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The Growth and Differentiation Capacity of Porcine Renal Papilla Progenitor Cells Decline with Passaging

When challenged by an ischemic insult, such as that accompanying traumatic hemorrhage, the kidney undergoes functional recovery via replacement of cells. Different theories about the cellular mechanisms behind this endogenous regeneration exist, however recent studies have identified a population of renal stem/progenitor cells from the renal papillae. With the increased use of swine in, for example, hemorrhagic shock models, we aimed to isolate and characterize progenitor cells from the renal papillae from pig kidneys. After excision and collagenase digestion of renal papillae, non‐adherent cells were removed after 2 days, and the ensuing renal progenitor cell (RPC) population was expanded under normal culture conditions. At passages 2 and 6, RPCs were examined for their: growth kinetics; expression of markers CD24, CD133, CD90, and NFATC1 via flow cytometry; and potential to differentiate into osteoblasts and adipocytes. Additionally, passage 2 RPCs were used in a mixed lymphocyte reaction to determine immunomodulatory activity. At passage 2, RPCs displayed a characteristic spindle‐shaped morphology with substantial proliferative capacity. By passage 6, accelerated vacuolization and minimal growth was seen in RPCs. Flow cytometry revealed that 96.3% of RPCs at passage 2 expressed CD24, which was dramatically reduced to 23.9% at passage 6. Expression of CD90 at the two passages was similar (44.4% and 47.2% at passage 2 and 6, respectively), while there was low expression (~10%) of CD133 or NFATC1 at both passages. Differentiation studies revealed that RPCs were able to differentiate into both adipocytes and osteoblasts at passage 2, but not at passage 6. Moreover, RPCs from passage 2 increased the amounts of IL‐6 and IL‐8 (p<0.05) released in the mixed lymphocyte reaction, but tended to reduce the amount of Interferon‐γ released. Taken together, these data further indicate that porcine RPCs are heterogeneous and lose their “stemness” properties with serial passaging. However, their immunomodulatory capabilities lend them the potential to be leveraged as therapies or therapeutic targets. In instances of ischemic insult, augmentation of RPCs may potentiate the recovery and regenerative properties of the kidney. Further work exploring the characteristics of renal stem cell populations, their interactions with resuscitation fluids, and their efficacy in pre‐clinical animal models is warranted.