Longitudinal Examination of Bone Loss in Male Rats After Moderate-Severe Contusion Spinal Cord Injury

Transcriptomics reveals transient and dynamic muscle fibrosis and atrophy differences following spinal cord injury in rats

BACKGROUND

The rate and magnitude of skeletal muscle wasting after severe spinal cord injury (SCI) exceeds most other disuse conditions. Assessing the time course of molecular changes can provide insight into the progression of muscle wasting post-SCI. The goals of this study were (1) to identify potential targets that may prevent the pathologic features of SCI in soleus muscles and (2) to establish therapeutic windows for treating these pathologic changes.

METHODS

Four-month-old Sprague-Dawley male rats received T9 laminectomy (SHAM surgery) or severe contusion SCI. Hindlimb locomotor function was assessed weekly, with soleus muscles obtained 1 week, 2 weeks, 1 month and 3 months post-surgery (n = 6-7 per group per timepoint). RNA was extracted from muscles for bulk RNA-sequencing analysis (n = 3-5 per group per timepoint). Differentially expressed genes (DEGs) were evaluated between age-matched SHAM and SCI animals. Myofiber size, muscle fibre type and fibrosis were assessed on contralateral muscles.

RESULTS

SCI produced immediate and persistent hindlimb paralysis, with Basso-Beattie-Bresnahan locomotor scores remaining below 7 throughout the study, contributing to a progressive 25-50% lower soleus mass and myofiber atrophy versus SHAM (P < 0.05 at all timepoints). Transcriptional comparisons of SCI versus SHAM resulted in 184 DEGs (1 week), 436 DEGs (2 weeks), 133 DEGs (1 month) and 1200 DEGs (3 months). Upregulated atrophy-related genes included those associated with cell senescence, nuclear factor kappa B, ubiquitin proteasome and unfolded protein response pathways, along with upregulated genes that negatively influence muscle growth through the transforming growth factor beta pathway and inhibition of insulin-like growth factor-I/Akt/mechanistic target of rapamycin and p38/mitogen-activated protein kinase signalling. Genes associated with extracellular matrix (ECM), including collagens, collagen crosslinkers, proteoglycans and those regulating ECM integrity, were enriched within upregulated DEGs at 1 week but subsequently downregulated at 2 weeks and 3 months and were accompanied by >50% higher ECM areas and hydroxyproline levels in SCI muscles (P < 0.05). Myofiber remodelling genes were enriched in upregulated DEGs at 2 weeks and 1 month and were downregulated at 3 months. Genes that regulate neuromuscular junction remodelling were evident in muscles post-SCI, along with slow-to-fast fibre-type shifts: 1 week and 2 weeks SCI muscles were composed of 90% myosin heavy chain (MHC) type I fibres, which decreased to only 16% at 3 months and were accompanied by 50% fibres containing MHC IIX (P < 0.05). Metabolism genes were enriched in upregulated DEGs at 1 month and were further enriched at 3 months.

CONCLUSIONS

Our results substantiate many known pathologic features of SCI-induced wasting in rat skeletal muscle and identify a progressive and dynamic transcriptional landscape within the post-SCI soleus. Future studies are warranted to consider these therapeutic treatment windows when countering SCI muscle pathology.

A moderate spinal contusion injury in rats alters bone turnover both below and above the level of injury with sex-based differences apparent in long-term recovery

Spinal cord injury (SCI) leads to significant sublesional bone loss and high fracture rates. While loss of mechanical loading plays a significant role in SCI-induced bone loss, animal studies have demonstrated mechanical loading alone does not fully account for loss of bone following SCI. Indeed, we have shown that bone loss occurs below the level of an incomplete moderate contusion SCI, despite the resumption of weight-bearing and stepping. As systemic factors could also impact bone after SCI, bone alterations may also be present in bone sites above the level of injury. To examine this, we assessed bone microarchitecture and bone turnover in the supralesional humerus in male and female rats at two different ages following a moderate contusion injury in both sub-chronic (30 days) and chronic (180 days) time points after injury. At the 30-day timepoint, we found that both young and adult male SCI rats had decrements in trabecular bone volume at the supralesional proximal humerus (PH), while female SCI rats were not different from age-matched shams. At the 180-day timepoint, there were no statistical differences between SCI and sham groups, irrespective of age or sex, at the supralesional proximal humerus. At the 30-day timepoint, all SCI rats had lower BFR and higher osteoclast-covered trabecular surfaces in the proximal humerus compared to age-matched sham groups generally matching the pattern of SCI-induced changes in bone turnover seen in the sublesional proximal tibia. However, at the 180-day timepoint, only male SCI rats had lower BFR at the supralesional proximal humerus while female SCI rats had higher or no different BFR than their age-matched counterparts. Overall, this preclinical study demonstrates that a moderate contusion SCI leads to alterations in bone turnover above the level of injury within 30-days of injury; however male SCI rats maintained lower BFR in the supralesional humerus into long-term recovery. These data further highlight that bone loss after SCI is not driven solely by disuse. Additionally, these data allude to potential systemic factors exerting influence on bone following SCI and highlight the need to consider treatments for SCI-induced bone loss that impact both sublesional and systemic factors.

Rehabilitation: Neurogenic Bone Loss after Spinal Cord Injury

Osteoporosis is a common skeletal disorder which can severely limit one's ability to complete daily tasks due to the increased risk of bone fractures, reducing quality of life. Spinal cord injury (SCI) can also result in osteoporosis and sarcopenia. Most individuals experience sarcopenia and osteoporosis due to advancing age; however, individuals with SCI experience more rapid and debilitating levels of muscle and bone loss due to neurogenic factors, musculoskeletal disuse, and cellular/molecular events. Thus, preserving and maintaining bone mass after SCI is crucial to decreasing the risk of fragility and fracture in vulnerable SCI populations. Recent studies have provided an improved understanding of the pathophysiology and risk factors related to musculoskeletal loss after SCI. Pharmacological and non-pharmacological therapies have also provided for the reduction in or elimination of neurogenic bone loss after SCI. This review article will discuss the pathophysiology and risk factors of muscle and bone loss after SCI, including the mechanisms that may lead to muscle and bone loss after SCI. This review will also focus on current and future pharmacological and non-pharmacological therapies for reducing or eliminating neurogenic bone loss following SCI.

