Cyclophilin D deficiency attenuates mitochondrial perturbation and ameliorates hepatic steatosis

Microenvironment-induced programmable nanotherapeutics restore mitochondrial dysfunction for the amelioration of non-alcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a metabolic liver disorder with severe complications. Mitochondrial dysfunction due to over-opening of the mitochondrial permeability transition pore (mPTP) in liver cells plays a central role in the development and progression of NAFLD. Restoring mitochondrial function is a promising strategy for NAFLD therapy. Herein, we designed and developed a microenvironment-induced programmable nanotherapeutic to restore mitochondrial function and ameliorate NAFLD. Cyclosporine A (CsA), as a highly effective inhibitors of the opening of mPTP, was chosen in the present work. Nanotherapeutics were prepared by assembling two structurally simple multifunctional glucosamine derivatives: dextran-grafted galactose (Dex-Gal) and Dex-triphenylphosphine (Dex-TPP). Galactose units in the nanotherapeutics guide the hepatocyte-specific uptake. Detachment of galactose from acidic lysosomes via Schiff base cleavage exposes the TPP moieties, which subsequently steers the nanotherapeutics to escape from lysosomes and target mitochondria through an enhanced positive charge, enabling precise in situ drug delivery. Simultaneously, the nanotherapeutics improved mitochondrial dysfunction by inhibiting palmitic acid-induced opening of the mitochondrial permeability transition pore in HepG2 cells, maintaining mitochondrial membrane potential, and decreasing reactive oxygen species production. Furthermore, CsA@Dex-Gal/TPP accumulated in the livers of NAFLD mice, restored mitochondrial autophagy, regulated abnormalities in glucose and lipid metabolism, and improved hepatic lipid deposition. This study offers a new cascading strategy for targeting liver cell mitochondria to treat NAFLD and other mitochondria-associated diseases. STATEMENT OF SIGNIFICANCE: We design microenvironment-induced programmable nanotherapeutics for NAFLD Nanotherapeutics has the capabilities of lysosomal escape and mitochondrial targeting Nanotherapeutics improves mitochondrial dysfunction and ameliorates NAFLD This study offers a new cascading strategy for other mitochondria-associated diseases.

A new perspective on liver diseases: Focusing on the mitochondria-associated endoplasmic reticulum membranes

The pathogenesis of liver diseases is multifaceted and intricate, posing a persistent global public health challenge with limited therapeutic options. Therefore, further research into liver diseases is imperative for better comprehension and advancement in treatment strategies. Numerous studies have confirmed the endoplasmic reticulum (ER) and mitochondria as key organelles driving liver diseases. Notably, the mitochondrial-associated ER membranes (MAMs) establish a physical and functional connection between the ER and mitochondria, highlighting the importance of inter-organelle communication in maintaining their functional homeostasis. This review delves into the intricate architecture and regulative mechanism of the integrated MAM that facilitate the physiological transfer of signals and substances between organelles. Additionally, we also provide a detailed overview regarding the varied pathogenic roles of malfunctioning MAM in liver diseases, focusing on its involvement in the progression of ER stress and mitochondrial dysfunction, the regulation of mitochondrial dynamics and Ca2+ transfer, as well as the disruption of lipid and glucose homeostasis. Furthermore, the current challenges and prospects associated with MAM in liver disease research are thoroughly discussed. In conclusion, elucidating the specific structure and function of MAM in different liver diseases may pave the way for novel therapeutic strategies.

Programmed cell death, from liver Ischemia-Reperfusion injury perspective: An overview

Liver ischemia-reperfusion injury (LIRI) commonly occurs in liver resection, liver transplantation, shock, and other hemorrhagic conditions, resulting in profound local and systemic effects via associated inflammatory responses and hepatic cell death. Hepatocyte death is a significant component of LIRI and its mechanism was previously thought to be limited to apoptosis and necrosis. With the discovery of novel types of programmed cell death (PCD), necroptosis, ferroptosis, pyroptosis, autophagy, NETosis, and parthanatos have been shown to be involved in LIRI. Understanding the mechanisms underlying cell death following LIRI is indispensable to mitigating the widespread effects of LIRI. Here, we review the roles of different PCD and discuss potential therapy in LIRI.

A nanoenzyme-modified hydrogel targets macrophage reprogramming-angiogenesis crosstalk to boost diabetic wound repair

Diabetic wounds has a gradually increasing incidence and morbidity. Excessive inflammation due to immune imbalance leads to delayed wound healing. Here, we reveal the interconnection between activation of the NLRP3 inflammatory pathway in endotheliocyte and polarization of macrophages via the cGAS-STING pathway in the oxidative microenvironment. To enhance the immune-regulation based on repairing mitochondrial oxidative damage, a zeolitic imidazolate framework-8 coated with cerium dioxide that carries Rhoassociated protein kinase inhibition Y-27632 (CeO2-Y@ZIF-8) is developed. It is encapsulated in a photocross-linkable hydrogel (GelMA) with cationic quaternary ammonium salt groups modified to endow the antibacterial properties (CeO2-Y@ZIF-8@Gel). CeO2 with superoxide dismutase and catalase activities can remove excess reactive oxygen species to limit mitochondrial damage and Y-27632 can repair damaged mitochondrial DNA, thus improving the proliferation of endotheliocyte. After endotheliocyte uptakes CeO2-Y@ZIF-8 NPs to degrade peroxides into water and oxygen in cells and mitochondria, NLRP3 inflammatory pathway is inhibited and the leakage of oxidatively damaged mitochondrial DNA (Ox-mtDNA, a damage-associated molecular pattern) through mPTP decreases. Futhermore, as the cGAS-STING pathway activated by Ox-mtDNA down-regulated, the M2 phenotype polarization and anti-inflammatory factors increase. Collectively, CeO2-Y@ZIF-8@Gel, through remodulating the crosstalk between macrophage reprogramming and angiogenesis to alleviate inflammation in the microenvironment and accelerates wound healing.

Reactive Oxygen Species Damage Bovine Endometrial Epithelial Cells via the Cytochrome C-mPTP Pathway

After parturition, bovine endometrial epithelial cells (BEECs) undergo serious inflammation and imbalance between oxidation and antioxidation, which is widely acknowledged as a primary contributor to the development of endometritis in dairy cows. Nevertheless, the mechanism of oxidative stress-mediated inflammation and damage in bovine endometrial epithelial cells remains inadequately defined, particularly the molecular pathways associated with mitochondria-dependent apoptosis. Hence, the present study was designed to explore the mechanism responsible for mitochondrial dysfunction-induced BEEC damage. In vivo, the expressions of proapoptotic protein caspase 3 and cytochrome C were increased significantly in dairy uteri with endometritis. Similarly, the levels of proapoptotic protein caspase 3, BAX, and cytochrome C were markedly increased in H2O2-treated BEECs. Our findings revealed pronounced BEEC damage in dairy cows with endometritis, accompanied by heightened expression of cyto-C and caspase-3 both in vivo and in vitro. The reduction in apoptosis-related protein of BEECs due to oxidant injury was notably mitigated following N-acetyl-L-cysteine (NAC) treatment. Furthermore, mitochondrial vacuolation was significantly alleviated, and mitochondrial membrane potential returned to normal levels after the removal of ROS. Excessive ROS may be the main cause of mitochondrial dysfunction. Mitochondrial permeability transition pore (mPTP) blockade by cyclophilin D (CypD) knockdown with CSA significantly blocked the flow of cytochrome C (cyto-C) and Ca2+ to the cytoplasm from the mitochondria. Our results indicate that elevated ROS and persistent opening of the mPTP are the main causes of oxidative damage in BEECs. Collectively our results reveal a new mechanism involving ROS-mPTP signaling in oxidative damage to BEECs, which may be a potential avenue for the clinical treatment of bovine endometritis.

Distinct Types of Cell Death and Implications in Liver Diseases: An Overview of Mechanisms and Application

Cell death is associated with a variety of liver diseases, and hepatocyte death is a core factor in the occurrence and progression of liver diseases. In recent years, new cell death modes have been identified, and certain biomarkers have been detected in the circulation during various cell death modes that mediate liver injury. In this review, cell death modes associated with liver diseases are summarized, including some cell death modes that have emerged in recent years. We described the mechanisms associated with liver diseases and summarized recent applications of targeting cell death in liver diseases. It provides new ideas for the diagnosis and treatment of liver diseases. In addition, multiple cell death modes can contribute to the same liver disease. Different cell death modes are not isolated, and they interact with each other in liver diseases. Future studies may focus on exploring the regulation between various cell death response pathways in liver diseases.

