Severe Spinal Cord Injury Causes Immediate Multi-cellular Dysfunction at the Chondro-Osseous Junction

Osteoclast-specific Plastin 3 knockout in mice fail to develop osteoporosis despite dramatic increased osteoclast resorption activity

PLS3 loss-of-function mutations in humans and mice cause X-linked primary osteoporosis. However, it remains largely unknown how PLS3 mutations cause osteoporosis and which function PLS3 plays in bone homeostasis. A recent study showed that ubiquitous Pls3 KO in mice results in osteoporosis. Mainly osteoclasts were impacted in their function However, it has not been proven if osteoclasts are the major cell type affected and responsible for osteoporosis development in ubiquitous Pls3 KO mice. Here, we generated osteoclast-specific Pls3 KO mice. Additionally, we developed a novel polyclonal PLS3 antibody that showed specific PLS3 loss in immunofluorescence staining of osteoclasts in contrast to previously available antibodies against PLS3, which failed to show PLS3 specificity in mouse cells. Moreover, we demonstrate that osteoclast-specific Pls3 KO causes dramatic increase in resorptive activity of osteoclasts in vitro. Despite these findings, osteoclast-specific Pls3 KO in vivo failed to cause any osteoporotic phenotype in mice as proven by micro-CT and three-point bending test. This demonstrates that the pathomechanism of PLS3-associated osteoporosis is highly complex and cannot be reproduced in a system singularly focused on one cell type. Thus, the loss of PLS3 in alternative bone cell types might contributes to the osteoporosis phenotype in ubiquitous Pls3 KO mice.

A human bone infection organ model for biomaterial research

The aim of this work was to establish an organ model for staphylococcal infection of human bone samples and to investigate the influence and efficacy of a microporous β-tricalcium phosphate ceramic (β-TCP, RMS Foundation) loaded with hydrogels (alginate, alginate-di-aldehyde (ADA)-gelatin) and clindamycin on infected human bone tissue over a period of 28 days. For this purpose, human tibia plateaus, collected during total knee replacement surgery, were used as a source of bone material. Samples were infected with S. aureus ATCC29213 and treated with differently loaded β-TCP composites (alginate +/- clindamycin, ADA-gelatin +/- clindamycin, unloaded). The loading of the composites was carried out by means of a flow chamber. The infection was observed for 28 days, quantifying bacteria in the medium and the osseus material on day 1, 7, 14, 21 and 28. All samples were histologically processed for bone vitality evaluation. Bone infection could be consistently performed within the organ model. In addition, a strong reduction in bacterial counts was recorded in the groups treated with ADA-gelatin + clindamycin and alginate + clindamycin, while the bacterial count in the control groups remained constant. No significant differences between groups could be observed in the number of lacunae filled with osteocytes suggesting no differences in bone vitality among groups. In an ex-vivo human bone infection model, over a period of 28 days bacterial growth could be reduced by treatment with ADA-Gel + CLI and ALG + CLI -releasing β-TCP composites. This could be relevant for its clinical use. Further work will be necessary to improve the loading of β-TCP and the bone infection organ model itself. STATEMENT OF SIGNIFICANCE: The common treatment of bone infections is debridement and systemic administration of antibiotics. In some cases, antibiotic-containing carriers are already used, but these must be removed again. Our work is intended to show another treatment option. The scaffold we have developed, made of a calcium phosphate ceramic and a hydrogel as the active substance carrier, can, in addition to releasing the active substance, also assume a load-bearing function of the bone and is biodegradable. In addition, the model we developed can also be used for the analysis and treatment of bone infections other than those of the musculoskeletal system. More importantly, it can also serve as a substitute for previously used animal experiments.

