Growth Hormone Stops Excessive Inflammation After Partial Hepatectomy, Allowing Liver Regeneration and Survival Through Induction of H2-Bl/HLA-G.

BACKGROUND AND AIMS: Growth hormone (GH) is important for liver regeneration after partial hepatectomy (PHx). We investigated this process in C57BL/6 mice that express different forms of the GH receptor (GHR) with deletions in key signaling domains. APPROACH AND RESULTS: PHx was performed on C57BL/6 mice lacking GHR (Ghr-/- ), disabled for all GH-dependent Janus kinase 2 signaling (Box1-/- ), or lacking only GH-dependent signal transducer and activator of transcription 5 (STAT5) signaling (Ghr391-/- ), and wild-type littermates. C57BL/6 Ghr-/- mice showed striking mortality within 48 hours after PHx, whereas Box1-/- or Ghr391-/- mice survived with normal liver regeneration. Ghr-/- mortality was associated with increased apoptosis and elevated natural killer/natural killer T cell and macrophage cell markers. We identified H2-Bl, a key immunotolerance protein, which is up-regulated by PHx through a GH-mediated, Janus kinase 2-independent, SRC family kinase-dependent pathway. GH treatment was confirmed to up-regulate expression of the human homolog of H2-Bl (human leukocyte antigen G [HLA-G]) in primary human hepatocytes and in the serum of GH-deficient patients. We find that injury-associated innate immune attack by natural killer/natural killer T cell and macrophage cells are instrumental in the failure of liver regeneration, and this can be overcome in Ghr-/- mice by adenoviral delivery of H2-Bl or by infusion of HLA-G protein. Further, H2-Bl knockdown in wild-type C57BL/6 mice showed elevated markers of inflammation after PHx, whereas Ghr-/- backcrossed on a strain with high endogenous H2-Bl expression showed a high rate of survival following PHx. CONCLUSIONS: GH induction of H2-Bl expression is crucial for reducing innate immune-mediated apoptosis and promoting survival after PHx in C57BL/6 mice. Treatment with HLA-G may lead to improved clinical outcomes following liver surgery or transplantation.

Contemporary Review to Reduce Groin Surgical Site Infections in Vascular Surgery.

Surgical site infection (SSIs) in lower extremity vascular procedures is a major contributor to patient morbidity and mortality. Despite previous advancements in preoperative and postoperative care, the surgical infection rate in vascular surgery remains high, particularly when groin incisions are involved. However, successfully targeting modifiable risk factors reduces the surgical site infection incidence in vascular surgery patients. We conducted an extensive literature review to evaluate the efficacy of various preventive strategies for groin surgical site infections. We discuss the role of preoperative showers, preoperative and postoperative antibiotics, collagen gentamicin implants, iodine impregnated drapes, types of skin incisions, negative pressure wound therapy, and prophylactic muscle flap transposition in preventing surgical site infection in the groin after vascular surgical procedures.

Mitofusin gain and loss of function drive pathogenesis in Drosophila models of CMT2A neuropathy.

Charcot-Marie-Tooth disease type 2A (CMT2A) is caused by dominant alleles of the mitochondrial pro-fusion factor Mitofusin 2 (MFN2). To address the consequences of these mutations on mitofusin activity and neuronal function, we generate Drosophila models expressing in neurons the two most frequent substitutions (R94Q and R364W, the latter never studied before) and two others localizing to similar domains (T105M and L76P). All alleles trigger locomotor deficits associated with mitochondrial depletion at neuromuscular junctions, decreased oxidative metabolism and increased mtDNA mutations, but they differently alter mitochondrial morphology and organization. Substitutions near or within the GTPase domain (R94Q, T105M) result in loss of function and provoke aggregation of unfused mitochondria. In contrast, mutations within helix bundle 1 (R364W, L76P) enhance mitochondrial fusion, as demonstrated by the rescue of mitochondrial alterations and locomotor deficits by over-expression of the fission factor DRP1. In conclusion, we show that both dominant negative and dominant active forms of mitofusin can cause CMT2A-associated defects and propose for the first time that excessive mitochondrial fusion drives CMT2A pathogenesis in a large number of patients.

The heptad repeat domain 1 of Mitofusin has membrane destabilization function in mitochondrial fusion.