Cyclophilin D as a potential therapeutic target of liver ischemia/reperfusion injury by mediating crosstalk between apoptosis and autophagy

Background

Liver ischemia/reperfusion (I/R) injury is a complex and multifactorial pathophysiological process. It is well recognized that the membrane permeability transition pore (mPTP) opening of mitochondria plays a crucial role in cell death after I/R injury. Cyclophilin D (CypD) is a critical positive regulator of mPTP. However, the effect of CypD on the pathogenesis of liver I/R injury and whether CypD is a potential therapeutic target are still unclear.

Methods

We constructed liver-specific CypD knockout and AAV8-peptidyl prolyl isomerase F (PPIF) overexpression mice. Then, a 70% liver I/R injury model was established in mice, with 90 min of ischemia and 6 h of reperfusion. The liver function was detected by the level of serum glutamic pyruvic transaminase (alanine transaminase) and glutamic oxaloacetic transaminase (aspartate aminotransferase), the liver damage score and degree of necrosis were measured by hematoxylin and eosin (H&E) staining of liver tissues. Reactive oxygen species (ROS) staining, apoptosis, and autophagy-related molecules were used to detect apoptosis and autophagy during liver I/R.

Results

The liver-specific knockout of CypD alleviated necrosis and dysfunction in liver I/R injury, by reducing the excessive production of ROS, and inhibiting cell apoptosis and autophagy. On the contrary, overexpression of CypD exacerbated I/R-induced liver damage.

Conclusion

We found that the downregulation of CypD expression alleviated liver I/R injury by reducing apoptosis and autophagy through caspase-3/Beclin1 crosstalk; in contrast, the upregulation of CypD expression aggravated liver I/R injury. Therefore, interfering with the expression of CypD seems to be a promising treatment for liver I/R injury.

Natural Drugs: A New Direction for the Prevention and Treatment of Diabetes

Insulin resistance, as a common pathological process of many metabolic diseases, including diabetes and obesity, has attracted much attention due to its relevant influencing factors. To date, studies have mainly focused on the shared mechanisms between mitochondrial stress and insulin resistance, and they are now being pursued as a very attractive therapeutic target due to their extensive involvement in many human clinical settings. In view of the complex pathogenesis of diabetes, natural drugs have become new players in diabetes prevention and treatment because of their wide targets and few side effects. In particular, plant phenolics have received attention because of their close relationship with oxidative stress. In this review, we briefly review the mechanisms by which mitochondrial stress leads to insulin resistance. Moreover, we list some cytokines and genes that have recently been found to play roles in mitochondrial stress and insulin resistance. Furthermore, we describe several natural drugs that are currently widely used and give a brief overview of their therapeutic mechanisms. Finally, we suggest possible ideas for future research related to the unique role that natural drugs play in the treatment of insulin resistance through the above targets.

GRP78/BiP alleviates oxLDL-induced hepatotoxicity in familial hypercholesterolemia caused by missense variants of LDLR in a HepG2 cellular model

BACKGROUND AND AIMS

The accumulation of misfolded proteins, encoded by genetic variants of functional genes leads to Endoplasmic Reticulum (ER) stress, which is a critical consequence in human disorders such as familial hypercholesterolemia, cardiovascular and hepatic diseases. In addition to the identification of ER stress as a contributing factor to pathogenicity, extensive studies on the role of oxidized Low-Density Lipoprotein (oxLDL) and its ill effects in expediting cardiovascular diseases and other metabolic comorbidities are well documented. However, the current understanding of its role in hepatic insults needs to be revised. This study elucidates the molecular mechanisms underlying the progression of oxLDL and ER stress-induced cytotoxicity in HepG2.

METHODS

HepG2 cells stably expressing wild-type Low-Density lipoprotein receptor (WT-LDLR) and missense variants of LDLR that are pathogenically associated with familial hypercholesterolemia were used as the in vitro models. The relative mRNA expression and protein profiles of ER stress sensors, inflammatory and apoptotic markers, together with cytotoxic assays and measurement of mitochondrial membrane potential, were carried out in HepG2 cells treated with 100 µg per ml oxLDL for 24 to 48 h. 1-way or 2-way ANOVA was used for statistical analyses of datasets.

RESULTS

ER stress responses are elicited along all three arms of the unfolded protein response (UPR), with adverse cytotoxic and inflammatory responses in oxLDL-treated conditions. Interestingly, oxLDL-treated ER-stressed HepG2 cells manifested intriguingly low expression of BiP- the master regulator of ER stress, as observed earlier by various researchers in liver biopsies of Non-Alcoholic Steatohepatitis (NASH) patients. This study shows that overexpression of BiP rescues hepatic cells from cytotoxic and inflammatory mechanisms instigated by ER stress in combination with oxLDL, along the ER and mitochondrial membrane and restores cellular homeostasis.

CONCLUSION

The data provide interesting leads that identify patients with familial hypercholesterolemia conditions and potentially other Endoplasmic Reticulum Associated Degradation (ERAD) diseases as highly susceptible to developing hepatic insults with molecular signatures like those manifested in Non-Alcoholic Fatty Liver Disease (NAFLD) and NASH.

LIMITATIONS AND FUTURE PERSPECTIVES

Although the use of HepG2 cells as the model is a major caveat of the study, the findings of this research may be used as the pilot study to expand further investigations in primary hepatocytes or iPSC- derived cellular models.

SIK2 protects against renal tubular injury and the progression of diabetic kidney disease

Despite optimal medical therapy, many patients with diabetic kidney disease (DKD) progress to end-stage renal disease. The identification of new biomarkers and drug targets for DKD is required for the development of more effective therapies. The apoptosis of renal tubular epithelial cells is a key feature of the pathogenicity associated with DKD. SIK2, a salt-inducible kinase, regulates important biological processes, such as energy metabolism, cell cycle progression and cellular apoptosis. In our current study, a notable decrease in the expression of SIK2 was detected in the renal tubules of DKD patients and murine models. Functional experiments demonstrated that deficiency or inactivity of SIK2 aggravates tubular injury and interstitial fibrosis in diabetic mice. Based on transcriptome sequencing, molecular mechanism exploration revealed that SIK2 overexpression reduces endoplasmic reticulum (ER) stress-mediated tubular epithelial apoptosis by inhibiting the histone acetyltransferase activity of p300 to activate HSF1/Hsp70. Furthermore, the specific restoration of SIK2 in tubules blunts tubular and interstitial impairments in diabetic and vancomycin-induced kidney disease mice. Together, these findings indicate that SIK2 protects against renal tubular injury and the progression of kidney disease, and make a compelling case for targeting SIK2 for therapy in DKD.

Emerging novel targets for nonalcoholic fatty liver disease treatment: Evidence from recent basic studies

Nonalcoholic fatty liver disease (NAFLD), a leading chronic disease worldwide, affects approximately a quarter of the global population. Nonalcoholic steatohepatitis (NASH) is an advanced form of NAFLD and is more likely to progress to liver fibrosis than simple steatosis. NASH is also identified as the most rapidly growing cause of hepatocellular carcinoma. Although in the past decade, several phase II/III clinical trials have shown promising results in the use of novel drugs targeting lipid synthase, farnesoid X receptor signaling, peroxisome proliferator-activated receptor signaling, hepatocellular injury, and inflammatory signaling, proven pharmaceutical agents to treat NASH are still lacking. Thus, continuous exploration of the mechanism underlying the pathogenesis of NAFLD and the identification of novel therapeutic targets remain urgent tasks in the field. In the current review, we summarize studies reported in recent years that not only provide new insights into the mechanisms of NAFLD development but also explore the possibility of treating NAFLD by targeting newly identified signaling pathways. We also discuss evidence focusing on the intrahepatic targets involved in the pathogenesis of NAFLD as well as extrahepatic targets affecting liver metabolism and function.

