The spatial distribution of inorganic nanoparticles within calcified Peyronie's plaque
Calcified Peyronie&[prime]s plaque (CPP) is an ectopic calcification at the tunica albuginea (TA) - corpus cavernosum interface within the human penis. Previously, CPP has been described as being of bone phenotype; however, the mechanistic processes resulting in mineralization are still unknown. Through advanced correlative microscopy and material science approaches, we aim to illustrate that CPP is a regulated biochemical process that involves intervening events associated with multiple enzymatic activities and matrix protein synthesis.
Two surgically excised CPP (n = 2) were fixed, dehydrated, scanned with a X-ray micro computed tomography (micro-XCT), and processed for histology. Sections were stained with H&E (matrix vs. cell nuclei), trichrome (collagen), and Verhoff&[prime]s stain (elastin). Mineral forming and resorbing enzymes such as alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) activities were localized. Immunolocalization of non-collagenous proteins (NCPs): osteocalcin (OCN), and osteopontin (OPN) was performed using immunogold labeling on ultrathin sections, and were viewed under a scanning transmission electron microscope (STEM) equipped with an energy-dispersive X-ray spectroscopy detector (EDS) for elemental analysis.
Cells were localized at the ALP positive mineralizing front (red arrows). TRAP (blue arrows) was identified in the calcified fibrous matrix. Osteocyte-like cells were found embedded within the mineralized tissue (STEM image). OPN was substantially distributed in the non-calcified fibrous tissue adjacent (red asterisk) to calcified plaque, while OCN was localized specifically in calcified plaque (blue asterisk). High resolution images illustrated formation of inorganic nanoparticles within the ECM (black lines) and site-specific EDS revealed Ca and P in CPP.
The high content of Ca, P, and collagen fibrous tissue within CPP was similar to that of bone. The enzymatic activities associated with osteoblasts (ALP) and osteoclasts (TRAP) as well as distribution of various NCPs in calcified and non-calcified regions provided insights, in that, CPP could be a progressive mineralization process similar to bone. Therapeutic studies can aim to inhibit the production of, or break down of inorganic nanoparticles and NCPs.
Funding: NIH/NIDCR R01DE022032 (SPH), NIH/NCRR S10RR026645 (SPH), Department of Preventive and Restorative Dental Sciences, School of Dentistry; NIH/NIDDK R21 DK109912 (SPH, MLS), NIDDK/P20DK100863 (MLS), Department of Urology, School of Medicine, UCSF.