen administration (GIOA), which entails making the arterial blood hypoxemic early in resuscitation and subsequently gradually increasing to hyperoxic, and compared its effects with normoxic resuscitation, hyperoxic resuscitation, and hypoxemic resuscitation in severe HS. METHODS: Rats were subjected to HS, and on resuscitation, the rats were randomly assigned to four groups (n = 8): the normoxic, the hyperoxic, the hypoxemic, and the GIOA groups. Rats were observed for an additional 1 h. Hemodynamics, acid-base status, oxygenation, and oxidative injury were observed and evaluated. RESULTS: Central venous oxygen saturation promptly recovered only in the hyperoxic and the GIOA groups, and the liver tissue partial pressure of oxygen was highest in the GIOA group after resuscitation. Oxidative stress in GIOA group was significantly reduced compared with the hyperoxic group as indicated by the reduced malondialdehyde content, increased catalase activity, and the lower histologic injury scores in the liver. In addition, the tumor necrosis factor-α and interleukin-6 expressions in the liver were markedly decreased in the GIOA group than in the hyperoxic and normoxic groups as shown by the immunohistochemical staining. CONCLUSIONS: GIOA improved systemic/tissue oxygenation and mitigated oxidative stress simultaneously after resuscitation from severe HS. GIOA may be a promising strategy to improve resuscitation from HS and deserves further investigation.

The stem cell adjuvant with Exendin-4 repairs the heart after myocardial infarction via STAT3 activation.

The poor survival of cells in ischaemic myocardium is a major obstacle for stem cell therapy. Exendin-4 holds the potential of cardioprotective effect based on its pleiotropic activity. This study investigated whether Exendin-4 in conjunction with adipose-derived stem cells (ADSCs) could improve the stem cell survival and contribute to myocardial repairs after infarction. Myocardial infarction (MI) was induced by the left anterior descending artery ligation in adult male Sprague-Dawley rats. ADSCs carrying double-fusion reporter gene [firefly luciferase and monomeric red fluorescent protein (fluc-mRFP)] were quickly injected into border zone of MI in rats treated with or without Exendin-4. Exendin-4 enhanced the survival of transplanted ADSCs, as demonstrated by the longitudinal in vivo bioluminescence imaging. Moreover, ADSCs adjuvant with Exendin-4 decreased oxidative stress, apoptosis and fibrosis. They also improved myocardial viability and cardiac function and increased the differentiation rates of ADSCs into cardiomyocytes and vascular smooth muscle cells in vivo. Then, ADSCs were exposed to hydrogen peroxide/serum deprivation (H(2)O(2)/SD) to mimic the ischaemic environment in vitro. Results showed that Exendin-4 decreased the apoptosis and enhanced the paracrine effect of ADSCs. In addition, Exendin-4 activated signal transducers and activators of transcription 3 (STAT3) through the phosphorylation of Akt and ERK1/2. Furthermore, Exendin-4 increased the anti-apoptotic protein Bcl-2, but decreased the pro-apoptotic protein Bax of ADSCs. In conclusion, Exendin-4 could improve the survival and therapeutic efficacy of transplanted ADSCs through STAT3 activation via the phosphorylation of Akt and ERK1/2. This study suggests the potential application of Exendin-4 for stem cell-based heart regeneration.

C-type natriuretic peptide attenuates LPS-induced endothelial activation: involvement of p38, Akt, and NF-κB pathways.

Endothelial activation elicited by inflammatory agents is regarded as a key event in the pathogenesis of several vascular inflammatory diseases. In the present study, the inhibitory effects and underlying mechanism of C-type natriuretic peptide (CNP) on LPS-induced endothelial activation were examined in human umbilical vein endothelial cells (HUVECs). The effect of CNP on adhesion molecule expression was assessed using quantitative real-time RT-PCR and western blotting analyses. The nuclear factor-κB (NF-κB), MAPK, and PI3K/Akt signaling pathways in LPS-stimulated HUVECs were investigated using western blotting analyses, and the production of intracellular reactive oxygen species (ROS) was measured using a fluorescence method. Pretreatment with CNP inhibited LPS-induced expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1, E-selectin, and P-selectin in a concentration-dependent manner. CNP suppressed the phosphorylation of p65 and NF-κB activation in LPS-stimulated cells. Moreover, CNP reduced ERK1/2 and p38 phosphorylation induced by LPS but not JNK. Furthermore, CNP induced Akt phosphorylation and activation of hemeoxygenase-1 (HO-1) expression. CNP significantly inhibited the production of intracellular ROS. These results suggest that CNP effectively attenuated LPS-induced endothelial activation by inhibiting the NF-κB and p38 signaling pathways, eliminating LPS-induced intracellular ROS production, and activating the PI3K/Akt/HO-1 pathway in HUVECs; thereby, demonstrating that CNP may be a potential therapeutic target for the treatment of sepsis and inflammatory vascular diseases.

AMPK phosphorylation of FNIP1 (S220) controls mitochondrial function and muscle fuel utilization during exercise.

