ABSTRACT Background Although antiretroviral therapies (ART) have substantially reduced HIV‐associated mortality, HIV infection is still linked to an unexplained earlier onset and increased incidence of aging‐associated conditions like sarcopenia that negatively impact healthspan. Complex syndromes, like sarcopenia, often arise from a combination of genetic and environmental factors, so in this study, we investigated effects of short‐term treatment with emtricitabine (2′,3′‐dideoxy‐5‐fluoro‐3′‐thiacytidine; FTC), an FDA‐approved ART, on skeletal muscle DNA methylation patterns and transcriptome‐wide responses in a male murine model of HIV phenotypic biology (Tg26 mice). Methods We treated 6‐month‐old male Tg26 (+/−) mice or wildtype (WT) littermates on a C57BL/6 genetic background with FTC in the drinking water for 1 month; control groups received drinking water vehicle alone (VEH). Muscle function and body composition were measured longitudinally. Skeletal muscle methylation patterns, transcriptional changes and histological features were quantified at sacrifice. Results Although neither gross structural nor functional muscle deficits were observed in this short‐term study with ART usage, relative decreases in muscle endurance measured by hang time over the study were twofold more severe in the Tg26 as compared to WT mice (p = 0.0453), and markers of myogenic cell maturation (Myf5, Myf6) were disrupted in the Tg26 HIV model as compared to WT littermates in a manner exacerbated by FTC treatment. Fat mass, measured by DXA, also tended (p = 0.085) to be uniquely increased by FTC treatment in the Tg26 mice over the study. Differential methylation patterns and pathway enrichment data suggested that the presence of an HIV phenotype and exposure to an FTC regimen altered the methylation status in skeletal muscle genes such as Camk2B, Pcolce2 and Lima1 in a manner consistent with promoting eventual functional impairment in muscle. Additionally, RNAseq revealed differential gene expression profiles and key regulatory pathways including cellular differentiation, regulation of lipid metabolism and neuroactive ligand‐receptor interactions. Lipodystrophy‐related genes including Lep and Adipoq involved in fat distribution and metabolism along with skeletal genes related to regulation of muscle strength were affected by the presence of an HIV phenotype and ART treatment. Conclusions The current study provides insights into mechanisms by which a clinically relevant ART may influence DNA methylation and transcriptome changes in skeletal muscle in the context of HIV biology. The differentially regulated pathways suggest novel targets for understanding and eventually abrogating the harmful effects of long‐term ART use in people living with HIV (PLWH) on skeletal muscle mass and function.

Tryptophan is an essential amino acid metabolized in the body primarily through enzymatic degradation involving indoleamine and tryptophan 2,3-dioxygenase (IDO and TDO), generating kynurenine as the initial step, and ultimately leads to multiple bioactive metabolites including NAD and quinolinic acid. We have previously shown that kynurenine accumulates with age and contributes to age-induced bone loss, and we hypothesized that knocking out IDO1 might be protective against bone loss in states such as aging by decreasing kynurenine levels in osteoprogenitor cells. To begin to characterize the target cell responsible for this effect, we generated conditional IDO1 knockout (KO) mouse model using floxed mice created by EUCOMM/IMPC and an osteoprogenitor-expressed (Osterix-promoter-driven) Cre possessing a Tet-off element. In an IACUC-approved protocol using male/female conditional IDO1 KO (cKO) C57BL/6 mice, we found sex-dependent differences in changes in bone mass. We report that bone mineral density (BMD) at the femoral (but not spinal) site was significantly higher in 21-month-old cKO male mice compared to wild-type (WT). In contrast, spinal (but not femoral) BMD was higher in 21-month-old female cKO mice versus WT. There were no significant differences in trabecular μCT parameters in female mice; however, male cKO mice showed increased trabecular number and decreased trabecular separation. In contrast, there were no differences between male mice in cortical bone measurements whereas female cKO mice had decreased cortical thickness. These data suggest that there are sex-dependent differences in the role of IDO1 in osteoprogenitor cells with aging.

