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The immune system undergoes marked changes during aging characterized by a state of chronic, low-grade inflammation, so called inflammaging. Domestic dogs are the most morphological and physiological diverse group of mammals, with the widest range in body masses for a single species. Additionally, smaller dogs tend to live significantly longer than larger dogs across all breeds. Body mass is intricately linked to mass-specific metabolism and aging rates, thus, dogs are exemplary for studies in inflammaging. Dermal fibroblasts cells play an important role in skin inflammation, and as such, are a good cell type to determine inflammatory patterns in dogs. Here, we examine aerobic and glycolytic cellular metabolism, and IL-6 concentrations in primary fibroblast cells isolated from small and large, young and old dogs when treated with lipopolysaccharide (LPS) from Escherichia coli to stimulate an inflammatory phenotype. We found no differences in cellular metabolism of any group when treated with LPS. Unlike mice and humans, there was a less drastic amplification of IL-6 concentration after LPS treatment in the geriatric population of dogs compared with puppies. We also found evidence that large breed puppies have significantly less background or control IL-6 concentrations compared with small breed puppies. This implies that the patterns of inflammaging in dogs may be distinct and different from other mammals commonly studied. 

Abstract Animals display tremendous variation in their rates of growth, reproductive output, and longevity. While the physiological and molecular mechanisms that underlie this variation remain poorly understood, the performance of the mitochondrion has emerged as a key player. Mitochondria not only impact the performance of eukaryotes via their capacity to produce ATP, but they also play a role in producing heat and reactive oxygen species and function as a major signaling hub for the cell. The papers included in this special issue emerged from a symposium titled “Inside the Black Box: The Mitochondrial Basis of Life-history Variation and Animal Performance.” Based on studies of diverse animal taxa, three distinct themes emerged from these papers. (1) When linking mitochondrial function to components of fitness, it is crucial that mitochondrial assays are performed in conditions as close as the intracellular conditions experienced by the mitochondria in vivo. (2) Functional plasticity allows mitochondria to retain their performance, as well as that of their host, over a range of exogenous conditions, and selection on mitochondrial and nuclear-derived proteins can optimize the match between the environment and the bioenergetic capacity of the mitochondrion. Finally, (3) studies of wild and wild-derived animals suggest that mitochondria play a central role in animal performance and life history strategy. Taken as a whole, we hope that these papers will foster discussion and inspire new hypotheses and innovations that will further our understanding of the mitochondrial processes that underlie variation in life history traits and animal performance.