Inhibition of TGF-β Signaling Attenuates Disuse-induced Trabecular Bone Loss After Spinal Cord Injury in Male Mice

Bone loss is one of the most common complications of immobilization after spinal cord injury (SCI). Whether transforming growth factor (TGF)-β signaling plays a role in SCI-induced disuse bone loss has not been determined. Thus, 16-week-old male mice underwent sham or spinal cord contusion injury to cause complete hindlimb paralysis. Five days later, 10 mg/kg/day control (IgG) or anti-TGF-β1,2,3 neutralizing antibody (1D11) was administered twice weekly for 4 weeks. Femurs were examined by micro-computed tomography (micro-CT) scanning and histology. Bone marrow (BM) supernatants were analyzed by enzyme-linked immunosorbent assay for levels of procollagen type 1 intact N-terminal propeptide (P1NP), tartrate-resistant acid phosphatase (TRAcP-5b), receptor activator of nuclear factor-kappa B ligand (RANKL), osteoprotegerin (OPG), and prostaglandin E2 (PGE2). Distal femoral micro-CT analysis showed that SCI-1D11 mice had significantly (P < .05) attenuated loss of trabecular fractional bone volume (123% SCI-1D11 vs 69% SCI-IgG), thickness (98% vs 81%), and connectivity (112% vs 69%) and improved the structure model index (2.1 vs 2.7). Histomorphometry analysis revealed that osteoclast numbers were lower in the SCI-IgG mice than in sham-IgG control. Biochemically, SCI-IgG mice had higher levels of P1NP and PGE2 but similar TRAcP-5b and RANKL/OPG ratio to the sham-IgG group. The SCI-1D11 group exhibited higher levels of P1NP but similar TRAcP-5b, RANKL/OPG ratio, and PGE2 to the sham-1D11 group. Furthermore, 1D11 treatment prevented SCI-induced hyperphosphorylation of tau protein in osteocytes, an event that destabilizes the cytoskeleton. Together, inhibition of TGF-β signaling after SCI protects trabecular bone integrity, likely by balancing bone remodeling, inhibiting PGE2 elevation, and preserving the osteocyte cytoskeleton.

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.

Growth profile assessment of young adults with tethered cord syndrome: a retrospective cohort analysis of Korean conscription data

PURPOSE

Tethered cord syndrome (TCS) is characterized by progressive spinal cord degeneration secondary to congenital spinal dysraphism. The associated accompanying physical inactivity and musculoskeletal deformities have raised interest in the growth profile of adult TCS patients. However, few previous studies have investigated the growth profile of adult TCS patients.

METHODS

We retrospectively reviewed the demographic data and medical records of 20-year-old Korean conscription examinees who were registered between April 2004 and September 2019. In total, 151 examinees with a diagnosis of TCS were enrolled. The height, weight, and body mass index (BMI) of 300 randomly selected examinees were compared to the TCS group. Obesity was defined by the World Health Organization and Asian-Pacific criteria for BMI and compared between the groups. Growth profile differences according to tethering location and musculoskeletal deformities were analyzed in both groups.

RESULTS

The mean height, weight, and BMI values of the TCS group were lower than those of the control group. The TCS group had a lower proportion of obese and overweight individuals, and a higher proportion of underweight individuals, according to both BMI criteria. The tethering level was not associated with the degree of obesity in the tethered group. The mean height, weight, and BMI were lower in the tethered group regardless of the existence of musculoskeletal deformity.

CONCLUSION

Enrollees with a history of TCS were smaller than controls of the same age. Monitoring of health behaviors, including nutrition, diet, and exercise, is warranted for TCS patients.

Absence of αβ T cells accelerates disuse bone loss in male mice after spinal cord injury

Whether T cells promote bone loss following immobilization after spinal cord injury (SCI) remains undetermined. Therefore, wild-type (WT) and T cell-deficient (Tcrb-/- ) male mice underwent sham or contusion SCI to cause hindlimb paralysis. Femurs were isolated and distal and midshaft regions were evaluated by microcomputed tomography scanning. Bone marrow (BM) levels of bone turnover markers, as well as receptor activator of nuclear factor-kappa B ligand (RANKL) and osteoprotegerin (OPG), were measured by ELISA. At 2 weeks post-SCI, immobilization resulted in marked reduction in trabecular fractional bone volume (55%), thickness (40%), connectivity, and cortical thickness only in the Tcrb-/- animals (interaction with P < 0.05). BM analysis revealed lower bone formation (procollagen type 1 intact N-terminal propeptide), higher bone resorption (tartrate-resistant acid phosphatase-5b), and a higher RANKL/OPG ratio in the Tcrb-/- SCI animals. At 5 weeks post-SCI, while both WT and Tcrb-/- paralyzed animals showed deterioration of all indices of bone structure, they were more severe in Tcrb-/- animals. In summary, unlike other skeletal disorders, loss of αβ T cells compromises, rather than preserves, skeletal integrity under conditions of immobilization.