Chronic intermittent hypobaric hypoxia ameliorates osteoporosis after spinal cord injury through balancing osteoblast and osteoclast activities in rats

Introduction

As a common complication of spinal cord injury (SCI), most SCI patients suffer from osteoporosis. In our previous study, chronic intermittent hypobaric hypoxia (CIHH) could promote bone fracture healing. We speculated that it may act a role in the progression of osteoporosis. The current study purposed to explore the role of CIHH in the osteoporosis triggered by SCI in rats.

Methods

A SCI-induced SCI model was established by completed transection at T9-T10 spinal cord of Wistar rats. One week after SCI, the rats were conducted to CIHH treatment (PB = 404 mmHg, Po2 = 84 mmHg) 6 hours a day for continuously 7 weeks.

Results

The results of X-radiography and Micro-CT assessment demonstrated that compared with sham rats, the areal bone mineral density (BMD), bone volume to tissue volume, volumetric BMD, trabecular thickness, trabecular number, and trabecular connectivity were decreased. Trabecular bone pattern factor, trabecular separation, as well as structure model index were increased at the distal femur and proximal tibia of SCI rats, which were effectively reversed by CIHH treatment. Histomorphometry showed that CIHH treatment increased bone formation of SCI rats, as evidenced by the increased osteoid formation, the decreased number and surface of TRAP-positive osteoclasts. Furthermore, ELISA and real time PCR results showed that the osteoblastogenesis-related biomarkers, such as procollagen type 1 N-terminal propeptide, osteocalcin in serum, as well as ALP and OPG mRNAs in bone tissue were decreased, while the osteoclastogenesis-related biomarkers, including scleorostin in serum and RANKL and TRAP mRNAs in bone tissue were increased in SCI rats. Importantly, the deviations of aforementioned biomarkers were improved by CIHH treatment. Mechanically, the protective effects of CIHH might be at least partly mediated by hypoxia-inducible factor-1 alpha (HIF-1α) signaling pathway.

Conclusion

The present study testified that CIHH treatment ameliorates osteoporosis after SCI by balancing osteoblast and osteoclast activities in rats.

Passive Cycle Training Promotes Bone Recovery after Spinal Cord Injury without Altering Resting-State Bone Perfusion

INTRODUCTION

Spinal cord injury (SCI) produces diminished bone perfusion and bone loss in the paralyzed limbs. Activity-based physical therapy (ABPT) modalities that mobilize and/or reload the paralyzed limbs (e.g., bodyweight-supported treadmill training (BWSTT) and passive-isokinetic bicycle training) transiently promote lower-extremity blood flow (BF). However, it remains unknown whether ABPT alter resting-state bone BF or improve skeletal integrity after SCI.

METHODS

Four-month-old male Sprague-Dawley rats received T 9 laminectomy alone (SHAM; n = 13) or T 9 laminectomy with severe contusion SCI ( n = 48). On postsurgery day 7, SCI rats were stratified to undergo 3 wk of no ABPT, quadrupedal (q)BWSTT, or passive-isokinetic hindlimb bicycle training. Both ABPT regimens involved two 20-min bouts per day, performed 5 d·wk -1 . We assessed locomotor recovery, bone turnover with serum assays and histomorphometry, distal femur bone microstructure using in vivo microcomputed tomography, and femur and tibia resting-state bone BF after in vivo microsphere infusion.

RESULTS

All SCI animals displayed immediate hindlimb paralysis. SCI without ABPT exhibited uncoupled bone turnover and progressive cancellous and cortical bone loss. qBWSTT did not prevent these deficits. In comparison, hindlimb bicycle training suppressed surface-level bone resorption indices without suppressing bone formation indices and produced robust cancellous and cortical bone recovery at the distal femur. No bone BF deficits existed 4 wk after SCI, and neither qBWSTT nor bicycle altered resting-state bone perfusion or locomotor recovery. However, proximal tibia BF correlated with several histomorphometry-derived bone formation and resorption indices at this skeletal site across SCI groups.

CONCLUSIONS

These data indicate that passive-isokinetic bicycle training reversed cancellous and cortical bone loss after severe SCI through antiresorptive and/or bone anabolic actions, independent of locomotor recovery or changes in resting-state bone perfusion.

Inflammaging and bone loss in a rat model of spinal cord injury

Spinal cord injury (SCI) results in significant loss of sublesional bone, adding to the comorbidity of SCI with an increased risk of fracture and post-fracture complications. Unfortunately, the effect of SCI on skeletal health is also likely to rise as the average age of SCI has increased and there are well-known negative effects of age on bone. To date, however, the impact of age and age-associated inflammation (inflammaging) on skeletal health after SCI remains largely unknown. To address this, we compared bone parameters in young (3 month) and middle-aged (9 month) male and female rats with a moderate thoracic contusion injury, to age and sex matched sham-operated controls. Skeletal parameters, locomotor function and serum cytokine levels were assessed at both subchronic (30 days) and chronic (180 days) time points post injury. We hypothesized that SCI would lead to a dramatic loss of bone immediately after injury in all SCI-groups, with inflammaging leading to greater loss in middle-aged SCI rats. We also predicted that while younger rats may re-establish bone properties in more chronic phases of SCI, middle-aged rats would not. Supporting these hypothesis, trabecular bone volume was significantly lower in male and young female SCI rats early after injury. Contrary to our hypothesis, however, there was greater loss of trabecular bone volume, relative to age-matched shams, in young compared to middle-aged SCI rats with no effects of SCI on trabecular bone volume in middle-aged female rats. Moreover, despite recovery of weight-supported locomotor activity, bone loss persisted into the chronic phase of injury for the young rats. Bone formation rates were lower in young male SCI rats, regardless of the time since injury, while both young and middle-aged female SCI rats had lower bone formation in the subchronic but not chronic phase of SCI. In middle-aged rats, SCI-induced higher osteoclast surfaces, which also persisted into the chronic phase of SCI in middle-aged females. Neither age nor SCI-induced increases in inflammation seemed to be associated with bone loss. In fact, SCI had more dramatic and persistent effects on bone in male rats, while aging and SCI elevated serum cytokines only in female rats. Overall, this study demonstrates SCI-induced loss of bone and altered bone turnover in male and female rats that persists into the chronic phase post-injury. The sex and age dependent variations in bone turnover and serum cytokines, however, underscore the need to further explore both mechanisms and potential therapeutics in multiple demographics.

