Biology subjects

Kuhn, G. A.

Publications and source records attributed to Kuhn, G. A..

At least 19 recordsLinked to original sources

bioRxiv2026

Dysregulated mechanoregulation of load-induced bone adaptation in prematurely aged mice: insights from a micro-multiphysics agent-based model

Bone exhibits remarkable ability to adapt to varying mechanical demands. Aging can lead to changes in distribution of cells and proteins that directly affect bone formation and resorption. Given the inherent challenges of quantifying these cellular and protein alterations in vivo, innovative in silico tools have proven useful to contribute to studying the impact of aging on bone mechanobiology and associated cellular mechanisms. Here, we employed an agent-based in silico analysis of in vivo micro-computed tomography data of prematurely aged mice to examine the effects of aging and mechanical loading on bone cells and their mechanome, the intrinsic cellular system sensing mechanical forces. Our results from applying a micro-multiphysics agent-based model to an in vivo model of premature aging (PolG) showed that aging disrupts mechanoregulation of load-induced bone formation and resorption by eliminating the increase in bone formation through diminished osteoblast activity and mineralization, alongside mechanomic alterations. Specifically, prematurely aged mice exhibited a higher frequency of quiescence at higher mechanical signals and the simulations showed that the number of lining cells and osteoclasts per bone surface increased with age. Normalized trabecular thickness was more positively associated with the ratio of osteoblast to osteoclast number (Ob.N/Oc.N) in the aged control and aged loading groups (R2=0.58 and 0.61), than in young control and loading groups (R2=0.06 and 0.27), indicating dysregulated remodeling dynamics during aging. In conclusion, our results show that in silico tools can give valuable insights into the changes in mechanoregulation and cellular mechanisms occurring under physiological and aging conditions.

synthetic biology↗

bioRxiv2026

Differential Adaptation of Osteocyte Lacunar Morphology at Bone (Re)modeling Sites under Mechanical Loading and Pharmacological Therapies in a Mouse Model of Osteoporosis

Postmenopausal osteoporosis is a highly prevalent disease characterized by low bone mass and structural deterioration of bone tissue leading to increased bone fragility and fracture risk. Osteocytes orchestrate local bone (re)modeling and therefore, characterizing their 3D morphological and spatial distribution across distinct (re)modeling microenvironments is essential for understanding the cellular mechanisms underlying divergent tissue-level responses. To address this, we used a 3D-3D multiscale registration framework mapping endpoint osteocyte lacunae onto dynamic, time-lapsed in vivo (re)modeling sites. Ovariectomized 15-week-old mice were subjected to 4 weeks of anabolic parathyroid hormone (PTH) or anti-catabolic bisphosphonate (BIS) treatment as monotreatment or combined with cyclic mechanical loading (ML). Biweekly in vivo micro-computed tomography (micro-CT) to identify (re)modeling sites and endpoint ultra-high resolution (ultra-HR) micro-CT to characterize osteocyte lacunae was performed. Osteocyte lacunae were characterized by lacunar density, volume and sphericity. Our findings showed that physical and pharmacological therapies differentially regulate the osteocyte lacunar network through distinct perilacunar adaptations across functional microenvironments. While BIS stabilizes local lacunar architecture, PTH drives asymmetrical lacunar expansion (increased volume with reduced sphericity) through perilacunar remodeling that supersedes any added ML effects. Crucially, estrogen loss disrupts the natural spatial maturation gradient by inducing rounding of lacunae in newly formed bone. Therapies counteract this disruption, restoring the healthy gradients in lacunar morphometry between spatially distinct microenvironments. Additionally, despite restoring tissue-level bone volume, physical and pharmacological osteoporosis therapies do not fully recover persistent lacunar density deficits. The overall lacunar morphological spatial signatures confirm active osteocytic tuning to endocrine, physical and matrix cues.

bioengineering↗

bioRxiv2026

The Mechanosensitivity of the Regenerative Response in Bone is Retained with Aging in a Mouse Model of Premature Aging.

