Friday, January 2, 2015

Fat Cells in Skin Kill Bacteria

Scientists reported today that adipocytes in mouse and human skin produce an antimicrobial peptide (AMP) called cathelicidin is response to Staph aureus infections, including MRSA. Experimental animals that were deficient in the AMP were more susceptible to skin infections.

Adipocytes may recognize S. aureus by detecting bacterial peptides with toll-like receptors (TLRs), but more work is needed to fully understand the mechanisms.

This finding adds more to our understanding of human skin as a vital part of our body's defenses against infection. It also opens the door to understanding how diabetes, metabolic syndrome, and other conditions can reduce resistance to skin infections by altering the availability of AMPs in the fat associated with skin.

All of this may eventually lead to additional—perhaps more effective—strategies in preventing or curing serious skin infections such as MRSA.

I realize that we generally think of fat cells as belonging to the hypodermis, not the dermis, as described in the research. However, recent evidence shows the presence of adipocytes in the dermis that are distinct from those in the hypodermis. These adipocytes derive from a common precursor cell that produces both dermal fibroblasts and intradermal adipocytes. These dermal adipocytes have been shown to have a role in wound healing and the regeneration of hair follicles. And the research summarized here suggests that they also have a role in immunity.

What can we use from this in teaching undergraduate A&P?

  • Mention this discovery when discussing the roles of adipose tissue and adipocytes in your coverage of tissues of the body.

    • Consider clarifying that dermal adipocytes are distinct from fat cells in the hypdermis. And perhaps mention that it's a detail often left out of introductory discussions of skin.

  • This is a good point to mention when discussing the protective functions of the skin when covering the integumentary system.

  • When discussing the immune system, this concept helps illustrate several important principles:

    • The role of the skin as the first line of defense against infection

      • The variety of mechanisms available in the skin to act defensively

    • The role of TLRs and pattern recognition in immunity

    • The fact that immunity is a role for many tissues—not just lymphocytes and other WBCs

  • Take a moment NOW to add this to your course notes!

Want to know more?

Killer Fat
  • J. Alcorn and J. Kolls. Science 2 January 2015: Science Vol. 347 no. 6217 pp. 26-27 DOI: 10.1126/science.aaa4567
  • Editorial summary of the research in plain English. Includes a really nice, simple illustration of the concept (includes FREE teaching slide)

Dermal adipocytes protect against invasive Staphylococcus aureus skin infection
  • L. Zhang1, et al. Science 2 January 2015: Vol. 347 no. 6217 pp. 67-71 DOI: 10.1126/science.126097
  • Original research article. Additional images available here, including some nice micrographs showing increase in adipocytes in response to S. aureus infection

Defining dermal adipose tissue.
  • Driskell RR, et al. Exp Dermatol. 2014. Exp Dermatol. 2014 Sep;23(9):629-31. doi: 10.1111/exd.12450.
  • Review article describing dermal adipocytes.

FREE teaching slide
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to download a

Adipose image credit:
This post was updated 6 OCT 2015

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