Expression of adipokines and adipocytokines by epidural adipose tissue in cauda equina syndrome in dogs

Background

Compression of epidural adipose tissue (EAT) within the scope of cauda equina syndrome (CES) could lead to an enhanced expression of inflammatory mediators, possibly contributing to pain amplification in dogs.

Objectives

To analyze expression of inflammatory adipo(‐cyto)kines within the EAT of dogs with CES.

Animals

Client‐owned dogs: 15 dogs with CES and 9 dogs euthanized for unrelated medical reasons (controls).

Methods

Prospective, experimental study. Epidural adipose tissue and subcutaneous adipose tissue were collected during dorsal laminectomy and used for real‐time quantitative polymerase chain reaction. Tissue explants were cultured for measurements of inflammation‐induced release of cytokines.

Results

Results show a CES‐associated upregulation of the cytokines tumor necrosis factor alpha (TNFα: mean ± SD: 18.88 ± 11.87, 95% CI: 10.90‐26.86 vs 9.66 ± 5.22, 95% CI: 5.29‐14.02, *: P = .04) and interleukin‐ (IL‐) 10 (20.1 ± 9.15, 95% CI: 14.82‐25.39 vs 11.52 ± 6.82, 95% CI: 5.82‐17.22, *: P = .03), whereas the expression of the adipokine leptin was attenuated in EAT of dogs with CES (3.07 ± 2.29, 95% CI: 1.80‐3.34 vs 9.83 ± 8.42, 95% CI: 3.36‐16.30, **: P = .007). Inflammatory stimulation of EAT explant cultures resulted in an enhanced release of IL‐6 (LPS: 5491.55 ± 4438, 95% CI: 833.7‐10 149; HMGB1: 1001.78 ± 522.2, 95% CI: 518.8‐1485; PBS: 310.9 ± 98.57, 95% CI: 228.5‐393.3, ***: P < .001).

Conclusion and Clinical Importance

Expression profile of inflammatory adipo(‐cyto)kines by EAT is influenced from compressive forces acting in dogs with CES and might contribute to amplification of pain.

Spatiotemporal responses of trabecular and cortical bone to complete spinal cord injury in skeletally mature rats

Objective

Methods

Results

Conclusions

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Skeletally mature spinal cord transected rats display biphasic bone loss

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The osteoporosis manifests over slower time scales than in skeletally immature rats.

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Relevancy for testing efficacy of interventions against SCI-induced osteoporosis.

Administration of High-Dose Methylprednisolone Worsens Bone Loss after Acute Spinal Cord Injury in Rats

The administration of high-dose methylprednisolone (MP) for 24–48 h after traumatic spinal cord injury (SCI) has been shown to improve functional recovery. The known adverse effects of MP on skeletal muscle and the immune system, though, have raised clinically relevant safety concerns. However, the effect of MP administration on SCI-induced bone loss has not been evaluated to date. This study examined the adverse effects of high-dose MP administration on skeletal bone after acute SCI in rodents. Male rats underwent spinal cord transection at T3–T4, which was followed by an intravenous injection of MP and subsequent infusion of MP for 24 h. At 2 days, animals were euthanized and hindlimb bone samples were collected. MP significantly reduced bone mineral density (−6.7%) and induced deterioration of bone microstructure (trabecular bone volume/tissue volume, −18.4%; trabecular number, −19.4%) in the distal femur of SCI rats. MP significantly increased expression in the hindlimb bones of osteoclastic genes receptor activator of nuclear factor-κB ligand (RANKL; +402%), triiodothyronine receptor auxiliary protein (+32%), calcitonin receptor (+41%), and reduced osteoprotegerin/RANKL ratio (−72%) compared to those of SCI-vehicle animals. Collectively, 1 day of high-dose MP at a dose comparable to the dosing regimen prescribed to patients who qualify to receive this treatment approach with acute SCI increased loss of bone mass and integrity below the level of lesion than that of animals that had SCI alone, and was associated with further elevation in the expression of genes involved in pathways associated with osteoclastic bone resorption than that observed in SCI animals.

The Effects of Exercise and Activity-Based Physical Therapy on Bone after Spinal Cord Injury

Spinal cord injury (SCI) produces paralysis and a unique form of neurogenic disuse osteoporosis that dramatically increases fracture risk at the distal femur and proximal tibia. This bone loss is driven by heightened bone resorption and near-absent bone formation during the acute post-SCI recovery phase and by a more traditional high-turnover osteopenia that emerges more chronically, which is likely influenced by the continual neural impairment and musculoskeletal unloading. These observations have stimulated interest in specialized exercise or activity-based physical therapy (ABPT) modalities (e.g., neuromuscular or functional electrical stimulation cycling, rowing, or resistance training, as well as other standing, walking, or partial weight-bearing interventions) that reload the paralyzed limbs and promote muscle recovery and use-dependent neuroplasticity. However, only sparse and relatively inconsistent evidence supports the ability of these physical rehabilitation regimens to influence bone metabolism or to increase bone mineral density (BMD) at the most fracture-prone sites in persons with severe SCI. This review discusses the pathophysiology and cellular/molecular mechanisms that influence bone loss after SCI, describes studies evaluating bone turnover and BMD responses to ABPTs during acute versus chronic SCI, identifies factors that may impact the bone responses to ABPT, and provides recommendations to optimize ABPTs for bone recovery.

Time course changes to structural, mechanical and material properties of bone in rats after complete spinal cord injury

OBJECTIVE

Characterise the spatiotemporal trabecular and cortical bone responses to complete spinal cord injury (SCI) in young rats.

