Related Experiment Videos
Secretion of apoB- and apoA-I-containing lipoproteins by chick kidney
P Tarugi1, G Ballarini, B Pinotti
1Dipartimento di Scienze Biomediche, Università di Modena, Italy.
Insights
Chickens synthesize apolipoprotein B (apoB) and apolipoprotein A-I (apoA-I) in their kidneys, not just the liver. These proteins are secreted as part of lipoproteins, suggesting a role for kidneys in the bird
Area of Science:
- Biochemistry
- Cell Biology
- Comparative Physiology
Background:
- Previous research identified chick kidney as a site for apolipoprotein B (apoB) and apolipoprotein A-I (apoA-I) synthesis.
- The precise contribution of the kidney to circulating lipoproteins in birds remains incompletely understood.
Purpose of the Study:
- To quantitatively compare apoB and apoA-I production in chick kidney versus liver.
- To determine if kidney-synthesized apolipoproteins are secreted within lipoprotein particles.
- To identify the specific kidney cell types responsible for apolipoprotein synthesis.
Main Methods:
- Incubation of chick kidney and liver slices with 35S-labeled amino acids.
- Immunoprecipitation of radioactive apoB and apoA-I from cellular homogenates and incubation media.
- Density gradient ultracentrifugation of secreted lipoproteins.
- Immunohistochemical analysis of kidney tissue sections.
Main Results:
- Kidney produced significantly lower amounts of apoB and apoA-I compared to liver (P < 0.05).
- Kidney-derived apoB was found in VLDL, LDL, and light HDL fractions; liver apoB was mainly in VLDL, IDL, and LDL.
- ApoA-I from both organs was associated with HDL and other lipoprotein classes.
- Immunohistochemistry localized apoB and apoA-I to epithelial cells of proximal and distal convoluted tubules.
Conclusions:
- Chick kidneys synthesize and secrete apoB and apoA-I as components of lipoprotein particles.
- These kidney-derived lipoproteins circulate within the density range of plasma lipoproteins.
- The findings suggest that chick kidneys contribute to the overall plasma lipoprotein pool.
Abstract:
Previous studies showed that chick kidney is a site of synthesis of apolipoprotein (apo) B(B-100) and A-I. Aims of the present study were: a) to compare apoB and apoA-I production in chick kidney and liver; b) to investigate whether kidney apolipoproteins were secreted as constituents of lipoproteins; and c) to define the cellular sites of renal apolipoprotein synthesis. Kidney and liver slices taken from the same animals were incubated with 35S-labeled amino acids and radioactive apoB and apoA-I were immunoprecipitated from cell homogenate and incubation medium. The percentage of total protein radioactivity incorporated into cell plus medium apoB and apoA-I was 0.23+/-0.08 and 0.19+/-0.11 in kidney and 0.38+/-0.05 and 0.38+/-0.07 in liver, respectively (P < 0.05 kidney vs. liver). 35S-labeled medium lipoproteins were separated by density gradient ultracentrifugation and three major classes corresponding to VLDL + IDL, LDL, and HDL were identified. Most of the apoB secreted by the liver was found in VLDL, IDL, and LDL whereas kidney apoB was found in VLDL, LDL and "light" HDL (d 1.070-1.130 g/ml). In both hepatic and renal lipoproteins apoA-I was found not only in HDL but also in the other lipoproteins. Immunohistochemical analysis of kidney sections showed that apoB and apoA-I were present almost exclusively in the epithelial cells of proximal and distal convoluted tubules. Thus apoB and apoA-I synthesized by the epithelial cells of the proximal and distal convoluted tubules of chick kidneys are secreted as constituents of lipoprotein particles floating within the density range of plasma lipoproteins. These observations suggest that in the chick, the kidneys may contribute to the plasma lipoprotein pool.