Dynamic changes of p27(kip1) and Skp2 expression in injured rat sciatic nerve

The role of kinases in peripheral nerve regeneration: mechanisms and implications

Peripheral nerve injury disease is a prevalent traumatic condition in current medical practice. Despite the present treatment approaches, encompassing surgical sutures, autologous nerve or allograft nerve transplantation, tissue engineering techniques, and others, an effective clinical treatment method still needs to be discovered. Exploring novel treatment methods to improve peripheral nerve regeneration requires more effort in investigating the cellular and molecular mechanisms involved. Many factors are associated with the regeneration of injured peripheral nerves, including the cross-sectional area of the injured nerve, the length of the nerve gap defect, and various cellular and molecular factors such as Schwann cells, inflammation factors, kinases, and growth factors. As crucial mediators of cellular communication, kinases exert regulatory control over numerous signaling cascades, thereby participating in various vital biological processes, including peripheral nerve regeneration after nerve injury. In this review, we examined diverse kinase classifications, distinct nerve injury types, and the intricate mechanisms involved in peripheral nerve regeneration. Then we stressed the significance of kinases in regulating autophagy, inflammatory response, apoptosis, cell cycle, oxidative processes, and other aspects in establishing conductive microenvironments for nerve tissue regeneration. Finally, we briefly discussed the functional roles of kinases in different types of cells involved in peripheral nerve regeneration.

p27Kip1 Deficiency Impairs Brown Adipose Tissue Function Favouring Fat Accumulation in Mice

The aim of this work was to investigate the effect of the whole-body deletion of p27 on the activity of brown adipose tissue and the susceptibility to develop obesity and glucose homeostasis disturbances in mice, especially when subjected to a high fat diet. p27 knockout (p27^-/-) and wild type (WT) mice were fed a normal chow diet or a high fat diet (HFD) for 10-weeks. Body weight and composition were assessed. Insulin and glucose tolerance tests and indirect calorimetry assays were performed. Histological analysis of interscapular BAT (iBAT) was carried out, and expression of key genes/proteins involved in BAT function were characterized by qPCR and Western blot. iBAT activity was estimated by ¹⁸F-fluorodeoxyglucose (¹⁸FDG) uptake with microPET. p27^-/- mice were more prone to develop obesity and insulin resistance, exhibiting increased size of all fat depots. p27^-/- mice displayed a higher respiratory exchange ratio. iBAT presented larger adipocytes in p27^-/- HFD mice, accompanied by downregulation of both Glut1 and uncoupling protein 1 (UCP1) in parallel with defective insulin signalling. Moreover, p27^-/- HFD mice exhibited impaired response to cold exposure, characterized by a reduced iBAT ¹⁸FDG uptake and difficulty to maintain body temperature when exposed to cold compared to WT HFD mice, suggesting reduced thermogenic capacity. These data suggest that p27 could play a role in BAT activation and in the susceptibility to develop obesity and insulin resistance.

Comparative study of microarray and experimental data on Schwann cells in peripheral nerve degeneration and regeneration: big data analysis

A Schwann cell has regenerative capabilities and is an important cell in the peripheral nervous system. This microarray study is part of a bioinformatics study that focuses mainly on Schwann cells. Microarray data provide information on differences between microarray-based and experiment-based gene expression analyses. According to microarray data, several genes exhibit increased expression (fold change) but they are weakly expressed in experimental studies (based on morphology, protein and mRNA levels). In contrast, some genes are weakly expressed in microarray data and highly expressed in experimental studies; such genes may represent future target genes in Schwann cell studies. These studies allow us to learn about additional genes that could be used to achieve targeted results from experimental studies. In the current big data study by retrieving more than 5000 scientific articles from PubMed or NCBI, Google Scholar, and Google, 1016 (up- and downregulated) genes were determined to be related to Schwann cells. However, no experiment was performed in the laboratory; rather, the present study is part of a big data analysis. Our study will contribute to our understanding of Schwann cell biology by aiding in the identification of genes. Based on a comparative analysis of all microarray data, we conclude that the microarray could be a good tool for predicting the expression and intensity of different genes of interest in actual experiments.

Releasing 'brakes' to nerve regeneration: intrinsic molecular targets

Restoring critical neuronal architecture after peripheral nerve injury is challenging. Although immediate regenerative responses to peripheral axon injury involve the synthesis of regeneration-associated proteins in neurons and Schwann cells, an unfavorable balance between growth facilitatory and growth inhibitory signaling impairs the growth continuum of injured peripheral nerves. Molecules involved with the signaling network of tumor suppressors play crucial roles in shifting the balance between growth and restraint during axon regeneration. An understanding of the molecular framework of tumor suppressor molecules in injured neurons and its impact on stage-specific regeneration events may expose therapeutic intervention points. In this review we discuss how signaling networks of the specific tumor suppressors PTEN, Rb1, p53, p27 and p21 are altered in injured peripheral nerves and how this impacts peripheral nerve regeneration. Insights into the roles and importance of these pathways may open new avenues for improving the neurological deficits associated with nerve injury.

Peripheral nerve injury induces down-regulation of Foxo3a and p27kip1 in rat dorsal root ganglia

FOXO3a, as a forkhead transcription factor, can control cell cycle through transcriptionally down-regulating p27(kip1) level, which is a key regulator of the mammalian cell cycle and a good candidate to regulate multiple aspects of neurogenesis. To elucidate their expression and function in nervous system lesion and repair, we performed an acute sciatic nerve crush model and studied differential expressions of Foxo3a and p27(kip1) in lumbar dorsal root ganglia. Temporally, Foxo3a protein level was reduced 1 day after injury, and following Foxo3a down-regulation, p27(kip1) mRNA and protein levels were also decreased after injury. Spatially, decreased levels of Foxo3a and p27(kip1) were predominant in neurons and glial cells, which were regenerating axons and largely proliferated after injury, respectively. Together with previous reports, we hypothesized decreased levels of Foxo3a and p27(kip1) in lumbar dorsal root ganglia were implicated in axonal regeneration and the proliferation of glial cells after sciatic nerve injury.

The cyclin-dependent kinase inhibitor p57kip2 is a negative regulator of Schwann cell differentiation and in vitro myelination

The p57kip2 gene encodes a member of the cyclin-dependent kinase inhibitor family, proteins known to block G(1)/S transition during the mammalian cell cycle. We observed that expression of p57kip2 in Schwann cells of the developing and injured adult peripheral nervous system is dynamically regulated. Using gene knockdown by means of vector-based RNA interference in cultured primary Schwann cells we found that reduced levels of p57kip2 lead to cell cycle exit, actin filament stabilization, altered cell morphology and growth, and down-regulation of promyelinating markers as well as induction of myelin genes and proteins. In addition, we could demonstrate that in vitro myelination is enhanced by p57kip2-suppressed Schwann cells. Using microarray technology we found that these cellular reactions are specific to lowered p57kip2 expression levels and detected a shift of the transcriptional expression program toward the pattern known from Schwann cells in developing peripheral nerves. Because in the absence of axons primary Schwann cells normally do not display differentiation-associated reactions, we conclude that we have identified a mechanism and an important intrinsic negative regulator of myelinating glia differentiation.