Excessive mineralocorticoid receptor (MR) activation in the heart and vasculature leads to pathological effects such as extracellular matrix accumulation, oxidative stress, and sustained inflammation. While MR's role in cardiovascular and renal systems is well understood, MR signaling has also been implicated as a key driver of homeostasis and pathological changes in several other body systems including skeletal muscle and adipose tissue. The glucocorticoid receptor (GR) and MR are structurally and functionally linked, sharing 95% similarity in DNA binding domains and recognizing many of the same hormone response elements (HRE) as transcriptional regulators of target genes. The role of GR in bone has been defined through several mechanistic studies, whereas the role of MR in bone is understudied. Because mineralocorticoid signaling regulates renal sodium and calcium handling, chronic hyperaldosteronism may indirectly disrupt skeletal homeostasis through urinary calcium wasting and secondary alterations in parathyroid hormone signaling. Furthermore, MR inhibition through MR antagonists (MRAs) has been associated with beneficial skeletal effects, particularly in settings of hyperaldosteronism and 11β-HSD2 deficiency. In this review, we present historical and current scientific findings on the role of genomic MR signaling in bone and extra-skeletal tissues that may be involved in crosstalk with the skeletal system. Furthermore, we also highlight the availability of tools to study MR signaling in the context of the musculoskeletal system.

The aryl hydrocarbon receptor (AhR) is activated by kynurenine (Kyn), a tryptophan metabolite that accumulates with age, and this process drives osteoblast dysfunction. However, Kyn can be further metabolized, and the extent to which downstream metabolite molecules activate AhR in mesenchymal lineage cells and impact bone formation activity was unclear from previous studies. We hypothesized that Kyn metabolites activate AhR signaling and impair bone formation to drive bone loss. In the current study, tryptophan, Kyn, and 3-hydroxy-kynurenine (3HK) dose-dependently activated AhR in mesenchymal stem cell models, with 3HK being the most potent activator. Treating mesenchymal stem cells with 3HK and 3-hydroxyanthranilic acid (3HAA) dose-dependently induced DNA damage that at lower concentrations induced senescence and at higher concentrations promoted apoptotic cell death. This cell death was rescued upon scavenging reactive oxygen species with N-acetylcysteine, suggesting a mechanism of apoptosis related to increased oxidative stress. With regards to bone formation activity, the differentiation of primary bone marrow stromal cells into matrix-producing osteoblasts was blunted upon the introduction of Kyn, 3HK or 3HAA into osteogenic differentiation media, with 3HK and 3HAA inducing the greatest deficits in mineralized matrix production. In vivo administration of 3HAA to C57BL/6 mice was detrimental to whole-body bone mineral density and cortical bone mass, although trabecular bone was largely unaffected. Together, our results suggest that several intermediate metabolites in the tryptophan-Kyn pathway activate AhR and impede the differentiation of osteoblasts by inducing DNA damage, senescence and oxidative stress, which may have negative consequences for cortical bone in vivo.

HIV-associated mortality has been reduced by antiretroviral therapies (ART), but prolonged ART usage by people living with HIV (PLWH) is associated with frailty and poor healthspan. Mechanisms driving this phenomenon are not fully known, but clinical and preclinical studies suggest that HIV and ART may drive aberrant activation of the aryl hydrocarbon receptor (AhR) by kynurenine (KYN), an endogenous metabolite of tryptophan. Therefore, we investigated whether the combination of an HIV-like phenotype (Tg26 mice) and treatment with ART (emtricitabine; FTC) in female mice alters skeletal muscle homeostasis in an AhR-dependent manner to promote premature muscle aging phenotypes. Short-term FTC treatment increased serum KYN:tryptophan ratio and activated AhR signaling in skeletal muscle of Tg26 mice, although the study duration was not sufficient to induce significant FTC-related functional decline. FTC, alone or in combination with other ART (tenofovir alafenamide and tenofovir disproxil fumarate), activated AhR and induced senescence of female myoblasts in a manner comparable to KYN. Sequencing-based studies revealed targets and pathways related to the impacts of an HIV phenotype and ART in female skeletal muscle, including Gnas (encoding Gsα protein, critical for muscle glucose metabolism), inflammatory pathways, and lipid metabolism. Our studies suggest that the combined presence of HIV viral proteins and exposure to ART induced activation of AhR-mediated signaling in female muscle, as well as widespread changes across the skeletal muscle transcriptome and methylation landscape that may contribute to development of muscle dysfunction. This suggests AhR may represent a novel target for addressing persistent disparities in healthspan for PLWH.

