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Synthesis and secretion of apolipoprotein A-I by chick skin
P Tarugi1, L Albertazzi, S Nicolini
1Istituto di Patologia Generale, Università di Modena, Italy.
Abstract:
Chick skin slices were incubated with [35S]methionine and labeled apoA-I was immunoprecipitated from incubation medium and tissue homogenate. ApoA-I accounted for approximately 13 and 2.5% of radioactive medium and cell proteins, respectively. After ultracentrifugation of the medium, 55% of labeled apoA-I was found as a constituent of lipoproteins (d less than 1.210 g/ml) and 45% in a lipid-poor form (1.210-1.260 g/ml). To ascertain whether this large proportion of lipid-poor apoA-I was due to a dissociation of this peptide from medium lipoproteins during ultracentrifugation, labeled incubation medium was applied to an anti-chick apoA-I immunoaffinity column. The material bound to the column was analyzed by nondenaturing polyacrylamide gradient gel electrophoresis and found to contain three subpopulations of lipoproteins with a particle size of 12, 11, and 9 nm, respectively. The radioactivity of these subpopulations accounted for 82% of total radioactive medium apoA-I. ApoA-I was localized by immunohistochemistry in the viable cells of the epidermis and in the stratum corneum. Rat skin slices were found to synthesize and secrete apoE but no apoA-I. ApoA-I and apoE secreted by chick and rat skin, respectively, may play a role in the secretion of lipids from the differentiating keratinocytes and thus contribute to the formation of the hydrophobic barrier of the skin.
Insights
Chick skin synthesizes apolipoprotein A-I (apoA-I), secreting it in both lipoprotein-bound and lipid-poor forms. This apoA-I may aid lipid secretion, crucial for forming the skin's hydrophobic barrier.
Area of Science:
- Biochemistry
- Dermatology
- Lipid Metabolism
Background:
- Apolipoprotein A-I (apoA-I) is a key component of high-density lipoproteins.
- The role of apoA-I in skin physiology, particularly in lipid transport and barrier formation, is not fully understood.
Purpose of the Study:
- To investigate the synthesis and secretion of apoA-I by chick skin.
- To characterize the forms of apoA-I secreted by chick skin.
- To explore the potential role of secreted apoA-I in skin lipid metabolism.
Main Methods:
- Incubation of chick skin slices with [35S]methionine.
- Immunoprecipitation of labeled apoA-I from medium and tissue.
- Ultracentrifugation and immunoaffinity chromatography of secreted apoA-I.
- Nondenaturing polyacrylamide gradient gel electrophoresis.
- Immunohistochemistry for apoA-I localization.
- Comparison with rat skin synthesis of apoE.
Main Results:
- Chick skin synthesizes and secretes apoA-I, accounting for significant portions of radioactive medium and cell proteins.
- Secreted apoA-I exists as both lipoprotein-associated and lipid-poor forms.
- Lipoprotein-associated apoA-I is found in subpopulations of 9-12 nm particles.
- ApoA-I is localized in viable epidermal cells and the stratum corneum.
- Rat skin secretes apoE but not apoA-I.
Conclusions:
- Chick skin actively synthesizes and secretes apoA-I.
- Secreted apoA-I exists in multiple forms, suggesting complex processing and function.
- Both chick apoA-I and rat apoE may be involved in lipid secretion by keratinocytes, contributing to the skin's hydrophobic barrier.