The lysosome is the final destination for degradation of endocytic cargo, plasma membrane constituents, and intracellular components sequestered by macroautophagy. Fusion of endosomes and ...autophagosomes with the lysosome depends on the GTPase Rab7 and the homotypic fusion and protein sorting (HOPS) complex, but adaptor proteins that link endocytic and autophagy pathways with lysosomes are poorly characterized. Herein, we show that Pleckstrin homology domain containing protein family member 1 (PLEKHM1) directly interacts with HOPS complex and contains a LC3-interacting region (LIR) that mediates its binding to autophagosomal membranes. Depletion of PLEKHM1 blocks lysosomal degradation of endocytic (EGFR) cargo and enhances presentation of MHC class I molecules. Moreover, genetic loss of PLEKHM1 impedes autophagy flux upon mTOR inhibition and PLEKHM1 regulates clearance of protein aggregates in an autophagy- and LIR-dependent manner. PLEKHM1 is thus a multivalent endocytic adaptor involved in the lysosome fusion events controlling selective and nonselective autophagy pathways.
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•PLEKHM1 interacts directly with LC3/GABARAP proteins on autophagosomes•PLEKHM1 forms a complex with HOPS and SNARE proteins•Genetic loss of PLEKHM1 inhibits autophagosome-lysosome fusion•PLEKHM1 regulates the removal of protein aggregates in a LIR dependent manner.
Endocytic and autophagy pathways converge at the cell’s “waste disposal center” (lysosome) for cargo destruction. McEwan et al. identify PLEKHM1 as a critical adaptor platform at the pathway’s juncture. Absence of PLEKHM1 prevents removal of toxic protein aggregates, potentially becoming a risk factor for proteinopathies like Parkinson’s.
Osteopetrosis is a genetic condition of increased bone mass, which is caused by defects in osteoclast formation and function. Both autosomal recessive and autosomal dominant forms exist, but this ...Review focuses on autosomal recessive osteopetrosis (ARO), also known as malignant infantile osteopetrosis. The genetic basis of this disease is now largely uncovered: mutations in TCIRG1, CLCN7, OSTM1, SNX10 and PLEKHM1 lead to osteoclast-rich ARO (in which osteoclasts are abundant but have severely impaired resorptive function), whereas mutations in TNFSF11 and TNFRSF11A lead to osteoclast-poor ARO. In osteoclast-rich ARO, impaired endosomal and lysosomal vesicle trafficking results in defective osteoclast ruffled-border formation and, hence, the inability to resorb bone and mineralized cartilage. ARO presents soon after birth and can be fatal if left untreated. However, the disease is heterogeneous in clinical presentation and often misdiagnosed. This article describes the genetics of ARO and discusses the diagnostic role of next-generation sequencing methods. The management of affected patients, including guidelines for the indication of haematopoietic stem cell transplantation (which can provide a cure for many types of ARO), are outlined. Finally, novel treatments, including preclinical data on in utero stem cell treatment, RANKL replacement therapy and denosumab therapy for hypercalcaemia are also discussed.
Autophagy: A new player in skeletal maintenance? Hocking, Lynne J; Whitehouse, Caroline; Helfrich, Miep H
Journal of bone and mineral research,
July 2012, Letnik:
27, Številka:
7
Journal Article
Bone remodelling at a glance Crockett, Julie C; Rogers, Michael J; Coxon, Fraser P ...
Journal of cell science,
2011-Apr-01, 2011-04-01, 20110401, Letnik:
124, Številka:
Pt 7
Journal Article
The host endolysosomal compartment is often manipulated by intracellular bacterial pathogens. Salmonella (Salmonella enterica serovar Typhimurium) secrete numerous effector proteins, including SifA, ...through a specialized type III secretion system to hijack the host endosomal system and generate the Salmonella-containing vacuole (SCV). To form this replicative niche, Salmonella targets the Rab7 GTPase to recruit host membranes through largely unknown mechanisms. We show that Pleckstrin homology domain-containing protein family member 1 (PLEKHM1), a lysosomal adaptor, is targeted by Salmonella through direct interaction with SifA. By binding the PLEKHM1 PH2 domain, Salmonella utilize a complex containing PLEKHM1, Rab7, and the HOPS tethering complex to mobilize phagolysosomal membranes to the SCV. Depletion of PLEKHM1 causes a profound defect in SCV morphology with multiple bacteria accumulating in enlarged structures and significantly dampens Salmonella proliferation in multiple cell types and mice. Thus, PLEKHM1 provides a critical interface between pathogenic infection and the host endolysosomal system.
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•PLEKHM1 loss impairs Salmonella proliferation and vacuole formation•PLEKHM1 simultaneously interacts with Salmonella effector SifA and Rab7 via a PH2 domain•SifA recruits the PLEKHM1/Rab7/HOPS complex for SCV maintenance
Salmonella hijack the lysosomal compartment to provide a stable intracellular proliferative niche. McEwan et al. show that the Salmonella effector SifA recruits the HOPS complex and Rab7 through PLEKHM1. Loss of PLEKHM1 decreases Salmonella proliferation and alters vacuole structure, leading to multiple Salmonella encased in enlarged structures.