Aging impairs the regenerative capacity of bone and is associated with poor healing outcomes. The mechanical environment is of fundamental importance to the regenerative response in bone - yet the effect of aging on the mechano-responsive capacity of bone regeneration remains largely unresolved. To investigate age-dependent mechanobiological responses in bone regeneration, we established an experimental framework consisting of: (i) an established femur defect mouse model, (ii) the use of PolgAD257A/D257A (PolgA) mice - a mouse model of premature aging, and (iii) our recently established spatial transcriptomics-based "mechanomics" platform which permits gene expression to be analyzed as a function of the local in vivo mechanical environment. Aging impaired the regenerative response in PolgA mice, resulting in an increased occurrence of delayed and non-unions, delayed bone formation / resorption responses, impaired osteogenesis and delayed mineralization of new bone. Cyclic mechanical loading significantly enhanced the regenerative response in young PolgA mice inducing sustained bone formation, suppressing bone resorption, and enhancing mineralization, with the strongest effects observed in peripheral regions of the fracture site. In aged PolgA mice, the mechanosensitivity of the regenerative response was retained with an anabolic response localized to the defect center. Cyclic mechanical loading applied during the reparative and remodelling phases of fracture healing thus represents a potential translational strategy to harness the mechanosensitivity of aged bone.

physiology↗

bioRxiv2025

Spatial μProBe: a correlative multimodal imaging approach for spatial profiling of biological micro-environments

Despite fundamental advances in spatial omics, investigating cellular and molecular functions within their native environment remains a challenge in multiscale systems biology, especially in response to organ-level events. Here, we introduce Spatial {micro}ProBe (micro-ProBe), a multimodal imaging approach for spatial profiling of biological micro-environments. Spatial {micro}ProBe enables preprocessing, registration and correlative analysis of 2D and 3D imaging modalities, supported by an intuitive user interface. As an application, we investigated bone mechanobiology and characterised the cellular and molecular responses to mechanical loading during adaptation and regeneration, which continuously regulate the local microarchitecture. By integrating time-lapsed micro-computed tomography and end-point spatial transcriptomics, we profiled the local mechanical in vivo environment of thousands of musculoskeletal cells, revealing the spatiotemporal interplay between local mechanics and gene expression driving tissue development. Spatial {micro}ProBe marks a crucial advance in the characterisation of multiscale tissues and signalling, facilitating the exploration of targeted molecular therapies for pathological conditions.

systems biology↗

bioRxiv2024

Mechanical loading potentiates the bone response of anabolic osteoporosis treatments through mechanoregulation at the tissue level

Bones ability to adapt to mechanical demands is governed by mechanoregulation, the process by which cells sense and respond to mechanical stimuli to maintain skeletal integrity. In osteoporosis, increased bone resorption activity leads to structural deterioration and elevated fracture risk. While existing pharmacological therapies aim to restore bone mass to reduce fracture risk, it is unclear how they modulate mechanoregulation, especially when combined with physical interventions. Here, we investigate the joint effects of load-bearing physical and pharmacological treatment in a female mouse model of osteoporosis using longitudinal in vivo micro-computed tomography and computational mechanics. We demonstrate that mechanical loading additively and synergistically enhanced predicted strength, bone volume, and mechanoregulation parameters when combined with anabolic therapies (parathyroid hormone and sclerostin antibody) but not with anti-catabolic treatments (bisphosphonates). Increases in predicted strength are associated with reductions in bone resorption rates, shifts in the (re)modeling thresholds as anticipated by Frost in the mechanostat theory, and the modeling capacity of anabolic pharmacological treatments. These findings underscore the therapeutic potential of combining anabolic pharmacological therapies with load-bearing physical activity, particularly in early treatment phases, to optimize bone adaptation and fracture prevention in osteoporosis management.

bioengineering↗

bioRxiv2024

Daily Rhythms in Metabolic and Locomotor Behaviour of Prematurely Ageing PolgA Mice

