AGE-RELATED CHANGES TO MACROPHAGES AFFECT FRACTURE HEALING

Abstract Fracture healing follows a strict temporal sequence characterized by an initial inflammatory phase. Perturbation of the inflammatory phase may be responsible for the poorer fracture healing outcomes in older adults. Herein, we examine age-related changes to the macrophage during fracture healing. Macrophages regulate inflammation through pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes. Anti-inflammatory activity is promoted via activation of triggering receptor expressed on myeloid cells 2 (TREM2). Tibia fractures were made in old (24 months) and young (3 months) mice. Immune cells from the fracture callus were analyzed via RNAseq and FACS, and fracture healing was evaluated histologically. Old mice demonstrated significantly delayed fracture healing compared to young (p<0.05). The quantity of infiltrating macrophages into the fracture callus was similar in young and old mice. However, 1222 genes were significantly differentially regulated (FDR<0.1) in callus macrophages from old mice compared to young, and old macrophages demonstrated a more pro-inflammatory phenotype. TREM2 expression was increased in macrophages after fracture in both groups but was significantly less in old mice compared to young via RNAseq and FACS (FDR<0.1, p<0.05). TREM2-/- mice demonstrated increased pro-inflammatory cytokine expression within the callus with resulting significant delays in fracture healing compared to age-matched controls (p<0.05). Inhibition of macrophage infiltration into the fracture callus significantly improved fracture healing in old mice compared to age-matched controls. Age-related changes to macrophages, including increased pro-inflammatory cytokine expression and dysregulated TREM2 expression, may explain fracture healing deficits observed in older adults. Therapeutically targeting macrophages may improve management of fractures in older adults.

We have recently demonstrated that dietary nitrate, a source of nitric oxide via the enterosalivary pathway, can improve muscle contractile function in healthy older men and women. Nitrate ingestion has also been shown to reduce blood pressure in older individuals. However, the optimal dose for eliciting these beneficial effects is unknown. We therefore performed a randomized, double-blind, crossover study to determine the effects of ingesting 3.3 mL/kg of beetroot juice (BRJ) containing 0, 212, or 425 µmol/kg of nitrate in six healthy older (age 69±3 y) subjects. Maximal knee extensor speed (Vmax) and power (Pmax) were measured 2 h after BRJ ingestion using isokinetic dynamometry; blood pressure was monitored periodically throughout each study. Mean arterial pressure (in mmHg) was lower (P<0.05) after the high (80±4) vs. the low (84±3) or placebo (88±2) doses. Vmax (in rad/s), however, was higher (P<0.05) after the low dose (11.7±0.8), but not the high dose (10.8±1.0), compared to the placebo (10.5±1.0). Pmax (in W/kg) also tended to be higher (P=0.11) in the low (3.9±0.5) compared to the placebo (3.7±0.5) or high (3.7±0.5) trials. Five out of six subjects achieved a higher Vmax and Pmax after the low vs. the high dose. We conclude that dietary nitrate has differential effects on muscle function and blood pressure in older individuals. A high dose of nitrate intake further lowers blood pressure but does not enhance muscle contractility as much as a lower dose. Supported by Indiana University Purdue University Indianapolis and by the NIA (R21 AG053606)

