Telomerase activity in clinically normal dogs and dogs with malignant lymphoma

Telomerase activity and telomerase reverse transcriptase catalytic subunit expression in canine lymphoma: correlation with Ki67 immunoreactivity

Increased telomerase activity (TA) has been found in human and canine solid tumours, stem cells and somatic tissues with enhanced proliferative potential. The relationship between TA in normal and malignant lymphoid tissues remains unclear. The TA and the expression of canine telomerase reverse transcriptase catalytic subunit (dogTERT) messenger RNA (mRNA) were analyzed in malignant lymph nodes from 30 dogs with lymphoma, from two dogs with non-neoplastic illness and from two clinically normal dogs, demonstrating a statistically significant difference between TA in lymphoma lymph nodes (n = 30) and normal nodes (n = 4) but no significant difference in dogTERT mRNA expression. In addition, the expression of telomerase reverse transcriptase catalytic subunit (TERT) protein and Ki67 was analyzed in malignant lymph nodes from 10 dogs with lymphoma and from two clinically normal dogs by immunohistochemistry. TERT expression was associated with Ki67 in all lymphoma nodes (n = 10), and differences were illustrated between TERT and Ki67 expression between lymphoma (n = 10) and non-lymphoma (n = 2) nodes. This data support further investigation of telomerase in canine haematopoietic neoplasia through large-scale prospective studies.

Telomeres and telomerase: Biological and clinical importance in dogs

In recent years in human oncology the enzyme telomerase has emerged as an ideal target for cancer therapy. This has led to the assessment of telomerase in cancers in companion animals, mainly dogs and these studies confirm that in dogs, like humans, telomere maintenance by telomerase is the primary mechanism by which cancer cells overcome their mortality and extend their lifespan. This review aims to provide an introduction to the biology of telomeres and telomerase and to discuss some of the telomere/telomerase directed therapeutic methodologies currently under development which may be of benefit to the canine cancer patient.

Telomeres and telomerase biology in vertebrates: progress towards a non-human model for replicative senescence and ageing

Studies on telomere and telomerase biology are fundamental to the understanding of human ageing and age-related diseases such as cancer. However, human studies of whole body ageing are hampered by the lack of suitable fully reflective animal model systems, the wild-type mouse model being unsuitable due to differences in telomere biology. Here we summarise recent data on the biology of telomeres, telomerase, and the tumour suppressor protein p53 in various animals, and examine their possible roles in replicative senescence, ageing, and tumourigenesis. The advantages and disadvantages of various animals as model systems for whole body ageing in humans are discussed.

Replicative senescence in sheep fibroblasts is a p53 dependent process

Studies on telomere and telomerase biology are fundamental to the understanding of human ageing, and age-related diseases such as cancer. However, human studies are hampered by the lack of fully reflective animal model systems. Here we describe basic studies of telomere length and telomerase activity in sheep tissues and cells. Terminal restriction fragment lengths from sheep tissues ranged from 9 to 23 kb, with telomerase activity present in testis but suppressed in somatic tissues. Sheep fibroblasts had a finite lifespan in culture, after which the cells entered senescence. During in vitro growth the mean terminal restriction fragment lengths decreased in size at a rate of 210 and 350 bp per population doubling (PD). Senescent skin fibroblasts had increased levels of p53 and p21WAF1 compared to young cells. Incubation of senescent cells with siRNA duplexes specific for p53 suppressed p53 expression and allowed the cells to re-enter the cell cycle. Five PDs beyond senescence the siRNA-treated cells reached a second proliferative barrier. This study shows that telomere biology in sheep is similar to that in humans, with senescence in sheep GM03550 fibroblasts being a telomere-driven, p53-(p21WAF1)-dependent process. Therefore sheep may represent an alternative model system for studying telomere biology, replicative senescence, and by implication human ageing.

Lymphoma updates

Canine and feline lymphoma is a common hematopoietic malignancy that generally responds well to systemic chemotherapy. In dogs, several recent investigations have underscored the beneficial effects of adjunctive radiation therapy for the treatment of multicentric lymphoma. With the emergence of effective immunotherapeutic agents against non-Hodgkin's lymphoma in people, some of these specific targeted immunotherapeutics may soon be a viable option for treating lymphoid malignancies in dogs. Although the effective and durable treatment of feline lymphoma remains disappointing, the identification of environmental etiologic factors may help to shape future recommendations for disease prevention. It is only reasonable to assume that as our fundamental understanding of lymphoid malignancies grows, better diagnostic tools, predictive markers, and therapeutic options will also emerge.