Regulation of cargo transfer between ESCRT-0 and ESCRT-I complexes by flotillin-1 during endosomal sorting of ubiquitinated cargo

Ubiquitin-dependent sorting of membrane proteins in endosomes directs them to lysosomal degradation. In the case of receptors such as the epidermal growth factor receptor (EGFR), lysosomal degradation is important for the regulation of downstream signalling. Ubiquitinated proteins are recognised in endosomes by the endosomal sorting complexes required for transport (ESCRT) complexes, which sequentially interact with the ubiquitinated cargo. Although the role of each ESCRT complex in sorting is well established, it is not clear how the cargo is passed on from one ESCRT to the next. We here show that flotillin-1 is required for EGFR degradation, and that it interacts with the subunits of ESCRT-0 and -I complexes (hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) and Tsg101). Flotillin-1 is required for cargo recognition and sorting by ESCRT-0/Hrs and for its interaction with Tsg101. In addition, flotillin-1 is also required for the sorting of human immunodeficiency virus 1 Gag polyprotein, which mimics ESCRT-0 complex during viral assembly. We propose that flotillin-1 functions in cargo transfer between ESCRT-0 and -I complexes.

Ovarian stimulation in the luteal phase: systematic review and meta-analysis

PURPOSE

The purpose of this study was to evaluate whether outcomes are different if controlled ovarian stimulation (COS) is started in the luteal phase rather than the follicular phase.

METHODS

A systematic review and meta-analysis was performed. Sixteen studies were included in the qualitative analysis, and eight studies with a total of 338 women were included in the quantitative analysis.

RESULTS

Cycles initiated in the luteal phase were slightly longer (WMD 1.1 days, 95 % CI 0.39-1.9) and utilized more total gonadotropins (WMD 817 IU, 95 % CI 489-1144). However, no differences were noted in peak estradiol levels (WMD -411 pg/ml, 95 % CI -906-84.7) or in the total number of oocytes retrieved (WMD 0.52 oocytes, 95 % CI -0.74-1.7). There were slightly more mature oocytes retrieved in the luteal phase (WMD 0.77 oocytes, 95 % CI 0.21-1.3), and fertilization rates were significantly higher (WMD 10 %, 95 % CI 0.03-0.18). While only three studies reported pregnancy outcomes, no difference was noted in the FET pregnancy rates after COS in the luteal versus follicular phase (RR 0.95, 95 % CI 0.56-1.7). A post hoc power analysis revealed that a sample of this size was sufficient to detect a clinically meaningful difference of 2 oocytes retrieved with 93 % power.

CONCLUSION

Although initiating COS in the luteal phase requires a longer stimulation and a higher dose of total gonadotropin, these differences are not clinically significant. Furthermore, COS initiated in the luteal phase does not compromise the quantity or quality of oocytes retrieved compared to outcomes of traditional stimulation in the follicular phase.

Postnatal growth of the human optic nerve

PurposeAlthough the length of the average human adult optic nerve (ON) is known, the average length of the normal full-term, newborn ON has never been adequately evaluated, nor has the in vivo growth rate of the human ON been determined. We wanted to identify both the average length of the newborn human ON and its rate of anteroposterior growth.Patients and methodsUsing MRIs from a newly generated set of normal newborn infants rescanned at 1 year, and from different aged groups, we calculated average newborn ON length and growth rate.ResultsThe newborn human ON is 25.3±0.3 mm in length from globe to chiasm, and grows by 80% in length after birth, with maximum speed of elongation occurring in the first 3 years of life, attaining full length by 15 years of age.ConclusionThe human ON grows dramatically in the first 3 years of life, and continues to grow for the first two decades. These data are relevant for pediatric treatments that may impede or alter orbital growth in infants, and maximal susceptibility to oncological procedures in early childhood.

Cellular protein quality control and the evolution of aggregates in spinocerebellar ataxia type 3 (SCA3)

AIMS

A characteristic of polyglutamine diseases is the increased propensity of disease proteins to aggregate, which is thought to be a major contributing factor to the underlying neurodegeneration. Healthy cells contain mechanisms for handling protein damage, the protein quality control, which must be impaired or inefficient to permit proteotoxicity under pathological conditions.

METHODS

We used a quantitative analysis of immunohistochemistry of the pons of eight patients with the polyglutamine disorder spinocerebellar ataxia type 3. We employed the anti-polyglutamine antibody 1C2, antibodies against p62 that is involved in delivering ubiquitinated protein aggregates to autophagosomes, antibodies against the chaperones HSPA1A and DNAJB1 and the proteasomal stress marker UBB⁺¹.

RESULTS

The 1C2 antibody stained neuronal nuclear inclusions (NNIs), diffuse nuclear staining (DNS), granular cytoplasmic staining (GCS) and combinations, with reproducible distribution. P62 always co-localized with 1C2 in NNI. DNS and GCS co-stained with a lower frequency. UBB⁺¹ was present in a subset of neurones with NNI. A subset of UBB⁺¹-containing neurones displayed increased levels of HSPA1A, while DNAJB1 was sequestered into the NNI.