Exercise may improve dual-tasking and mobility impairments among people living with dementia (PWD), but more evidence is needed. The purpose of this pilot randomized controlled trial (RCT) was to determine the effect of six months of exercise on single- and dual-task mobility compared to usual care alone in PWD. This assessor-blinded RCT (1:1) included n = 21 PWD in the usual care and n = 21 PWD in the exercise group at two residential care facilities (Age = 82 years, 35% female, Montreal Cognitive Assessment (MoCA) = 10.2±5.9; NCT05488951). The physical therapist-led adapted Otago Exercise Program involved 30 minutes of lower body strength and balance exercises and 30 minutes walking 3x/week for 6 months in groups of 5-7. At baseline and 6 months, participants completed two trials of single- (walk 4m) and dual-task gait (walk 4m while naming words), and single-task timed-up-and-go (TUG), and dual-task TUG with a category task using APDM inertial sensors. We measured double limb support (%), gait speed (m/s), and stride length (m) for gait, and duration (s), turns angle (°), and turn velocity (m/s) for the TUG. Intent-to-treat (ITT) and per protocol (all usual care and exercisers with ≥2/3 adherence) analyses were performed. We controlled for age, race, sex, and the MoCA. In the ITT analysis, exercise provoked faster dual-task gait speed (+0.03 m/s, p = 0.006), increased single-task TUG turn velocity (+24.01 m/s, p = 0.001), decreased dual-task TUG duration (-11.54 s, p = 0.01), and increased dual-task TUG turn velocity (+18.96 m/s, p<0.001). In the per Protocol analysis, both the exercise (-22.04%, p = 0.007, n = 9) and usual care groups (-18.90%, p<0.001, n = 21) decreased double limb support during single-task gait. Additionally, only the exercise group increased stride length during dual-task gait (+0.24 m, p = 0.007) and increased turn velocity during the single- (+28.27 m/s, p = 0.002) and dual-task TUG (+17.75 m/s, p = 0.002). Six months of exercise improved both single- and dual-task mobility in PWD compared to usual care. Similar findings in both ITT and per protocol analyses indicate that exercising in any amount can improve dual-task mobility in PWD. Our findings may inform therapeutic interventions for improving dual-task mobility in PWD in residential care facilities.