Non-Immunosuppressive Cyclophilin Inhibitors

Cyclophilins, enzymes with peptidyl-prolyl cis/trans isomerase activity, are relevant to a large variety of biological processes. The most abundant member of this enzyme family, cyclophilin A, is the cellular receptor of the immunosuppressive drug cyclosporine A (CsA). As a consequence of the pathophysiological role of cyclophilins, particularly in viral infections, there is a broad interest in cyclophilin inhibition devoid of immunosuppressive activity. This Review first gives an introduction into the physiological and pathophysiological roles of cyclophilins. The presentation of non-immunosuppressive cyclophilin inhibitors will commence with drugs based on chemical modifications of CsA. The naturally occurring macrocyclic sanglifehrins have become other lead structures for cyclophilin-inhibiting drugs. Finally, de novo designed compounds, whose structures are not derived from or inspired by natural products, will be presented. Relevant synthetic concepts will be discussed, but the focus will also be on biochemical studies, structure-activity relationships, and clinical studies.

Remodeling of Liver and Plasma Lipidomes in Mice Lacking Cyclophilin D

In recent years, several studies aimed to investigate the metabolic effects of non-functioning or absent cyclophilin D (CypD), a crucial regulatory component of mitochondrial permeability transition pores. It has been reported that the lack of CypD affects glucose and lipid metabolism. However, the findings are controversial regarding the metabolic pathways involved, and most reports describe the effect of a high-fat diet on metabolism. We performed a lipidomic analysis of plasma and liver samples of CypD-/- and wild-type (WT) mice to reveal the lipid-specific alterations resulting from the absence of CypD. In the CypD-/- mice compared to the WT animals, we found a significant change in 52% and 47% of the measured 225 and 201 lipid species in liver and plasma samples, respectively. The higher total lipid content detected in these tissues was not accompanied by abdominal fat accumulation assessed by nuclear magnetic resonance imaging. We also documented characteristic changes in the lipid composition of the liver and plasma as a result of CypD ablation with the relative increase in polyunsaturated membrane lipid species. In addition, we did not observe remarkable differences in the lipid distribution of hepatocytes using histochemistry, but we found characteristic changes in the hepatocyte ultrastructure in CypD-/- animals using electron microscopy. Our results highlight the possible long-term effects of CypD inhibition as a novel therapeutic consideration for various diseases.

Small-molecule inhibitors of cyclophilin D as potential therapeutics in mitochondria-related diseases

Cyclophilin D (CypD) is a key regulator of mitochondrial permeability transition pore (mPTP) opening. This pathophysiological phenomenon is associated with the development of several human diseases, including ischemia-reperfusion injury and neurodegeneration. Blocking mPTP opening through CypD inhibition could be a novel and promising therapeutic approach for these conditions. While numerous CypD inhibitors have been discovered to date, none have been introduced into clinical practice, mostly owing to their high toxicity, unfavorable pharmacokinetics, and low selectivity for CypD over other cyclophilins. This review summarizes current knowledge of CypD inhibitors, with a particular focus on small-molecule compounds with regard to their in vitro activity, their selectivity for CypD, and their binding mode within the enzyme's active site. Finally, approaches for improving the molecular design of CypD inhibitors are discussed.

Cationic antimicrobial peptide NRC-03 induces oral squamous cell carcinoma cell apoptosis via CypD-mPTP axis-mediated mitochondrial oxidative stress

Pleurocidin-family cationic antimicrobial peptide NRC-03 exhibits potent and selective cytotoxicity towards cancer cells. However, the anticancer effect of NRC-03 in oral squamous cell carcinoma (OSCC) and the molecular mechanism of NRC-03 induced cancer cell death is still unclear. This study focused to investigate mitochondrial oxidative stress-mediated altered mitochondrial function involved in NRC-03-induced apoptosis of OSCC cells. NRC-03 entered the OSCC cells more easily than that of normal cells and bound to mitochondria as well as the nucleus, causing cell membrane blebbing, mitochondria swelling, and DNA fragmentation. NRC-03 induced high oxygen consumption, reactive oxygen species (ROS) release, mitochondrial dysfunction, and apoptosis in OSCC cells. Non-specific antioxidant N-acetyl-l-cysteine (NAC), or mitochondria-specific antioxidant mitoquinone (MitoQ) alleviated NRC-03-induced apoptosis and mitochondrial dysfunction indicated that NRC-03 exerts a cytotoxic effect in cancer cells via inducing cellular and mitochondrial oxidative stress. Moreover, the expression of cyclophilin D (CypD), the key component of mitochondrial permeability transition pore (mPTP), was upregulated in NRC-03-treated cancer cells. Blockade of CypD by siRNA-mediated depletion or pharmacological inhibitor cyclosporine A (CsA) significantly suppressed NRC-03-induced mitochondrial oxidative stress, mitochondrial dysfunction, and apoptosis. NRC-03 also activated MAPK/ERK and NF-κB pathways. Importantly, intratumoral administration of NRC-03 inhibited the growth of CAL-27 cells-derived tumors on xenografted animal models. Taken together, our study indicates that NRC-03 induces apoptosis in OSCC cells via the CypD-mPTP axis mediated mitochondrial oxidative stress.

A Proteomic Approach to Study the Biological Role of Hepatitis C Virus Protein Core+1/ARFP

Hepatitis C virus is the major cause of chronic liver diseases and the only cytoplasmic RNA virus known to be oncogenic in humans. The viral genome gives rise to ten mature proteins and to additional proteins, which are the products of alternative translation initiation mechanisms. A protein-known as ARFP (alternative reading frame protein) or Core+1 protein-is synthesized by an open reading frame overlapping the HCV Core coding region in the (+1) frame of genotype 1a. Almost 20 years after its discovery, we still know little of the biological role of the ARFP/Core+1 protein. Here, our differential proteomic analysis of stable hepatoma cell lines expressing the Core+1/Long isoform of HCV-1a relates the expression of the Core+1/Long isoform with the progression of the pathology of HCV liver disease to cancer.

Aggravation of hepatic lipidosis in red-footed tortoise Chelonoidis carbonaria with age is associated with alterations in liver mitochondria

The occurrence of hepatic lipidosis is commonly reported in different reptilian species, especially in animals under captivity. Liver accumulation of fat is associated with disorders, better described in mammals as non-alcoholic fatty liver diseases (NAFLD), ranging from simple steatosis, to non-alcoholic steatohepatitis (NASH), and to more severe lesions of cirrhosis and hepatocellular carcinoma. Mitochondria play a central role in NAFLD pathogenesis, therefore in this study we characterized livers of ad libitum fed captive red-footed tortoise Chelonoidis carbonaria through histological and mitochondrial function evaluations of juvenile and adult individuals. Livers from adult tortoises exhibited higher levels of lipids, melanomacrophages centers and melanin than juveniles. The observed high score levels of histopathological alterations in adult tortoises, such as microvesicular steatosis, inflammation and fibrosis, indicated the progression to a NASH condition. Mitochondrial oxygen consumption at different respiratory states and with different substrates was 30 to 58% lower in adult when compared to juvenile tortoises. Despite citrate synthase activity was also lower in adults, cardiolipin content was similar to juveniles, indicating that mitochondrial mass was unaffected by age. Mitochondrial Ca²⁺ retention capacity was reduced by 70% in adult tortoises. Overall, we found that aggravation of NAFLD in ad libitum fed captive tortoises is associated with compromised mitochondrial function, indicating a critical role of the organelle in liver disease progression in reptiles.

Adipose-derived stem cells alleviate liver injury induced by type 1 diabetes mellitus by inhibiting mitochondrial stress and attenuating inflammation

Background

Type 1 diabetes mellitus (T1D) is a worldwide health priority due to autoimmune destruction and is associated with an increased risk of multiorgan complications. Among these complications, effective interventions for liver injury, which can progress to liver fibrosis and hepatocellular carcinoma, are lacking. Although stem cell injection has a therapeutic effect on T1D, whether it can cure liver injury and the underlying mechanisms need further investigation.

Methods

Sprague–Dawley rats with streptozotocin (STZ)-induced T1D were treated with adipose-derived stem cell (ADSC) or PBS via the tail vein formed the ADSC group or STZ group. Body weights and blood glucose levels were examined weekly for 6 weeks. RNA-seq and PCR array were used to detect the difference in gene expression of the livers between groups.

