Defensin-related cryptdin-8

Cryptdin is a defensin-related peptide, and its mRNA accumulates to high abundance in epithelial cells of intestinal crypts beginning in the second week of postnatal development. The cryptdin (Defcr) locus was assigned to mouse chromosome 8 by Southern blotting of DNAs from mouse/hamster somatic hybrid cell lines. Analysis of somatic hybrid DNAs for mouse-specific restriction fragments showed zero discordance and perfect concordance with chromosome 8. The Defcr locus was localized on chromosome 8 by analysis of DNAs from recombinant inbred (RI) strains of mice after identification of three potential Defcr alleles based on restriction fragment length polymorphisms (RFLPs) in inbred strains. The strain distribution patterns of the Defcr locus were compared with those of chromosome 8 markers in five panels of RI strains. Analysis of cosegregation of Defcr with xenotropic proviral locus Xmv-26 and additional loci confirmed the chromosomal assignment and showed that Defcr is on proximal chromosome 8 within approximately 6 (1.3 to 21.3) cM of Xmv-26. The mouse Defcr locus and the human defensin gene(s) located on chromosome 8p23 appear to map to homologous regions.

Cryptdin mRNA codes for the apparent precursor to a corticostatin/defensin-related peptide that accumulates to high levels in mouse intestinal crypt epithelium during postnatal development. The primary structure, intestinal cell distribution, and developmental appearance of cryptdin mRNA have been determined. Cryptdin mRNA is 450-480 nucleotides long. Translation of the partial cryptdin cDNA sequence reveals a 70-amino acid open reading frame that includes 32 carboxy-terminal residues that align with those in the consensus sequence, C.CR...C....ER..G.C....CCR, which is a common feature of leukocyte defensins and lung corticostatins (Selsted, M. E., D. M. Brown, R. J. DeLange, S. S. L. Harwig, and R. I. Lehrer. 1985. J. Biol. Chem. 260:4579-4584; Zhu, Q., J. Hu, S. Mulay, F. Esch, S. Shimasaki, and S. Solomon. 1988. Proc. Natl. Acad. Sci. USA. 85:592-596). In situ hybridization of cryptdin cDNA to paraformaldehyde-fixed, frozen sections of adult jejunum and ileum showed intense and specific labeling of epithelial cells in the base of all crypts. Analysis of sections from suckling mice showed that cryptdin mRNA is detectable in 10-20% of crypts in 10-d-old mice, in approximately 80% of crypts in 16-d-old mice, and in all crypts of mice 20 d and older. During the fourth week, the sequence accumulates in crypts to the maximal adult level. Cryptdin mRNA content in adult small intestine is independent both of T cell involvement and luminal bacteria. The role of cryptdin in small bowel physiology remains to be determined: cryptdin may inhibit bacterial translocation, modulate intestinal hormone synthesis, influence hormonal sensitivity of the intestinal epithelium, or exhibit a multiplicity of related activities.

The role of respiratory tract microbes and the relationship between respiratory tract and gut microbiomes in coronavirus disease 2019 (COVID-19) remain uncertain. Here, the metagenomes of sputum and fecal samples from 66 patients with COVID-19 at three stages of disease progression are sequenced. Respiratory tract, gut microbiome, and peripheral blood mononuclear cell (PBMC) samples are analyzed to compare the gut and respiratory tract microbiota of intensive care unit (ICU) and non-ICU (nICU) patients and determine relationships between respiratory tract microbiome and immune response. In the respiratory tract, significantly fewer Streptococcus, Actinomyces, Atopobium, and Bacteroides are found in ICU than in nICU patients, while Enterococcus and Candida increase. In the gut, significantly fewer Bacteroides are found in ICU patients, while Enterococcus increases. Significant positive correlations exist between relative microbiota abundances in the respiratory tract and gut. Defensin-related pathways in PBMCs are enhanced, and respiratory tract Streptococcus is reduced in patients with COVID-19. A respiratory tract-gut microbiota model identifies respiratory tract Streptococcus and Atopobium as the most prominent biomarkers distinguishing between ICU and nICU patients. The findings provide insight into the respiratory tract and gut microbial dynamics during COVID-19 progression, considering disease severity, potentially contributing to diagnosis, and treatment strategies.