Patients with end‐stage renal disease (ESRD) have elevated circulating calcium (Ca) and phosphate (Pi), and exhibit accelerated progression of calcific aortic valve disease (CAVD). We hypothesized ...that matrix vesicles (MVs) initiate the calcification process in CAVD. Ca induced rat valve interstitial cells (VICs) calcification at 4.5 mM (16.4‐fold; p < 0.05) whereas Pi treatment alone had no effect. Ca (2.7 mM) and Pi (2.5 mM) synergistically induced calcium deposition (10.8‐fold; p < 0.001) in VICs. Ca treatment increased the mRNA of the osteogenic markers Msx2, Runx2, and Alpl (p < 0.01). MVs were harvested by ultracentrifugation from VICs cultured with control or calcification media (containing 2.7 mM Ca and 2.5 mM Pi) for 16 hr. Proteomics analysis revealed the marked enrichment of exosomal proteins, including CD9, CD63, LAMP‐1, and LAMP‐2 and a concomitant up‐regulation of the Annexin family of calcium‐binding proteins. Of particular note Annexin VI was shown to be enriched in calcifying VIC‐derived MVs (51.9‐fold; p < 0.05). Through bioinformatic analysis using Ingenuity Pathway Analysis (IPA), the up‐regulation of canonical signaling pathways relevant to cardiovascular function were identified in calcifying VIC‐derived MVs, including aldosterone, Rho kinase, and metal binding. Further studies using human calcified valve tissue revealed the co‐localization of Annexin VI with areas of MVs in the extracellular matrix by transmission electron microscopy (TEM). Together these findings highlight a critical role for VIC‐derived MVs in CAVD. Furthermore, we identify calcium as a key driver of aortic valve calcification, which may directly underpin the increased susceptibility of ESRD patients to accelerated development of CAVD.
Matrix vesicle (MV) deposition in the extracellular matrix of human calcified aortic valve tissue. Aortic valve calcification was confirmed by Alizarin red and Von Kossa staining. Arrows indicate positive areas of staining. Transmission electron microscopy (TEM) shows MVs with spindle‐like projections resembling hydroxyapatite crystal needles in calcified tissue, and “empty” vesicle structures in control tissue (arrows). Scale bars = 500 µm (Alizarin red/Von Kossa); 500 nm (TEM).
Osteoclasts are the specialised cells that resorb bone matrix and are important both for the growth and shaping of bones throughout development as well as during the process of bone remodelling that ...occurs throughout life to maintain a healthy skeleton. Osteoclast formation, function and survival are tightly regulated by a network of signalling pathways, many of which have been identified through the study of rare monogenic diseases, knockout mouse models and animal strains carrying naturally occurring mutations in key molecules. In this review, we describe the processes of osteoclast formation, activation and function and discuss the major transcription factors and signalling pathways (including those that control the cytoskeletal rearrangements) that are important at each stage.
Autosomal recessive osteopetrosis is usually associated with normal or elevated numbers of nonfunctional osteoclasts. Here we report mutations in the gene encoding RANKL (receptor activator of ...nuclear factor-KB ligand) in six individuals with autosomal recessive osteopetrosis whose bone biopsy specimens lacked osteoclasts. These individuals did not show any obvious defects in immunological parameters and could not be cured by hematopoietic stem cell transplantation; however, exogenous RANKL induced formation of functional osteoclasts from their monocytes, suggesting that they could, theoretically, benefit from exogenous RANKL administration.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The multinucleated osteoclast has a unique function: degradation of mineralized tissues. It is generally taken that all osteoclasts are alike, independent of the skeletal site where they exert their ...activity. Recent data, however, question this view as they show that osteoclasts at different bony sites appear to differ, for example in the machinery responsible for resorption. Support for the notion that there may be heterogeneity in osteoclasts is obtained from studies in which osteoclast activity is inhibited and from observations in osteopetrosis and inflammatory bone conditions. In this review we discuss the available evidence and propose the existence of bone-site-specific osteoclast heterogeneity.
Autosomal recessive osteopetrosis (ARO) is a heterogeneous disorder, characterized by defective osteoclastic resorption of bone that results in increased bone density. We have studied nine ...individuals with an intermediate form of ARO, from the county of Västerbotten in Northern Sweden. All afflicted individuals had an onset in early infancy with optic atrophy, and in four patients anemia was present at diagnosis. Tonsillar herniation, foramen magnum stenosis, and severe osteomyelitis of the jaw were common clinical features. Whole exome sequencing, verified by Sanger sequencing, identified a splice site mutation c.212 + 1 G > T in the SNX10 gene encoding sorting nexin 10. Sequence analysis of the SNX10 transcript in patients revealed activation of a cryptic splice site in intron 4 resulting in a frame shift and a premature stop (p.S66Nfs * 15). Haplotype analysis showed that all cases originated from a single mutational event, and the age of the mutation was estimated to be approximately 950 years. Functional analysis of osteoclast progenitors isolated from peripheral blood of patients revealed that stimulation with receptor activator of nuclear factor kappa-B ligand (RANKL) resulted in a robust formation of large, multinucleated osteoclasts which generated sealing zones; however these osteoclasts exhibited defective ruffled borders and were unable to resorb bone in vitro.
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