Peritubular Myoid Cells and Protection of Sperm Stem Cells
Peritubular myoid cells do NOT directly protect sperm stem cells from large molecules—this protective function is performed by the blood-testis barrier, which is formed by Sertoli cells through tight junctions, not by peritubular myoid cells. 1, 2
The Actual Protective Mechanism
The blood-testis barrier, created by tight junctions between Sertoli cells (not peritubular myoid cells), is what protects sperm stem cells from systemic immune surveillance and large molecules. 1, 2 This distinction is clinically critical because:
- The blood-testis barrier's protective function creates theoretical risks of reintroducing malignant cells when performing testicular tissue cryopreservation and autotransplantation in cancer patients, as the barrier may shield cancer cells from immune detection. 1, 2
What Peritubular Myoid Cells Actually Do
Peritubular myoid cells serve entirely different functions that support spermatogenesis but do not involve molecular barrier protection:
Structural and Contractile Functions
- They form the walls of seminiferous tubules and are responsible for tubular contractility and sperm transport through their abundant actin filaments. 3, 4
- They provide structural integrity to the tubule through their myofibroblast-like properties. 4, 5
Paracrine Signaling and Niche Support
- They contribute to the spermatogonial stem cell niche through secretion of paracrine factors, not through physical barrier formation. 3
- They secrete extracellular matrix components (fibronectin, collagens, proteoglycans) and growth factors (PModS, TGF-β, IGF-I, activin-A) that regulate Sertoli cell function and spermatogenesis. 4, 6
- Wnt/β-catenin signaling in peritubular myoid cells is essential for maintaining their function and supporting spermatogenesis. 7
Immune Surveillance Role
- They participate in immune surveillance of the testis through cytokine production and Toll-like receptor activation, but this is an inflammatory response mechanism, not a protective barrier against large molecules. 3
- They express purinergic receptors (P2RX4 and P2RX7) that respond to extracellular ATP as a danger signal, promoting inflammatory responses. 3
Clinical Pitfall to Avoid
Do not confuse the structural location of peritubular myoid cells (surrounding tubules) with the functional location of the blood-testis barrier (between Sertoli cells). The peritubular cells are outside the seminiferous epithelium and therefore cannot form a selective permeability barrier for molecules entering the tubule. 4, 5