Ageing is an inherent and intricate biological process that takes place in living organisms as time progresses. It involves the decline of multiple physiological functions, leading to body structure and overall performance modifications. The ageing process differs among individuals and is influenced by various factors, including lifestyle, environment, and genetic makeup. Metabolic changes and reduced locomotor activity are common hallmarks of ageing. Our study focuses on exploring these phenomena in prematurely ageing PolgA(D257A/D257A) mice (also known as PolgA) aged 41-42 weeks, as they closely mimic human ageing. We assess parameters such as oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory exchange ratio (RER), and locomotor activity using a metabolic cage for four days and comparing them with age-matched wild-type littermates (WT). Our findings revealed that VO2, VCO2, RER, locomotor activities, water intake, and feeding behaviour show a daily rhythm, aligning with roughly a 24-hour cycle. We observed that the RER was significantly increased in PolgA mice compared to WT mice during the night-time of the light-dark cycle, suggesting a shift towards a higher reliance on carbohydrate metabolism due to more food intake during the active phase. Additionally, female PolgA mice displayed a distinct phenotype with reduced walking speed, walking distance, body weight, and grip strength in comparison to male PolgA and WT mice, indicating an early sign of ageing. Taken together, our research highlights the impact of sex-specific patterns on ageing traits in PolgA mice aged 41-42 weeks, which may be attributable to human ageing phenotypes. The unique genetic composition and accelerated ageing characteristics of PolgA mice make them invaluable in ageing studies, facilitating the investigation of underlying biological mechanisms and the identification of potential therapeutic targets for age-related diseases.

physiology↗

bioRxiv2024

Unveiling Frailty: Comprehensive and Sex-Specific Characterization in Prematurely Aging PolgA Mice

Frailty, a geriatric syndrome, is assessed using the frailty phenotype (FP) and frailty index (FI). While these approaches have been applied to aging mice, their effectiveness in prematurely aging mouse models such as PolgAD257A/D257A (PolgA) has not been completely explored. We demonstrated that frailty became evident in PolgA mice around 40 weeks, validated through body weight loss, reduced walking speed, decreased physical activity, and weaker grip strength. Moreover, we also identified sex differences in these mice with females exhibiting higher frailty compared to males. Frailty prevalence in PolgA mice at 40 weeks parallels that observed in naturally aging mice at 27 months and aging humans at 65-70 years. These findings contribute to understanding frailty onset and sex-specific patterns, emphasizing the significance of the PolgA mouse model in investigating aging and related disorders.

physiology↗

bioRxiv2022

Trabecular bone remodeling in the ageing mouse: a micro-multiphysics agent-based in silico model using cell-type-specific mechanomic profiles

Bone remodeling is regulated by the interaction between different cells and tissues across many spatial and temporal scales. Notably, in silico models are regarded as powerful tools to further understand the signaling pathways that regulate this intricate spatial cellular interplay. To this end, we have established a 3D multiscale micro-multiphysics agent-based (micro-MPA) in silico model of trabecular bone remodeling using longitudinal in vivo data from the sixth caudal vertebra (CV6) of PolgA(D257A/D257A) mice, a mouse model of premature aging. Our model includes a variety of cells as single agents and receptor-ligand kinetics, mechanomics, diffusion and decay of cytokines which regulate the cells behavior. We highlighted its capabilities by simulating trabecular bone remodeling in the CV6 of 5 mice over 4 weeks and we evaluated the static and dynamic morphometry of the trabecular bone microarchitecture. Based on the progression of the average trabecular bone volume fraction (BV/TV), we identified a configuration of the model parameters to simulate homeostatic trabecular bone remodeling, here named basal. Crucially, we also produced anabolic, anti-anabolic, catabolic and anti-catabolic responses with an increase or decrease by one standard deviation in the levels of osteoprotegerin (OPG), receptor activator of nuclear factor kB ligand (RANKL), and sclerostin (Scl) produced by the osteocytes. Our results showed that changes in the levels of OPG and RANKL were positively and negatively correlated with the BV/TV values after 4 weeks in comparison to basal levels, respectively. Conversely, changes in Scl levels produced small fluctuations in BV/TV in comparison to the basal state. From these results, Scl was deemed to be the main driver of equilibrium while RANKL and OPG were shown to be involved in changes in bone volume fraction with potential relevance for age-related bone features. Ultimately, this micro-MPA model provides valuable insights into how cells respond to their local mechanical environment and can help to identify critical pathways affected by degenerative conditions and ageing.