[Study on vascular remodeling, inflammatory response, and their correlations in acute spinal cord injury in rats]

Objective

To study the local vascular remodeling, inflammatory response, and their correlations following acute spinal cord injury (SCI) with different grades, and to assess the histological changes in SCI rats.

Methods

One hundred and sixteen adult female Sprague Dawley rats were randomly divided into 4 groups ( n=29). The rats in sham group were received laminectomy only. A standard MASCIS spinal cord compactor was applied with drop height of 12.5, 25.0, or 50.0 mm to establish the mild, moderate, or severe SCI model, respectively. Quantitative rat endothelial cell antigen 1 (RECA1) and CD68 positive areas and the correlations were studied by double immunofluorescent (DIF) staining at 12 hours, 24 hours, 3 days, 7 days, and 28 days following SCI. Moreover, qualitative neurofilament-H (NF-H) and glial fibrillary acidic protein (GFAP) positive glial cells were studied by DIF staining at 28 days. ELISA was used to detect the levels of tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and IL-6 in spinal cord homogenates at 12 hours, 24 hours, and 3 days, and the correlations between TNF-α, IL-1β, or IL-6 levels and microvascular density (RECA1) were accordingly studied. Moreover, the neural tissue integrity and neuron damage were assessed by HE staining at 12 hours, 24 hours, 3 days, 7 days, and 28 days, and Nissl's staining at 28 days following SCI, respectively.

Results

DIF staining revealed that the ratio of RECA1 positive area was the highest in moderate group, higher in mild and severe groups, and the lowest in sham group with significant differences between groups ( P<0.05). The ratio of CD68 positive area was the highest in severe group, higher in moderate and mild groups, and the lowest in sham group with significant differences between groups ( P<0.05), except the comparisons between mild and moderate groups at 24 hours and 28 days after SCI ( P>0.05). There was no significant correlation between the RECA1 and CD68 expressions in sham group at different time points ( P>0.05). At 12 and 24 hours after SCI, the RECA1 and CD68 expressions in mild and moderate groups showed significant positive correlations ( P<0.05), while no significant correlation was found in severe group ( P>0.05). No significant correlations between the RECA1 and CD68 expressions was shown in all SCI groups at 3 days and in severe group at 7 days ( P>0.05), while the negative correlations were shown in mild and moderate groups at 7 days, and in all SCI groups at 28 days ( P<0.05). In mild, moderate, and severe groups, the axons became disrupted, shorter and thicker rods-like, or even merged blocks with increased injury, while the astrocytes decreased in number, unorganized and condensed in appearance. ELISA studies showed that TNF-α, IL-1β, and IL-6 levels in sham group were significantly lower than those in other 3 groups at different time points ( P>0.05). The differences in TNF-α, IL-1β, and IL-6 levels between SCI groups at different time points were sinificant ( P<0.05), except IL-1β levels between the mild and moderate groups at 12 hours ( P>0.05). Three inflammatory factors were all significantly correlated with the microvascular density grades ( P<0.05). Histological analysis indicated that the damage to spinal cord tissue structure correlated with the extent of SCI. In severe group, local hemorrhage, edema, and infiltration of inflammatory cells were found the most drastic, the grey/white matter boundary was disappeared concurrently with the formation of cavity and shortage of normal neurons.

Conclusion

In the acute stage following mild or moderate SCI, progressively aggravated injury result in higher microvessel density and increased inflammation. However, at the SCI region, the relation between microvessel density and inflammation inverse with time in the different grades of SCI. Accordingly, the destruction of neural structures positively relate to the grades of SCI and severity of inflammation.

