Amphibian regeneration and mammalian cancer: Similarities and contrasts from an evolutionary biology perspective: Comparing the regenerative potential of mammalian embryos and urodeles to develop effective strategies against human cancer

"Cell dedifferentiation" versus "evolutionary reversal" theories of cancer: The direct contest of transcriptomic features

Cell dedifferentiation is considered an important hallmark of cancer. The atavistic reversal to a unicellular-like (UC) state is a less widely accepted concept, so far not included in the conventional hallmarks. The activated expression of ontogenetically earlier and evolutionary earlier genes in cancers supports both theories because ontogenesis partially recapitulates phylogenesis during cell differentiation (the cellular biogenetic law). We directly contested both types of gene signatures in stem vs. differentiated and cancer vs. normal cells, using meta-analysis of human single-cell transcriptomes (totally, 38 pairwise comparisons involving over 18,600 cells). Because compared cells can differ in proliferation rate, the correction for cell cycle activity was applied. Taken together as multiple variables in stem vs. differentiated cells analyses, the ontogenetic signature excluded the UC signature from predictive variables, usually even forcing it to change the sign of prediction (from plus to minus). In contrast, in cancer vs. normal cells, the UC signature excluded the ontogenetic signature. Thus, the direct contest decided in favor of the atavistic theory and placed a UC-like state as a central hallmark of cancer, which has a plausible evolutionarily formed mechanism (UC attractor) and can generate other hallmarks. These data suggest a paradigm shift in the understanding of oncogenesis and propose an integrative framework for cancer research. In a practical sense, the upregulation of UC signature over ontogenetic signature indicates potential tumorigenicity, which can be used in early diagnostics and regenerative medicine. For therapy, these results suggest the UC center of cellular networks as a universal target.

Gradistics: An underappreciated dimension in evolutionary space

The growth of complexity is an unsolved and underappreciated problem. We consider possible causes of this growth, hypotheses testing, molecular mechanisms, complexity measures, cases of simplification, and significance for biomedicine. We focus on a general ability of regulation, which is based on the growing information storage and processing capacities, as the main proxy of complexity. Natural selection is indifferent to complexity. However, complexification can be inferred from the same first principle, on which natural selection is founded. Natural selection depends on potentially unlimited reproduction under limited environmental conditions. Because of the demographic pressure, the simple ecological niches become fulfilled and diversified (due to species splitting and divergence). Diversification increases complexity of biocenoses. After the filling and diversification of simple niches, the more complex niches can arise. This is the 'atomic orbitals' (AO) model. Complexity has many shortcomings but it has an advantage. This advantage is ability to regulatory adaptation, including behavioral, formed in the evolution by means of genetic adaptation. Regulatory adaptation is much faster than genetic one because it is based on the information previously accumulated via genetic adaptation and learning. Regulatory adaptation further increases complexity of biocenoses. This is the 'regulatory advantage' (RA) model. The comparison of both models allows testable predictions. We focus on the animal evolution because of the appearance of higher regulatory level (nervous system), which is absent in other lineages, and relevance to humans (including biomedical aspects).

Cancer in Amphibia, a rare phenomenon?

Compared to other animals, the spontaneous occurrence of tumors in wild amphibians is relatively rare, generally limited to specific populations or species. The number of reports of spontaneous tumors in amphibians known up to 1986 was 491 cases in anurans and about 253 cases in urodeles. Similarly, there have been many, unsuccessful attempts to chemically or biologically induce tumors in amphibians. With these considerations, it is inevitable to wonder: do urodeles and anurans have an inherent resistance to cancer? Here, we review the spontaneous and induced occurrence of tumors in amphibians in a timeline, as well as failed attempts to induce tumors in these amphibians. Indeed, recent studies seem to indicate that there is a relationship between regeneration and cancer because regenerating tissues seem to resist tumorigenesis, as opposed to nonregenerative tissues of the same amphibian models. Although the mechanisms that allow regenerating tissues to resist tumorigenesis have not been elucidated, it is worth to note that, in addition to the apparent relationship between regeneration and cancer, amphibians possess characteristics that could contribute to their ability to resist the development of neoplastic events. The implications of these features in cancer susceptibility are discussed.

Biomimetic immunomodulation strategies for effective tissue repair and restoration

Inflammation plays a central role in wound healing following injury or disease and is mediated by a precise cascade of cellular and molecular events. Unresolved inflammatory processes lead to chronic inflammation and fibrosis, which can result in prolonged wound healing lasting months or years that hampers tissue function. Therapeutic interventions mediated by immunomodulatory drugs, cells, or biomaterials, are therefore most effective during the inflammatory phase of wound healing when a pro-regenerative environment is essential. In this review, we discuss the advantages of exploiting knowledge of the native tissue microenvironment to develop therapeutics capable of modulating the immune response and promoting functional tissue repair. In particular, we provide examples of the most recent biomimetic platforms proposed to accomplish this goal, with an emphasis on those able to induce macrophage polarization towards a pro-regenerative phenotype.