Mitochondria are double-membrane-bound organelles that constantly change shape through membrane fusion and fission. Outer mitochondrial membrane fusion is controlled by Mitofusin, whose molecular architecture consists of an N-terminal GTPase domain, a first heptad repeat domain (HR1), two transmembrane domains, and a second heptad repeat domain (HR2). The mode of action of Mitofusin and the specific roles played by each of these functional domains in mitochondrial fusion are not fully understood. Here, using a combination of in situ and in vitro fusion assays, we show that HR1 induces membrane fusion and possesses a conserved amphipathic helix that folds upon interaction with the lipid bilayer surface. Our results strongly suggest that HR1 facilitates membrane fusion by destabilizing the lipid bilayer structure, notably in membrane regions presenting lipid packing defects. This mechanism for fusion is thus distinct from that described for the heptad repeat domains of SNARE and viral proteins, which assemble as membrane-bridging complexes, triggering close membrane apposition and fusion, and is more closely related to that of the C-terminal amphipathic tail of the Atlastin protein.

Unraveling the Role of Leptin in Liver Function and Its Relationship with Liver Diseases.

Since its discovery twenty-five years ago, the fat-derived hormone leptin has provided a revolutionary framework for studying the physiological role of adipose tissue as an endocrine organ. Leptin exerts pleiotropic effects on many metabolic pathways and is tightly connected with the liver, the major player in systemic metabolism. As a consequence, understanding the metabolic and hormonal interplay between the liver and adipose tissue could provide us with new therapeutic targets for some chronic liver diseases, an increasing problem worldwide. In this review, we assess relevant literature regarding the main metabolic effects of leptin on the liver, by direct regulation or through the central nervous system (CNS). We draw special attention to the contribution of leptin to the non-alcoholic fatty liver disease (NAFLD) pathogenesis and its progression to more advanced stages of the disease as non-alcoholic steatohepatitis (NASH). Likewise, we describe the contribution of leptin to the liver regeneration process after partial hepatectomy, the mainstay of treatment for certain hepatic malignant tumors.

MicroRNA Sequencing Identifies a Serum MicroRNA Panel, Which Combined With Aspartate Aminotransferase to Platelet Ratio Index Can Detect and Monitor Liver Disease in Pediatric Cystic Fibrosis.

Cystic fibrosis (CF)-associated liver disease (CFLD) is a hepatobiliary complication of CF. Current diagnostic modalities rely on nonspecific assessments, whereas liver biopsy is the gold standard to assess severity of fibrosis. MicroRNAs (miRNAs) regulate liver disease pathogenesis and are proposed as diagnostic biomarkers. We investigated the combined use of serum miRNAs and aspartate aminotransferase (AST) to platelet ratio (APRI) to diagnose and assess CFLD severity. This was a cross-sectional cohort study of the circulatory miRNA signature of 124 children grouped by clinical, biochemical, and imaging assessments as follows: CFLD (n = 44), CF patients with no evidence of liver disease (CFnoLD; n = 40), and healthy controls (n = 40). Serum miRNAs were analyzed using miRNA sequencing (miRNA-Seq). Selected differentially expressed serum miRNA candidates were further validated by qRT-PCR and statistical analysis performed to evaluate utility to predict CFLD and fibrosis severity validated by liver biopsy, alone or in combination with APRI. Serum miR-122-5p, miR-365a-3p, and miR-34a-5p levels were elevated in CFLD compared to CFnoLD, whereas miR-142-3p and let-7g-5p were down-regulated in CFLD compared to CFnoLD. Logistic regression analysis combining miR-365a-3p, miR-142-3p, and let-7g-5p with APRI showed 21 times greater odds of accurately predicting liver disease in CF with an area under the receiver operating characteristics curve (AUROC) = 0.91 (sensitivity = 83%, specificity = 92%; P < 0.0001). Expression levels of serum miR-18a-5p were correlated with increasing hepatic fibrosis (HF) stage in CFLD (rs  = 0.56; P < 0.0001), showing good diagnostic accuracy for distinguishing severe (F3-F4) from mild/moderate fibrosis (F0-F2). A unit increase of miR-18a-5p showed a 7-fold increased odds of having severe fibrosis with an AUROC = 0.82 (sensitivity = 93%, specificity = 73%; P = 0.004), indicating its potential to predict fibrosis severity. Conclusion: We identified a distinct circulatory miRNA profile in pediatric CFLD with potential to accurately discriminate liver disease and fibrosis severity in children with CF.

