Bone deterioration precedes overt motor symptoms in SOD1(G93A) ALS mice and is linked to osteoblast premature senescence, reduced osteogenic factors, and early structural deficits independent of muscle denervation.
Key Findings
Results
Three-point bending revealed significant reductions in femoral rigidity and maximum bending force in SOD1(G93A) mutants at presymptomatic stage P45.
Three-point bending biomechanical testing was performed on femora from presymptomatic (P45) and symptomatic (P110) SOD1(G93A) mice and wild-type controls.
Reductions in femoral rigidity and maximum bending force were statistically significant at P45, indicating early structural deficits before overt motor symptoms.
These biomechanical deficits were present at the presymptomatic stage, suggesting bone deterioration is not solely secondary to muscle denervation.
Results
Micro-CT analysis demonstrated reduced trabecular bone mineral density and trabecular thickness at P45, with progressive trabecular loss and cortical thinning by P110.
Micro-CT was used to assess bone microarchitecture at both presymptomatic (P45) and symptomatic (P110) stages.
Trabecular bone mineral density and thickness were reduced at P45 in SOD1(G93A) mice compared to controls.
By P110, SOD1(G93A) mice showed progressive trabecular loss in addition to cortical thinning, indicating worsening bone pathology with disease progression.
Results
Histological examination revealed marked osteoblast loss at P45 in SOD1(G93A) mice, suggesting impaired bone formation as the primary early mechanism of bone deterioration.
Histological examination of bone tissue was performed at the presymptomatic P45 stage.
A marked reduction in osteoblast number was observed in SOD1(G93A) mice compared to controls.
This osteoblast loss was identified as the primary early mechanism underlying bone structural deficits, preceding symptomatic motor neuron disease.
Results
Transcriptomic analysis of bulk bone and cultured osteoblasts from P45 SOD1(G93A) mice identified dysregulation of bone differentiation genes, including downregulation of osteoblast differentiation genes and upregulation of negative regulators of ossification.
Transcriptomics was performed on both bulk bone tissue and cultured osteoblasts isolated from P45 SOD1(G93A) mice.
Osteoblast differentiation genes were downregulated in SOD1(G93A) samples.
Negative regulators of ossification were upregulated in SOD1(G93A) samples.
These transcriptomic changes were present at the presymptomatic stage, consistent with early autonomous bone pathology.
Results
Transcriptomic profiling revealed increased cell senescence signatures and upregulation of the unfolded protein response in SOD1(G93A) osteoblasts at P45.
Cell senescence gene signatures were upregulated in bulk bone and cultured osteoblasts from P45 SOD1(G93A) mice.
Unfolded protein response pathways were upregulated specifically in SOD1(G93A) osteoblasts.
These findings link SOD1 mutation-associated proteotoxic stress to premature osteoblast senescence.
Results
Immunohistochemistry confirmed the osteoblast senescence phenotype with increased p16Ink4a levels in SOD1(G93A) osteoblasts.
Immunohistochemistry for the senescence marker p16Ink4a was performed on bone sections from SOD1(G93A) mice.
Increased p16Ink4a levels were detected in osteoblasts of SOD1(G93A) mice, confirming premature cellular senescence.
This finding corroborated the transcriptomic senescence signatures identified in bulk bone and cultured osteoblasts.
Conclusions
Bone deterioration in the SOD1(G93A) ALS mouse model precedes overt motor symptoms and is associated with osteoblast premature senescence.
Structural, cellular, and molecular bone deficits were all detected at the presymptomatic P45 stage.
The combination of early osteoblast loss, senescence markers, and transcriptomic dysregulation supports an autonomous bone pathology rather than one solely secondary to muscle denervation.
The authors conclude that bone alterations are part of the ALS disease process, not merely a downstream consequence of motor neuron loss.