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Mitochondrial N-formylmethionyl proteins as chemoattractants for neutrophils
Abstract:
Mitochondria synthesize several hydrophobic proteins. Like bacteria, mitochondria initiate protein synthesis with an N-formylmethionine residue. Because N-formylmethionyl peptides have been found to be chemotactic for polymorphonuclear leukocytes (PMN), mitochondria isolated from cultured human cells and purified bovine mitochondrial proteins were tested for PMN chemotactic activity in vitro. Nondisrupted mitochondria were not chemotactic. However, intact mitochondria that had been incubated with a lysosomal lysate did stimulate PMN migration. Antibodies directed against two mitochondrial enzymes, cytochrome oxidase and ATPase, (both of which contain mitochondrially synthesized subunits) but not anti-C3 or anti-C5 decreased mitochondrially derived chemotactic activity. In addition, purified bovine mitochondrial N-formylmethionyl proteins stimulated PMN migration in vitro, whereas nonformylated mitochondrial proteins did not. Furthermore, the chemotactic activity of purified mitochondrial proteins and disrupted mitochondria was decreased by the formyl peptide antagonist butyloxycarbonyl-phenylalanine-leucine-phenylalanine-leucine-phenylalanine. Finally, disrupted mitochondria and purified mitochondrial proteins stimulated PMN-directed migration (chemotaxis), according to accepted criteria. In addition to other chemotactic factors, release of N-formylmethionyl proteins from mitochondria at sites of tissue damage, may play a role in the accumulation of inflammatory cells at these sites.
Insights
Mitochondria release N-formylmethionyl proteins that attract inflammatory cells. This discovery suggests a new role for mitochondria in inflammation and tissue damage responses.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Mitochondria synthesize hydrophobic proteins using a bacterial-like system.
- N-formylmethionyl peptides are known chemoattractants for polymorphonuclear leukocytes (PMN).
Purpose of the Study:
- To investigate the potential chemotactic activity of mitochondrial N-formylmethionyl proteins.
- To determine if mitochondria contribute to inflammatory cell recruitment.
Main Methods:
- Testing chemotactic activity of isolated human and bovine mitochondria.
- Incubation with lysosomal lysate to assess PMN migration.
- Using antibodies against mitochondrial enzymes (cytochrome oxidase, ATPase) and complement components (C3, C5).
- Assessing chemotaxis with purified mitochondrial proteins and a formyl peptide antagonist.
Main Results:
- Intact mitochondria incubated with lysosomal lysate showed chemotactic activity.
- Antibodies against mitochondrial enzymes reduced chemotactic activity.
- Purified N-formylmethionyl mitochondrial proteins stimulated PMN migration.
- A formyl peptide antagonist inhibited the chemotactic activity.
Conclusions:
- Mitochondria release N-formylmethionyl proteins that are chemotactic for PMN.
- Mitochondrial N-formylmethionyl proteins may contribute to inflammatory cell accumulation at sites of tissue damage.