Abstract
Muscle lim protein (MLP) has long been regarded as a cytosolic and nuclear muscular protein. Here, we show that MLP is also expressed in a subpopulation of adult rat dorsal root ganglia (DRG) neurons in response to axonal injury, while the protein was not detectable in naïve cells. Detailed immunohistochemical analysis of L4/L5 DRG revealed ~3% of MLP-positive neurons 2 days after complete sciatic nerve crush and maximum ~10% after 4–14 days. Similarly, in mixed cultures from cervical, thoracic, lumbar and sacral DRG ~6% of neurons were MLP-positive after 2 days and maximal 17% after 3 days. In both, histological sections and cell cultures, the protein was detected in the cytosol and axons of small diameter cells, while the nucleus remained devoid. Moreover, the vast majority could not be assigned to any of the well characterized canonical DRG subpopulations at 7 days after nerve injury. However, further analysis in cell culture revealed that the largest population of MLP expressing cells originated from non-peptidergic IB4-positive nociceptive neurons, which lose their ability to bind the lectin upon axotomy. Thus, MLP is mostly expressed in a subset of axotomized nociceptive neurons and can be used as a novel marker for this population of cells.
Highlights
Muscle lim protein (MLP), known as cysteine rich protein 3 (CRP3, CSRP3), is a member of the family of cysteine rich proteins (CRP)
The current study shows for the first time that MLP expression in mature neurons upon axotomy
Only a small percentage of dorsal root ganglia (DRG) neurons expressed this protein, most of which represented non-peptidergic nociceptors. As this neuronal subpopulation lost its Isolectin B4 (IB4) staining over time after injury, MLP could serve as a new marker to track the fate of these axotomized neurons
Summary
Muscle lim protein (MLP), known as cysteine rich protein 3 (CRP3, CSRP3), is a member of the family of cysteine rich proteins (CRP). Rat dorsal root ganglion (DRG) neurons reportedly express Mlp-RNA, the protein was never detected in these cells so that its translation remained questionable[1, 2]. MLP protein is located in the cytosol and/or nucleus of cardiac and skeletal myocytes There, it is essential for diverse biological processes, such as myocyte differentiation[4, 5], response to mechanical stress[6, 7], modulation of the actin-cytoskeleton[8], maintenance of the cytoarchitecture[9] and metabolism[10]. MLP can be used as a novel marker for this subpopulation of neurons
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