AGE-RELATED CHANGES TO MACROPHAGES AFFECT FRACTURE HEALING
Daniel Clark, 1 Theodore Miclau, 1 Mary Nakamura, 1 and Ralph Marcucio 1 , 1. University of California San Francisco, San Francisco, California, United States Fracture healing follows a strict temporal sequence characterized by an initial inflammatory phase. Perturbation of the inflammatory phase may be responsible for the poorer fracture healing outcomes in older adults. Herein, we examine age-related changes to the macrophage during fracture healing. Macrophages regulate inflammation through pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes. Anti-inflammatory activity is promoted via activation of triggering receptor expressed on myeloid cells 2 (TREM2). Tibia fractures were made in old (24 months) and young (3 months) mice. Immune cells from the fracture callus were analyzed via RNAseq and FACS, and fracture healing was evaluated histologically. Old mice demonstrated significantly delayed fracture healing compared to young (p<0.05). The quantity of infiltrating macrophages into the fracture callus was similar in young and old mice. However, 1222 genes were significantly differentially regulated (FDR<0.1) in callus macrophages from old mice compared to young, and old macrophages demonstrated a more pro-inflammatory phenotype. TREM2 expression was increased in macrophages after fracture in both groups but was significantly less in old mice compared to young via RNAseq and FACS (FDR<0.1, p<0.05). TREM2-/-mice demonstrated increased pro-inflammatory cytokine expression within the callus with resulting significant delays in fracture healing compared to age-matched controls (p<0.05). Inhibition of macrophage infiltration into the fracture callus significantly improved fracture healing in old mice compared to age-matched controls.
Age-related changes to macrophages, including increased pro-inflammatory cytokine expression and dysregulated TREM2 expression, may explain fracture healing deficits observed in older adults. Therapeutically targeting macrophages may improve management of fractures in older adults.

THE ROLE OF PERCEIVED SOCIAL SUPPORT AND PRUDENT DIET INTAKE ON ALLOSTATIC LOAD AMONG OLDER ADULTS
Danielle D'Amico, 1 Vivian Huang, 1 Geneva Millett, 1 Alexandra J. Fiocco 1 , 1. Ryerson University, Toronto, Ontario, Canada Allostatic load (AL), an index of multisystem physiological dysregulation due to chronic stress, has been identified as a predictor of poor health outcomes in late life. Research suggests that perceived social support (PSS) improves health outcomes by buffering the negative effects of stress on wellbeing and increasing health promoting behaviours including consumption of a healthy prudent diet (i.e., fruits, vegetables, lean meats, nuts, and seeds). Research to date has independently demonstrated that higher PSS and prudent diet intake have an effect on AL. A paucity of research, however, has examined how dietary consumption and PSS interact to effect AL in older adults. The objective of this study was to examine the interaction between PSS and prudent diet pattern on AL in 164 non-demented, community-dwelling older adults (Mage= 68.5(.52), 64% female). PSS and diet intake were measured using the Perceived Social Support Scale and the EPIC-Norfolk Food Frequency Questionnaire, respectively. AL was composed of 16 biomarkers stemming from neuroendocrine, metabolic, inflammatory, and cardiovascular systems, stratified by sex. Controlling for age and usual daily energy intake, higher prudent diet consumption (B=-2.04, p=.001), but not PSS, was associated with lower AL. Moderation analysis revealed that higher prudent diet intake was associated with lower AL only for those with low PSS (B=-.83, p=.0006) and mean level of PSS (B=-.43, p=.02). These findings suggest that chronic biological stress may be mitigated by consuming a healthy diet specifically for older adults with lower social support and may further inform intervention strategies to promote healthy aging.

METABOLOMICS IN MEN WITH DISTINCT INFLAMMATION TRAJECTORIES FOLLOWING HIP FRACTURE REVEAL RESPONSE MECHANISMS
Shabnam Salimi, 1 Alice Ryan, 1 Denise Orwig, 1 Ann Gruber-Baldini, 1 Jack Guralnik, 1 Jay S. Magaziner, 1 and March Hochberg 1 , 1. University of Maryland Baltimore School of Medicine, Baltimore, Maryland, United States Introduction: Following hip fracture, men exhibit different trajectories of inflammation: high (HiInf) vs. low (LoInf). The purpose of this analyses was to compare metabolomics Between these groups. Methods: Seven men with HiInf and 7 with LoInf were randomly selected to quantify serum metabolites at baseline, 2, and 6 months following hip fracture in Baltimore Hip Study-7. We performed analysis of variance and mixed effects models. A p <0.05 was considered significant. Results: At baseline, men with HiInf had higher oxidative stress, lipid-related inflammatory markers, and antioxidant compounds compared to Innovation in Aging, 2019, Vol. 3, No. S1