One of Two Human Lactoferrin Variants Exhibits Increased Antibacterial and Transcriptional Activation Activities and Is Associated with Localized Juvenile Periodontitis

Abstract

The iron-binding protein lactoferrin is a ubiquitous and abundant constituent of human exocrine secretions. Lactoferrin inhibits bacterial growth by sequestering essential iron and also exhibits non-iron-dependent antibacterial, antifungal, antiviral, antitumor, anti-inflammatory, and immunoregulatory activities. All of these non-iron-dependent activities are mediated by the highly charged N terminus of lactoferrin. In this study we characterized a Lys/Arg polymorphism at position 29 in the N-terminal region of human lactoferrin that results from a single nucleotide polymorphism in exon 1 of the human lactoferrin gene. We expressed cDNAs encoding both lactoferrin variants in insect cells and purified the two proteins by ion exchange chromatography. The two lactoferrin variants exhibited nearly identical iron-binding and iron-releasing activities and equivalent bactericidal activities against a strain of the gram-negative bacterium Actinobacillus actinomycetemcomitans. When tested against the gram-positive species Streptococcus mutans and Streptococcus mitis, however, lactoferrin containing Lys at position 29 exhibited significantly greater bactericidal activity than did lactoferrin containing Arg. In addition, the Lys-containing lactoferrin stimulated bovine tracheal epithelial cells to synthesize much higher levels of tracheal antimicrobial peptide mRNA than did the Arg-containing variant. A genotyping assay that distinguished between the two alleles based on a polymorphic EarI restriction site showed that the Lys and Arg alleles had frequencies of 24% and 76%, respectively, among 17 healthy human subjects, and 72% and 28%, respectively, among nine patients with localized juvenile periodontitis. Our findings suggest that these two lactoferrin variants are functionally different and that these differences may contribute to the pathogenesis of localized juvenile periodontitis.

Human Polymorphonuclear Leukocytes Inhibit Aspergillus fumigatus Conidial Growth by Lactoferrin-Mediated Iron Depletion

“…Human neutrophil-specific granule deficiency, caused by a mutation in the C/EBP trancription factor (39), also results in decreased or absent neutrophil LF (among many other specific granule proteins) (40,41), and is associated with an increased risk of pyogenic bacterial infections, but not fungal infection. Several single nucleotide polymorphisms in human LF have been reported and are associated with an increased risk for periodontitis possibly by altering the oral microflora (42,43); however, it is unknown whether these polymorphisms are risk factors for aspergillosis. Despite the overall similarity between normal and CGD PMN and their postsecretory supernatants in arresting the growth of A. fumigatus conidia, we found that CGD PMN actually contained less LF than normal PMN.…”

A nonconservative, coding single-nucleotide polymorphism in the N-terminal region of lactoferrin is associated with aggressive periodontitis in an African-American, but not a Caucasian population

“…However, from studying different ethnic populations, the data could not help explain why African Americans appear to be more susceptible to periodontitis due to this organism. 22 In the present report, we examine further the genetic associations between this gene and aggressive periodontal disease in both African-American and Caucasian populations, using a novel, nonconservative, SNP in the human lactoferrin gene. …”

“…One recent study has identified two variants of lactoferrin and demonstrated that these variants exhibit different antibacterial and transcriptional activation activities. 22 Examination of a small population of periodontal patients suggested that these differences may go some way in explaining susceptibility to periodontal disease. However, from studying different ethnic populations, the data could not help explain why African Americans appear to be more susceptible to periodontitis due to this organism.…”

Expression levels of JNK associated with polymorphic lactotransferrin haplotypes in human nasopharyngeal carcinoma

“…Velliyagounder et al (13) found that a Lys/Arg polymorphism (rs1126478) at position 29 in the N-terminal region of human LTF produced functional differences, and Expression levels of JNK associated with polymorphic lactotransferrin haplotypes in human nasopharyngeal carcinoma that this difference may contribute to the pathogenesis of localized juvenile periodontitis. Similarly, control individuals who were G carriers at rs1126478 had significantly lower fasting triglyceride concentrations and significantly higher high-density lipoprotein cholesterol concentrations than AA homozygotes (14).…”