Here, we are able to show the downregulated COL1A1 and COL6A1 expressions in hypospadias patients, with moderate and severe penile curvature. These results are consistent with the previous research which found that the mean number of total collagen fibers of dartos tissue in hypospadias was lower but has thicker fibers compared to normal patients. The study also found the abnormality of hypospadias tissue gave it the thick and inelastic character although it was not followed by the increasing of collagen (11). Another study showed no evidence of fibrous band or dysplastic tissue in subepithelial biopsies analyzed in 17 prepubertal boys undergoing hypospadias repair (12). Eros et al. proposed no difference in collagen intensity between normal areas and under urethral plate of patients with hypospadias (13).
Type 1 collagen is the most abundant collagen. It is the predominant component of interstitial membranes. It is also associated with fibrosis and fibrogenesis (14). Hayashi et al., (2011) explained the excess deposition of type 1 collagen occurs in the maturation phase of scar formation, making the fibrils become large with stiff bands. It may cause less tumescence in patients with scar formation or fibrosis of the corpus cavernosum penis (6).
This paper also investigated the gene expression of COL6A1 as the most studied type of collagen in the beaded- filament-forming collagens group. It plays a central role in cell attachments and connection between tissues and surrounding matrix (15). Type 6 collagen also regulates fibrogenesis by modulating the interactions among cells. It stimulates the activation of mesenchymal cells into myofibroblasts resulting the extracellular matrix deposition and tissue fibrosis (15). In lung fibrosis, type 6 collagen is increasingly expressed (15). However, this study found decreasing gene expression of COL6A1 in the hypospadias group compared to the control group. This finding might relate with the downregulation of COL1A1 which was found in this paper, suggesting type 6 collagen is bound together to the sides of type 1 collagen to form thicker collagen fibers (7). We found significant positive correlation between COL1A1 and COL6A1.
The etiology of chordee in hypospadias remains unclear. Resection of dartos tissue usually can straighten the penis in patients with chordee and buried penis, suggesting the pathophysiology of these anomalies is related to dartos tissue (4). The composition of dartos fibromuscular tissue determines tissue elasticity and skin mobility (4,12).
Collagen is a part of the tissue backbone. During tissue turnover, it is formed and degraded to maintain tissue health and homeostasis. Imbalance of that process leads to fibrosis. Fibrosis is known as excessive formation of connective tissue which damages the structure and function of its tissue (16). Chordee occurs because of fibrosis in dartos tissue which disrupts the tissue elasticity and results in the curving of penile (17).
We also investigated the statistical difference of COL1A1 and COL6A1 expressions among groups based on penile curvature in the hypospadias group. Mostly, severe forms of hypospadias are related to a significant chordee and a urethral meatus located proximal to the midshaft of the penis (18). Another study proposed that severity of chordee is generally proportional to the degree of hypospadias (19). Many factors, such as abnormal development of the urethral plate, fibrotic mesenchymal tissue at the urethral meatus, and ventral-dorsal corporal disproportion may be interconnected resulting in different degrees in the final severity of curvature in each patient (20). Dartos tissue pattern is not influenced by age. Race and genetics mayaffect penile development and need a further investigation (4). Finally, for the clinical implications, it is recommended to excise inelastic dartos tissue during reconstructive surgery (11).