KLK5/6/7: Important factors for maintaining skin barrier homeostasis and local immune regulation.

• Gene Information: Kallikrein-5 (KLK5) is a protein-coding gene located on chromosome 19q13.41. Kallikrein-6 is a protein-coding gene located on chromosome 19q13.41. Kallikrein-7 is a protein-coding gene located on chromosome 19q13.41. All of them are members of the kallikrein subfamily.
• Protein Expression: KLK5 encodes kallikrein-5, a secreted serine protease that functions in proteolysis and epidermal homeostasis. Skin shows high expression, consistent with a role in the epidermis.
• KLK6 encodes kallikrein-6, a serine protease that is activated by glycosaminoglycans such as heparan sulfate and operates in the extracellular region. Its expression is high in brain tissue, with additional expression in the male reproductive system and proximal digestive tract.
• KLK7 encodes kallikrein-related peptidase 7, a serine protease that acts in the skin to degrade intercellular cohesive structures and facilitate desquamation.
• Signaling Pathway: Functionally, KLK5 is typically expressed in the epidermis and regulates cell shedding together with KLK7 and KLK14. KLK5 can be activated from the secreted KLK5 precursor, thereby activating several other KLK enzymes such as KLK2, -3, -6, -7, -11, -12, and -14. In the skin, KLK5 is involved in desquamation and may act as a physiological activator of KLK7.
• Therapeutic Inhibition: Targeting KLK5/KLK7 has the potential to treat atopic dermatitis or Netherton Syndrome (NS).

KLK5/KLK6/KLK7

• The exons 1 6 of mouse Klk5 gene, the exons 1 7 of mouse Klk6 gene, exons 1 6 of mouse Klk7 gene, that encode the whole molecule were replaced by human counterparts in B hKLK5/hKLK6/hKLK7 mice.
• The promoter, 5’UTR and 3’UTR region of the mouse gene were replaced by human counterparts. The human KLK5, KLK6, KLK7 expression is driven by human KLK5, KLK6, KLK7 promoter, while mouse Klk5, Klk6, Klk7 gene transcription and translation will be disrupted.

• Human KLK5, KLK6 and KLK7 were detected in homozygous B-hKLK5/hKLK6/hKLK7 mice, but not in wild-type mice.

Strain specific KLK5, KLK6 and KLK7 expression analysis in wild-type C57BL/6JNifdc mice and homozygous B-hKLK5/hKLK6/hKLK7 mice by ELISA. Ear was collected from wild-type C57BL/6JNifdc mice (+/+) and homozygous B-hKLK5/hKLK6/hKLK7 mice (H/H;H/H;H/H). Expression levels of human KLK5, human KLK6 and human KLK7 were analyzed by ELISA. Human KLK5, human KLK6 and human KLK7 were exclusively detectable in homozygous B-hKLK5/hKLK6/hKLK7 mice but not in wild-type mice. ND: not detectable. Values are expressed as mean ± SEM.

Experimental schedule for the induction of atopic dermatitis (AD) skin lesions and in vivo efficacy of anti-human KLK5/KLK7 BsAb analog in B-hKLK5/hKLK6/hKLK7 mice. OXA was applied to the ear skin of mice on day 0, followed by five challenges to the same site from days 7 to 16. The anti-human KLK5/KLK7 BsAb analog (in-house) was administered by intraperitoneal injection. OXA, oxazolone.

• Anti-human KLK5/KLK7 BsAb analog significantly reduced ear thickness compared with controls.

Efficacy of anti-human KLK5/KLK7 BsAb analog in B-hKLK5/hKLK6/hKLK7 mice. Mice in each group were treated with anti-human KLK5/KLK7 BsAb analog (in house). (A) Body weight changes during the treatment. (B) Statistical analysis of ear thickness in each group. Anti-human KLK5/KLK7 BsAb analog significantly reduced ear thickness compared with controls (n = 5). *P < 0.05, **P < 0.01, ***P < 0.001.