Taurocholate Induces Biliary Differentiation of Liver Progenitor Cells Causing Hepatic Stellate Cell Chemotaxis in the Ductular Reaction: Role in Pediatric Cystic Fibrosis Liver Disease.

Cystic fibrosis liver disease (CFLD) in children causes progressive fibrosis leading to biliary cirrhosis; however, its cause(s) and early pathogenesis are unclear. We hypothesized that a bile acid-induced ductular reaction (DR) drives fibrogenesis. The DR was evaluated by cytokeratin-7 immunohistochemistry in liver biopsies, staged for fibrosis, from 60 children with CFLD, and it demonstrated that the DR was significantly correlated with hepatic fibrosis stage and biliary taurocholate levels. To examine the mechanisms involved in DR induction, liver progenitor cells (LPCs) were treated with taurocholate, and key events in DR evolution were assessed: LPC proliferation, LPC biliary differentiation, and hepatic stellate cell (HSC) chemotaxis. Taurocholate induced a time-dependent increase in LPC proliferation and expression of genes associated with cholangiocyte differentiation (cytokeratin 19, connexin 43, integrin ß4, and γ-glutamyltranspeptidase), whereas the hepatocyte specification marker HNF4α was suppressed. Functional cholangiocyte differentiation was demonstrated via increased acetylated α-tubulin and SOX9 proteins, the number of primary cilia+ LPCs, and increased active γ-glutamyltranspeptidase enzyme secretion. Taurocholate induced LPCs to release MCP-1, MIP1α, and RANTES into conditioned medium causing HSC chemotaxis, which was inhibited by anti-MIP1α. Immunofluorescence confirmed chemokine expression localized to CK7+ DR and LPCs in CFLD liver biopsies. This study suggests that taurocholate is involved in initiating functional LPC biliary differentiation and the development of the DR, with subsequent induction of chemokines that drive HSC recruitment in CFLD.

General surgeon management of complex hepatopancreatobiliary trauma at a level I trauma center.

BACKGROUND: The impact of general surgeons (GS) taking trauma call on patient outcomes has been debated. Complex hepatopancreatobiliary (HPB) injuries present a particular challenge and often require specialized care. We predicted no difference in the initial management or outcomes of complex HPB trauma between GS and trauma/critical care (TCC) specialists. MATERIALS AND METHODS: A retrospective review of patients who underwent operative intervention for complex HPB trauma from 2008 to 2015 at an ACS-verified level I trauma center was performed. Chart review was used to obtain variables pertaining to demographics, clinical presentation, operative management, and outcomes. Patients were grouped according to whether their index operation was performed by a GS or TCC provider and compared. RESULTS: 180 patients met inclusion criteria. The GS (n = 43) and TCC (n = 137) cohorts had comparable patient demographics and clinical presentations. Most injuries were hepatic (73.3% GS versus 72.6% TCC) and TCC treated more pancreas injuries (15.3% versus GS 13.3%; P = 0.914). No significant differences were found in HPB-directed interventions at the initial operation (41.9% GS versus 56.2% TCC; P = 0.100), damage control laparotomy with temporary abdominal closure (69.8% versus 69.3%; P = 0.861), LOS, septic complications or 30-day mortality (13.9% versus 10.2%; P = 0.497). TCC were more likely to place an intraabdominal drain than GS (52.6% versus 34.9%; P = 0.043). CONCLUSIONS: We found no significant differences between GS and TCC specialists in initial operative management or clinical outcomes of complex HPB trauma. The frequent and proper use of damage control laparotomy likely contribute to these findings.

Pseudocoarctation following elephant trunk intervention.

We describe the case of a 55-year-old man with a pseudocoarctation of the descending aorta following a conventional elephant trunk technique. The patient underwent aortic arch replacement with the conventional elephant trunk technique. After the operation, he had developed an increasing creatinine level, hemolysis, and cyanosis of his toes. Femoral arterial line placement confirmed a 50-mm Hg systolic pressure gradient between his radial and femoral arteries. Computed tomography angiography revealed that the elephant trunk graft within the true lumen was compressed, resulting in a pseudocoarctation. The patient was successfully treated with thoracic endovascular aneurysm repair.

The heavy subunit of ferritin stimulates NLRP3 inflammasomes in hepatic stellate cells through ICAM-1 to drive hepatic inflammation.

