FT-IR Microspectroscopy of Rat Ear Cartilage

PLoS One. 2016 Mar 25;11(3):e0151989. doi: 10.1371/journal.pone.0151989. eCollection 2016.

Abstract

Rat ear cartilage was studied using Fourier transform-infrared (FT-IR) microspectroscopy to expand the current knowledge which has been established for relatively more complex cartilage types. Comparison of the FT-IR spectra of the ear cartilage extracellular matrix (ECM) with published data on articular cartilage, collagen II and 4-chondroitin-sulfate standards, as well as of collagen type I-containing dermal collagen bundles (CBs) with collagen type II, was performed. Ear cartilage ECM glycosaminoglycans (GAGs) were revealed histochemically and as a reduction in ECM FT-IR spectral band heights (1140-820 cm-1) after testicular hyaluronidase digestion. Although ear cartilage is less complex than articular cartilage, it contains ECM components with a macromolecular orientation as revealed using polarization microscopy. Collagen type II and GAGs, which play a structural role in the stereo-arrangement of the ear cartilage, contribute to its FT-IR spectrum. Similar to articular cartilage, ear cartilage showed that proteoglycans add a contribution to the collagen amide I spectral region, a finding that does not recommend this region for collagen type II quantification purposes. In contrast to articular cartilage, the symmetric stretching vibration of -SO3- groups at 1064 cm-1 appeared under-represented in the FT-IR spectral profile of ear cartilage. Because the band corresponding to the asymmetric stretching vibration of -SO3- groups (1236-1225 cm-1) overlapped with that of amide III bands, it is not recommended for evaluation of the -SO3- contribution to the FT-IR spectrum of the ear cartilage ECM. Instead, a peak (or shoulder) at 1027-1016 cm-1 could be better considered for this intent. Amide I/amide II ratios as calculated here and data from the literature suggest that protein complexes of the ear cartilage ECM are arranged with a lower helical conformation compared to pure collagen II. The present results could motivate further studies on this tissue under pathological or experimental states involving ear cartilage.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cartilage, Articular / metabolism*
  • Chondroitin Sulfates / metabolism
  • Collagen Type I / metabolism
  • Collagen Type II / metabolism
  • Ear Cartilage / metabolism*
  • Extracellular Matrix / metabolism*
  • Glycosaminoglycans / metabolism
  • Rats
  • Spectroscopy, Fourier Transform Infrared*

Substances

  • Collagen Type I
  • Collagen Type II
  • Glycosaminoglycans
  • Chondroitin Sulfates

Grants and funding

This work was funded by Fundação de Amparo à Pesquisa do Estado de São Paulo, grants no. 2003/04597-0, 2007/058251-8 and 2013/1078-0. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.