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Characterization of stanniocalcin-1 receptors in the rainbow trout
Timothy D J Richards1, Amanda L Fenton, Rahma Syed
1Department of Physiology and Pharmacology, Faculty of Medicine and Dentistry, University of Western Ontario, London, ON, Canada N6A 5C1.
Abstract:
Mammalian stanniocalcin-1 (STC-1) is one of several ligands targeted to mitochondria. High affinity STC-1 receptors are present on the mitochondrial membranes of nephron cells, myocytes, and hepatocytes, to enable ligand sequestration within the matrix. However, STC-1 receptors have not been characterized in fish. Nor is it known if mitochondrial targeting occurs in fish. The aim of the study was to address these questions. Saturation binding assays were carried out to obtain estimates of K(D) and B(max). They revealed the presence of saturable, high-affinity receptors on both membranes and mitochondria of liver, muscle, and gill filament. In situ ligand binding (ISLB) was used to localize receptors at the histological level and revealed some unexpected findings. In cranium, for instance, receptors were found mainly in the cartilage matrix, as opposed to the chondrocytes. In brain, the majority of receptors were located on neuropil areas as opposed to neuronal cell bodies. In skeletal muscle, receptors were confined to periodic striations, tentatively identified as the Z lines. Receptors were even found on STC-1 producing corpuscles of Stannius cells, raising the possibility of there being an autocrine feedback loop or, perhaps, a soluble binding protein that is released with the ligand to regulate its bioavailability.
Insights
Fish possess high-affinity stanniocalcin-1 (STC-1) receptors on membranes and mitochondria, particularly in liver, muscle, and gills. These receptors exhibit unique localization patterns in various fish tissues, suggesting novel biological roles.
Area of Science:
- Comparative physiology
- Endocrinology
- Molecular biology
Background:
- Mammalian stanniocalcin-1 (STC-1) targets mitochondria via high-affinity receptors in nephron, muscle, and liver cells.
- The presence and function of STC-1 receptors in fish remain uncharacterized.
- Mitochondrial targeting of STC-1 in fish is not established.
Purpose of the Study:
- To characterize STC-1 receptors in fish.
- To determine if mitochondrial targeting of STC-1 occurs in fish.
- To investigate the localization of STC-1 receptors in various fish tissues.
Main Methods:
- Saturation binding assays to determine receptor affinity (K(D)) and density (B(max)).
- In situ ligand binding (ISLB) for histological localization of receptors.
- Analysis of liver, muscle, and gill filament tissues.
Main Results:
- Saturable, high-affinity STC-1 receptors were identified on membranes and mitochondria of fish liver, muscle, and gill filaments.
- Unexpected receptor localizations were observed: cartilage matrix (cranium), neuropil areas (brain), and Z lines (skeletal muscle).
- Receptors were also found on STC-1 producing corpuscles of Stannius cells.
Conclusions:
- Fish possess functional, high-affinity STC-1 receptors with mitochondrial association.
- Novel receptor localizations suggest diverse roles beyond mitochondrial sequestration in fish.
- Potential autocrine feedback or soluble binding protein regulation of STC-1 bioavailability is proposed.