Exercise-induced activation of adenosine monophosphate-activated protein kinase (AMPK) and substrate phosphorylation modulate the metabolic capacity of mitochondria in skeletal muscle. However, the key effector(s) of AMPK and the regulatory mechanisms remain unclear. Here, we showed that AMPK phosphorylation of the folliculin interacting protein 1 (FNIP1) serine-220 (S220) controls mitochondrial function and muscle fuel utilization during exercise. Loss of FNIP1 in skeletal muscle resulted in increased mitochondrial content and augmented metabolic capacity, leading to enhanced exercise endurance in mice. Using skeletal muscle-specific nonphosphorylatable FNIP1 (S220A) and phosphomimic (S220D) transgenic mouse models as well as biochemical analysis in primary skeletal muscle cells, we demonstrated that exercise-induced FNIP1 (S220) phosphorylation by AMPK in muscle regulates mitochondrial electron transfer chain complex assembly, fuel utilization, and exercise performance without affecting mechanistic target of rapamycin complex 1-transcription factor EB signaling. Therefore, FNIP1 is a multifunctional AMPK effector for mitochondrial adaptation to exercise, implicating a mechanism for exercise tolerance in health and disease.

Muscle-bone cross-talk through the FNIP1-TFEB-IGF2 axis is associated with bone metabolism in human and mouse.

Clinical evidence indicates a close association between muscle dysfunction and bone loss; however, the underlying mechanisms remain unclear. Here, we report that muscle dysfunction-related bone loss in humans with limb-girdle muscular dystrophy is associated with decreased expression of folliculin-interacting protein 1 (FNIP1) in muscle tissue. Supporting this finding, murine gain- and loss-of-function genetic models demonstrated that muscle-specific ablation of FNIP1 caused decreased bone mass, increased osteoclastic activity, and mechanical impairment that could be rescued by myofiber-specific expression of FNIP1. Myofiber-specific FNIP1 deficiency stimulated expression of nuclear translocation of transcription factor EB, thereby activating transcription of insulin-like growth factor 2 (Igf2) at a conserved promoter-binding site and subsequent IGF2 secretion. Muscle-derived IGF2 stimulated osteoclastogenesis through IGF2 receptor signaling. AAV9-mediated overexpression of IGF2 was sufficient to decrease bone volume and impair bone mechanical properties in mice. Further, we found that serum IGF2 concentration was negatively correlated with bone health in humans in the context of osteoporosis. Our findings elucidate a muscle-bone cross-talk mechanism bridging the gap between muscle dysfunction and bone loss. This cross-talk represents a potential target to treat musculoskeletal diseases and osteoporosis.

Comparative study of the interactions between ovalbumin and three alkaloids by spectrofluorimetry.

The interaction between ovalbumin (OVA) and three purine alkaloids (caffeine, theophylline and diprophylline) was investigated by the aid of intrinsic and synchronous fluorescence, ultraviolet-vis absorbance, resonance light-scattering spectra and three-dimensional fluorescence spectra techniques. Results showed that the formation of complexes gave rise to the fluorescence quenching of OVA by caffeine, theophylline, and diprophylline. Static quenching was confirmed to results in the fluorescence quenching. The binding site number n, apparent binding constant KA and corresponding thermodynamic parameters were measured at different temperatures. The binding process was spontaneous molecular interaction procedures in which both enthalpy and Gibbs free energy decreased. Van der Waals forces and hydrogen bond played a major role in stabilizing the complex. The comparison between caffeine, theophylline, and diprophylline was made, and thermodynamic results showed that diprophylline was the strongest quencher and bound to OVA with the highest affinity among three compounds. The influence of molecular structure on the binding aspects was reported.

FNIP1 abrogation promotes functional revascularization of ischemic skeletal muscle by driving macrophage recruitment.

Ischaemia of the heart and limbs attributable to compromised blood supply is a major cause of mortality and morbidity. The mechanisms of functional angiogenesis remain poorly understood, however. Here we show that FNIP1 plays a critical role in controlling skeletal muscle functional angiogenesis, a process pivotal for muscle revascularization during ischemia. Muscle FNIP1 expression is down-regulated by exercise. Genetic overexpression of FNIP1 in myofiber causes limited angiogenesis in mice, whereas its myofiber-specific ablation markedly promotes the formation of functional blood vessels. Interestingly, the increased muscle angiogenesis is independent of AMPK but due to enhanced macrophage recruitment in FNIP1-depleted muscles. Mechanistically, myofiber FNIP1 deficiency induces PGC-1α to activate chemokine gene transcription, thereby driving macrophage recruitment and muscle angiogenesis program. Furthermore, in a mouse hindlimb ischemia model of peripheral artery disease, the loss of myofiber FNIP1 significantly improved the recovery of blood flow. Thus, these results reveal a pivotal role of FNIP1 as a negative regulator of functional angiogenesis in muscle, offering insight into potential therapeutic strategies for ischemic diseases.

Proteolytic rewiring of mitochondria by LONP1 directs cell identity switching of adipocytes.