Serum ferritin concentrations increase during hepatic inflammation and correlate with the severity of chronic liver disease. Here, we report a molecular mechanism whereby the heavy subunit of ferritin (FTH) contributes to hepatic inflammation. We found that FTH induced activation of the NLRP3 inflammasome and secretion of the proinflammatory cytokine interleukin-1ß (IL-1ß) in primary rat hepatic stellate cells (HSCs) through intercellular adhesion molecule-1 (ICAM-1). FTH-ICAM-1 stimulated the expression of Il1b, NLRP3 inflammasome activation, and the processing and secretion of IL-1ß in a manner that depended on plasma membrane remodeling, clathrin-mediated endocytosis, and lysosomal destabilization. FTH-ICAM-1 signaling at early endosomes stimulated Il1b expression, implying that this endosomal signaling primed inflammasome activation in HSCs. In contrast, lysosomal destabilization was required for FTH-induced IL-1ß secretion, suggesting that lysosomal damage activated inflammasomes. FTH induced IL-1ß production in liver slices from wild-type mice but not in those from Icam1-/- or Nlrp3-/- mice. Thus, FTH signals through its receptor ICAM-1 on HSCs to activate the NLRP3 inflammasome. We speculate that this pathway contributes to hepatic inflammation, a key process that stimulates hepatic fibrogenesis associated with chronic liver disease.

Caveolin-1 orchestrates the balance between glucose and lipid-dependent energy metabolism: implications for liver regeneration.

UNLABELLED: Caveolin-1 (CAV1) is a structural protein of caveolae involved in lipid homeostasis and endocytosis. Using newly generated pure Balb/C CAV1 null ((Balb/C)CAV1-/-) mice, CAV1-/- mice from Jackson Laboratories ((JAX)CAV1-/-), and CAV1-/- mice developed in the Kurzchalia Laboratory ((K)CAV1-/-), we show that under physiological conditions CAV1 expression in mouse tissues is necessary to guarantee an efficient progression of liver regeneration and mouse survival after partial hepatectomy. Absence of CAV1 in mouse tissues is compensated by the development of a carbohydrate-dependent anabolic adaptation. These results were supported by extracellular flux analysis of cellular glycolytic metabolism in CAV1-knockdown AML12 hepatocytes, suggesting cell autonomous effects of CAV1 loss in hepatic glycolysis. Unlike in (K)CAV1-/- livers, in (JAX)CAV1-/- livers CAV1 deficiency is compensated by activation of anabolic metabolism (pentose phosphate pathway and lipogenesis) allowing liver regeneration. Administration of 2-deoxy-glucose in (JAX)CAV1-/- mice indicated that liver regeneration in (JAX)CAV1-/- mice is strictly dependent on hepatic carbohydrate metabolism. Moreover, with the exception of regenerating (JAX)CAV1-/- livers, expression of CAV1 in mice is required for efficient hepatic lipid storage during fasting, liver regeneration, and diet-induced steatosis in the three CAV1-/- mouse strains. Furthermore, under these conditions CAV1 accumulates in the lipid droplet fraction in wildtype mouse hepatocytes. CONCLUSION: Our data demonstrate that lack of CAV1 alters hepatocyte energy metabolism homeostasis under physiological and pathological conditions.

Caveolin-1 plays a critical role in the differentiation of monocytes into macrophages.

OBJECTIVE: Monocyte to macrophage differentiation is an essential step in atherogenesis. The structure protein of caveolae, caveolin-1, is increased in primary monocytes after its adhesion to endothelium. We explore the hypothesis that caveolin-1 plays a role in monocyte differentiation to macrophages. METHODS AND RESULTS: Both phorbol myristate acetate-induced THP-1 and colony-stimulating factor-induced primary monocyte differentiation was associated with an increase in cellular caveolin-1 expression. Overexpression of caveolin-1 by transfection increased macrophage surface markers and inflammatory genes, whereas caveolin-1 knockdown by small interfering RNA or knockout reduced these. Also, caveolin-1 knockdown inhibited the differentiation-induced nuclear translocation of early growth response 1 (EGR-1) through extracellular signal-regulated kinase phosphorylation, further decreased the binding of EGR-1 to CD115 promoter, thus decreasing EGR-1 transcriptional activity. In functional assays, caveolin-1 inhibited transmigration but promoted phagocytosis in the monocyte-macrophage lineage. Decreasing caveolin-1 inhibited the uptake of modified low-density lipoprotein and reduced cellular lipid content. Finally, we showed that caveolin-1 knockout mice displayed less monocyte differentiation than wild-type mice and that EGR-1 transcription activity was also decreased in these mice because of the inhibition of extracellular signal-regulated kinase phosphorylation. CONCLUSIONS: Caveolin-1 promotes monocyte to macrophage differentiation through the regulation of EGR-1 transcriptional activity, suggesting that phagocytic caveolin-1 may be critical for atherogenesis.

