Expression of periostin and podoplanin in canine testicular tumours

Periostin (POSTN) and podoplanin (PDPN) are both proteins playing an important role in humans in the diagnosis and study of many malignant tumours. POSTN affects the regulation of intracellular signalling pathways involving protein kinases PI3-K/Akt and focal adhesion kinase, whereas PDPN increases fibroblast migration and affects the structure of the endothelium; both proteins participate in carcinogenesis, by increasing cell migration and intensifying angiogenesis. In veterinary medicine, their expression has been demonstrated in only a few types of neoplasms, however their presence has not been investigated in canine testicular tumours which are common in dogs and represent a reliable animal model for their human counterparts, due to their structure and biological behaviour. In the present retrospective study, 186 canine testicular tumours namely 61 Leydig cell tumours, 64 Sertoli cell tumours and 61 seminomas and 10 normal canine testicles were immunohistochemically tested for expression of POSTN, PDPN and Ki67 antigens. The polymerase chain reaction (PCR) analysis was also performed on stored frozen samples representative of the three tumour types: 10 Leydig cell tumours, 9 Sertoli cell tumours and 9 seminomas, which confirmed the presence of both proteins.

Normal testes were negative for both POSTN and PDPN, whereas 27 (44.3%) Leydig cell tumours, 54 (84.4%) Sertoli cell tumours and 56 (91.8%) seminomas were cytoplasmically positive for POSTN and 23 (37.7%), 49 (77.6%) and 44 (72.1%) were cytoplasmically positive for PDPN respectively. The intensity of POSTN and PDPN immunohistochemical reaction was stronger in Sertoli cell tumours and seminomas than in Leydig cell tumours. In addition, Ki67 antigen expression for both POSTN and PDPN correlated significantly with the number of positive cells and the intensity of the reaction in seminomas and Sertoli cell tumours.

The results showed the absence of expression of POSTN and PDPN in normal canine testes and their expression in neoplastic ones, suggesting a role for these proteins in the carcinogenesis of the testis and encouraging further studies, in particular, on seminomas and Sertoli cell tumours.