Department of Medical Sciences and Public Health, University of Cagliari, Electron Microscopy Laboratory, Division Pathological Anatomy, Cagliari, Italy.
Eur Rev Med Pharmacol Sci. 2022 Nov;26(22):8502-8507. doi: 10.26355/eurrev_202211_30385.
The notochord acts as a patterning structure, playing a key role in the formation of the vertebral column, both indirectly by inducing sclerotome cell differentiation and directly by forming the nucleus pulposus of intervertebral discs. The abnormal development of the notochord results in an easy equation with a variety of birth defects. Therefore, we focused our attention on the analysis of the early stages of human notochord development by highlighting the role of progenitor stem cells involved in the origin of intervertebral discs (IVDs).
Eight human fetuses, ranging from 8 up to 21 weeks of gestational age, were obtained from spontaneous abortion or voluntary interruption of gestation. Samples were 10% formalin-fixed, routinely processed, and paraffin-embedded. Five micron-tick paraffin sections were obtained from each sample. Sections were stained with hematoxylin-eosin and PAS stain for a morphological examination. Tissue samples were immunostained with a commercial anti-human CD44 rabbit monoclonal antibody at 1:100 dilution.
Immunoreactivity for CD44 was detected in six out of eight notochords examined in this study. Reactivity for CD44 was restricted to progenitor cells giving rise to the nucleus pulposus (NP) of the developing IVDs. Positive cells showed a membranous and/or cytoplasmic immunostaining, no reactivity was observed in the nuclear compartment. CD44 expression was always restricted to IVD precursor cells, whereas cartilage precursors were devoid of labelling.
Our study shows, for the first time, that the stem cell marker CD44 selectively marks intervertebral disc progenitor cells, paralleling their differentiation toward a discogenic phenotype. Therefore, our results suggest that CD44 plays a key role in IVD development, allowing its differentiation from surrounding undifferentiated notochordal cells toward a IVD phenotype. Given the role of CD44 in IVD development, we may hypothesize that low CD44 levels might be associated with changes in IVD development and with susceptibility to develop back pain later in life.
脊索作为一种模式结构，通过诱导软骨细胞分化和直接形成椎间盘的髓核，在椎骨的形成中起着关键作用。脊索的异常发育导致与多种出生缺陷易位。因此，我们通过强调参与椎间盘（IVD）起源的祖细胞的作用，将注意力集中在人脊索发育的早期阶段的分析上。
从自然流产或自愿终止妊娠中获得了 8 个人类胎儿，胎龄从 8 周到 21 周不等。样品用 10％福尔马林固定，常规处理，石蜡包埋。从每个样品中获得 5 微米的细石蜡切片。用苏木精-伊红和 PAS 染色对切片进行形态学检查。用商业抗人 CD44 兔单克隆抗体以 1:100 稀释度对组织样品进行免疫染色。
在本研究中检查的 8 个脊索中有 6 个检测到 CD44 的免疫反应性。CD44 的反应性仅限于产生发育中的 IVD 髓核（NP）的祖细胞。阳性细胞显示膜和/或细胞质免疫染色，核区没有反应。CD44 表达始终局限于 IVD 前体细胞，而软骨前体细胞没有标记。
我们的研究首次表明，干细胞标记物 CD44 选择性地标记椎间盘祖细胞，与其向椎间盘发生表型分化平行。因此，我们的结果表明 CD44 在 IVD 发育中起关键作用，允许其从周围未分化的脊索细胞分化为 IVD 表型。鉴于 CD44 在 IVD 发育中的作用，我们可以假设 CD44 水平降低可能与 IVD 发育的变化以及日后易患腰痛的易感性有关。
