From molecular structure to tissue architecture: collagen organization probed by SHG microscopy

Abstract

Second‐harmonic generation (SHG) microscopy is a fantastic tool for imaging collagen and probing its hierarchical organization from molecular scale up to tissue architectural level. In fact, SHG combines the advantages of a non‐linear microscopy approach with a coherent modality able to probe molecular organization. In this manuscript we review the physical concepts describing SHG from collagen, highlighting how this optical process allows to probe structures ranging from molecular sizes to tissue architecture, through image pattern analysis and scoring methods. Starting from the description of the most relevant approaches employing SHG polarization anisotropy and forward – backward SHG detection, we then focus on the most relevant methods for imaging and characterizing collagen organization in tissues through image pattern analysis methods, highlighting advantages and limitations of the methods applied to tissue imaging and to potential clinical applications. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In vivo non‐invasive monitoring of collagen remodelling by two‐photon microscopy after micro‐ablative fractional laser resurfacing

“…A more powerful imaging modality is represented by two-photon excited fluorescence (TPF) microscopy [20], which is a high-resolution laser scanning imaging technique enabling deep optical imaging of tissues, as demonstrated by studies performed on ex vivo tissue samples [21][22][23][24][25], fresh biopsies [26][27][28][29][30][31], and also in vivo on both animals [32] and humans [33][34][35][36][37][38]. Additional morphological information can be provided by second-harmonic generation (SHG) microscopy [39][40][41][42][43][44][45][46][47][48][49], which can be combined with TPF microscopy using the same laser source. Combined TPF-SHG microscopy represents a powerful tool for imaging skin dermis, since the main dermal components, collagen and elastin, can be imaged by SHG and TPF microscopy, respectively [22].…”

Imaging the noncentrosymmetric structural organization of tendon with Interferometric Second Harmonic Generation microscopy

“…One common aspect of all those biological structures is that they are composed of noncentrosymmetric proteins where, even at spatial scale much larger than the molecule, the lack of center of inversion remains macroscopically. An extensive review on collagen tissue imaging with SHG microscopy has been recently published and provides additional information [8].…”

A Heterotopic Xenograft Model of Human Airways for Investigating Fibrosis in Asthma

“…As such, they do not emit a second-harmonic signal and cannot be imaged using this technique. For the past 10 years, SHG microscopy has commonly been used to image fibrillar collagen in multiple biological tissues, including heart, skin, eye, and lung (35).…”