Kawakita Atsuo, Sato Kazuki, Makino Hatsune, Ikegami Hiroyasu, Takayama Shinichiro, Toyama Yoshiaki, Umezawa Akihiro
Department of Reproductive Biology, National Institute for Child Health and Development, Tokyo, Japan.
PLoS One. 2008;3(12):e3945. doi: 10.1371/journal.pone.0003945. Epub 2008 Dec 16.
Cigarette smoking adversely affects endochondral ossification during the course of skeletal growth. Among a plethora of cigarette chemicals, nicotine is one of the primary candidate compounds responsible for the cause of smoking-induced delayed skeletal growth. However, the possible mechanism of delayed skeletal growth caused by nicotine remains unclarified. In the last decade, localization of neuronal nicotinic acetylcholine receptor (nAChR), a specific receptor of nicotine, has been widely detected in non-excitable cells. Therefore, we hypothesized that nicotine affect growth plate chondrocytes directly and specifically through nAChR to delay skeletal growth.
METHODOLOGY/PRINCIPAL FINDINGS: We investigated the effect of nicotine on human growth plate chondrocytes, a major component of endochondral ossification. The chondrocytes were derived from extra human fingers. Nicotine inhibited matrix synthesis and hypertrophic differentiation in human growth plate chondrocytes in suspension culture in a concentration-dependent manner. Both human and murine growth plate chondrocytes expressed alpha7 nAChR, which constitutes functional homopentameric receptors. Methyllycaconitine (MLA), a specific antagonist of alpha7 nAChR, reversed the inhibition of matrix synthesis and functional calcium signal by nicotine in human growth plate chondrocytes in vitro. To study the effect of nicotine on growth plate in vivo, ovulation-controlled pregnant alpha7 nAChR +/- mice were given drinking water with or without nicotine during pregnancy, and skeletal growth of their fetuses was observed. Maternal nicotine exposure resulted in delayed skeletal growth of alpha7 nAChR +/+ fetuses but not in alpha7 nAChR -/- fetuses, implying that skeletal growth retardation by nicotine is specifically mediated via fetal alpha7 nAChR.
CONCLUSIONS/SIGNIFICANCE: These results suggest that nicotine, from cigarette smoking, acts directly on growth plate chondrocytes to decrease matrix synthesis, suppress hypertrophic differentiation via alpha7 nAChR, leading to delayed skeletal growth.
在骨骼生长过程中，吸烟会对软骨内成骨产生不利影响。在众多香烟化学成分中，尼古丁是导致吸烟引起骨骼生长延迟的主要候选化合物之一。然而，尼古丁导致骨骼生长延迟的可能机制仍未明确。在过去十年中，神经元烟碱型乙酰胆碱受体（nAChR），即尼古丁的特异性受体，已在非兴奋性细胞中被广泛检测到。因此，我们推测尼古丁通过nAChR直接且特异性地影响生长板软骨细胞，从而延迟骨骼生长。
方法/主要发现：我们研究了尼古丁对人生长板软骨细胞（软骨内成骨的主要成分）的影响。软骨细胞取自额外的人类手指。在悬浮培养中，尼古丁以浓度依赖的方式抑制人生长板软骨细胞的基质合成和肥大分化。人和小鼠的生长板软骨细胞均表达α7 nAChR，其构成功能性同五聚体受体。甲基lycaconitine（MLA），一种α7 nAChR的特异性拮抗剂，在体外逆转了尼古丁对人生长板软骨细胞基质合成和功能性钙信号的抑制作用。为了研究尼古丁对体内生长板的影响，在孕期给排卵受控的怀孕α7 nAChR +/-小鼠饮用含或不含尼古丁的水，并观察其胎儿的骨骼生长情况。母体暴露于尼古丁会导致α7 nAChR +/+胎儿的骨骼生长延迟，但不会导致α7 nAChR -/-胎儿的骨骼生长延迟，这意味着尼古丁引起的骨骼生长迟缓是通过胎儿α7 nAChR特异性介导的。
结论/意义：这些结果表明，吸烟产生的尼古丁直接作用于生长板软骨细胞，通过α7 nAChR减少基质合成，抑制肥大分化，导致骨骼生长延迟。