METHODS

8-week-old male Wistar rats received T9-transection SCI and were euthanised 2-, 6-, 10- or 16-weeks post-surgery. Outcome measures were assessed using micro-computed tomography, mechanical testing, serum markers and Fourier-transform infrared spectroscopy.

RESULTS

The trabecular and cortical bone responses to SCI are site-specific. Metaphyseal trabecular BV/TV was 59% lower, characterised by fewer and thinner trabeculae at 2-weeks post-SCI, while epiphyseal BV/TV was 23% lower with maintained connectivity. At later-time points, metaphyseal BV/TV remained unchanged, while epiphyseal BV/TV increased. The total area of metaphyseal and mid-diaphyseal cortical bone were lower from 2-weeks and between 6- and 10-weeks post-SCI, respectively. This suggested that SCI-induced bone changes observed in the rat model were not solely attributable to bone loss, but also to suppressed bone growth. No tissue mineral density differences were observed at any time-point, suggesting that decreased whole-bone mechanical properties were primarily the result of changes to the spatial distribution of bone.

CONCLUSION

Young SCI rat trabecular bone changes resemble those observed clinically in adult and paediatric SCI, while cortical bone changes resemble paediatric SCI only.

In vivo imaging in experimental spinal cord injury – Techniques and trends

Introduction

Traumatic Spinal Cord Injury (SCI) is one of the leading causes of disability in the world. Treatment is limited to supportive care and no curative therapy exists. Experimental research to understand the complex pathophysiology and potential mediators of spinal cord regeneration is essential to develop innovative translational therapies. A multitude of experimental imaging methods to monitor spinal cord regeneration in vivo have developed over the last years. However, little literature exists to deal with advanced imaging methods specifically available in SCI research.

Research Question

This systematic literature review examines the current standards in experimental imaging in SCI allowing for in vivo imaging of spinal cord regeneration on a neuronal, vascular, and cellular basis.

Material and Methods

Articles were included meeting the following criteria: experimental research, original studies, rodent subjects, and intravital imaging. Reviewed in detail are microstructural and functional Magnetic Resonance Imaging, Micro-Computed Tomography, Laser Speckle Imaging, Very High Resolution Ultrasound, and in vivo microscopy techniques.

Results

Following the PRISMA guidelines for systematic reviews, 689 articles were identified for review, of which 492 were sorted out after screening and an additional 104 after detailed review. For qualitative synthesis 93 articles were included in this publication.

Discussion and Conclusion

With this study we give an up-to-date overview about modern experimental imaging techniques with the potential to advance the knowledge on spinal cord regeneration following SCI. A thorough knowledge of the strengths and limitations of the reviewed techniques will help to optimally exploit our current experimental armamentarium in the field.

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In vivo imaging is essential to enhance the understanding of SCI pathophysiology.

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Multiple experimental imaging methods have evolved over the past years.

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Detailed review of in vivo (f)MRI, μCT, VHRUS, and Microcopy in experimental SCI.

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Experimental imaging allows for longitudinal examination to the cellular level.

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Knowledge of the strengths and limitations is essential for future research.

An examination of two different approaches for the study of femoral neck fracture: Towards a more relevant rodent model

Femoral neck fractures are a massive personal and health programme burden. Methods to study femoral neck strength, across its combined trabecular and cortical components are therefore essential. Rodent ovariectomy-induced osteoporosis models are commonly coupled with ex vivo 3-/4-point bending methods to measure changes in femoral cortical diaphysis. The loading direction used to assess these properties are often non-physiologic and, moreover, these ovariectomy models are linked to marked weight gain that can influence the biomechanical properties. Herein, we explore whether more physiological axial ex vivo loading protocols applied to femoral neck samples of ovariectomised (OVX) rodents provide anatomically-relevant models for the assessment of strength. We examine the use of mouse and rat femurs, loaded in constrained and unconstrained configuration, respectively, and explore whether weight-correction increases their utility. Accordingly, the mid-shaft of the proximal half of femurs from OVX and sham-operated (Sham) mice was methacrylate-anchored and the head loaded parallel to the diaphysis (constrained). Alternatively, femurs from OVX and Sham rats were isolated intact and axially-loaded through hip and knee joint articular surfaces (unconstrained). Yield displacement, stiffness, maximum load and resilience were measured and fracture pattern classified; effects of body weight-correction via a linear regression method or simple division were assessed. Our data reveal significant deficiencies in biomechanical properties in OVX mouse femurs loaded in constrained configuration, only after weight-correction by linear regression. In addition, evaluation of rat femur biomechanics in unconstrained loading demonstrated greater variation and that weight-correction by simple division improved scope to reveal significant OVX impact. We conclude that greater femoral neck fracture susceptibility can indeed be measured in OVX rodents as long as multiple biomechanical parameters are reported, care is taken in choosing the method for assessing load-bearing strength and weight-correction applied. These studies advance the establishment of more relevant rodent models for the study of femoral neck fracture.

Bone loss after severe spinal cord injury coincides with reduced bone formation and precedes bone blood flow deficits

Diminished bone perfusion develops in response to disuse and has been proposed as a mechanism underlying bone loss. Bone blood flow (BF) has not been investigated within the unique context of severe contusion spinal cord injury (SCI), a condition that produces neurogenic bone loss that is precipitated by disuse and other physiological consequences of central nervous system injury. Herein, 4-mo-old male Sprague-Dawley rats received T₉ laminectomy (SHAM) or laminectomy with severe contusion SCI (n = 20/group). Time course assessments of hindlimb bone microstructure and bone perfusion were performed in vivo at 1- and 2-wk postsurgery via microcomputed tomography (microCT) and intracardiac microsphere infusion, respectively, and bone turnover indices were determined via histomorphometry. Both groups exhibited cancellous bone loss beginning in the initial postsurgical week, with cancellous and cortical bone deficits progressing only in SCI thereafter. Trabecular bone deterioration coincided with uncoupled bone turnover after SCI, as indicated by signs of ongoing osteoclast-mediated bone resorption and a near-complete absence of osteoblasts and cancellous bone formation. Bone BF was not different between groups at 1 wk, when both groups displayed bone loss. In comparison, femur and tibia perfusion was 30%-40% lower in SCI versus SHAM at 2 wk, with the most pronounced regional BF deficits occurring at the distal femur. Significant associations existed between distal femur BF and cancellous and cortical bone loss indices. Our data provide the first direct evidence indicating that bone BF deficits develop in response to SCI and temporally coincide with suppressed bone formation and with cancellous and cortical bone deterioration.NEW & NOTEWORTHY We provide the first direct evidence indicating femur and tibia blood flow (BF) deficits exist in conscious (awake) rats after severe contusion spinal cord injury (SCI), with the distal femur displaying the largest BF deficits. Reduced bone perfusion temporally coincided with unopposed bone resorption, as indicated by ongoing osteoclast-mediated bone resorption and a near absence of surface-level bone formation indices, which resulted in severe cancellous and cortical microstructural deterioration after SCI.