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

To elucidate mechanisms of bone loss after spinal cord injury (SCI), we evaluated the time-course of cancellous and cortical bone microarchitectural deterioration via microcomputed tomography, measured histomorphometric and circulating bone turnover indices, and characterized the development of whole bone mechanical deficits in a clinically relevant experimental SCI model. 16-weeks-old male Sprague-Dawley rats received T₉ laminectomy (SHAM, n = 50) or moderate-severe contusion SCI (n = 52). Outcomes were assessed at 2-weeks, 1-month, 2-months, and 3-months post-surgery. SCI produced immediate sublesional paralysis and persistent hindlimb locomotor impairment. Higher circulating tartrate-resistant acid phosphatase 5b (bone resorption marker) and lower osteoblast bone surface and histomorphometric cancellous bone formation indices were present in SCI animals at 2-weeks post-surgery, suggesting uncoupled cancellous bone turnover. Distal femoral and proximal tibial cancellous bone volume, trabecular thickness, and trabecular number were markedly lower after SCI, with the residual cancellous network exhibiting less trabecular connectivity. Periosteal bone formation indices were lower at 2-weeks and 1-month post-SCI, preceding femoral cortical bone loss and the development of bone mechanical deficits at the distal femur and femoral diaphysis. SCI animals also exhibited lower serum testosterone than SHAM, until 2-months post-surgery, and lower serum leptin throughout. Our moderate-severe contusion SCI model displayed rapid cancellous bone deterioration and more gradual cortical bone loss and development of whole bone mechanical deficits, which likely resulted from a temporal uncoupling of bone turnover, similar to the sequalae observed in the motor-complete SCI population. Low testosterone and/or leptin may contribute to the molecular mechanisms underlying bone deterioration after SCI.

Daily parathyroid hormone administration enhances bone turnover and preserves bone structure after severe immobilization-induced bone loss

Immobilization, as a result of motor‐complete spinal cord injury (SCI), is associated with severe osteoporosis. Whether parathyroid hormone (PTH) administration would reduce bone loss after SCI remains unclear. Thus, female mice underwent sham or surgery to produce complete spinal cord transection. PTH (80 μg/kg) or vehicle was injected subcutaneously (SC) daily starting on the day of surgery and continued for 35 days. Isolated tibias and femurs were examined by microcomputed tomography scanning (micro‐CT) and histology and serum markers of bone turnover were measured. Micro‐CT analysis of tibial metaphysis revealed that the SCI‐vehicle animals exhibited 49% reduction in fractional trabecular bone volume and 18% in trabecular thickness compared to sham‐vehicle controls. SCI‐vehicle animals also had 15% lower femoral cortical thickness and 16% higher cortical porosity than sham‐vehicle counterparts. Interestingly, PTH administration to SCI animals restored 78% of bone volume, increased connectivity to 366%, and lowered structure model index by 10% compared to sham‐vehicle animals. PTH further favorably attenuated femoral cortical bone loss to 5% and prevented the SCI‐associated cortical porosity. Histomorphometry evaluation of femurs of SCI‐vehicle animals demonstrated a marked 49% and 38% decline in osteoblast and osteoclast number, respectively, and 35% reduction in bone formation rate. In contrast, SCI‐PTH animals showed preserved osteoblast and osteoclast numbers and enhanced bone formation rate. Furthermore, SCI‐PTH animals had higher levels of bone formation and resorption markers than either SCI‐ or sham‐vehicle groups. Collectively, these findings suggest that intermittent PTH receptor activation is an effective therapeutic strategy to preserve bone integrity after severe immobilization.

Testosterone Plus Finasteride Prevents Bone Loss without Prostate Growth in a Rodent Spinal Cord Injury Model

We have reported that testosterone-enanthate (TE) prevents the musculoskeletal decline occurring acutely after spinal cord injury (SCI), but results in a near doubling of prostate mass. Our purpose was to test the hypothesis that administration of TE plus finasteride (FIN; type II 5α-reductase inhibitor) would prevent the chronic musculoskeletal deficits in our rodent severe contusion SCI model, without inducing prostate enlargement. Forty-three 16-week-old male Sprague-Dawley rats received: 1) SHAM surgery (T₉ laminectomy); 2) severe (250 kdyne) contusion SCI; 3) SCI+TE (7.0 mg/week, intramuscular); or 4) SCI+TE+FIN (5 mg/kg/day, subcutaneous). At 8 weeks post-surgery, SCI animals exhibited reduced serum testosterone and levator ani/bulbocavernosus (LABC) muscle mass, effects that were prevented by TE. Cancellous and cortical (periosteal) bone turnover (assessed by histomorphometry) were elevated post-SCI, resulting in reduced distal femur cancellous and cortical bone mass (assessed by microcomputed tomography). TE treatment normalized cancellous and cortical bone turnover and maintained cancellous bone mass at the level of SHAM animals, but produced prostate enlargement. FIN coadministration did not inhibit the TE-induced musculoskeletal effects, but prevented prostate growth. Neither drug regimen prevented SCI-induced cortical bone loss, although no differences in whole bone strength were present among groups. Our findings indicate that TE+FIN prevented the chronic cancellous bone deficits and LABC muscle loss in SCI animals without inducing prostate enlargement, which provides a rationale for the inclusion of TE+FIN in multimodal therapeutic interventions intended to alleviate the musculoskeletal decline post-SCI.