Physiological changes, including metabolic and cellular aging, as well as increased inflammation, occur in people living with dementia (PWD). While there is existing evidence in other populations suggesting that exercise may improve physiological outcomes, their impact in PWD remains unclear. This randomized controlled trial (RCT) aimed to assess the effects of exercise on serum levels of metabolic aging, cellular aging, and inflammatory blood biomarkers relative to usual care alone in PWD. This pilot RCT involved n=42 PWD (exercise n=21; usual care n=21) in one nursing home and one assisted living facility (NCT05488951). The adapted Otago Exercise Program involved 30 minutes of tailored lower body strength and balance exercises and 30 minutes of walking 3x/week for 6 months. We drew fasted blood at baseline and 6 months. Blood samples were stored at -80°F and analyzed for metabolic aging (kynurenine), cellular aging (telomere length), and inflammatory biomarkers (interleukin-6, IL-1b, interferon alpha2, IFNg, tumor necrosis factor a, chemokine ligand 2, IL-8, IL-10, IL-12p70, IL-17A, IL-18, IL-23, IL-33). Generalized mixed models were used for intent-to-treat (n=42) and per protocol analyses (usual care: n=21; n=9 exercisers with ≥2/3 adherence), controlling for age, race, sex, and the Montreal Cognitive Assessment. The intent-to-treat analysis revealed no differences in physiological biomarkers between groups. The per protocol analysis revealed a trend for reduced inflammation in IL-1b (exercise: 9.73 to 6.16 pg/mL; usual care:10.51 to 15.46 pg/mL; p=0.09) and IL-8 (exercise: 39.34 to 25.92 pg/mL; usual care:78.99 to 93.04 pg/mL; p=0.09). Additionally, the control group increased telomere length compared to the exercise group (exercise:8.0 to 7.9 kb; usual care:7.9 to 8.7 kb; p=0.01). The trend for exercise reducing inflammation in the per protocol analysis suggests that a greater amount of exercise (i.e., ≥2/3 exercise adherence) may be necessary to reduce inflammation in PWD. The nuanced relationship between exercise reducing cellular aging in the usual care group requires further exploration, as we had a small sample size in our per protocol analysis. Our pilot findings may inform a larger RCT to determine a potential interplay between exercise and physiological biomarkers in PWD.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that is thought to play important roles in aging, oxidative stress, and cellular senescence. We have previously shown that the AhR agonist kynurenine (Kyn), a tryptophan metabolite that increases with age, can induce muscle atrophy in young mice. AhR overexpression can also lead to muscle atrophy and neuromuscular junction degradation. Here we utilized existing GEO data sets from skeletal muscles of aged mice to examine the impact of two longevity-related interventions, calorie restriction (CR) or treatment with the drug rapamycin (RM), on the expression of genes in the Kyn-AhR pathway. Data were examined in four skeletal muscles: soleus, gastrocnemius, tibialis anterior and triceps brachii. Results show that AhR expression increased with age in the triceps but was decreased with CR in the soleus and gastrocnemius. RM treatment did not significantly alter AhR expression in any of the four muscles of aged mice. Three enzymes that convert kynurenine to kynurenic acid in skeletal muscle, Kyat1, Kyat3 and Got2/Kyat4, are known to increase with endurance exercise and all three increased significantly with CR in aged skeletal muscle. In contrast, RM treatment did not increase Kyat1 expression in aged muscle and RM significantly decreased Kyat3 expression levels in muscles from aged mice. Together these data point to kynurenine aminotransferases as mediating some of the positive effects of CR on skeletal muscle with aging, and support prior research suggesting that CR and RM modulate different patterns of muscle-specific gene expression.

Background:Although antiretroviral therapies (ART) have substantially reduced HIV-associated mortality, the increased lifespan achieved by widespread ART deployment has revealed that HIV infection is linked to an unexplained earlier onset and increased incidence of aging-associated conditions like sarcopenia. Complex syndromes, like sarcopenia, often arise from a combination of genetic and environmental factors, so in this study, we investigated effects of short-term treatment with emtricitabine (2',3'-dideoxy-5-fluoro-3'-thiacytidine; FTC), an FDA approved ART, on skeletal muscle DNA methylation patterns and transcriptome-wide responses in a male murine model of HIV phenotypic biology (Tg26 mice). Methods:We treated 6 month old male Tg26 (+/-) mice or wildtype (WT) littermates on a C57BL/6 genetic background with FTC in the drinking water for one month; control groups received drinking water vehicle alone (VEH). Muscle function and body composition were measured longitudinally. Skeletal muscle methylation patterns, transcriptional changes, and histological features were quantified at sacrifice. Results:Although neither gross structural nor functional muscle deficits were observed in this short-term study with ART usage, relative decreases in muscle endurance measured by hang time over the study were 2-fold more severe in the Tg26 as compared to WT mice (p=0.0453), and markers of myogenic cell maturation ( Myf5, Myf6 ) were disrupted in the Tg26 HIV model as compared to WT littermates in a manner exacerbated by FTC treatment. Fat mass, measured by DXA, also tended (p=0.085) to be uniquely increased by FTC treatment in the Tg26 mice over the study. Differential methylation patterns and pathway enrichment data suggested that the presence of an HIV phenotype and exposure to an ART regimen altered the methylation status in skeletal muscle genes such as Camk2B, Pcolce2 and Lima1 in a manner consistent with promoting eventual functional impairment in muscle. Additionally, RNAseq revealed differential gene expression profiles and key regulatory pathways including cellular differentiation, regulation of lipid metabolism, and neuroactive ligand-receptor interactions. Lipodystrophy-related genes including LEP, ADIPOQ and PPARα involved in fat distribution and metabolism along with skeletal genes related to regulation of muscle strength were affected by the presence of an HIV phenotype and ART treatment. Conclusions:The current study provides insights into mechanisms by which a clinically relevant ART may influence DNA methylation and transcriptome changes in skeletal muscle in the context of HIV biology. The differentially regulated pathways suggest novel targets for understanding, and eventually abrogating, the harmful effects of long-term ART use in PLWH on skeletal muscle mass and function.

