Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Somlapura, M.
Distinguishable roles of human p62 isoforms in protein aggregation diseases
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Medizinische Universität Graz; 2023. pp.
- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Fickert Peter
- Hämmerle Guenter
- Zatloukal Kurt
- Altmetrics:
- Abstract:
- A multifunctional protein p62/Sequestosome-1 (p62/SQSTM1) is involved in various signaling pathways and found to be a constant component of various intracellular protein inclusions, including Mallory–Denk bodies (MDBs) in hepatocellular carcinoma (HCC) and steatohepatitis, and Lewy bodies (LBs) in Parkinson's Disease (PD). We investigated the role of p62 isoforms in both scenarios by analysing how keratins 8 (K8) and 18 (K18) (the key constituents of MDBs) and α-synuclein (the key constituents of LBs) interact with the two human p62 isoforms: a full-length isoform (p62-H1) and a shorter isoform partially lacking the PB1 domain (p62-H2). p62-H2 is differentially expressed in various tissues, unlike p62-H1. Co-transfection experiments revealed striking differences in the aggregation characteristics and cytoplasmic distribution of the two p62 isoforms concerning K8 and K18. However, in the absence of keratins, p62-H2 resembled intracytoplasmic hyaline bodies (IHB), and in the presence of keratin, the aggregates resembled MDBs. The development of a cross-β-sheet conformation occurs concurrently with the p62-H2 aggregate formation and is associated with K8 (but not K18), as shown by labelling with luminescent conjugated oligothiophenes (LCO's). Interestingly, we detected p62-H2 predominantly in the IHB of HCC samples, whereas in MDB, p62-H1 or both isoforms coexist. In contrast to humans, mice lack p62-H2. Therefore, we hypothesize that the differences between p62 isoforms in humans and mice may explain why mouse models of PD do not adequately reproduce human LB pathology. We showed that p62-H1 readily forms aggregates with α-synuclein and is predominantly found in the insoluble fraction of SH-SY5Y cells. Although a diffuse distribution of both proteins (p62-H2 and α-synuclein) was observed in transfected human neuroblastoma cells, NMR studies demonstrated that monomeric α-synuclein interacts with p62-H2. Humanized transgenic mouse models overexpressing α-synuclein in neuronal cells with either p62-H1 or p62-H2 show marked differences in behavioural deficits compared with age-matched control groups. In particular, the p62-H2_SNCA mice showed more pronounced motor deficits than a decline in cognitive abilities. These results demonstrate the distinct roles of p62 isoforms in two different types of disease-associated protein aggregations and that differential expression of p62 isoforms in humans and mouse models may result in different phenotypes.