Results

In this study, we found that ADSCs injection alleviated hepatic oxidative stress and injury and improved liver function in rats with T1D; potential mechanisms included cytokine activity, energy metabolism and immune regulation were potentially involved, as determined by RNA-seq. Moreover, ADSC treatment altered the fibroblast growth factor 21 (FGF21) and transforming growth factor β (TGF-β) levels in T1D rat livers, implying its repair capacity. Disordered intracellular energy metabolism, which is closely related to mitochondrial stress and dysfunction, was inhibited by ADSC treatment. PCR array and ingenuity pathway analyses suggested that the ADSC-induced suppression of mitochondrial stress is related to decreased necroptosis and apoptosis. Moreover, mitochondria-related alterations caused liver inflammation, resulting in liver injury involving the T lymphocyte-mediated immune response.

Conclusions

Overall, these results improve our understanding of the curative effect of ADSCs on T1D complications: ADSCs attenuate liver injury by inhibiting mitochondrial stress (apoptosis and dysfunctional energy metabolism) and alleviating inflammation (inflammasome expression and immune disorder). These results are important for early intervention in liver injury and for delaying the development of liver lesions in patients with T1D.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02760-z.

Molecular mechanisms and consequences of mitochondrial permeability transition

Mitochondrial permeability transition (mPT) is a phenomenon that abruptly causes the flux of low molecular weight solutes (molecular weight up to 1,500) across the generally impermeable inner mitochondrial membrane. The mPT is mediated by the so-called mitochondrial permeability transition pore (mPTP), a supramolecular entity assembled at the interface of the inner and outer mitochondrial membranes. In contrast to mitochondrial outer membrane permeabilization, which mostly activates apoptosis, mPT can trigger different cellular responses, from the physiological regulation of mitophagy to the activation of apoptosis or necrosis. Although there are several molecular candidates for the mPTP, its molecular nature remains contentious. This lack of molecular data was a significant setback that prevented mechanistic insight into the mPTP, pharmacological targeting and the generation of informative animal models. In recent years, experimental evidence has highlighted mitochondrial F₁F_o ATP synthase as a participant in mPTP formation, although a molecular model for its transition to the mPTP is still lacking. Recently, the resolution of the F₁F_o ATP synthase structure by cryogenic electron microscopy led to a model for mPTP gating. The elusive molecular nature of the mPTP is now being clarified, marking a turning point for understanding mitochondrial biology and its pathophysiological ramifications. This Review provides an up-to-date reference for the understanding of the mammalian mPTP and its cellular functions. We review current insights into the molecular mechanisms of mPT and validated observations - from studies in vivo or in artificial membranes - on mPTP activity and functions. We end with a discussion of the contribution of the mPTP to human disease. Throughout the Review, we highlight the multiple unanswered questions and, when applicable, we also provide alternative interpretations of the recent discoveries.

Nuclear Receptors Linking Metabolism, Inflammation, and Fibrosis in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) and its progressive form nonalcoholic steatohepatitis (NASH) comprise a spectrum of chronic liver diseases in the global population that can lead to end-stage liver disease and hepatocellular carcinoma (HCC). NAFLD is closely linked to the metabolic syndrome, and comorbidities such as type 2 diabetes, obesity and insulin resistance aggravate liver disease, while NAFLD promotes cardiovascular risk in affected patients. The pathomechanisms of NAFLD are multifaceted, combining hepatic factors including lipotoxicity, mechanisms of cell death and liver inflammation with extrahepatic factors including metabolic disturbance and dysbiosis. Nuclear receptors (NRs) are a family of ligand-controlled transcription factors that regulate glucose, fat and cholesterol homeostasis and modulate innate immune cell functions, including liver macrophages. In parallel with metabolic derangement in NAFLD, altered NR signaling is frequently observed and might be involved in the pathogenesis. Therapeutically, clinical data indicate that single drug targets thus far have been insufficient for reaching patient-relevant endpoints. Therefore, combinatorial treatment strategies with multiple drug targets or drugs with multiple mechanisms of actions could possibly bring advantages, by providing a more holistic therapeutic approach. In this context, peroxisome proliferator-activated receptors (PPARs) and other NRs are of great interest as they are involved in wide-ranging and multi-organ activities associated with NASH progression or regression. In this review, we summarize recent advances in understanding the pathogenesis of NAFLD, focusing on mechanisms of cell death, immunometabolism and the role of NRs. We outline novel therapeutic strategies and discuss remaining challenges.

Liver cyclophilin D deficiency inhibits the progression of early NASH by ameliorating steatosis and inflammation

Cyclophilin D (CypD) can stimulate the opening of the membrane permeability transition pore (mPTP) and regulate mitochondrial function. Whole-body knockout of CypD improved high fat diet-induced hepatic steatosis by reducing the excess opening of the mPTP and lipid deposition. However, whether CypD significantly ameliorates nonalcoholic steatohepatitis (NASH) has not been studied. Therefore, we established liver-specific CypD knockout (CypD LKO) mice and fed a HFHC diet to induce NASH. Compared with the wild-type mice, the CypD LKO not only showed improved lipid deposition and insulin resistance by increasing fatty acid oxidation but also displayed ameliorated hepatic inflammation, although the symptoms of fibrosis in the NASH model were not significantly improved. In addition, we used bile duct ligation (BDL) or a 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet to induce cholestatic disease and found that CypD LKO had also no significant effect on acute fibrosis. Thus, CypD LKO can inhibit the progression of early NASH by ameliorating steatosis and inflammatory symptoms. These results suggest a new strategy for the treatment of early NASH.

Programmed cell death and liver diseases

Cell death represents the most critical pathologic entity in liver disease, which dictates pathologic consequences such as inflammation, fibrosis, and cell transformation. We analyzed the conclusions of studies on the involvement of different types of programmed cell death (PCD) in the pathogenesis of liver diseases. Three main forms of PCD (autophagy, apoptosis, necrosis) and five additional, still insufficiently studied PCD – necroptosis, ferroptosis, pyroptosis, partanatosis and entosis – observed in the liver in various acute and chronic diseases are considered. The involvement of several PCD at once in the development of any one pathology and one type of PCD in different pathologies was established. This indicates the existence of cross-regulation of metabolism in the liver cells with different levels of damage in the formation of the main dominant type of PCD. Available results indicate the possibility of attenuation (correction) of functional and morphological manifestations of PCD in the organ by controlled blocking of effector-mediated PCD pathways, as well as targeted induction of autophagy, anti-apoptotic and anti-necrotic mechanisms in liver cells.

Elevated Serum Cyclophilin D Level is Associated with Nonalcoholic Fatty Liver Disease and Higher Fibrosis Scores in Patients with Diabetes Mellitus

Background

Cyclophilin D (CypD) is a mitochondrial matrix protein involved in liver steatosis and fibrosis in vitro. However, the role of CypD in the development of fatty liver and liver fibrosis in humans has not been determined.

Purpose

To measure the serum level of CypD in patients with type 2 diabetes (T2DM) and nonalcoholic fatty liver disease (NAFLD) and to assess its relation to the presence of hepatic steatosis and fibrosis in this group of patients.

Patients and Methods

In this cross-sectional study, 30 patients with diabetes and NAFLD were compared to 30 patients with diabetes without NAFLD and 30 age- and sex-matched healthy subjects. Abdominal ultrasound was used to diagnose NAFLD. Serum CypD was measured using ELISA. Fibrosis-4 (FIB-4) index, AST to platelet ratio index (APRI), and NAFLD fibrosis score (NFS) were used as markers of liver fibrosis in patients with NAFLD. Patients with NAFLD were divided into two subgroups based on FIB-4 index: patients with liver fibrosis (FIB-4 >1.45) and patients without liver fibrosis (FIB-4 <1.45). CypD and other clinical and biochemical parameters were validated as predictors of NAFLD and liver fibrosis in diabetic patients in multivariate logistic regression analysis.

Results

Diabetic patients with NAFLD had higher serum CypD levels than those without NAFLD (11.65±2.96 vs 6.58±1.90 ng/mL, respectively, P <0.001). Correlation analysis revealed a significant positive correlation between CypD and FIB-4 index (P=0.001), APRI (P=0.013) and NFS (P<0.001). GGT and CypD were the only predictors of NAFLD. For the prediction of significant fibrosis, AUROC of CypD was 0.835 with a cutoff >14.05 ng/mL provides specificity of 81.8% and sensitivity of 75%.