Sciatic neurectomy-related cortical bone loss exhibits delayed onset yet stabilises more rapidly than trabecular bone

Disuse osteoporosis occurs after extended periods of bed rest or nerve damage leading to increased risk of fracture. It remains to be established, however, whether the trajectory of bone loss is equivalent in bone's cortical and trabecular compartments following long-term periods of reduced loading. Herein, we evaluate sciatic neurectomy-related cortical and trabecular bone loss in the tibia by microCT. The right hind limb of seventeen 12 week-old female mice was subjected to sciatic neurectomy (right, SN; left, contralateral internal control) and the animals were sacrificed in four groups (n = 3-5/group) at 5, 35, 65 and 95 days thereafter. Cortical bone mass, geometry and mineral density were evaluated along almost the entire tibial length and trabecular bone was examined at the proximal metaphysis. We found that trabecular bone volume (BV/TV) and number were decreased within 5 days, with a trajectory of loss that only plateaued after 65 days post-SN. In contrast, decreases in cortical thickness, cross-sectional area, second moment of inertia along minor and major axes and predicted resistance to torsion were unmodified during the early 5 day period, attaining significance only after 35 days post-SN and, thereafter showed no further deterioration. Only cortical ellipticity and periosteal enclosed area, continued to change in the SN limbs (vs. contralateral) between 35 and 95 days along the tibia length. On the other hand, cortical tissue mineral density was unmodified by SN at any time point. These data indicate that SN-related cortical bone loss extends along almost the entire tibia, exhibits delayed onset and yet stabilises its architecture more rapidly than trabecular bone. These data suggest that the cortical and trabecular compartments behave as distinct modules in response to SN even within an individual bone.

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Responses to sciatic neurectomy (SN) in tibial trabecular bone are very protracted.

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Responses to SN in the cortices have delayed onset but stabilize more rapidly.

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Trabecular and cortical bone behave modularly in response to SN.

Unilateral cervical spinal cord injury induces bone loss and metabolic changes in non-human primates (Macaca fascicularis)

BACKGROUND/OBJECTIVE

The deleterious effects of chronic spinal cord injury (SCI) on the skeleton in rats, especially the lower extremities, has been proved previously. However, the long-term skeletal changes after SCI in non-human primates (NHP) have been scarcely studied. This study aimed to evaluate the bone loss in limbs and vertebrae and the bone metabolic changes in NHP after unilateral cervical spinal cord contusion injury.

METHODS

Twelve Macaca fascicularis were randomly divided into the SCI (n=8) and the Sham (n=4) groups. The SCI models were established using hemi-contusion cervical spinal cord injury on fifth cervical vertebra (C5), and were further evaluated by histological staining and neurophysiological monitoring. Changes of bone microstructures, bone biomechanics, and bone metabolism markers were assessed by micro-CT, micro-FEA and serological kit.

RESULTS

The NHP hemi-contusion cervical SCI model led to consistent unilateral limb dysfunction and potential plasticity in the face of loss of spinal cord. Furthermore, the cancellous bone mass of ipsilateral humerus and radius decreased significantly compared to the contralateral side. The bone volume fraction of humerus and radius were 17.2% and 20.1% on the ipsilateral while 29.0% and 30.1% on the contralateral respectively. Similarly, the thickness of the cortical bone in the ipsilateral forelimbs was significantly decreased, as well as the bone strength of the ipsilateral forelimbs. These changes were accompanied by diminished concentration of osteocalcin and total procollagen type 1 N-terminal propeptide (t-P1NP) as well as increased level of β-C-terminal cross-linking telopeptide of type 1collagen (β-CTX) in serological testing.

CONCLUSIONS

The present study demonstrated that hemi-SCI induced loss of bone mass and compromised biomechanical performance in ipsilateral forelimbs, which could be indicated by both muscle atrophy and serological changes of bone metabolism, and associated with a consistent loss of large-diameter cells of sensory neurons in the dorsal root ganglia.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Our study, for the first time, demonstrated the bone loss in limbs and vertebrae as well as the bone metabolic changes in non-human primates after unilateral spinal cord injury (SCI). This may help to elucidate the role of muscle atrophy, serological changes and loss of sensory neurons in the mechanisms of SCI-induced osteoporosis, which would be definitely better compared with rodent models.