bioengineering↗

bioRxiv2020

Longitudinal in vivo micro-CT-based approach allows spatio-temporal characterization of fracture healing patterns and assessment of biomaterials in mouse femur defect models

Thorough preclinical evaluation of functionalized biomaterials for treatment of large bone defects is essential prior to clinical application. Using in vivo micro-computed tomography (micro-CT) and mouse femoral defect models with different defect sizes, we were able to detect spatio-temporal healing patterns indicative of physiological and impaired healing in three defect sub-volumes and the adjacent cortex. The time-lapsed in vivo micro-CT-based approach was then applied to evaluate the bone regeneration potential of functionalized biomaterials using collagen and BMP-2. Both collagen and BMP-2 treatment led to distinct changes in bone turnover in the different healing phases. Despite increased periosteal bone formation, 87.5% of the defects treated with collagen scaffolds resulted in non-unions. Additional BMP-2 application significantly accelerated the healing process and increased the union rate to 100%. This study further shows potential of time-lapsed in vivo micro-CT for capturing spatio-temporal deviations preceding non-union formation and how this can be prevented by application of functionalized biomaterials. This study therefore supports the application of longitudinal in vivo micro-CT for discrimination of normal and disturbed healing patterns and for the spatio-temporal characterization of the bone regeneration capacity of functionalized biomaterials.

bioengineering↗

bioRxiv2020

Individualized cyclic mechanical loading improves callus properties during the remodelling phase of fracture healing in mice as assessed from time-lapsed in vivo imaging

Fracture healing is regulated by mechanical loading. Understanding the underlying mechanisms during the different healing phases is required for targeted mechanical intervention therapies. Here, the influence of individualized cyclic mechanical loading on the remodelling phase of fracture healing was assessed in a mouse femur defect model. After bridging of the defect, a loading group (n=10) received individualized cyclic mechanical loading (8-16 N, 10 Hz, 5 min, 3x/week) based on computed strain distribution in the callus using animal-specific real-time micro-finite element analysis. Controls (n=10) received 0 N treatment at the same post-operative time-points. By registration of consecutive scans, structural and dynamic callus morphometric parameters were followed in three callus sub-volumes and the adjacent cortex showing that the remodelling phase of fracture healing is highly responsive to cyclic mechanical loading with changes in dynamic parameters leading to significantly larger callus formation and mineralization. Loading-mediated maintenance of callus remodelling was associated with distinct effects on Wnt-signalling-associated molecular targets Sclerostin and RANKL in callus sub-regions and the adjacent cortex. Given these distinct local protein expression patterns induced by cyclic mechanical loading, the femur defect loading model with individualized load application seems suitable to understand the local spatio-temporal mechano-molecular regulation of the different fracture healing phases.

bioengineering↗

bioRxiv2020

Subject-specific mechanical loading of bones: Improved healing of mouse vertebral defects using adaptive loading regimes.