Conclusion

Serum CypD is related to hepatic steatosis and fibrosis in diabetic patients. Serum CypD may thus provide a novel marker and therapeutic target of NAFLD and liver fibrosis.

The mitochondrial permeability transition pore: an evolving concept critical for cell life and death

In this review, we summarize current knowledge of perhaps one of the most intriguing phenomena in cell biology: the mitochondrial permeability transition pore (mPTP). This phenomenon, which was initially observed as a sudden loss of inner mitochondrial membrane impermeability caused by excessive calcium, has been studied for almost 50 years, and still no definitive answer has been provided regarding its mechanisms. From its initial consideration as an in vitro artifact to the current notion that the mPTP is a phenomenon with physiological and pathological implications, a long road has been travelled. We here summarize the role of mitochondria in cytosolic calcium control and the evolving concepts regarding the mitochondrial permeability transition (mPT) and the mPTP. We show how the evolving mPTP models and mechanisms, which involve many proposed mitochondrial protein components, have arisen from methodological advances and more complex biological models. We describe how scientific progress and methodological advances have allowed milestone discoveries on mPTP regulation and composition and its recognition as a valid target for drug development and a critical component of mitochondrial biology.

Nampt controls skeletal muscle development by maintaining Ca2+ homeostasis and mitochondrial integrity

Objective

NAD⁺ is a co-factor and substrate for enzymes maintaining energy homeostasis. Nicotinamide phosphoribosyltransferase (NAMPT) controls NAD⁺ synthesis, and in skeletal muscle, NAD⁺ is essential for muscle integrity. However, the underlying molecular mechanisms by which NAD⁺ synthesis affects muscle health remain poorly understood. Thus, the objective of the current study was to delineate the role of NAMPT-mediated NAD⁺ biosynthesis in skeletal muscle development and function.

Methods

To determine the role of Nampt in muscle development and function, we generated skeletal muscle-specific Nampt KO (SMNKO) mice. We performed a comprehensive phenotypic characterization of the SMNKO mice, including metabolic measurements, histological examinations, and RNA sequencing analyses of skeletal muscle from SMNKO mice and WT littermates.

Results

SMNKO mice were smaller, with phenotypic changes in skeletal muscle, including reduced fiber area and increased number of centralized nuclei. The majority of SMNKO mice died prematurely. Transcriptomic analysis identified that the gene encoding the mitochondrial permeability transition pore (mPTP) regulator Cyclophilin D (Ppif) was upregulated in skeletal muscle of SMNKO mice from 2 weeks of age, with associated increased sensitivity of mitochondria to the Ca²⁺-stimulated mPTP opening. Treatment of SMNKO mice with the Cyclophilin D inhibitor, Cyclosporine A, increased membrane integrity, decreased the number of centralized nuclei, and increased survival.

Conclusions

Our study demonstrates that NAMPT is crucial for maintaining cellular Ca²⁺ homeostasis and skeletal muscle development, which is vital for juvenile survival.

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NAD⁺ salvage capacity is important for skeletal muscle development and survival.

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Skeletal muscle-specific Nampt knockout mice exhibit a dystrophy-like phenotype.

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Nampt deletion alters Ca²⁺ homeostasis and impairs mitochondrial function.

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Low NAD⁺ levels signals mitochondrial permeability transition pore opening.

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Cyclosporin A treatment improves sarcolemma integrity and increases survival rate.

Berberine improves intralipid-induced insulin resistance in murine

Insulin resistance (IR) is a major metabolic risk factor even before the onset of hyperglycemia. Recently, berberine (BBR) is found to improve hyperglycemia and IR. In this study, we investigated whether BBR could improve IR independent of hyperglycemia. Acute insulin-resistant state was induced in rats by systemic infusion of intralipid (6.6%). BBR was administered via different delivery routes before or after the beginning of a 2-h euglycemic-hyperinsulinemic clamp. At the end of experiment, rats were sacrificed, gastrocnemius muscle was collected for detecting mitochondrial swelling, phosphorylation of Akt and AMPK, as well as the mitochondrial permeability regulator cyclophilin D (CypD) protein expression. We showed that BBR administration markedly ameliorated intralipid-induced IR without affecting blood glucose, which was accompanied by alleviated mitochondrial swelling in skeletal muscle. We used human skeletal muscle cells (HSMCs), AML12 hepatocytes, human umbilical vein endothelial cells, and CypD knockout mice to investigate metabolic and molecular alternations. In either HSMCs or AML12 hepatocytes, BBR (5 μM) abolished palmitate acid (PA)-induced increase of CypD protein levels. In CypD-deficient mice, intralipid-induced IR was greatly attenuated and the beneficial effect of BBR was diminished. Furthermore, we demonstrated that the inhibitory effect of BBR on intralipid-induced IR was mainly mediated by skeletal muscle, but not by intestine, liver, or microvasculature; BBR administration suppressed intralipid-induced upregulation of CypD expression in skeletal muscle. These results suggest that BBR alleviates intralipid-induced IR, which is related to the inhibition of CypD protein expression in skeletal muscle.

Changes in hepatic triglyceride content with the activation of ER stress and increased FGF21 secretion during pregnancy

Background

To meet the needs of foetal growth and development, marked changes in lipid profiles occur during pregnancy. Abnormal lipid metabolism is often accompanied by adverse pregnancy outcomes, which seriously affect maternal and infant health. Further understanding of the mechanism of lipid metabolism during pregnancy would be helpful to reduce the incidence of adverse pregnancy outcomes.

Methods

Pregnant mice were euthanized in the virgin (V) state, on day 5 of pregnancy (P5), on day 12 of pregnancy (P12), on day 19 of pregnancy (P19) and on lactation day 2 (L2). Body weight and energy expenditure were assessed to evaluate the general condition of the mice. Triglyceride (TG) levels, the cholesterol content in the liver, liver histopathology, serum lipid profiles, serum β-hydroxybutyrate levels, fibroblast growth factor-21 (FGF21) levels and the levels of relevant target genes were analysed.

Results

During early pregnancy, anabolism was found to play a major role in liver lipid deposition. In contrast, advanced pregnancy is an overall catabolic condition associated with both increased energy expenditure and reduced lipogenesis. Moreover, the accumulation of hepatic TG did not appear until P12, after the onset of endoplasmic reticulum (ER) stress on P5. Then, catabolism was enhanced, and FGF21 secretion was increased in the livers of female mice in late pregnancy. We further found that the expression of sec23a, which as the coat protein complex II (COPII) vesicle coat proteins regulates the secretion of FGF21, in the liver was decreased on P19.

Conclusion

With the activation of ER stress and increased FGF21 secretion during pregnancy, the hepatic TG content changes, suggesting that ER stress and FGF21 may play an important role in balancing lipid homeostasis and meeting maternal and infant energy requirements in late pregnancy.

Mitochondrial dysfunction and mitochondrion-targeted therapeutics in liver diseases

The liver is a vital metabolic and detoxifying organ and suffers diverse endogenous or exogenous damage. Hepatocyte mitochondria experience various structural and functional defects from liver injury, bearing oxidative stress, metabolic dysregulation, and the disturbance of mitochondrial quality control (MQC) mechanisms. Mitochondrial malfunction initiates the mitochondria-mediated apoptotic pathways and the release of damage signals, aggravating liver damage and disease progression via inflammation and reparative fibrogenesis. Removal of mitochondrial impairment or the improvement of MQC mechanisms restore mitochondrial homeostasis and benefit liver health. This review discusses the association of mitochondrial disorders with hepatic pathophysiological processes and the resultant potential of mitochondrion-targeting therapeutics for hepatic disorders. The recent advances in the MQC mechanisms and the mitochondrial-derived damage-associated molecular patterns (DAMPs) in the pathology and treatment of liver disease are particularly focussed.

Calcium transfer between endoplasmic reticulum and mitochondria in liver diseases

Calcium (Ca²⁺ ) is a second messenger essential for cellular homeostasis. Inside the cell, Ca²⁺ is compartmentalized and exchanged among organelles in response to both external and internal stimuli. Mitochondria-associated membranes (MAMs) provide a platform for proteins and channels involved in Ca²⁺ transfer between the endoplasmic reticulum (ER) and mitochondria. Deregulated Ca²⁺ signaling and proteins regulating ER-mitochondria interactions have been linked to liver diseases and intensively investigated in recent years. In this review, we summarize the role of MAM-resident proteins in Ca²⁺ transfer and their association with different liver diseases.