Spinal Cord Injury Reduces Serum Levels of Fibroblast Growth Factor-21 and Impairs Its Signaling Pathways in Liver and Adipose Tissue in Mice

Spinal cord injury (SCI) results in dysregulation of carbohydrate and lipid metabolism; the underlying cellular and physiological mechanisms remain unclear. Fibroblast growth factor 21 (FGF21) is a circulating protein primarily secreted by the liver that lowers blood glucose levels, corrects abnormal lipid profiles, and mitigates non-alcoholic fatty liver disease. FGF21 acts via activating FGF receptor 1 and ß-klotho in adipose tissue and stimulating release of adiponectin from adipose tissue which in turn signals in the liver and skeletal muscle. We examined FGF21/adiponectin signaling after spinal cord transection in mice fed a high fat diet (HFD) or a standard mouse chow. Tissues were collected at 84 days after spinal cord transection or a sham SCI surgery. SCI reduced serum FGF21 levels and hepatic FGF21 expression, as well as β-klotho and FGF receptor-1 (FGFR1) mRNA expression in adipose tissue. SCI also reduced serum levels and adipose tissue mRNA expression of adiponectin and leptin, two major adipokines. In addition, SCI suppressed hepatic type 2 adiponectin receptor (AdipoR2) mRNA expression and PPARα activation in the liver. Post-SCI mice fed a HFD had further suppression of serum FGF21 levels and hepatic FGF21 expression. Elevated serum free fatty acid (FFA) levels after HFD feeding were observed in post-SCI mice but not in sham-mice, suggesting defective FFA uptake after SCI. Moreover, after SCI several genes that are implicated in insulin's action had reduced expression in tissues of interest. These findings suggest that downregulated FGF21/adiponectin signaling and impaired responsiveness of adipose tissues to FGF21 may, at least in part, contribute to the overall picture of metabolic dysfunction after SCI.

Electrical stimulation of hindlimb skeletal muscle has beneficial effects on sublesional bone in a rat model of spinal cord injury

Spinal cord injury (SCI) results in marked atrophy of sublesional skeletal muscle and substantial loss of bone. In this study, the effects of prolonged electrical stimulation (ES) and/or testosterone enanthate (TE) on muscle mass and bone formation in a rat model of SCI were tested. Compared to sham-transected animals, a significant reduction of the mass of soleus, plantaris and extensor digitorum longus (EDL) muscles was observed in animals 6 weeks post-SCI. Notably, ES or ES + TE resulted in the increased mass of the EDL muscles. ES or ES + TE significantly decreased mRNA levels of muscle atrophy markers (e.g., MAFbx and MurF1) in the EDL. Significant decreases in bone mineral density (BMD) (-27%) and trabecular bone volume (-49.3%) at the distal femur were observed in animals 6 weeks post injury. TE, ES and ES + TE treatment significantly increased BMD by +6.4%, +5.4%, +8.5% and bone volume by +22.2%, and +56.2% and+ 60.2%, respectively. Notably, ES alone or ES + TE resulted in almost complete restoration of cortical stiffness estimated by finite element analysis in SCI animals. Osteoblastogenesis was evaluated by colony-forming unit-fibroblastic (CFU-F) staining using bone marrow mesenchymal stem cells obtained from the femur. SCI decreased the CFU-F+ cells by -56.8% compared to sham animals. TE or ES + TE treatment after SCI increased osteoblastogenesis by +74.6% and +67.2%, respectively. An osteoclastogenesis assay revealed significantly increased TRAP+ multinucleated cells (+34.8%) in SCI animals compared to sham animals. TE, ES and TE + ES treatment following SCI markedly decreased TRAP+ cells by -51.3%, -40.3% and -46.9%, respectively. Each intervention greatly reduced the ratio of RANKL to OPG mRNA of sublesional long bone. Collectively, our findings demonstrate that after neurologically complete paralysis, dynamic muscle resistance exercise by ES reduced muscle atrophy, downregulated genes involved in muscle wasting, and restored mechanical loading to sublesional bone to a degree that allowed for the preservation of bone by inhibition of bone resorption and/or by facilitating bone formation.

A 50 kdyne contusion spinal cord injury with or without the drug SS-31 was not associated with major changes in muscle mass or gene expression 14 d after injury in young male mice

Spinal cord injury (SCI) leads to rapid muscle atrophy due to paralysis/paresis and subsequent disuse. SS-31 is a mitochondrial-targeting peptide that has shown efficacy in protecting skeletal muscle mass and function in non-SCI models of muscle wasting. We aimed to determine if SS-31 could prevent muscle loss after SCI. Male C57BL/6 mice aged 9 weeks underwent sham surgery or 50 kdyne contusion SCI and were administered daily injections of vehicle or 5 mg/kg SS-31 for 14 d. Both SCI groups had sustained losses in body mass compared to Sham animals and ~10% reductions in gastrocnemius, plantaris and tibialis anterior muscle mass after SCI with no clear effect of SS-31. Measurements of protein synthesis in the soleus and plantaris were similar among all groups. mRNA expression of atrophy-associated proinflammatory cytokines was also similar among all groups. There was elevation in MYH7 mRNA and a statistical reduction in MYH2 mRNA expression in the SCI+SS-31 animals compared to Sham animals. There was an SCI-induced reduction in mRNA expression of the E3 ligase FBXO32 (MAFbx), but no effect of SS-31. In summary, a 50 kdyne contusion SCI was able to reduce body mass but was not associated with substantial muscle atrophy or alterations in gene expression profiles associated with muscle health and function 14 d post-injury. SS-31 was not associated with protection against SCI-related changes in body or muscle mass, protein synthesis or gene expression in hindlimb muscles.

Activin type IIA decoy receptor and intermittent parathyroid hormone in combination overturns the bone loss in disuse-osteopenic mice

Damage of the lower motor neuron cell bodies or their axons results in reduced or abolished voluntary movement accompanied by a substantial loss of bone and muscle mass. Intermittent parathyroid hormone 1-34 (PTH) (teriparatide) is one of the most potent bone-anabolic treatment regimens. ActRIIA-mFc is an activin type IIA decoy receptor that increases bone mass mediated by inhibition of the activin receptor signaling pathway. We investigated whether PTH or ActRIIA-mFc alone or in combination could prevent loss of bone and muscle mass induced by injecting botulinum toxin A (BTX) into the right hind limb in mice. Seventy-two 16-week-old female C57BL/6 mice were allocated to the following groups: Baseline, Control, BTX, BTX + ActRIIA-mFc (10 mg/kg), BTX + PTH (100 μg/kg), and BTX + ActRIIA-mFc + PTH. The mice were sacrificed after three weeks of disuse and treatment. In contrast to monotherapy with PTH, ActRIIA-mFc alone or in combination with PTH was able partly or completely to prevent disuse-induced loss of whole femoral bone mass, trabecular thickness, and bone strength. Moreover, an additive effect of ActRIIA-mFc and PTH on areal bone mineral density and trabecular bone volume was found. In summary, ActRIIA-mFc and PTH in combination were more effective in preventing disuse-induced bone loss and deterioration of trabecular micro-architecture than either treatment alone.