Methods to repair bone defects arising from trauma, resection, or disease, continue to be sought after. Cyclic mechanical loading is well established to influence bone (re)modelling activity, in which bone formation and resorption are correlated to micro-scale strain. Based on this, the application of mechanical stimulation across a bone defect could improve healing. However, if ignoring the mechanical integrity of defected bone, loading regimes have a high potential to either cause damage or be ineffective. This study explores real-time finite element (rtFE) methods that use three-dimensional structural analyses from micro-computed tomography images to estimate effective peak cyclic loads in a subject-specific and time-dependent manner. It demonstrates the concept in a cyclically loaded mouse caudal vertebral bone defect model. Using rtFE analysis combined with adaptive mechanical loading, mouse bone healing was significantly improved over non-loaded controls, with no incidence of vertebral fractures. Such rtFE-driven adaptive loading regimes demonstrated here could be relevant to clinical bone defect healing scenarios, where mechanical loading can become patient-specific and more efficacious. This is achieved by accounting for initial bone defect conditions and spatio-temporal healing, both being factors that are always unique to the patient.

bioengineering↗

bioRxiv2020

Development of a micro-CT mouse holder for a femur defect mouse model

Correct fixation of an object is essential for accurate micro computed tomography scanning. In this document, we provide a motivation for, description of, and use cases for a mouse holder appropriate for holding an externally fixated mouse in femur fracture/defect healing experiments. In addition to rigid fixation, the holder provides heating and anaesthetic gas to ensure correct anaesthetic conditions for the animal. We provide the description and design files for a Scanco viva40 scanner, but with small changes, the holder can be used with other scanners.

systems biology↗

bioRxiv2020

Reducing variance in a mouse defect healing model: Real-time Finite Element Analysis allows homogenization of tissue scale strains

Mechanical loading allows both investigation into the mechano-regulation of fracture healing as well as interventions to improve fracture-healing outcomes such as delayed healing or non-unions. However, loading is seldom individualised or even targeted to an effective mechanical stimulus level within the bone tissue. In this study, we use micro-finite element analysis to demonstrate the result of using a constant loading assumption for all mouse femurs in a given group. We then contrast this with the application of an adaptive loading approach, denoted real time Finite Element (rtFE) adaptation, in which micro-computed tomography images provide the basis for micro-FE based simulations and the resulting strains are manipulated and targeted to a reference distribution. Using this approach, we demonstrate that individualised femoral loading leads to a better-specified strain distribution and lower variance in tissue mechanical stimulus across all mice, both longitudinally and cross-sectionally, while making sure that no overloading is occurring leading to refracture of the femur bones.

systems biology↗

bioRxiv2020

Effects of early life stress on bone homeostasis in mice and humans

Bone pathology is frequent in stressed individuals. A comprehensive examination of mechanisms linking life stress, depression and disturbed bone homeostasis is missing. In this translational study, mice exposed to early life stress (MSUS) were examined on bone microarchitecture (CT), metabolism (qPCR), and neuronal stress mediator expression (qPCR) and contrasted with a sample of depressive patients with or without early life stress by analyzing bone mineral density [BMD] (DXA) and metabolic changes in serum (osteocalcin, PINP, CTX-I). MSUS mice showed a significant decrease in NGF, NPYR1, VIPR1 and TACR1 expression, higher innervation density in bone and increased serum levels of CTX-I, suggesting a milieu in favor of catabolic bone turnover. MSUS mice had a significantly lower body weight compared to control mice, and this caused minor effects on bone micro-CT. Depressive patients with experiences of childhood neglect also showed a catabolic pattern. A significant reduction in BMD was observed in depressive patients with childhood abuse and stressful life events during childhood. Therefore, future studies on prevention and treatment strategies for both mental and bone disease should consider early life stress as a risk factor for bone pathologies.

physiology↗

bioRxiv2020

Mechano-regulation of bone adaptation is controlled by the local in vivo environment and logarithmically dependent on loading frequency