Osteocytic signalling pathways as therapeutic targets for bone fragility

Osteocytes are differentiated osteoblasts that become surrounded by matrix during the process of bone formation. Acquisition of the osteocyte phenotype is achieved by profound changes in gene expression that facilitate adaptation to the changing cellular environment and constitute the molecular signature of osteocytes. During osteocytogenesis, the expression of genes that are characteristic of the osteoblast are altered and the expression of genes and/or proteins that impart dendritic cellular morphology, regulate matrix mineralization and control the function of cells at the bone surface are ordely modulated. The discovery of mutations in human osteocytic genes has contributed, in a large part, to our understanding of the role of osteocytes in bone homeostasis. Osteocytes are targets of the mechanical force imposed on the skeleton and have a critical role in integrating mechanosensory pathways with the action of hormones, which thereby leads to the orchestrated response of bone to environmental cues. Current, therapeutic approaches harness this accumulating knowledge by targeting osteocytic signalling pathways and messengers to improve skeletal health.

Treatment with resveratrol attenuates sublesional bone loss in spinal cord-injured rats

BACKGROUND AND PURPOSE

Sublesional osteoporosis predisposes individuals with spinal cord injury (SCI) to an increased risk of low-trauma fracture. The aim of the present work was to investigate the effect of treatment with resveratrol (RES) on sublesional bone loss in spinal cord-injured rats.

EXPERIMENTAL APPROACH

Complete SCI was generated by surgical transaction of the cord at the T10-12 level. Treatment with RES (400 mg·kg(-1) body mass per day(-1) , intragastrically) was initiated 12 h after the surgery for 10 days. Then, blood was collected and femurs and tibiae were removed for evaluation of the effects of RES on bone tissue after SCI.

KEY RESULTS

Treatment of SCI rats with RES prevented the reduction of bone mass including bone mineral content and bone mineral density in tibiae, preserved bone structure including trabecular bone volume fraction, trabecular number, and trabecular thickness in tibiae, and preserved mechanical strength including ultimate load, stiffness, and energy in femurs. Treatment of SCI rats with RES enhanced femoral total sulfhydryl content, reduced femoral malondialdehyde and IL-6 mRNA levels. Treatment of SCI rats with RES suppressed the up-regulation of mRNA levels of PPARγ, adipose-specific fatty-acid-binding protein and lipoprotein lipase, and restored mRNA levels of Wnt1, low-density lipoprotein-related protein 5, Axin2, ctnnb1, insulin-like growth factor 1 (IGF-1) and receptor for IGF-1 in femurs and tibiae.

CONCLUSIONS AND IMPLICATIONS

Treatment with RES attenuated sublesional bone loss in spinal-cord-injured rats, associated with abating oxidative stress, attenuating inflammation, depressing PPARγ signalling, and restoring Wnt/β-catenin and IGF-1 signalling.

Apoptotic osteocytes and the control of targeted bone resorption

Studies from the 1950s and 1960s already recognize the fact that osteocytes, although long living cells, die, as evidenced by accumulation of osteocytic lacunae devoid of cells. More recently, it was demonstrated that these cells die by apoptosis. The rate of osteocyte apoptosis is regulated by the age of the bone, as well as by systemic hormones, local growth factors, cytokines, pharmacological agents, and mechanical forces. Apoptotic osteocytes, in turn, recruit osteoclasts to initiate targeted bone resorption. This results in the removal of "dead" bone and may improve the mechanical properties of the skeleton. However, the molecular regulators of osteocyte survival and targeted bone remodeling are not completely known. In this review, the current knowledge on the molecular mechanism that lead to osteocyte death or survival, and the signals that mediate targeted bone resorption is discussed.