Inhibition of fibroblast IL-6 production by ACKR4 deletion alleviates cardiac remodeling after myocardial infarction

Fibrotic scarring is tightly linked to the development of heart failure in patients with post-myocardial infarction (MI). Atypical chemokine receptor 4 (ACKR4) can eliminate chemokines, such as C-C chemokine ligand 21 (CCL21), which is independently associated with heart failure mortality. However, the role of ACKR4 in the heart during MI is unrevealed. This study aimed to determine whether ACKR4 modulates cardiac remodeling following MI and to illuminate the potential molecular mechanisms. The expression of ACKR4 was upregulated in the border/infarct area, and ACKR4 was predominantly expressed in cardiac fibroblasts (CFs). Knockout of ACKR4 protected against adverse ventricular remodeling in mice post-MI. These protective effects of ACKR4 deficiency were independent of dendritic cell immune response but could be attributed to downregulated CF-derived IL-6, affecting CF proliferation and endothelial cell (EC) functions, which consequently inhibited cardiac fibrosis. ACKR4 promoted IL-6 generation and proliferation of CFs. Besides, ACKR4 induced endothelial-to-mesenchymal transition (EndMT) in ECs through IL-6 paracrine effect. The p38 MAPK/NF-κB signaling pathway was involved in ACKR4 facilitated IL-6 generation. Moreover, ACKR4 overexpression in vivo via AAV9 carrying a periostin promoter aggravated heart functional impairment post-MI, which was abolished by IL-6 neutralizing antibody. Therefore, our study established a novel link between ACKR4 and IL-6 post-MI, indicating that ACKR4 may be a novel therapeutic target to ameliorate cardiac remodeling.

Anterior gradient 2 increases long-chain fatty acid uptake via stabilizing FABP1 and facilitates lipid accumulation

Anterior gradient 2 (AGR2), a protein disulfide isomerase (PDI), is a well-established oncogene. Here, we found that Agr2-/- mice had a decreased fat mass and hepatic and serum lipid levels compared with their wild-type littermates after fasting, and exhibited reduced high-fat diet (HFD)-induced fat accumulation. Transgenic mice overexpressing AGR2 (Agr2/Tg) readily gained fat weight on a HFD but not a normal diet. Proteomic analysis of hepatic samples from Agr2-/- mice revealed that depletion of AGR2 impaired long-chain fatty acid uptake and activation but did not affect de novo hepatic lipogenesis. Further investigations led to the identification of several effector substrates, particularly fatty acid binding protein-1 (FABP1) as essential for the AGR2-mediated effects. AGR2 was coexpressed with FABP1, and knockdown of AGR2 resulted in a reduction in FABP1 stability. Physical interactions of AGR2 and FABP1 depended on the PDI motif in AGR2 and the formation of a disulfide bond between these two proteins. Overexpression of AGR2 but not a mutant AGR2 protein lacking PDI activity suppressed lipid accumulation in cells lacking FABP1. Moreover, AGR2 deficiency significantly reduced fatty acid absorption in the intestine, which might be resulted from decreased fatty acid transporter CD36 in mice. These findings demonstrated a novel role of AGR2 in fatty-acid uptake and activation in both the liver and intestine, which contributed to the AGR2-mediated lipid accumulation, suggesting that AGR2 is an important regulator of whole-body lipid metabolism and down-regulation of AGR2 may antagonize the development of obesity.

Physiological evidence of mitochondrial permeability transition pore opening caused by lipid deposition leading to hepatic steatosis in db/db mice

Mitochondrial permeability transition pore (mPTP) is an important regulator in cell apoptosis and necrosis. However, its role in hepatic steatosis, especially its electrophysiological properties transformation remains elusive. Herein, using diabetes mice, we investigated the role of mPTP in hepatic steatosis triggered by diabetes and the mechanisms involved. We found that hepatic steatosis altered mitochondrial morphology, generating mega mitochondria, mitochondria swelling, calcein fluorescence quenching and mitochondrial membrane potential depolarization. At the same time, we confirmed an augmented mPTP opening with patch clamping in liver mitoplasts in db/db mice and a similar transformation with arachidonic acid (AA) simulating liquid deposition. We also found mPTP opening was significantly attenuated in wt mice after removing mitochondrial matrix, while that in db/db mice remained active. In addition, we observed that AA could directly activate mPTP in inside-out mode, independent of matrix calcium. In conclusion, we for the first time provided a physiological evidence of mPTP opening in lipid deposition, which could be directly induced by AA without Ca²⁺ and can be inhibited by cyclosporine A. As a result, it led to mitochondria morphology and function transformation. This might provide insights into potential therapeutic target for future treatment of mitochondrial liver disease.

Trypanosoma cruzi infection in Cyclophilin D deficient mice

Trypanosoma cruzi is the causative agent of Chagas disease, which is endemic in Latin America and around the world through mother to child transmission. The heart is the organ most frequently affected in the chronic stage of the human infection and depends on mitochondria for the required energy for its activity. Cyclophilins are involved in protein folding and the mitochondrial isoform, Cyclophilin D (CyPD), has a crucial role in the opening of the mitochondrial permeability transition pore. In the present study, we infected CyPD deficient mice, with ablation of the Ppif gene, with T. cruzi parasites and the course of the infection was analyzed. Parasite load, quantified by PCR, was significantly lower in skeletal and cardiac tissues of Ppif-/- mice compared to wild type mice. In vitro cultured cardiomyocytes and macrophages from mice lacking CyPD exhibited lower percentage of infected cells and number of intracellular parasites than those observed for wild type mice. Although histopathological analysis of heart and mRNA of heart cytokines showed differences between T. cruzi-infected mice compared to the uninfected animals, no significant differences were found mice due to the ablation of the Ppif gene. Our results suggest that cells deficient for mitochondrial CyPD, inhibited for the mitochondrial membrane potential collapse, reduces the severity of parasite aggression and spread of cellular infection.

Cell Death in Liver Diseases: A Review

Regulated cell death (RCD) is pivotal in directing the severity and outcome of liver injury. Hepatocyte cell death is a critical event in the progression of liver disease due to resultant inflammation leading to fibrosis. Apoptosis, necrosis, necroptosis, autophagy, and recently, pyroptosis and ferroptosis, have all been investigated in the pathogenesis of various liver diseases. These cell death subroutines display distinct features, while sharing many similar characteristics with considerable overlap and crosstalk. Multiple types of cell death modes can likely coexist, and the death of different liver cell populations may contribute to liver injury in each type of disease. This review addresses the known signaling cascades in each cell death pathway and its implications in liver disease. In this review, we describe the common findings in each disease model, as well as the controversies and the limitations of current data with a particular focus on cell death-related research in humans and in rodent models of alcoholic liver disease, non-alcoholic fatty liver disease and steatohepatitis (NASH/NAFLD), acetaminophen (APAP)-induced hepatotoxicity, autoimmune hepatitis, cholestatic liver disease, and viral hepatitis.

Cell Death and Liver Disease

Cell death is now reclassified into several types based on the mechanisms and morphologic phenotype. Understanding of such classifications offers insights into the pathogenesis of liver disease, as well as diagnostic or therapeutic implications. Apoptosis is recognized relatively easily due to its unique morphology, but lytic cell death may occur in the form of accidental necrosis, mitochondria permeability transition-driven necrosis, necroptosis, pyroptosis, ferroptosis, and parthanatos. The cell may be engulfed by neighboring cells due to a loss of integrin signaling or cancer cell competition by entosis, a type of cell death. The classification also includes mechanistically termed cell death such as autophagy-dependent cell death and lysosome-dependent cell death. These different types of cell death may occur uniquely in certain liver diseases but may coexist in the evolution of the disease. They occur in parenchymal and non-parenchymal liver cells, as well as inflammatory cells, causing distinct pathologic consequences. This review briefly covers the recently revised classifications of cell death and discusses their relevance to liver diseases of different etiologies.