It is well established that cyclic, but not static, mechanical loading has anabolic effects on bone. However, the function describing the relationship between the loading frequency and the amount of bone adaptation remains unclear. Using a combined experimental and computational approach, this study aimed to investigate whether bone mechano-regulation is controlled by mechanical signals in the local in vivo environment and dependent on loading frequency. Specifically, by combining in vivo micro-computed tomography (micro-CT) imaging with micro-finite element (micro-FE) analysis, we monitored the changes in microstructural as well as the mechanical in vivo environment (strain energy density (SED) and SED gradient) of mouse caudal vertebrae over 4 weeks of either cyclic loading at varying frequencies of 2Hz, 5Hz, or 10Hz, respectively or static loading. Higher values of SED and SED gradient on the local tissue level led to an increased probability of bone formation and a decreased probability of bone resorption. In all loading groups, the SED gradient was superior in the determination of local bone formation and resorption events as compared to SED. Cyclic loading induced positive net remodeling rates when compared to sham and static loading, mainly due to an increase in mineralizing surface and a decrease in eroded surface. Consequently, bone volume fraction increased over time in 2Hz, 5Hz and 10Hz (+15%, +21% and +24%, p<0.0001), while static loading led to a decrease in bone volume fraction (-9%, p[≤]0.001). Furthermore, regression analysis revealed a logarithmic relationship between loading frequency and the net change in bone volume fraction over the four week observation period (R2=0.74). In conclusion, these results suggest that bone adaptation is regulated by mechanical signals in the local in vivo environment and furthermore, that mechano-regulation is logarithmically dependent on loading frequency with frequencies below a certain threshold having catabolic effects, and those above anabolic effects. This study thereby provides valuable insights towards a better understanding of the mechanical signals influencing bone formation and resorption in the local in vivo environment.

physiology↗

bioRxiv2020

Effects of long-term in vivo micro-CT imaging on hallmarks of osteopenia and frailty in aging mice

In vivo micro-CT has already been used to monitor microstructural changes of bone in mice of different ages and in models of age-related diseases such as osteoporosis. However, as aging is accompanied by frailty and subsequent increased sensitivity to external stimuli such as handling and anesthesia, the extent to which longitudinal imaging can be applied in aging studies remains unclear. Consequently, the potential of monitoring individual mice during the entire aging process - from healthy to frail status - has not yet been exploited. In this study, we assessed the effects of long-term in vivo micro-CT imaging - consisting of 11 imaging sessions over 20 weeks - on hallmarks of aging both on a local (i.e., static and dynamic bone morphometry) and systemic (i.e., frailty index (FI) and body weight) level at various stages of the aging process. Furthermore, using a premature aging model (PolgA(D257A/D257A)), we assessed whether these effects differ between genotypes. The 6th caudal vertebrae of 4 groups of mice (PolgA(D257A/D257A) and PolgA(+/+)) were monitored by in vivo micro-CT every 2 weeks. One group was subjected to 11 scans between weeks 20 and 40 of age, whereas the other groups were subjected to 5 scans between weeks 26-34, 32-40 and 40-46, respectively. The long-term monitoring approach showed small but significant changes in the static bone morphometric parameters compared to the other groups. However, no interaction effect between groups and genotype was found, suggesting that PolgA mutation does not render bone more or less susceptible to long-term micro-CT imaging. The differences between groups observed in the static morphometric parameters were less pronounced in the dynamic morphometric parameters. Moreover, the body weight and FI were not affected by more frequent imaging sessions. Finally, we observed that longitudinal designs including baseline measurements at young adult age are more powerful at detecting effects of in vivo micro-CT imaging on hallmarks of aging than cross-sectional comparisons between multiple groups of aged mice subjected to fewer imaging sessions.

physiology↗

bioRxiv2019

Tau deposition is associated with imaging patterns of tissue calcification in the P301L mouse model of human tauopathy