Mitochondrial proteases are emerging as key regulators of mitochondrial plasticity and acting as both protein quality surveillance and regulatory enzymes by performing highly regulated proteolytic reactions. However, it remains unclear whether the regulated mitochondrial proteolysis is mechanistically linked to cell identity switching. Here we report that cold-responsive mitochondrial proteolysis is a prerequisite for white-to-beige adipocyte cell fate programming during adipocyte thermogenic remodelling. Thermogenic stimulation selectively promotes mitochondrial proteostasis in mature white adipocytes via the mitochondrial protease LONP1. Disruption of LONP1-dependent proteolysis substantially impairs cold- or ß3 adrenergic agonist-induced white-to-beige identity switching of mature adipocytes. Mechanistically, LONP1 selectively degrades succinate dehydrogenase complex iron sulfur subunit B and ensures adequate intracellular succinate levels. This alters the histone methylation status on thermogenic genes and thereby enables adipocyte cell fate programming. Finally, augmented LONP1 expression raises succinate levels and corrects ageing-related impairments in white-to-beige adipocyte conversion and adipocyte thermogenic capacity. Together, these findings reveal that LONP1 links proteolytic surveillance to mitochondrial metabolic rewiring and directs cell identity conversion during adipocyte thermogenic remodelling.

FNIP1 regulates adipocyte browning and systemic glucose homeostasis in mice by shaping intracellular calcium dynamics.

Metabolically beneficial beige adipocytes offer tremendous potential to combat metabolic diseases. The folliculin interacting protein 1 (FNIP1) is implicated in controlling cellular metabolism via AMPK and mTORC1. However, whether and how FNIP1 regulates adipocyte browning is unclear. Here, we demonstrate that FNIP1 plays a critical role in controlling adipocyte browning and systemic glucose homeostasis. Adipocyte-specific ablation of FNIP1 promotes a broad thermogenic remodeling of adipocytes, including increased UCP1 levels, high mitochondrial content, and augmented capacity for mitochondrial respiration. Mechanistically, FNIP1 binds to and promotes the activity of SERCA, a main Ca2+ pump responsible for cytosolic Ca2+ removal. Loss of FNIP1 resulted in enhanced intracellular Ca2+ signals and consequential activation of Ca2+-dependent thermogenic program in adipocytes. Furthermore, mice lacking adipocyte FNIP1 were protected against high-fat diet-induced insulin resistance and liver steatosis. Thus, these findings reveal a pivotal role of FNIP1 as a negative regulator of beige adipocyte thermogenesis and unravel an intriguing functional link between intracellular Ca2+ dynamics and adipocyte browning.

Mitochondrial proteostasis stress in muscle drives a long-range protective response to alleviate dietary obesity independently of ATF4.

Mitochondrial quality in skeletal muscle is crucial for maintaining energy homeostasis during metabolic stresses. However, how muscle mitochondrial quality is controlled and its physiological impacts remain unclear. Here, we demonstrate that mitoprotease LONP1 is essential for preserving muscle mitochondrial proteostasis and systemic metabolic homeostasis. Skeletal muscle-specific deletion of Lon protease homolog, mitochondrial (LONP1) impaired mitochondrial protein turnover, leading to muscle mitochondrial proteostasis stress. A benefit of this adaptive response was the complete resistance to diet-induced obesity. These favorable metabolic phenotypes were recapitulated in mice overexpressing LONP1 substrate ΔOTC in muscle mitochondria. Mechanistically, mitochondrial proteostasis imbalance elicits an unfolded protein response (UPRmt) in muscle that acts distally to modulate adipose tissue and liver metabolism. Unexpectedly, contrary to its previously proposed role, ATF4 is dispensable for the long-range protective response of skeletal muscle. Thus, these findings reveal a pivotal role of LONP1-dependent mitochondrial proteostasis in directing muscle UPRmt to regulate systemic metabolism.

Disuse-associated loss of the protease LONP1 in muscle impairs mitochondrial function and causes reduced skeletal muscle mass and strength.

Mitochondrial proteolysis is an evolutionarily conserved quality-control mechanism to maintain proper mitochondrial integrity and function. However, the physiological relevance of stress-induced impaired mitochondrial protein quality remains unclear. Here, we demonstrate that LONP1, a major mitochondrial protease resides in the matrix, plays a role in controlling mitochondrial function as well as skeletal muscle mass and strength in response to muscle disuse. In humans and mice, disuse-related muscle loss is associated with decreased mitochondrial LONP1 protein. Skeletal muscle-specific ablation of LONP1 in mice resulted in impaired mitochondrial protein turnover, leading to mitochondrial dysfunction. This caused reduced muscle fiber size and strength. Mechanistically, aberrant accumulation of mitochondrial-retained protein in muscle upon loss of LONP1 induces the activation of autophagy-lysosome degradation program of muscle loss. Overexpressing a mitochondrial-retained mutant ornithine transcarbamylase (ΔOTC), a known protein degraded by LONP1, in skeletal muscle induces mitochondrial dysfunction, autophagy activation, and cause muscle loss and weakness. Thus, these findings reveal a role of LONP1-dependent mitochondrial protein quality-control in safeguarding mitochondrial function and preserving skeletal muscle mass and strength, and unravel a link between mitochondrial protein quality and muscle mass maintenance during muscle disuse.