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cells can also be obtained from synovium, dermis, periodontal ligament, dental pulp and other adult tissues [8-12]. However, the most primitive MSCs are nowadays isolated from umbilical cord blood and from umbilical cord tissue, known as Wharton’s jelly (Figure 1). In the veterinary field there are many species from which the umbilical cord can be collected [3, 13, 14]. The preferable method for acquiring an umbilical cord is by caesarean section, when the risk of contamination is reduced to a minimum. Canine umbilical cord blood and Wharton’s jelly can serve as good sources of MSCs, which is why many different isolation protocols have already been established [14-17]. On the other hand, the MSCs used in feline regenerative medicine are mostly isolated from bone marrow, Arch Vet Sci Med 2020; 3 (2):40-50 DOI: 10.26502/avsm.014 Archives of Veterinary Science and Medicine 42 adipose tissue or amniotic fluid through minimal manipulation, but not from umbilical cord up to now [18-20]. The first isolation of equine MSCs from umbilical cord blood was published in 2007 by Koch et al [13]. Since then many studies have described different application strategies for equine MSCs derived from both umbilical cord blood and Wharton´s jelly from horses or other larger species such as sheep, goats and cows [13, 21-27]. However, due to their anatomical, genetic and physiological similarities with humans, pigs serve as the best preclinical model for safety evaluation and clinical application of UC MSCs in veterinary practice as well as in translation studies for human medicine [28, 29]. Nowadays, standard protocols for effective isolation of Wharton´s jelly MSCs from different animals and tissues have been established, thus opening up possibilities for cell-based therapies in veterinary clinics [14, 15]. Figure 1: Schematic design of UCMSC based therapy in veterinary practice: animal donors, umbilical cord derived MSCs, minimal properties, banking and therapy. 3. Characterization of MSCs Mesenchymal stem cells are multipotent cells capable of differentiating into multiple lineages. According to the International Society for Cellular Therapy they have to meet three criteria, which are plastic adherence, expression of specific cell surface markers and three lineage differentiation potential [31]. Even though these criteria were firstly established for human MSCs, they also apply to animal MSCs [31, 32]. MSCs show spindle-like and fibroblastic morphology, and after the first two or three passages they express stromal markers CD105, CD73 and CD90, and they lacki hematopoietic factors such as CD45, CD34, CD14 or CD11b, CD79a or CD19 and HLA class [31, 33, 34]. According to the literature, there are also other CD markers expressed by umbilical cord-derived MSCs such as CD44 or CD29 [21]. MSCs are assumed to differentiate into Arch Vet Sci Med 2020; 3 (2):40-50 DOI: 10.26502/avsm.014 Archives of Veterinary Science and Medicine 43 osteoblasts, chondrocytes and adipocytes, proven by staining with Alizarin Red, Alcian blue and Oil Red O respectively [31]. Interestingly, some studies do not support UC MSC differentiation into adipocytes, while others demonstrate their adipogenic potential [21, 30, 33]. Three lineage differentiations of UC MSCs can also be proven by means of RT- PCR and specific gene expression [35]. Chondrogenic differentiation of UC MSCs is associated with expression of Sox9, COL1 and COL2 genes [36]. Genes specific for osteogenic differentiation are osteonectin and Runx2 [37], but there are also other markers used in human medicine such as ALP (alkaline phosphatase), PSAT1, HSP27, OAT and CRB1 [38]. Adipogenic differentiation is routinely demonstrated through the expression of lipoprotein lipase (LPL), leptin and fatty acid-binding protein 4 (FABP4) [16]. In addition, under specific experimental conditions MSCs can give rise to other cell types, such as hepatocytes, which was indicated through the expression of albumin and cytokeratin 18. Neural differentiation potential was confirmed with glial fibrillary acidic protein (GFAP) and microtubule-associated protein 2 (MAP2) [16, 39]. As a result of the effort to establish what particular tissue-specific cells can differentiate into in vitro or in vivo, there is a need to analyse the gene-expression patterns of differentiated MSCs together with their protein content. 4. Preclinical and Clinical Studies As the idea of using MSC-based therapy developed, animals were first selected for safety testing. Very soon MSCs made their way out from laboratories, from mouse and rat experimental studies into veterinary clinics, where pets are “tested” and treated side-by-side [3]. Developed veterinary approaches give us opportunities for safety studies and for researching the most appropriate MSC application strategies in disorders which pets and humans have in common, whether identical or similar [3]. Donors Sources Stem cells Disease Dog Skin Bone marrow Adipose tissue Umbilical cord iPSCs, NPCs MSC More primitive > MSC Kidney failure Neurologic disorders Cutaneous wound Bone and cartilage defects Cat Bone marrow Adipose tissue MSC Kidney failure Neurologic disorders Horse Bone marrow Adipose tissue Umbilical cord MSC More primitive > MSC Tendon cyst Bone and cartilage defect Pig Umbilical cord More primitive > MSC Bone and cartilage