Brain calcification is associated with several neurodegenerative proteinopathies. Here, we report a new phenotype of intracranial calcification in transgenic P301L mice overexpressing 4 repeat tau. P301L mice (Thy1.2) of 3, 5, 9 and 18-25 months-of-age and age-matched non-transgenic littermates were assessed using in vivo/ex vivo magnetic resonance imaging (MRI) with a gradient recalled echo sequence and micro computed tomography (CT). Susceptibility weighted images computed from the gradient recalled echo data revealed regional hypointensities in the hippocampus, cortex, caudate nucleus and thalamus of P301L mice, which in corresponding phase images indicated diamagnetic lesions. Concomitantly, {micro}CT detected hyperdense lesions. Occurrence of diamagnetic susceptibility lesions in the hippocampus, increased with age. Immunochemical staining of brain sections revealed bone protein-positive deposits. Furthermore, intra-neuronal and vessel-associated protein-containing nodules co-localized with phosphorylated-tau (AT8 and AT100) in the hippocampus. Protein-containing nodules were detected also in the thalamus in the absence of phosphorylated-tau deposition. In contrast, osteocalcin-containing nodules were vessel-associated, indicating ossified vessels, in the thalamus in absence of phosphorylated-tau. In summary, MRI and {micro}CT demonstrated imaging pattern of intracranial calcification, concomitant with immunohistochemical evidence of formation of protein deposits containing bone proteins along with phosphorylated-tau in the P301L mouse model of human tauopathy. The P301L mouse model may thus serve as a future model to study the pathogenesis of brain calcifications in tauopathies.

neuroscience↗

bioRxiv2019

Hallmarks of frailty and osteosarcopenia in prematurely aged PolgAD257A/D257A mice: a preclinical model to test anabolic interventions

BackgroundFrailty is a geriatric syndrome characterized by increased susceptibility to adverse health outcomes. One major determinant thereof is the gradual weakening of the musculoskeletal system and the associated osteosarcopenia. To improve our understanding of the underlying pathophysiology and, more importantly, to test potential interventions aimed at counteracting frailty suitable animal models are needed. MethodsTo evaluate the relevance of prematurely aged PolgA(D257A/D257A) mice as a model for frailty and osteosarcopenia, we quantified the clinical mouse frailty index in PolgA(D257A/D257A) and wild type littermates (PolgA(+/+), WT) with age and concertedly assessed the quantity and quality of bone and muscle tissue. Lastly, the anabolic responsiveness of skeletal muscle, muscle progenitors and bone was assessed. ResultsPolgA(D257A/D257A) accumulated health deficits at a higher rate compared to WT, resulting in a higher frailty index at 40 and 46 weeks of age (+166%, +278%, p<0.0001), respectively, with no differences between genotypes at 34 weeks. Concomitantly, PolgA(D257A/D257A) displayed progressive musculoskeletal deterioration such as reduced bone and muscle mass as well as impaired functionality thereof. In addition to lower muscle weights (-14%, p<0.05, -23%, p<0.0001) and fiber area (-20%, p<0.05, -22%, p<0.0001) at 40 and 46 weeks, respectively, PolgA(D257A/D257A) showed impairments in grip-strength and concentric muscle forces (p<0.05). PolgA(D257A/D257A) mutation altered the acute response to various anabolic stimuli in skeletal muscle and muscle progenitors. While PolgA(D257A/D257A) muscles were hypersensitive to eccentric contractions as well as leucine administration, shown by larger downstream signaling response of the mechanistic target of rapamycin complex 1 (mTORC1), myogenic progenitors cultured in vitro showed severe anabolic resistance to leucine and robust impairments in cell proliferation. Longitudinal micro-CT analysis of the 6th caudal vertebrae showed that PolgA(D257A/D257A) had lower bone morphometric parameters (e.g. bone volume fraction, trabecular and cortical thickness, p<0.05) as well as reduced remodeling activities (e.g. bone formation and resorption rate, p<0.05) compared to WT. When subjected to 4 weeks of cyclic loading, young but not aged PolgA(D257A/D257A) caudal vertebrae showed load-induced bone adaptation suggesting reduced mechanosensitivity with age. ConclusionsPolgA(D257A/D257A) mutation leads to hallmarks of age-related frailty and osteosarcopenia and provides a powerful model to better understand the relationship between frailty and the aging musculoskeletal system.

physiology↗