Here, we are able to show downregulated COL1A1 and COL6A1 expression in hypospadias patients with moderate and severe penile curvature. These results are consistent with previous research, which found that the mean number of total collagen fibers in dartos tissue in hypospadias was lower but had thicker fibers compared to normal patients (9). They also found that the hypospadias tissue anomaly consisted of a thick and inelastic tissue, although it was not always followed by an increase in collagen (9). Another study showed no evidence of fibrous bands 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 the 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. (6) revealed that during the maturation stage of scar formation, the collagen subtype I is produced excessively, developing the fibrils with large and stiff bands. This process might be associated with the less tumescence in the penis with fibrosis of the corpus cavernosum (6).
This paper also investigated the gene expression of COL6A1 as the most studied type of collagen in the beaded filament-forming collagen group. It plays a central role in cell attachments and connections between tissues and the 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 in extracellular matrix deposition and tissue fibrosis (15). In lung fibrosis, type 6 collagen is increasingly expressed (15). However, this study found decreased gene expression of COL6A1 in the hypospadias group compared to the control group. This finding might be related to the downregulation of COL1A1, which was found in this paper, suggesting that type 6 collagen is bound together to the sides of type 1 collagen to form thicker collagen fibers (7). We found a 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 that 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 darto tissue, which disrupts tissue elasticity and results in penis curving (17).
We also investigated the significant difference in COL1A1 and COL6A1 expression 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 the 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). The Dartos tissue pattern is not influenced by age. Race and genetics may affect penis development and need further investigation (4). Finally, for clinical implications, one of the important steps before urethroplasty is the release of fibrous tissue. The urethral plate malformation might be not associated with the most penile curvature (6). Therefore, leaving the urethral plate is preferred by most hypospadiologists (6). In addition, removal of the tissue under the urethral plate is still debatable (6), while excision of the inelastic dartos tissue during reconstructive surgery is recommended (9).