Effects of a High-Fat Diet on Tissue Mass, Bone, and Glucose Tolerance after Chronic Complete Spinal Cord Transection in Male Mice

Spinal cord injury (SCI) is associated with obesity and is a risk factor for type 2 diabetes mellitus (T2DM). Immobilization, muscle atrophy, obesity, and loss of sympathetic innervation to the liver are believed to contribute to risks of these abnormalities. Systematic study of the mechanisms underlying SCI-induced metabolic disorders has been limited by a lack of animal models of insulin resistance following SCI. Therefore, the effects of a high-fat diet (HFD), which causes weight gain and glucose intolerance in neurologically intact mice, was tested in mice that had undergone a spinal cord transection at thoracic vertebra 10 (T10) or a sham-transection. At 84 days after surgery, Sham-HFD and SCI-HFD mice showed impaired intraperitoneal glucose tolerance when compared with Sham control (Sham-Con) or SCI control (SCI-Con) mice fed a standard control chow. Glucose tolerance in SCI-Con mice was comparable to that of Sham-Con mice. The mass of paralyzed skeletal muscle, liver, and epididymal, inguinal, and omental fat deposits were lower in SCI versus Sham groups, with lower liver mass present in SCI-HFD versus SCI-Con animals. SCI also produced sublesional bone loss, with no differences between SCI-Con and SCI-HFD groups. The results suggest that administration of a HFD to mice after SCI may provide a model to better understand mechanisms leading to insulin resistance post-SCI, as well as an approach to study pathogenesis of glucose intolerance that is independent of obesity.

Rapid bone loss occurs as early as 2 days after complete spinal cord transection in young adult rats

STUDY DESIGN

Animal study.

OBJECTIVE

This study examined how soon after spinal cord injury (SCI) bone loss occurs, and investigated the underlying molecular mechanism.

METHODS

Eight-week-old male Wistar rats underwent complete transection of the thoracic spinal cord at T3-4 or sham operation (n = 10-12 per group). Blood, hindlimb bone samples, and bone marrows were collected at 2 and 7 days after SCI.

RESULTS

The neurologically motor-complete SCI causes loss of bone mass and deterioration of trabecular bone microstructure as early as 2 days after injury; these skeletal defects become more evident at 7 days. These changes are associated with a dramatic increase in levels of bone resorption maker CTX in blood. Alternations of gene expression in hindlimb bone tissues and bone marrow cells at the first week after SCI were examined. Gene expressions responsible for both bone resorption and formation are increased at 2 days post-SCI, and the associated bone loss and bone deterioration are likely the result of higher levels of osteoclastic resorption over osteoblastic formation, as may be extrapolated from findings at molecular levels.

CONCLUSIONS

Rapid bone loss occurs as early as 2 days after motor-complete SCI and interventions for inhibiting bone resorption and prompting bone formation should start as soon as possible after the injury to prevent bone loss.

Contusion spinal cord injury upregulates p53 protein expression in rat soleus muscle at multiple timepoints but not key senescence cytokines

To determine whether muscle disuse after a spinal cord injury (SCI) produces elevated markers of cellular senescence and induces markers of the senescence-associated secretory phenotypes (SASPs) in paralyzed skeletal muscle. Four-month-old male Sprague-Dawley rats received a moderate-severe (250 kiloDyne) T-9 contusion SCI or Sham surgery and were monitored over 2 weeks, and 1-, 2-, or 3 months. Animals were sacrificed via isoflurane overdose and terminal exsanguination and the soleus was carefully excised and snap frozen. Protein expression of senescence markers p53, p27, and p16 was determined from whole soleus lysates using Western immunoblotting and RT-qPCR was used to determine the soleus gene expression of IL-1α, IL-1β, IL-6, CXCL1, and TNFα. SCI soleus muscle displayed 2- to 3-fold higher total p53 protein expression at 2 weeks, and at 1 and 2 months when compared with Sham. p27 expression was stable across all groups and timepoints. p16 protein expression was lower at 3 months in SCI versus Sham, but not earlier timepoints. Gene expression was relatively stable between groups at 2 weeks. There were Surgery x Time interaction effects for IL-6 and TNFα mRNA expression but not for IL-1α, IL-1β, or CXCL1. There were no main effects for time or surgery for IL-1α, IL-1β, or CXCL1, but targeted t tests showed reductions in IL-1α and CXCL1 in SCI animals compared to Sham at 3 months and IL-1β was reduced in SCI animals compared to Sham animals at the 2-month timepoint. The elevation in p53 does not appear consistent with the induction of SASP because mRNA expression of cytokines associated with senescence was not uniformly upregulated and, in some instances, was downregulated in the early chronic phase of SCI.

Locomotor training with adjuvant testosterone preserves cancellous bone and promotes muscle plasticity in male rats after severe spinal cord injury

Loading and testosterone may influence musculoskeletal recovery after spinal cord injury (SCI). Our objectives were to determine (a) the acute effects of bodyweight-supported treadmill training (TM) on hindlimb cancellous bone microstructure and muscle mass in adult rats after severe contusion SCI and (b) whether longer-term TM with adjuvant testosterone enanthate (TE) delivers musculoskeletal benefit. In Study 1, TM (40 min/day, 5 days/week, beginning 1 week postsurgery) did not prevent SCI-induced hindlimb cancellous bone loss after 3 weeks. In Study 2, TM did not attenuate SCI-induced plantar flexor muscles atrophy nor improve locomotor recovery after 4 weeks. In our main study, SCI produced extensive distal femur and proximal tibia cancellous bone deficits, a deleterious slow-to-fast fiber-type transition in soleus, lower muscle fiber cross-sectional area (fCSA), impaired muscle force production, and levator ani/bulbocavernosus (LABC) muscle atrophy after 8 weeks. TE alone (7.0 mg/week) suppressed bone resorption, attenuated cancellous bone loss, constrained the soleus fiber-type transition, and prevented LABC atrophy. In comparison, TE+TM concomitantly suppressed bone resorption and stimulated bone formation after SCI, produced near-complete cancellous bone preservation, prevented the soleus fiber-type transition, attenuated soleus fCSA atrophy, maintained soleus force production, and increased LABC mass. 75% of SCI+TE+TM animals recovered voluntary over-ground hindlimb stepping, while no SCI and only 20% of SCI+TE animals regained stepping ability. Positive associations between testosterone and locomotor function suggest that TE influenced locomotor recovery. In conclusion, short-term TM alone did not improve bone, muscle, or locomotor recovery in adult rats after severe SCI, while longer-term TE+TM provided more comprehensive musculoskeletal benefit than TE alone.