CONCLUSION

Based on our results, we propose a model for the aggregation-associated pathology of spinocerebellar ataxia type 3: GCS and DNS aggregation likely represents early stages of pathology, which progresses towards formation of p62-positive NNI. A fraction of NNI exhibits UBB⁺¹ staining, implying proteasomal overload at a later stage. Subsequently, the stress-inducible HSPA1A is elevated while DNAJB1 is recruited into NNIs. This indicates that the stress response is only induced late when all endogenous protein quality control systems have failed.

Visual EMG Biofeedback to Improve Ankle Function in Hemiparetic Gait

Spasticity in stroke patients interferes with coordinated muscle firing patterns of the lower extremity leading to gait abnormalities. The goal of this study was to improve ankle function during walking by augmenting treadmill gait retraining with a visual EMG biofeedback technique. Eight stroke patients who could ambulate between 0.5 and 0.9 m/s participated in the study. The training consisted of 12 sessions of treadmill walking during which the activity of the tibialis anterior and gastrocnemius lateralis muscles of the affected side was displayed on a computer screen. Targets were shown to indicate to the subject when to activate the monitored muscles. Gait evaluations were performed before and after the training period to test the hypothesis that ankle mechanics improved following the intervention. Improvements in gait function were characterized by changes in temporal gait parameters and lower extremity kinematics and kinetics. Subjects showed an increase in gait speed, time of single leg support on the affected side, ankle power generation at push-off and a reduction in knee extensor moment. These results indicate that treadmill gait retraining augmented via visual EMG-biofeedback facilitates improvements in hemiparetic gait.

Epigenetic screen identifies genotype-specific promoter DNA methylation and oncogenic potential of CHRNB4

Genome-wide association studies have highlighted three major lung cancer susceptibility regions at 15q25.1, 5p15.33 and 6p21.33. To gain insight into the possible mechanistic relevance of the genes in these regions, we investigated the regulation of candidate susceptibility gene expression by epigenetic alterations in healthy and lung tumor tissues. For genes up- or downregulated in lung tumors the influence of genetic variants on DNA methylation was investigated and in vitro studies were performed.

We analyzed 394 CpG units within 19 CpG islands in the susceptibility regions in a screening set of 34 patients. Significant findings were validated in an independent patient set (n=50) with available DNA and RNA. The most consistent overall DNA methylation difference between tumor and adjacent normal tissue on 15q25 was tumor hypomethylation in the promoter region of CHRNB4 with a median difference of 8% (p<0.001) which resulted in overexpression of the transcript in tumors (p<0.001). Confirming previous studies we also found hypermethylation in CHRNA3 and TERT with significant expression changes. Decitabine treatment of H1299 cells resulted in reduced methylation levels in gene promoters, elevated transcript levels of CHRNB4 and CHRNA3 and a slight downregulation of TERT demonstrating epigenetic regulation of lung cancer cells. SNPs rs421629 on 5p15.33 and rs1948, rs660652, rs8040868 and rs2036527 on 15q25.1, previously identified as lung cancer risk or nicotine addiction modifiers were associated with tumor DNA methylation levels in the promoters of TERT and CHRNB4 (p<0.001) respectively in two independent sample sets (n=82; n=150). In addition, CHRNB4 knock down in two different cell lines (A549 and H1299) resulted in reduced proliferation (p_A549<0.05;p_H1299L<0.001) and propensity to form colonies in H1299 cells.

These results suggest epigenetic deregulation of nicotinic acetylcholinereceptor subunit (nAChR) genes which in the case of CHRNB4 is strongly associated with genetic lung cancer susceptibility variants and a functional impact on tumorigenic potential.

The HSPB8-BAG3 chaperone complex is upregulated in astrocytes in the human brain affected by protein aggregation diseases

AIMS

HSPB8 is a small heat shock protein that forms a complex with the co-chaperone BAG3. Overexpression of the HSPB8-BAG3 complex in cells stimulates autophagy and facilitates the clearance of mutated aggregation-prone proteins, whose accumulation is a hallmark of many neurodegenerative disorders. HSPB8-BAG3 could thus play a protective role in protein aggregation diseases and might be specifically upregulated in response to aggregate-prone protein-mediated toxicity. Here we analysed HSPB8-BAG3 expression levels in post-mortem human brain tissue from patients suffering of the following protein conformation disorders: Alzheimer's disease, Parkinson's disease, Huntington's disease and spinocerebellar ataxia type 3 (SCA3).

METHODS

Western blotting and immunohistochemistry techniques were used to analyse HSPB8 and BAG3 expression levels in fibroblasts from SCA3 patients and post-mortem brain tissues, respectively.

RESULTS

In all diseases investigated, we observed a strong upregulation of HSPB8 and a moderate upregulation of BAG3 specifically in astrocytes in the cerebral areas affected by neuronal damage and degeneration. Intriguingly, no significant change in the HSPB8-BAG3 expression levels was observed within neurones, irrespective of their localization or of the presence of proteinaceous aggregates.

CONCLUSIONS

We propose that the upregulation of HSPB8 and BAG3 may enhance the ability of astrocytes to clear aggregated proteins released from neurones and cellular debris, maintain the local tissue homeostasis and/or participate in the cytoskeletal remodelling that astrocytes undergo during astrogliosis.