Histochemical methods of detecting iron in the rodent brain result mainly in the labeling of oligodendrocytes, but as all cells utilize iron, this observation suggests that much of the iron in the central nervous system goes undetected. Paraffin embedding of tissue is a standard procedure that is used to prepare sections for microscopic analysis. In the present study, we questioned whether we could modify the iron histochemical procedure to enable a greater detection of iron in paraffin sections. Indeed, various modifications led to the widespread labeling of iron in mouse brain tissue (for instance, labeling of neurons and neuropil). Sites of focal concentrations, such as cytoplasmic punctate or nucleolar staining, were also observed. The modified procedures were applied to paraffin sections of a mouse model (APP/PS1) of Alzheimer's disease. Iron was revealed in the plaque core and rim. The plaque rim had a fibrillary or granular appearance, and it frequently contained iron-labeled cells. Further analysis indicated that the iron was tightly associated with the core of the plaque, but less so with the rim. In conclusion, modifications to the histochemical staining revealed new insights into the deposition of iron in the central nervous system. In theory, the approach should be transferrable to organs besides the brain and to other species, and the underlying principles should be incorporable into a variety of staining methods.
Heterotopic ossification (HO), the pathologic formation of extraskeletal bone, can be disabling and lethal. However, the underlying molecular mechanisms were largely unknown. The present study aimed to clarify the involvement of secreted protein acidic and rich in cysteine (SPARC) and the underlying mechanism in rat model of HO. The mechanistic investigation on roles of SPARC in HO was examined through gain- and loss-of-function approaches of SPARC, with alkaline-phosphatase (ALP) activity, mineralized nodules, and osteocalcin (OCN) content measured. To further confirm the regulatory role of SPARC, levels of mitogen-activated protein kinase (MAPK) signaling pathways-related proteins (extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), p38, nuclear factor κ-B (NF-κB), and IkB kinase β (IKKβ)) were determined. Bone marrow mesenchymal stem cells were treated with pathway inhibitor to investigate the relationship among SPARC, MAPK signaling pathway, and HO. The results suggested that SPARC expression was up-regulated in Achilles tendon tissues of HO rats. Silencing of SPARC could decrease phosphorylation of ERK, JNK, p38, NF-κB, and IKKβ. Additionally, silencing of SPARC or inhibition of MAPK signaling pathway could reduce the ALP activity, the number of mineralized nodules, and OCN content, thus impeding HO. To sum up, our study identifies the inhibitory role of SPARC gene silencing in HO via the MAPK signaling pathway, suggesting SPARC presents a potential target for HO therapy.
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