Hänzi, Barbara. The role of Memo in premature aging and FGFR signaling. 2012, PhD Thesis, University of Basel, Faculty of Science.
Official URL: http://edoc.unibas.ch/diss/DissB_9784
By investigation of the Memo null and kidney-specific Memo KO mice we found that only the Memo null mice showed premature aging symptoms. However, both KO models showed deregulation of the FGF23-Klotho axis measuring expression of enzymes involved in vitamin D metabolism and phosphate reabsorption. Moreover, blood analysis of both models showed renal insufficiency and hypercalcemia. For the kidney-specific Memo KO animals we also performed analysis of the urine and found hypercaliuria. Surprisingly, for both models there was no difference in serum phosphate levels, which has earlier been shown by others to be causative for the premature aging syndrome.
In conclusion, we found that deletion of Memo in the full body or specifically in the kidney induces renal insufficiency and hypercalcemia. Furthermore, Memo deletion in the full body results in severe premature aging symptoms that cannot be explained by elevated serum phosphate levels. To date, it is not clear how hypercalcemia and hypercalciuria affects Memo mice and what specifically induces the premature aging in Memo null animals.
To investigate the function of Memo in vitro we isolated and immortalized mouse embryonic fibroblasts (MEFs) from Memofl/fl embryos. These cells were then infected with a Cre recombinase containing vector, which following 4-hydroxytamoxifen treatment ablated Memo expression (KO MEFs). Our studies showed that signaling downstream of FGF2 was reduced in activity and duration in Memo KO MEFs and furthermore that Memo was associated with the FGFR signaling complex (FGFR-FRS2-GRB2-GAB1). In addition, we tested mammary carcinoma cells (4T1) for sensitivity to FGFR inhibition and revealed lower sensitivity to FGFR inhibition in Memo downregulated cells. To investigate the role of Memo in the metabolic signaling we used HEK293 cells that are stably transfected with Klotho or ßKlotho and therefore responsive to FGF19, 21 and 23. We found that in Memo downregulated HEK293-Klotho and –ßKlotho cells, FGFR signaling activity after stimulation with FGF23 and FGF19 was affected.
In summary, this study provides evidence for a physiological role of Memo downstream of the FGFR pathway. We show that Memo is part of the FGFR signaling complex. Loss of Memo affects the intensity and duration of the FGFR signaling and modulates sensitivity to FGFR inhibition and to oxidative stress. Furthermore, we uncovered an important role of Memo in renal physiology that contributed to a premature aging phenotype, which is similar to that observed in Klotho mutant or FGF23 knock out animals.
|Committee Members:||Sommer, Lukas and Monard, Denis|
|Faculties and Departments:||09 Associated Institutions > Friedrich Miescher Institut FMI|
|Bibsysno:||Link to catalogue|
|Number of Pages:||193 S.|
|Last Modified:||30 Jun 2016 10:42|
|Deposited On:||21 Mar 2012 13:43|
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