Collagen and elastic system in the remodelling process of major types of idiopathic interstitial pneumonias (IIP)

Abstract

Acute and chronic IIP cause a similar increase in the collagen and elastic contents of the lungs, representing a process of 'fibroelastosis' rather than an exclusive process of fibrosis. A profibrogenic mechanism is responsible for the unparallelled collagen augmentation observed in UIP subjects, the nature of which is yet to be determined.

Always cleave up your mess: targeting collagen degradation to treat tissue fibrosis

“…In studies conducted in the 1970s and 1980s of what was then called IPF (likely representing a mix of ILD pathologies with UIP predominating), the increase in collagen was found to be primarily an increase in type I collagen that represented ϳ80% of the total collagen (7,101,151,155,160). These studies indicate that in addition to an increase in total collagen in IPF (150,151) there is also a shift toward the less elastic type I collagen, which contributes to pathophysiological abnormalities in fibrosis (51,125,145). A relative increase in type I collagen production (as well as an increase in total lung collagen content) has also been demonstrated in the lungs of patients with ARDS (87,140) as well as in human fibrotic livers (85).…”

Second harmonic generation microscopy analysis of extracellular matrix changes in human idiopathic pulmonary fibrosis

“…4,7,8 Changes in elastin also contribute to the ECM remodeling, where the proportion of collagen/elastin determines the elastic recoil of the lungs and airway patency. 9,10 Elastin in normal alveolar septa is found as an organized epithelial layer of mature elastin fibers providing the elasticity required for proper lung function; however, in early IPF, these fibers are degraded by MMP-9 and elastase that are released from the inflammatory cells and compromise lung patency. As IPF progresses and elastin is degraded, fibroblasts respond through synthesis not only of collagen but also elastin; however, the new elastin is highly disordered and results in poor mechanical properties of the new lung matrix.…”

“…As IPF progresses and elastin is degraded, fibroblasts respond through synthesis not only of collagen but also elastin; however, the new elastin is highly disordered and results in poor mechanical properties of the new lung matrix. 9,10 High-resolution computed tomography (HRCT) scans can be used to diagnose IPF when a classic radiographic pattern is present; 11 however, in many cases, the appearance may not be sufficient to establish a positive diagnosis. In these cases, the gold-standard for IPF diagnosis still remains surgical biopsy followed by pathology.…”

Systemic sclerosis and idiopathic interstitial pneumonia: histomorphometric differences in lung biopsies

“…We quantified 10 fields per biopsy in cases of NSIP, whereas we quantified 30 fields per biopsy in cases of UIP: 10 in normal areas; 10 in intermediate areas (alveolar collapse); and 10 in remodeling areas (mural fibrosis and honeycombing areas). (19,20) The thresholds for fibers of the collagenous and elastic systems were established for each slide, after enhancing the contrast up to a point at which the fibers were easily identified as black (elastic) or birefringent (collagen) bands. The area occupied by the fibers was determined through digital densitometric recognition, by adjusting the threshold level of measurement up to the gray density of the fibers of the collagenous and elastic systems.…”

“…Septal length was carefully measured through the eyepiece and with the image analysis system, using points and a cursor that allows the free determination of the length of the basal lamina even if there is associated septal shortening by atelectasis or retraction. (19) The measurements of cells and fibers by morphometry (stereology and digital imaging) are corrected taking into account the septal length. The results express the area of collagen and elastic fibers per total area of interstitial wall, expressed as a percentage.…”