The aryl hydrocarbon receptor (AhR) is proposed to mediate the frailty-promoting effects of the tryptophan metabolite kynurenine, which increases with age in mice and humans. The goal of the current study was to test whether administration of pharmacological AhR inhibitors, BAY2416964 and CH-223191, could abrogate musculoskeletal decline in aging mice. Female C57BL/6 mice (18 months old) were treated with vehicle (VEH) or 30 mg/kg BAY2416964 (BAY) via daily oral gavage 5 days/week for 8 weeks. A second AhR antagonist, CH-223191, was administered to 16-month-old male and female C57BL/6 mice via intraperitoneal injections (3.3 mg/kg) 3 days/week for 12 weeks. While grip strength declined over time in VEH-treated mice, BAY preserved grip strength in part by improving integrity of neuromuscular junctions (NMJs), an effect replicated during in vitro studies with siRNA against AhR. Cortical bone mass was also greater in BAY- than VEH-treated mice. Similarly, CH-223191 treatment improved cortical bone and showed beneficial effects in skeletal muscle, including reducing oxidative stress as compared with VEH-treated animals. Transcriptomic and proteomic data from BAY-treated mice supported a positive impact of BAY on molecular targets that affect NMJ function. Taken together, these data support AhR as a therapeutic target for improving musculoskeletal health during aging.

People living with dementia (PWD) have upregulated inflammatory pathways, exaggerated metabolic aging, and cellular aging. They also have declines in physical function and heightened fall-risk. Understanding the physiologic factors that influence physical decline and fall-risk in PWD is vital to assess and prevent adverse health outcomes, such as future falls. The purpose of this study was to explore the association between physiological biomarkers, physical decline, and fall-risk in PWD. In this cross-sectional study, we used the baseline data of n=42 PWD in residential care facilities from our pilot randomized controlled trial [NCT05488951]. We assessed fall-risk with the Morse Fall Scale and pulled fall history in the last 6 months from incident reports in medical charts. Participants completed two 4-meter usual pace walking trials. We assessed two trials of maximum quadriceps strength on each leg with a portable dynamometer. We drew fasted blood and measured inflammatory biomarkers (Interleukin(IL)-1b, IL-6, IL-8, IL-10, IL-12p70, IL-17A, IL-18, IL23, IL-33, chemokine ligand 2, tumor necrosis factor-a, human interferon (INF)-a2, INFg), metabolic aging (kynurenine), and cellular aging (telomere length). Separate multiple linear regressions were performed for each biomarker, with gait speed, leg strength, fall history, and the Morse Fall Scale as variables of interest. We controlled for age, sex, and the Montreal Cognitive Assessment in each model. Fall history (β=5.61, p=0.03) and older age (β=0.49, p=0.005) were associated with greater INF-a2 (R 2 =0.49, p=0.07). Fall history (β=4.93, p=0.07) showed a trend for a relationship with greater IL-10 (R 2 =0.50, p=0.04). Older age (β=0.28, p=0.009) and lower MOCA scores (β=-0.40, p=0.04) were related to greater IL-12p70 (R 2 =0.64, p=0.003). Older age (β=9.26, p=0.01), fall history (β=74.42, p=0.04), and poorer leg strength (β=-7.40, p=0.06) were related to greater kynurenine (R 2 =0.49, p=0.02). Our exploratory findings suggest that there may be a relationship between certain physiological biomarkers (INF-a2, IL-10, kynurenine), physical function, and fall history. These inflammatory and metabolic aging biomarkers may play an important role for physical function and fall-risk in PWD. This preliminary research may have implications for screening and monitoring of physical decline and fall-risk among PWD.

