Elastogenic protein expression of a highly elastic murine spinal ligament: the ligamentum flavum.

Spinal ligaments, such as the ligamentum flavum (LF), are prone to degeneration and iatrogenic injury that can lead to back pain and nerve dysfunction. Repair and regeneration strategies for these tissues are lacking, perhaps due to limited understanding of spinal ligament formation, the elaboration of its elastic fibers, maturation and homeostasis. Using immunohistochemistry and histology, we investigated murine LF elastogenesis and tissue formation from embryonic to mature postnatal stages. We characterized the spatiotemporal distribution of the key elastogenic proteins tropoelastin, fibrillin-1, fibulin-4 and lysyl oxidase. We found that elastogenesis begins in utero with the microfibril constituent fibrillin-1 staining intensely just before birth. Elastic fibers were first detected histologically at postnatal day (P) 7, the earliest stage at which tropoelastin and fibulin-4 stained intensely. From P7 to P28, elastic fibers grew in diameter and became straighter along the axis. The growth of elastic fibers coincided with intense staining of tropoelastin and fibulin-4 staining, possibly supporting a chaperone role for fibulin-4. These expression patterns correlated with reported skeletal and behavioral changes during murine development. This immunohistochemical characterization of elastogenesis of the LF will be useful for future studies investigating mechanisms for elastogenesis and developing new strategies for treatment or regeneration of spinal ligaments and other highly elastic tissues.

Pathomechanism of loss of elasticity and hypertrophy of lumbar ligamentum flavum in elderly patients with lumbar spinal canal stenosis.

STUDY DESIGN: A histologic, biologic, and immunohistochemical assessment using human samples of lumbar ligamentum flavum. OBJECTIVE: To clarify the pathomechanism of loss of elasticity and hypertrophy of the lumbar ligamentum flavum (LF) in the elderly population. SUMMARY OF BACKGROUND DATA: The most common spinal disorder in elderly patients is lumbar spinal canal stenosis, causing low back and leg pain, and paresis. Canal narrowing, in part, results from hypertrophy of the LF. Although histologic and biologic literature on this topic is available, the pathomechanism of loss of elasticity and hypertrophy of the LF is still unknown. METHODS: One fetus, 5 young, and 5 elderly LF were obtained for histologic study. Hematoxylin and eosin, Alcian blue, Masson Trichrome, and Elastica Van Gieson stains were performed for each LF. Nine LF were collected and were used for biologic study of real time RT-PCR to quantitatively measure mRNA expression of Type I collagen and elastin in each LF. RESULTS: In the LF of the fetus, elastic fibers accounted for about 75% of the entire area. In the dural aspect of the LF in the young and elderly group, the ratio was also around 75%; however, the ratio of the dorsal aspect decreased with age. Almost half of the area showing loss of elastic fibers was shown to be converted to cartilaginous tissue producing Type II collagen and proteoglycan by Alcian blue and Type II collagen immunohistochemistry. The area, which did not stain black with EV nor blue with AB stain, was positively stained blue with T stain, indicating scarring. The area of the normal dural layer was 18.0 +/- 2.3 and 33.8 +/- 4.3 (mm2), for young and elderly group, respectively. Accordingly, it was 3.2 +/- 0.8 and 18.0 +/- 10.2 (mm2), for the dorsal abnormal layer. Elastin mRNA showed a relatively strong correlation (r = 0.44) with age; however, the slope was very gentle. Type I collagen mRNA showed a very strong correlation (r = 0.80) with age. The slope was steeper, and the value reached at 1000% (10-fold) around 65 years old when compared with the LF from younger patient. Elastin mRNA showed a weak correlation (r = 0.36) with thickness, and the slope was gentle. Type I collagen mRNA showed relatively strong correlation (r = 0.52) with thickness. The slope was steeper, and the line reached at 1000% (10-fold) around 6.5 (mm) when compared with a thin LF. CONCLUSION: Decreased elasticity of LF in the elderly is due to the loss of elastic fibers and a concomitant increase of collagenous fibers in the dorsal aspect. LF hypertrophy could be due to the thickening of the normal elastic layer as well as of the abnormal collagenous layer.