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Evolutionary life history theory predicts that tradeoffs among fitness-related phenotypes will occur as a result of resource limitations and/or physiological constraints. Such tradeoffs are defined as the cost(s) incurred on one component of fitness (e.g., reproduction) by the increased expression of another fitness-related trait (e.g., longevity). Only recently have researchers begun to investigate the mechanistic bases of life history tradeoffs. A recent proposal is that reactive oxygen species (ROS) have a central role in shaping life history traits and tradeoffs. Research on disparate animal taxa has highlighted strong correlations between oxidative stress resistance and fitness-related life history traits, for example. Here, I use the model organism Caenorhabditis elegans to test several hypotheses concerning the effects of ROS on life history traits and the manifestation of life history tradeoffs. Additionally, I use heat stress and an alternate food source to explore the responses of life history traits to other forms of physiological stress. Relative fitness and other traits related to reproduction were found to be affected in mostly negative ways by increasing oxidative insult. Lifespan was surprisingly unaffected by oxidative stress, but was modified by temperature. In vivo ROS levels as measured by fluorescent microscopy reveal a tradeoff between antioxidant production and reproduction in this species.

Indiana University-Purdue University Indianapolis (IUPUI) / Signal Transducers and Activators of Transcription 3 (STAT3), a transcription factor expressed in many cell types, including osteoblasts and osteoclasts, is emerging as a key regulator of bone mass and strength. STAT3 mutations cause a rare human immunodeficiency disease characterized by extremely elevated levels of IgE in serum that have associated craniofacial and skeletal features, such as reduced bone mineral density and recurrent pathological fractures. Our microarray data and immunohistochemical staining using a normal rat model have shown that STAT3 mRNA and protein levels markedly increase in response to mechanical loading. In addition, as indicated by STAT3 phosphorylation in MC3T3-E1 osteoblastic cells, STAT3 activity significantly increases in response to 30 to 90 minutes fluid shear stress. In order to further study the role that STAT3 plays in bone responsiveness to loading, tissue-selective STAT3 knockout (KO) mice, in which inactivation of STAT3 occurs in osteoblasts, were generated by breeding the transgenic mice in which Cre recombinase cDNA was cloned downstream of a 3.6 or 2.3 kb fragment of the rat Col1a1 promoter (Col3.6-Cre and Col2.3-Cre, respectively) with a strain of floxed mice in which the two loxP sites flank exons 18-20 of the STAT3 gene were used. Mice engineered with bone selective inactivation of STAT3 in osteoblasts exhibited significantly lower bone mineral density (7-12%, p<0.05) and reduced ultimate force (21-34%, p<0.01) compared to their age-matched littermate controls. The right ulnae of 16-week-old bone specific STAT3 KO mice and the age-matched control mice were loaded with peak forces of 2.5 N and 2.75 N for female and male mice, respectively, at 2 Hz, 120 cycles/day for 3 consecutive days. Mice with inactivation of STAT3 specific in bone were significantly less responsive to mechanical loading than the control mice as indicated by decreased relative mineralizing surface (rMS/BS, 47-59%, p<0.05) and relative bone formation rate (rBFR/BS, 64-75%, p<0.001). Bone responsiveness was equally decreased in mice in which STAT3 is inactivated either in early osteoblasts (Col3.6-Cre) or in mature osteoblasts (Col2.3-Cre). Accumulating evidence indicates that bone metabolism is significantly affected by activities in mitochondria. For instance, although STAT3 is reported to be involved in bone formation and resorption through regulation of nuclear genes, inactivation of STAT3 is shown to disrupt mitochondrial activities and result in an increased level of reactive oxygen species (ROS). Inactivation of STAT3 suppressed load-driven mitochondrial activity, which led to an elevated level of ROS in cultured primary osteoblasts. Oxidative stress induced by administration of buthionine sulfoximine (BSO) significantly inhibits load-induced bone formation in wild type mice. Taken together, the results support the notion that the loss-of-function mutation of STAT3 in osteoblasts and osteocytes diminishes load-driven bone formation and impairs the regulation of oxidative stress in mitochondria.

Indiana University-Purdue University Indianapolis (IUPUI) / The immune system initiates tissue repair following injury. In response to sterile tissue injury, neutrophils infiltrate the tissue to remove tissue debris and subsequently undergo apoptosis. Proper clearance of apoptotic neutrophils in the tissue by recruited macrophages, in a process termed efferocytosis, is critical to facilitate the resolution of inflammation and tissue repair. However, the events leading to suppression of sterile inflammation following efferocytosis, and the contribution of other innate cell types are not clearly defined in an in vivo setting. Using a sterile mouse peritonitis model, we identified IL-4 production from efferocytosing macrophages in the peritoneum that activate invariant NKT cells to produce cytokines including IL-4 and IL-13. Importantly, IL-4 from macrophages functions in autocrine and paracrine circuits to promote alternative activation of peritoneal exudate macrophages and augment type-2 cytokine production from NKT cells to suppress inflammation. The increased peritonitis in mice deficient in IL-4, NKT cells, or IL-4Ra expression on myeloid cells suggested that each is a key component for resolution of sterile inflammation. The phagocyte NADPH oxidase, a multi-subunit enzyme complex we demonstrated to require a physical interaction between the Rac GTPase and the oxidase subunit gp91phox for generation of reactive oxygen species (ROS), is required for production of ROS within macrophage phagosomes containing ingested apoptotic cells. In mice with X-linked chronic granulomatous disease (X-CGD) that lack gp91phox, efferocytosing macrophages were unable to produce ROS and were defective in activating iNKT during sterile peritonitis, resulting in enhanced and prolonged inflammation. Thus, efferocytosis-induced IL-4 production and activation of IL-4-producing iNKT cells by macrophages are immunomodulatory events in an innate immune circuit required to resolve sterile inflammation and promote tissue repair.