The mammary gland provides a spectacular example of physiological cell death whereby the cells that produce milk during lactation are removed swiftly, efficiently, and without inducing inflammation upon the cessation of lactation. The milk-producing cells arise primarily during pregnancy and comprise the alveolar lineage that is specified by signalling pathways and factors that are activated in response to pregnancy hormones. There are at least two alveolar sub-lineages, one of which is marked by the presence of binucleate cells that are especially susceptible to programmed cell death during involution. This process of post-lactational regression, or involution, is carefully orchestrated and occurs in two phases, the first results in a rapid switch in cell fate with the secretory epithelial cells becoming phagocytes whereupon they destroy dead and dying cells from milk. This reversible phase is followed by the second phase that is marked by an influx of immune cells and a remodelling of the gland to replace the alveolar cells with re-differentiated adipocytes, resulting in a return to the pre-pregnant state in preparation for any subsequent pregnancies. The mouse mammary gland provides an excellent experimental tool with which to investigate lineage commitment and the mechanisms of programmed cell death that occur in a normal physiological process. Importantly, involution has highlighted a role for lysoptosis, a mechanism of cell death that is mediated by lysosomal cathepsins and their endogenous inhibitors, serpins. In this review, I discuss alveolar lineage commitment during pregnancy and the programmed cell death pathways that destroy these cells during involution.

中文翻译：

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乳腺中的肺泡细胞：谱系定型和细胞死亡。

乳腺提供了一个生理性细胞死亡的壮观例子，在这种情况下，在哺乳期间产生乳汁的细胞被迅速、有效地去除，并且不会在哺乳停止时诱发炎症。产奶细胞主要在怀孕期间出现，并包含由信号通路和响应妊娠激素而激活的因子指定的肺泡谱系。至少有两个肺泡亚系，其中一个以双核细胞的存在为标志，这些细胞在退化过程中特别容易发生程序性细胞死亡。这种泌乳后退化或退化的过程是精心策划的，分两个阶段进行，第一个导致细胞命运的快速转变，分泌性上皮细胞变成吞噬细胞，随后它们从牛奶中摧毁死亡和垂死的细胞。这个可逆阶段之后是第二阶段，其标志是免疫细胞的涌入和腺体的重塑，以用重新分化的脂肪细胞取代肺泡细胞，从而恢复到孕前状态，为任何后续的任何准备做准备怀孕。小鼠乳腺提供了一种极好的实验工具，可用于研究谱系定型和正常生理过程中发生的程序性细胞死亡机制。重要的是，退化突出了溶细胞凋亡的作用，溶细胞凋亡是一种由溶酶体组织蛋白酶及其内源性抑制剂 serpin 介导的细胞死亡机制。在这篇评论中，