Robotic resection of a second rib osteochondroma.

A 43-year-old man presented with a several-month history of worsening left shoulder pain. On imaging, he was found to have an osseous mass arising from his left second rib and protruding into the soft tissues of his chest. The mass had radiographic characteristics consistent with those of an osteochondroma. He had point tenderness over the mass, and the area of point tenderness was consistent with his description of the location of his pain over the past several months. Based on his symptoms, he was taken to the operating room for robotic excision of this mass. He was placed in a right lateral decubitus position, and three robotic ports were inserted. The mass was identified based on landmarks and was dissected free. The bony attachment of the mass to the second rib was transected using a Kerrison rongeur. The mass was delivered into the chest and removed using an endobag. The patient was discharged the following day after removal of his Blake drain. His pain had completely resolved at the postoperative follow-up examination, and his final pathological report confirmed the benign diagnosis of osteochondroma.

Malaysian and Chinese King Cobra Venom Cytotoxicity in Melanoma and Neonatal Foreskin Fibroblasts Is Mediated by Age and Geography.

Snake venoms constitute a complex, rapidly evolving trait, whose composition varies between and within populations depending on geographical location, age and preys (diets). These factors have determined the adaptive evolution for predatory success and link venom heterogeneity with prey specificity. Moreover, understanding the evolutionary drivers of animal venoms has streamlined the biodiscovery of venom-derived compounds as drug candidates in biomedicine and biotechnology. The king cobra (Ophiophagus hannah; Cantor, 1836) is distributed in diverse habitats, forming independent populations, which confer differing scale markings, including between hatchlings and adults. Furthermore, king cobra venoms possess unique cytotoxic properties that are used as a defensive trait, but their toxins may also have utility as promising anticancer-agent candidates. However, the impact of geographical distribution and age on these potential venom applications has been typically neglected. In this study, we hypothesised that ontogenetic venom variation accompanies the morphological distinction between hatchlings and adults. We used non-transformed neonatal foreskin (NFF) fibroblasts to examine and compare the variability of venom cytotoxicity between adult captive breeding pairs from Malaysian and Chinese lineages, along with that of their progeny upon hatching. In parallel, we assessed the anticancer potential of these venoms in human-melanoma-patient-derived cells (MM96L). We found that in a geographical distribution and gender-independent manner, venoms from hatchlings were significantly less cytotoxic than those from adults (NFF; ~Log EC50: 0.5-0.6 vs. 0.2-0.35 mg/mL). This is consistent with neonates occupying a semifossorial habitat, while adults inhabit more above-ground habitats and are therefore more conspicuous to potential predators. We also observed that Malaysian venoms exhibited a slightly higher cytotoxicity than those from the Chinese cobra cohorts (NFF; Log EC50: 0.1-0.3 vs. 0.3-0.4 mg/mL), which is consistent with Malaysian king cobras being more strongly aposematically marked. These variations are therefore suggestive of differential anti-predator strategies associated with the occupation of distinct niches. However, all cobra venoms were similarly cytotoxic in both melanoma cells and fibroblasts, limiting their potential medical applications in their native forms.

Enhancing European capabilities for application of multi-omics studies in biology and biomedicine space research.

Following on from the NASA twins' study, there has been a tremendous interest in the use of omics techniques in spaceflight. Individual space agencies, NASA's GeneLab, JAXA's ibSLS, and the ESA-funded Space Omics Topical Team and the International Standards for Space Omics Processing (ISSOP) groups have established several initiatives to support this growth. Here, we present recommendations from the Space Omics Topical Team to promote standard application of space omics in Europe. We focus on four main themes: i) continued participation in and coordination with international omics endeavors, ii) strengthening of the European space omics infrastructure including workforce and facilities, iii) capitalizing on the emerging opportunities in the commercial space sector, and iv) capitalizing on the emerging opportunities in human subjects research.

