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Role of calcium signaling for GDNF secretion, ureter branching and early nephron formation
Author(s) -
Fontana Jacopo Maria,
Jess David Unnersjö,
Blom Hans,
Brismar Hjalmar,
Aperia Anita
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.969.23
Subject(s) - glial cell line derived neurotrophic factor , nephron , calcium , endocrinology , medicine , ureteric bud , kidney , microbiology and biotechnology , chemistry , receptor , biology , neurotrophic factors , kidney development , biochemistry , embryonic stem cell , gene
Low nephron endowment has an adverse effect on the outcome of many kidney diseases and is a risk factor for chronic kidney disease. The formation of nephrons occurs as a result of the reciprocal interaction between metanephric mesenchymal (MM) cells and the ureteric bud (UB). MM cells secrete the trophic factor GDNF, which binds to the Ret receptors on the UB. Signaling via GDNF and the Ret receptor promotes UB branching and plays a central role for initiating nephron formation. The mechanisms controlling the release of GDNF from the MM cells has been elusive, despite its fundamental importance for kidney development. Most secretory processes are controlled by calcium signaling. Here we demonstrate, using embryonic E14 rat kidneys cultured for 1–2 days, the occurrence of spontaneous calcium transients in MM cells with a frequency of 2–29 min −1 . Depletion of calcium stores in the endoplasmic reticulum (ER) with cyclopiazonic acid (CPA) caused drastic reduction of calcium activity, while acute exposure of kidneys to calcium‐free extracellular solution had no effect. To chronically reduce the ER calcium stores and downregulate the spontaneous calcium activity in MM cells, kidneys were exposed to low concentration of CPA from DIV1 to DIV2. This resulted in swelling and significant reduction of UB as well as of significant reduction of UB branching points and of newly formed pre‐glomeruli. In addition, GDNF concentration in the culture media was significantly lower for CPA treated than for control kidneys. To further assess the role of calcium signaling for GDNF secretion, we stained the kidneys for MM and UB markers (WT‐1 and E‐Cadherin respectively) and for GDNF, as well as synaptotagmin‐1 (SYT1), a calcium binding protein that is the major calcium sensor activating secretory processes in the brain. By applying a tissue clearing protocol and super‐resolution microscopy, we could resolve the localization of SYT1 and GDNF in the MM cells, both surrounding the UB tips. In summary we have identified a novel calcium dependent link in the complex process of nephron formation. In the light of this, our results indicate that the vesicle transport and calcium‐regulated fusion that control neurotransmitter release at the synapsis could also have fundamental importance for early embryonic development of methanephric kidney. Support or Funding Information The Swedish Research Council (AA and HB).