Kynurenine (KYN), a tryptophan metabolite that increases with age, impairs osteoblast function. The aryl hydrocarbon receptor (AhR) has been proposed to mediate KYN's actions in bone. To test whether deletion of AhR in osteoblasts is beneficial for bone, we established an adult-onset AhR conditional knockout (CKO) model using Osx-Cre and examined the effects of AhR CKO at 4.5 and 6 mo of age (representing ~6 and 12 wk of CKO). While BMSC-derived osteoblasts from WT mice demonstrated reduced matrix formation from KYN treatment, AhR CKO osteoblasts were unaffected by KYN. Kynurenine's harmful effects were most pronounced in the middle of an osteoblastic differentiation time course, and these effects could be rescued via the AhR antagonist BAY2416964. In vivo, AhR deletion in Osx-expressing cells promoted sex- and compartment-specific skeletal phenotypes. Trabecular bone was increased in the distal femur of male and female AhR CKO mice at both 4.5 and 6 mo of age, potentially driven by a net decrease in the ratio of trabecular osteoclasts to osteoblasts despite a reduction in mineral apposition rate at 6 mo of age. In contrast, cortical bone phenotypes induced by AhR deletion depended on age and sex. In males, cortical bone volume fraction (Ct.BV/TV) was elevated in AhR CKO mice vs WT littermates at 4.5 mo of age, but differences resolved by 6 mo of age. In contrast, cortical bone was reduced in female AhR CKO as compared to WT littermates at 6 mo of age. These results underscore the complexity of AhR signaling in skeletal biology that must be considered while exploring AhR as a therapeutic target for conditions like osteoporosis and musculoskeletal frailty. Future studies will be needed to test the effects of osteoblastic AhR deletion at advanced ages, when the endogenous AhR ligand KYN is elevated in the circulation and skeletal niche.

Dementia compromises physical function, posing risks for falls. People living with dementia (PWD) have been historically excluded from intervention trials due to researchers’ eligibility criteria. Exercise shows potential in enhancing physical function, but more evidence is needed. This pilot randomized controlled trial aimed to assess whether the adapted Otago Exercise Program improves physical function relative to usual care alone in PWD. 42 PWD (Montreal Cognitive Assessment<19/30) were randomized (1:1) into the exercise (n = 21) or usual care (n = 21) group at two residential care facilities [NCT05488951]. The adapted Otago Exercise Program was a physical therapist-led strength, balance, and walking program for 1 hour, 3x/week for 6 months in groups of 5-7 participants. Physical function was evaluated by the short physical performance battery (balance, gait speed, and chair stands), timed-up-and-go (TUG), and strength at baseline and 6 months. Gait speed (m/s) was measured over 4m. The single-task TUG involved getting up, walking 3m, walking back, and sitting down (s); the dual-task TUG involved simultaneously performing a category task. We used dynamometers to measure leg and grip strength (kg). We performed intent-to-treat (ITT; n = 42) and per protocol (n = 21 usual care and n = 9 exercisers with 2/3 adherence) generalized mixed models, controlling for age, race, sex, and the MoCA. For the ITT analysis, left leg strength increased in the exercise group (baseline = 13.4kg; follow-up = 16.7kg) and decreased in the usual care group (baseline = 14.4kg; follow-up = 13.7kg; p = 0.03). Exercise provoked faster dual-task gait speed (baseline = 0.4m/s; follow-up = 0.5m/s; p<0.01) and decreased TUG dual-task duration (baseline = 37.3s; follow-up = 27.6s; p = 0.01) with no change following usual care. The per protocol analysis showed no differences. The improvements in strength, gait speed, and functional mobility in the exercise group, plus the decline in strength in the usual care group suggest that exercise may prevent decline and improve physical function among PWD. There were no differences in the per protocol analysis, however, this could be due to our small sample of only n = 9 participants with ≥2/3 exercise adherence. Our results suggest that implementing any level of exercise into care plans may improve physical function in PWD, but further research should confirm these preliminary findings.