Chronic-plus-binge alcohol intake induces production of proinflammatory mtDNA-enriched extracellular vesicles and steatohepatitis via ASK1/p38MAPKα-dependent mechanisms

Alcohol-associated liver disease is a spectrum of liver disorders with histopathological changes ranging from simple steatosis to steatohepatitis, cirrhosis, and hepatocellular carcinoma. Recent data suggest that chronic-plus-binge ethanol intake induces steatohepatitis by promoting release by hepatocytes of proinflammatory mitochondrial DNA-enriched (mtDNA-enriched) extracellular vesicles (EVs). The aim of the present study was to investigate the role of the stress kinase apoptosis signal-regulating kinase 1 (ASK1) and p38 mitogen-activated protein kinase (p38) in chronic-plus-binge ethanol-induced steatohepatitis and mtDNA-enriched EV release. Microarray analysis revealed the greatest hepatic upregulation of metallothionein 1 and 2 (Mt1/2), which encode 2 of the most potent antioxidant proteins. Genetic deletion of the Mt1 and Mt2 genes aggravated ethanol-induced liver injury, as evidenced by elevation of serum ALT, neutrophil infiltration, oxidative stress, and ASK1/p38 activation in the liver. Inhibition or genetic deletion of Ask1 or p38 ameliorated ethanol-induced liver injury, inflammation, ROS levels, and expression of phagocytic oxidase and ER stress markers in the liver. In addition, inhibition of ASK1 or p38 also attenuated ethanol-induced mtDNA-enriched EV secretion from hepatocytes. Taken together, these findings indicate that induction of hepatic mtDNA-enriched EVs by ethanol is dependent on ASK1 and p38, thereby promoting alcoholic steatohepatitis.

Physiopathology of the Permeability Transition Pore: Molecular Mechanisms in Human Pathology

Mitochondrial permeability transition (MPT) is the sudden loss in the permeability of the inner mitochondrial membrane (IMM) to low-molecular-weight solutes. Due to osmotic forces, MPT is paralleled by a massive influx of water into the mitochondrial matrix, eventually leading to the structural collapse of the organelle. Thus, MPT can initiate outer-mitochondrial-membrane permeabilization (MOMP), promoting the activation of the apoptotic caspase cascade and caspase-independent cell-death mechanisms. The induction of MPT is mostly dependent on mitochondrial reactive oxygen species (ROS) and Ca²⁺, but is also dependent on the metabolic stage of the affected cell and signaling events. Therefore, since its discovery in the late 1970s, the role of MPT in human pathology has been heavily investigated. Here, we summarize the most significant findings corroborating a role for MPT in the etiology of a spectrum of human diseases, including diseases characterized by acute or chronic loss of adult cells and those characterized by neoplastic initiation.

Proximal tubule cyclophilin D regulates fatty acid oxidation in cisplatin-induced acute kidney injury

Regardless of the etiology, acute kidney injury involves aspects of mitochondrial dysfunction and ATP depletion. Fatty acid oxidation is the preferred energy source of the kidney and is inhibited during acute kidney injury. A pivotal role for the mitochondrial matrix protein, cyclophilin D in regulating overall cell metabolism is being unraveled. We hypothesize that mitochondrial interaction of proximal tubule cyclophilin D and the transcription factor PPARα modulate fatty acid beta-oxidation in cisplatin-induced acute kidney injury. Cisplatin injury resulted in histological and functional damage in the kidney with downregulation of fatty acid oxidation genes and increase of intrarenal lipid accumulation. However, proximal tubule-specific deletion of cyclophilin D protected the kidneys from the aforementioned effects. Mitochondrial translocation of PPARα, its binding to cyclophilin D, and sequestration led to inhibition of its nuclear translocation and transcription of PPARα-regulated fatty acid oxidation genes during cisplatin-induced acute kidney injury. Genetic or pharmacological inhibition of cyclophilin D preserved nuclear expression and transcriptional activity of PPARα and prevented the impairment of fatty acid oxidation and intracellular lipid accumulation. Docking analysis identified potential binding sites between PPARα and cyclophilin D. Thus, our results indicate that proximal tubule cyclophilin D elicits impaired mitochondrial fatty acid oxidation via mitochondrial interaction between cyclophilin D and PPARα. Hence, targeting their interaction may be a potential therapeutic strategy to prevent energy depletion, lipotoxicity and cell death in cisplatin-induced acute kidney injury.

Delineating a role for the mitochondrial permeability transition pore in diabetic kidney disease by targeting cyclophilin D

Mitochondrial stress has been widely observed in diabetic kidney disease (DKD). Cyclophilin D (CypD) is a functional component of the mitochondrial permeability transition pore (mPTP) which allows the exchange of ions and solutes between the mitochondrial matrix to induce mitochondrial swelling and activation of cell death pathways. CypD has been successfully targeted in other disease contexts to improve mitochondrial function and reduced pathology. Two approaches were used to elucidate the role of CypD and the mPTP in DKD. Firstly, mice with a deletion of the gene encoding CypD (Ppif-/-) were rendered diabetic with streptozotocin (STZ) and followed for 24 weeks. Secondly, Alisporivir, a CypD inhibitor was administered to the db/db mouse model (5 mg/kg/day oral gavage for 16 weeks). Ppif-/- mice were not protected against diabetes-induced albuminuria and had greater glomerulosclerosis than their WT diabetic littermates. Renal hyperfiltration was lower in diabetic Ppif-/- as compared with WT mice. Similarly, Alisporivir did not improve renal function nor pathology in db/db mice as assessed by no change in albuminuria, KIM-1 excretion and glomerulosclerosis. Db/db mice exhibited changes in mitochondrial function, including elevated respiratory control ratio (RCR), reduced mitochondrial H2O2 generation and increased proximal tubular mitochondrial volume, but these were unaffected by Alisporivir treatment. Taken together, these studies indicate that CypD has a complex role in DKD and direct targeting of this component of the mPTP will likely not improve renal outcomes.

Thyroid Stimulating Hormone Triggers Hepatic Mitochondrial Stress through Cyclophilin D Acetylation

BACKGROUND & AIMS

Oxidative stress-related liver diseases were shown to be associated with elevated serum thyroid stimulating hormone (TSH) levels. Mitochondria are the main source of cellular reactive oxygen species. However, the relationship between TSH and hepatic mitochondrial stress/dysfunction and the underlying mechanisms are largely unknown. Here, we focused on exploring the effects and mechanism of TSH on hepatic mitochondrial stress.

METHODS

As the function of TSH is mediated through the TSH receptor (TSHR), Tshr -/- mice and liver-specific Tshr -/- mice and liver-specific Tshr -/- mice and liver-specific.

RESULTS

A relatively lower degree of mitochondrial stress was observed in the livers of Tshr -/- mice and liver-specific in vitro. Microarray and RT-PCR analyses showed that Tshr -/- mice and liver-specific.

CONCLUSIONS

TSH stimulates hepatic CypD acetylation through the lncRNA-AK044604/SIRT1/SIRT3 signaling pathway, indicating an essential role for TSH in mitochondrial stress in the liver.

Cyclophilin D participates in the inhibitory effect of high-fat diet on the expression of steroidogenic acute regulatory protein

OBJECTIVE

The high-fat diet (HFD)-induced obesity is responsible for the testosterone deficiency (TD). However, the mechanism remains unknown. Mitochondrial homeostasis is proved to be important for maintaining the function of steroidogenic acute regulatory protein (StAR), the first rate-limiting enzyme in testosterone synthesis. As the key regulator of mitochondrial membrane permeability, cyclophilin D (CypD) plays a crucial role in maintaining mitochondrial function. In this study, we sought to elucidate the role of CypD in the expression of StAR affected by HFD.

METHODS

To analyse the influence of CypD on StAR in vivo and in vitro, mouse models of HFD, CypD overexpression and CypD knockout (Ppif-/- ) as well as Leydig cells treated with palmitic acid (PA) and CypD overexpression plasmids were examined with an array of metabolic, mitochondrial function and molecular assays.

RESULTS

Compared with the normal diet mice, consistent with reduced testosterone in testes, the expressions of StAR in both mRNA and protein levels in HFD mice were down-regulated, while expressions of CypD were up-regulated. High-fat intake impaired mitochondrial function with the decrease in StAR in Leydig cells. Overexpression of CypD inhibited StAR expressions in vivo and in vitro. Compared with C57BL/6 mice with HFD, expressions of StAR were improved in Ppif-/- mice with HFD.