Global and site-specific analysis of bone in a rat model of spinal cord injury-induced osteoporosis

Micro-Computed Tomography bone analysis is the gold standard method for assessing trabecular and cortical bone microarchitecture in small animal bones. This technique reports morphometric parameters as averages over selected volumes of interest (VOIs). This study proposes the introduction of an additional global 2D morphometric step into the analysis process, that provides a survey of the underlying morphometric variation present throughout both trabecular and cortical bone. The visualisation of these morphometric distributions provides a systematic approach to VOI selection that provides rationale and adds confidence to subsequent 3D morphometric analysis. To test the applicability and value of this methodological addition it was applied to the distal femur of a rat model of spinal cord injury (SCI)-induced osteoporosis. The 2D morphometric variation of both trabecular and cortical bone was quantified as a function of bone length. SCI-induced osteoporosis was localised in i) trabecular bone, where metaphyseal bone was more severely affected than epiphyseal bone, and there was a significant reduction in Distal Femoral Trabecular Extent, a new parameter defined here that quantifies how far trabecular bone penetrates in to the marrow cavity, ii) cortical bone, where diaphyseal bone underwent significant lowering of both cortical area and thickness, while distal-metaphyseal bone did not. Theses site-specific changes were validated, further elucidated and compared with follow-up conventional 3D analysis. The techniques applied here are equally applicable to other long bones (tibia, humerus, radius, ulna), other types of imaging modality and other types of experimental design including the effects of rehabilitation, aging, loading, gene knockout and pharmacological intervention.

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2D morphological surveying identifies regions warranting further 3D investigation.

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Trabecular microarchitecture site-specifically varies in the distal femur.

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SCI-induced osteoporosis changes metaphyseal more than epiphyseal trabecular bone.

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SCI-induced osteoporosis reduced the extent of metaphyseal trabecular bone.

Gene expression changes are associated with severe bone loss and deficient fracture callus formation in rats with complete spinal cord injury

STUDY DESIGN

Animal study.

OBJECTIVES

To investigate the effects of SCI on bone quality and callus formation.

SETTING

University and hospital-based research center, Ribeirão Preto Medical School, Brazil.

METHODS

Rats sustaining a complete SCI for 10 days received a fracture at the femoral diaphysis and were followed-up for 14 days. Bone callus and contralateral nonfractured tibia were assessed by DXA, µCT, ELISA, histomorphometry, immunohistochemistry, biomechanical test, and gene expression.

RESULTS

SCI downregulated osteoblastic-related gene expression in the nonfractured tibias, associated with a twofold increase in osteoclasts and overexpression of RANK/RANKL, which resulted in lower bone mass, impaired microarchitecture, and weaker bones. On day 14 postfracture, we revealed early and increased trabecular formation in the callus of SCI rats, despite a marked 75% decrease in OPG-positive cells, and 41% decrease in density. Furthermore, these calluses showed higher porosity and thinner newly formed trabeculae, leading to lower strength and angle failure.

CONCLUSIONS

SCI-induced bone loss resulted from increased bone resorption and decreased bone formation. We also evidenced accelerated bone healing in the SCI rats, which may be attributed to the predominant intramembranous ossification. However, the newly formed bone was thinner, less dense, and more porous than those in the non-SCI rats. As a result, these calluses are weaker and tolerate lesser torsion deformation than the controls, which may result in recurrent fractures and characterizes a remarkable feature that may severely impair life quality.

Diet-induced Generalized Periodontitis in Lewis Rats

Periodontitis is an important public health concern worldwide. Because rodents from the genus Rattus are resistant to spontaneous periodontitis, experimental periodontitis must be initiated by mechanical procedures and interventions. Due to their exacerbated Th1 response and imbalanced Th17 regulatory T-cell responses, Lewis rats are highly susceptible to inducible inflammatory and autoimmune diseases. We hypothesized that feeding Lewis rats a diet high in sucrose and casein (HSC) would alter the oral microenvironment and induce inflammation and the development of periodontitis lesions without mechanical intervention. A baseline group (BSL, n = 8) was euthanized at age 6 wk. Beginning at 6 wk of age, 2 groups of Lewis rats were fed standard (STD, n = 12) or HSC (n = 20) chow and euthanized at 29 wk of age. We evaluated the degree of periodontitis through histology and μCT of maxillae and mandibles. The HSC-induced inflammatory response of periodontal tissues was assessed by using immunohistochemistry. Gene expression analysis of inflammatory cytokines associated with Th1 and Th17 responses, innate immunity cytokines, and tissue damage in response to bacteria were assessed also. The potential systemic effects of HSC diet were evaluated by assessing body composition and bone densitometry endpoints; serum leptin and insulin concentrations; and gene expression of inflammatory cytokines in the liver. Placing Lewis rats on HSC diet for 24 wk induced a host Th1-immune response in periodontal tissues and mild to moderate, generalized periodontitis characterized by inflammatory cell infiltration (predominantly T cells and macrophages), osteoclast resorption of alveolar bone, and hyperplasia and migration of the gingival epithelium. HSC-fed Lewis rats developed periodontitis without mechanical intervention in the oral cavity and in the absence of any noteworthy metabolic abnormalities. Consequently, the rat model we described here may be a promising approach for modeling mild to moderate periodontitis that is similar in presentation to the human disease.