People living with dementia (PWD) often have inactivity-induced muscle atrophy, increased sedentary behavior, and circadian rhythm disorders. Exercise may improve physical activity, sedentary behavior, and sleep in PWD, but further research is needed. The purpose of this pilot randomized controlled trial (RCT) was to examine whether a structured exercise program improves physical activity, sedentary behavior, and sleep in PWD. PWD were randomized (1:1) to exercise (n = 21) or usual care (n = 21) at two residential care facilities (NCT05488951; age = 82.1±8.05 years; Montreal Cognitive Assessment (MOCA) = 10.2 points; female = 35.7%; mobility device = 61.9%). Participants wore an actigraphy monitor on their non-dominant wrist for 7 days (minimum of 4 days to be included in the analysis) at baseline and 6 months. The adapted Otago Exercise Program involved a physical therapist-led strength, balance, and walking program for 1 hour, 3x/week for 6 months in groups of 5-7. We controlled for age, race, sex, and the MOCA in the intent-to-treat (ITT; n = 42) and per protocol analyses (PPA; n = 21 usual care; n = 9 exercisers with 2/3 adherence). The ITT analysis revealed that the exercise group (pre = 78.8%, post = 83.7%) had a greater percentage of sedentary activity than the usual care group (pre = 68.2%, post = 67.7%) at 6 months (p = 0.01). The PPA disclosed that the average length of sedentary bouts decreased in the usual care group (pre = 22.2, post = 20.1 minutes) compared to exercise group (pre = 46.9, post = 54.1 minutes) from baseline to 6 months (p = 0.01). Adherence to wearing the actigraphy monitor for ≥4 days was poor (pre: n = 25/42 PWD, post: n = 13/42 PWD). This RCT provides insufficient evidence to suggest that exercise impacts physical activity, sedentary behavior, or sleep among PWD. The results suggesting that usual care improves sedentary behavior over exercise should be interpreted with caution because this is a pilot RCT and adherence to wearing the actigraphy monitor was poor in both groups due to cognitive impairment. Future work is still needed to determine the effects of exercise on physical activity, sedentary behavior, and sleep, and should consider alternative placements of the actigraphy monitors, such as the back or lower leg, to increase adherence.

Aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is crucial in maintaining the skeletal system. Our study focuses on encapsulating the role of AhR in bone biology and identifying novel signaling pathways in musculoskeletal pathologies using the GEO dataset. The GEO2R analysis identified 8 genes (CYP1C1, SULT6B1, CYB5A, EDN1, CXCR4B, CTGFA, TIPARP, and CXXC5A) involved in the AhR pathway, which play a pivotal role in bone remodeling. The AhR knockout in hematopoietic stem cells showed alteration in several novel bone-related transcriptomes (eg, Defb14, ZNF 51, and Chrm5). Gene Ontology Enrichment Analysis demonstrated 54 different biological processes associated with bone homeostasis. Mainly, these processes include bone morphogenesis, bone development, bone trabeculae formation, bone resorption, bone maturation, bone mineralization, and bone marrow development. Employing Functional Annotation and Clustering through DAVID, we further uncovered the involvement of the xenobiotic metabolic process, p450 pathway, oxidation-reduction, and nitric oxide biosynthesis process in the AhR signaling pathway. The conflicting evidence of current research of AhR signaling on bone (positive and negative effects) homeostasis may be due to variations in ligand binding affinity, binding sites, half-life, chemical structure, and other unknown factors. In summary, our study provides a comprehensive understanding of the underlying mechanisms of the AhR pathway in bone biology.