Mapping early serum proteome signatures of liver regeneration in living donor liver transplant cases.

The liver is the only solid organ capable of regenerating itself to regain 100% of its mass and function after liver injury and/or partial hepatectomy (PH). This exceptional property represents a therapeutic opportunity for severe liver disease patients. However, liver regeneration (LR) might fail due to poorly understood causes. Here, we have investigated the regulation of liver proteome and phosphoproteome at a short time after PH (9 h), to depict a detailed mechanistic background of the early LR phase. Furthermore, we analyzed the dynamic changes of the serum proteome and metabolome of healthy living donor liver transplant (LDLT) donors at different time points after surgery. The molecular profiles from both analyses were then correlated. Insulin and FXR-FGF15/19 signaling were stimulated in mouse liver after PH, leading to the activation of the main intermediary kinases (AKT and ERK). Besides, inhibition of the hippo pathway led to an increased expression of its target genes and of one of its intermediary proteins (14-3-3 protein), contributing to cell proliferation. In association with these processes, metabolic reprogramming coupled to enhanced mitochondrial activity cope for the energy and biosynthetic requirements of LR. In human serum of LDLT donors, we identified 56 proteins and 13 metabolites statistically differential which recapitulate some of the main cellular processes orchestrating LR in its early phase. These results provide mechanisms and protein mediators of LR that might prove useful for the follow-up of the regenerative process in the liver after PH as well as preventing the occurrence of complications associated with liver resection.

Energetic requirements and bioenergetic modulation of mitochondrial morphology and dynamics.

Mitochondria are the site where oxidative phosphorylations (OXPHOSs) take place. Fusion and fission reactions allow them to change their overall morphology, which ranges from networks of elongated and branched filaments to collections of small individual organelles. It is assumed that mitochondrial bioenergetics and dynamics are linked and that mitochondrial morphology reflects their functional status. This review shows that the links between mitochondrial dynamics and bioenergetics are complex and that mitochondrial deficiencies are not systematically associated to fragmentation. In mammals, mitochondrial fragmentation is observed upon inhibition of OXPHOS with drugs, but not in most cellular models with OXPHOS deficits of genetic origin. In yeast, mitochondrial biogenesis and filament interconnectivity augment with increasing respiratory capacity, but mutation or inhibition of the respiratory chain does not provoke major morphological changes. Significant structural and morphological alterations appear restricted to mutation of genes involved in assembly or function of the F(1)F(0)-ATP-synthase. Finally, ex vivo studies (in mammals) and in vitro studies (in yeast) confirm the essential role of the inner membrane potential for mitochondrial fusion.

Mitofusin 1 and mitofusin 2 are ubiquitinated in a PINK1/parkin-dependent manner upon induction of mitophagy.

Mitochondrial dysfunction and perturbed degradation of proteins have been implicated in Parkinson's disease (PD) pathogenesis. Mutations in the Parkin and PINK1 genes are a cause of familial PD. PINK1 is a putative kinase associated with mitochondria, and loss of PINK1 expression leads to mitochondrial dysfunction, which increases with time. Parkin is suggested to be downstream of PINK1 and also mediates the removal of damaged mitochondria by macroautophagy (mitophagy). We investigated whether mitochondrial dysfunction in dopaminergic SH-SY5Y cells following decreased PINK1 expression by RNAi may in part be due to the inhibition of mitophagy. Reduced flux through the macroautophagy pathway was found to be coincident with the inhibition of ATP synthesis following 12 days of PINK1 silencing. Overexpression of parkin in these cells restored both autophagic flux and ATP synthesis. Overexpression and RNAi studies also indicated that PINK1 and parkin were required for mitophagy following CCCP-induced mitochondrial damage. The ubiquitination of several mitochondrial proteins, including mitofusin 1 and mitofusin 2, were detected within 3 h of CCCP treatment. These post-translational modifications were reduced following the silencing of parkin or PINK1. The ubiquitination of mitochondrial proteins appears to identify mitochondria for degradation and facilitate mitophagy. PINK1 and parkin are thus required for the removal of damaged mitochondria in dopaminergic cells, and inhibition of this pathway may lead to the accumulation of defective mitochondria which may contribute to PD pathogenesis.