CONCLUSIONS

Mitochondrial CypD involved in the inhibitory effect of HFD on StAR expression in testes.

A Pan-Cyclophilin Inhibitor, CRV431, Decreases Fibrosis and Tumor Development in Chronic Liver Disease Models

Previous studies show that cyclophilins contribute to many pathologic processes, and cyclophilin inhibitors demonstrate therapeutic activities in many experimental models. However, no drug with cyclophilin inhibition as the primary mode of action has advanced completely through clinical development to market. In this study, we present findings on the cyclophilin inhibitor, CRV431, that highlight its potential as a drug candidate for chronic liver diseases. CRV431 was found to potently inhibit all cyclophilin isoforms tested—A, B, D, and G. Inhibitory constant or IC₅₀ values ranged from 1 to 7 nM, which was up to 13 times more potent than the parent compound, cyclosporine A (CsA), from which CRV431 was derived. Other CRV431 advantages over CsA as a nontransplant drug candidate were significantly diminished immunosuppressive activity, less drug transporter inhibition, and reduced cytotoxicity potential. Oral dosing to mice and rats led to good blood exposures and a 5- to 15-fold accumulation of CRV431 in liver compared with blood concentrations across a wide range of CRV431 dosing levels. Most importantly, CRV431 decreased liver fibrosis in a 6-week carbon tetrachloride model and in a mouse model of nonalcoholic steatohepatitis (NASH). Additionally, CRV431 administration during a late, oncogenic stage of the NASH disease model resulted in a 50% reduction in the number and size of liver tumors. These findings are consistent with CRV431 targeting fibrosis and cancer through multiple, cyclophilin-mediated mechanisms and support the development of CRV431 as a safe and effective drug candidate for liver diseases.

Deficiency of Mitochondrial Glycerol 3-Phosphate Dehydrogenase Contributes to Hepatic Steatosis

Mitochondrial glycerol 3-phosphate dehydrogenase (mGPDH) is an integral component of the respiratory chain, and recent studies have suggested that it plays an important role in hepatic glucose homeostasis. However, its function in hepatic lipid metabolism is unclear. Here, we identified a role for mGPDH in nonalcoholic fatty liver disease (NAFLD). Specifically, mGPDH expression and activity were lower in fatty livers from patients and mice with NAFLD (ob/ob, high-fat diet [HFD] and db/db). Liver-specific depletion of mGPDH in mice or mGPDH knockdown in cultured hepatocytes exacerbated diet-induced triglyceride accumulation and steatosis through enhanced lipogenesis. RNA-sequencing revealed that mGPDH regulated endoplasmic reticulum (ER)-related proteins and processes. mGPDH deletion exacerbated tunicamycin (ER stress inducer)-induced hepatic steatosis, whereas tauroursodeoxycholic acid (ER stress inhibitor) rescued mGPDH depletion-induced steatosis on an HFD. Moreover, ER stress induced by mGPDH depletion could be abrogated by the intracellular Ca²⁺ chelator 1,2-bis (2-aminophenoxy) ethane N,N,N´,N´-tetraacetic acid acetoxymethyl ester, mitochondrial permeability transition pore (mPTP) inhibitor cyclosporine A, or cyclophilin-D (Cyp-D) knockdown. mGPDH promoting Cyp-D ubiquitination was also observed. Finally, liver-specific mGPDH overexpression attenuated hepatic steatosis in ob/ob and HFD mice. Conclusion: mGPDH is a pivotal regulator of hepatic lipid metabolism. Its deficiency induces ER stress by suppressing Cyp-D ubiquitination, a key regulator of the mitochondrial Ca²⁺ conductance channel mPTP, and results in hepatic steatosis. mGPDH may be a potential therapeutic target for the treatment of NAFLD.

Saturated Fatty Acid-Enriched Diet-Impaired Mitochondrial Bioenergetics in Liver From Undernourished Rats During Critical Periods of Development

The nutritional transition that the western population has undergone is increasingly associated with chronic metabolic diseases. In this work, we evaluated a diet rich in saturated fatty acids (hyperlipidic, HL) after weaning of the offspring rats submitted to maternal protein restriction on the hepatic mitochondrial bioenergetics. Wistar rats were mated and during gestation and lactation, mothers received control diets (NP, normal protein content 17%) or low protein (LP, 8% protein). After weaning, rats received either NL (normolipidic) or HL (+59% SFA) diets up to 90 days of life. It was verified that all respiratory states of hepatic mitochondria showed a reduction in the LP group submitted to the post-weaning HL diet. This group also presented greater mitochondrial swelling compared to controls, potentiated after Ca2+ addition and prevented in the presence of EGTA (calcium chelator) and cyclosporin A (mitochondrial permeability transition pore inhibitor). There was also an increase in liver protein oxidation and lipid peroxidation and reduction in catalase and glutathione peroxidase activities in the LP group fed HL diet after weaning. Our data suggest that adult rats subjected to maternal protein restriction were more susceptible to hepatic mitochondrial damage caused by a diet rich in saturated fatty acids post-weaning.

Eucommia ulmoides Leaf Extract Ameliorates Steatosis Induced by High-fat Diet in Rats by Increasing Lysosomal Function

The recent discovery that the impairment of autophagic flux in non-alcoholic fatty liver disease (NAFLD) might be a strong determining factor in steatosis suggests the potential of therapeutic control of autophagic flux with natural agents in restoring NAFLD. We investigated the potential of Eucommia ulmoides leaf extract (EUL) to control dyslipidemia in NAFLD. EUL supplementation (200 mg/kg) promoted recovery from high fat diet (HFD)-induced lipid dysmetabolism. This hepatoprotective efficacy was accompanied by suppression of endoplasmic reticulum (ER) stress, enhancing lysosomal functions, and thereby increasing autophagic flux. We found a strong indication that inhibition of the mTOR-ER stress pathway was related to the enhanced autophagic flux. However, the direct antioxidative effect of EUL on cytoprotection cannot be ruled out as a significant contributing factor in NAFLD. Our findings will aid in further elucidating the mechanism of the anti-steatosis activity of EUL and highlight the therapeutic potential of EUL in the treatment of NAFLD.

Amelioration of hepatic steatosis is associated with modulation of gut microbiota and suppression of hepatic miR-34a in Gynostemma pentaphylla (Thunb.) Makino treated mice

Background

Non-alcoholic fatty liver disease (NAFLD) is a chronic and progressive liver disease with an increased risk of morbidity and mortality. However, so far no specific pharmacotherapy has been approved. Gynostemma pentaphylla (Thunb.) Makino (GP) is a traditional Chinese medicine that is widely used against hyperlipemia as well as hyperglycemia. This study aims to evaluate the effect of GP on NAFLD and explore the possible mechanism.

Methods

High-fat-diet induced NAFLD mice model were orally administrated with GP at dose of 11.7 g/kg or equivalent volume of distilled water once a day for 16 weeks. Body weight, food intake and energy expenditure were assessed to evaluate the general condition of mice. The triglycerides, total cholesterol content in the liver and liver histopathology, serum lipid profile and serum insulin level, fecal microbiome, hepatic microRNAs and relative target genes were analyzed.

Results

Mice in GP treatment group displayed improved hepatic triglycerides content with lower lipid droplet in hepatocyte and NAFLD activity score. Besides, GP treatment altered the composition of gut microbiota and the relative abundance of some of the key components that are implicated in metabolic disorders, especially phylum Firmicutes (Eubacterium, Blautia, Clostridium and Lactobacillus). Several hepatic microRNAs were downregulated by GP treatment such as miR-130a, miR-34a, miR-29a, miR-199a, among which the expression miR-34a was altered by more than four-fold compared to that of HFD group (3:14). The correlation analysis showed that miR-34a was strongly related to the change of gut microbiota especially phylum Firmicutes (R = 0.796). Additionally, the target genes of miR-34a (HNF4α, PPARα and PPARα) were restored by GP both in mRNA and protein levels.

Conclusion

Our results suggested that GP modulated the gut microbiota and suppressed hepatic miR-34a, which was associated with the amelioration of hepatic steatosis.