Purpose Erectile dysfunction (ED) is one of the increasing diseases with aging society. The basis of ED derived from local penile abnormality is poorly understood because of the complex three‐dimensional (3D) distribution of sinusoids in corpus cavernosum (CC). Understanding the 3D histological structure of penis is thus necessary. Analyses on the status of regulatory signals for such abnormality are also performed. Methods To analyze the 3D structure of sinusoid, 3D reconstruction from serial sections of murine CC were performed. Histological analyses between young (2 months old) and aged (14 months old) CC were performed. As for chondrogenic signaling status of aged CC, SOX9 and RBPJK staining was examined. Results Sinusoids prominently developed in the outer regions of CC adjacent to tunica albuginea. Aged CC samples contained ectopic chondrocytes in such regions. Associating with the appearance of chondrocytes, the expression of SOX9, chondrogenic regulator, was upregulated. The expression of RBPJK, one of the Notch signal regulators, was downregulated in the aged CC. Conclusions Prominent sinusoids distribute in the outer region of CC which may possess important roles for erection. A possibility of ectopic chondrogenesis induced by alteration of SOX9/Notch signaling with aging is indicated.

Male penis is required to become erect during copulation. In the upper (dorsal) part of penis, the erectile tissue termed corpus cavernosum (CC) plays fundamental roles for erection by regulating the inner blood flow. When blood flows into the CC, the microvascular complex termed sinusoidal space is reported to expand during erection. A novel in vitro explant system to analyze the dynamic erectile responses during contraction/relaxation is established. The current data show regulatory contraction/relaxation processes induced by phenylephrine (PE) and nitric oxide (NO) donor mimicking dynamic erectile responses by in vitro CC explants. Two photon excitation microscopy (TPEM) observation shows the synchronous movement of sinusoidal space and the entire CC. By taking advantages of the CC explant system, tadalafil (cialis) was shown to increase sinusoidal relaxation. Histopathological changes have been generally reported associating with erection in several pathological conditions. Various stressed statuses have been suggested to occur in the erectile responses by previous studies. The current CC explant model enables to analyze such conditions through directly manipulating CC in the repeated contraction/relaxation processes. Expression of oxidative stress marker and contraction related genes, Hif1a, Gpx1, RhoA, Rock was significantly increased in such repeated contraction/relaxation. Altogether, it is suggested that the system is valuable for analyzing structural changes and physiological responses to several regulators in the field of penile medicine.

Erection is an essential process which requires the male penis for copulation. This copulatory process depends on the vascular dynamic regulation of the penis. The corpus cavernosum (CC) in the upper (dorsal) part of the penis plays a major role in regulating blood flow inside the penis. When the CC is filled with blood, the sinusoids, including micro-vessels, dilate during erection. The CC is an androgen-dependent organ, and various genital abnormalities including erectile dysfunction (ED) are widely known. Previous studies have shown that androgen deprivation by castration results in significantly decreased smooth muscles of the CC. Experimental works in erectile biology have previously measured intracavernosal penile pressure and mechanical tension. Such reports analyze limited features without assessing the dynamic aspects of the erectile process. In the current study, we established a novel explant system enabling direct visual imaging of the sinusoidal lumen to evaluate the dynamic movement of the cavernous space. To analyze the alternation of sinusoidal spaces, micro-dissected CC explants by patent blue dye injection were incubated and examined for their structural alternations during relaxation/contraction. The dynamic process of relaxation/contraction was analyzed with various external factors administered to the CC. The system enabled the imaging of relaxation/contraction of the lumens of the sinusoids and the collagen-containing tissues. Histological analysis on the explant system also showed the relaxation/contraction. Thus, the system mimics the regulatory process of dynamic relaxation/contraction in the erectile response. The current system also enabled evaluating the erectile pathophysiology. In the current study, the lumen of sinusoids relaxed/contracted in castrated mice similarly with normal mice. These results suggested that the dynamic erectile relaxation/contraction process was similarly retained in castrated mice. However, the system also revealed decreased duration time of erection in castrated mice. The current study is expected to promote further understanding of the pathophysiology of ED, which will be useful for new treatments in the future. Hence, the current system provides unique information to investigate the novel regulations of erectile function, which can provide tools for analyzing the pathology of ED.

The murine penile erectile tissues including corpus cavernosum (CC) are composed of blood vessels, smooth muscle, and connective tissue, showing marked sexual differences. It has been known that the androgens are required for sexually dimorphic organogenesis. It is however unknown about the features of androgen signaling during mouse CC development. It is also unclear how androgen-driven downstream factors are involved such processes. In the current study, we analyzed the onset of sexually dimorphic CC formation based on histological analyses, the dynamics of androgen receptor (AR) expression, and regulation of cell proliferation. Of note, we identified Dickkopf-related protein 2 (Dkk2), an inhibitor of β-catenin signaling, was predominantly expressed in female CC compared with male. Furthermore, administration of androgens resulted in activation of β-catenin signaling. We have found the Sox9 gene, one of the essential markers for chondrocyte, was specifically expressed in the developing CC. Hence, we utilized CC-specific, Sox9 CreERT2 , β-catenin conditional mutant mice. Such mutant mice showed defective cell proliferation. Furthermore, introduction of activated form of β-catenin mutation (gain of function mutation for Wnt/β-catenin signaling) in CC induced augmented cell proliferation. Altogether, we revealed androgen-Wnt/β-catenin signal dependent cell proliferation was essential for sexually dimorphic CC formation. These findings open new avenues for understanding developmental mechanisms of androgen-dependent cell proliferation during sexual differentiation.

The development of embryonic external genitalia (eExG) into characteristic male structures, such as urethra and penile erectile tissues, depends on 5α-dihydrotestosterone (DHT).Although the corpus cavernosum (CC) is well known as essential for erectile function in adults, its developmental process and its dependency on DHT have been unknown. To reveal the dimorphic formation of the murine CC from the embryonic stage, we first analyzed the production of the protein vascular endothelial growth factor receptor-2 (FLK1) via its expression (hereinafter referred as "expression of FLK1") and the expression of alphasmooth muscle actin (ACTA2) and collagen type 1 (COL1A1) in developing external genitalia. The 5-α reductase type 2 encoded by the SRD5A2 gene has been suggested to be a crucial enzyme for male sexual differentiation, as it converts testosterone (T) into DHT in the local urogenital organs. In fact, SRD5A2 mutation results in decreased synthesis of DHT, which leads to various degrees of masculinized human external genitalia (ExG). We further investigated the expression profile of SRD5A2 during the formation of the murine CC. We observed that SRD5A2 was expressed in smooth muscle of the CC. To determine the role of SRD5A2 in CC formation, we analyzed the formation of erectile tissue in the male Srd5a2 KO mice and measured the levels of androgens in the ExG by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Intriguingly, there were no obvious defects in the CCs of male Srd5a2 KO mice, possibly due to increased T levels. The current study suggests possible redundant functions of androgens in CC development.