Podcasts 科学播客 | 「母乳喂养“偷”走了钙质，为什么妈妈的骨骼依然健康？」

Nick Petrić Howe

There’s a bit of a mystery when it comes to bones, how are they maintained while breastfeeding? You see, ordinarily the hormone oestrogen helps keep bones healthy, by maintaining bone formation and preventing them from being broken down. But oestrogen levels drop precipitously during lactation, a time when demands on the bone are incredibly high. To get enough calcium to make milk during breastfeeding, bones are stripped of the mineral. And while bone loss does occur during this time, mostly people are able to breastfeed without their bones completely eroding away. But without oestrogen how is this accomplished? Well, there are some clues in previous studies. A few years ago, a team found that deleting a certain gene in female mice led to them having unusually strong bones, but exactly how this happened wasn’t exactly clear. Now, though, the same team has gotten to the bottom of it, and discovered a protein that gets produced during lactation that is central to building bones. To find out more about this protein, I called up one of the authors, Holly Ingraham. She told me that they were pretty sure it was circulating in the blood, but finding out what exactly it was, was a whole other challenge.

关于骨骼有个谜团，母乳喂养期间骨骼是如何保持健康的呢？通常，雌激素通过维持骨形成并防止骨分解保持骨骼健康。然而，在哺乳期，雌激素水平急剧下降，这时对骨骼的需求却非常高。为了在母乳喂养期间获取足够的钙质，骨骼中的矿物质被剥离。虽然这段时间确实会有骨质流失，但大多数人仍能正常哺乳而不至于骨骼完全损耗。然而，缺乏雌激素的情况下是如何达到这种平衡的呢？一些线索来自之前的研究。几年前，一支团队发现删除某个基因的雌性小鼠骨骼异常强壮，但具体原因并不清楚。而现在，同一个团队揭示了原因，发现一种在哺乳期产生的蛋白质在骨骼生成中起关键作用。为了了解更多，我联系了研究作者之一Holly Ingraham。她告诉我，他们确信这种蛋白质在血液中循环，但要确认它是什么仍是一大挑战。

Holly Ingraham

Well, so after you know, various things you know, trying to set up a standard biochemical assay which did not work, trying to do mass spec, which did not work. I forget what else we tried. We tried–we tried, almost everything we could think of. But it was actually when Muriel Babey, who's one of the lead along with William Kraus, she came to lab, she decided to put these mutant mice on a high-fat diet. I mean, we knew that a high-fat diet may change the activity of these neurons, but we had no idea that what it was going to do. Which is that when we put these mice on high fat diet, we lost the bone phenotype, and then we basically had a hook to figure out, okay, what are the gene changes that occur in the body of these mutant mice? And we found a set of genes were changed, and we narrowed it down to two. And then it turned out that the gene that was responsible or encoded the protein that was responsible for this phenotype was this protein called cellular communication network-3, CCN-3. And then we showed, in many, many ways, that this is the protein that is really having a huge effect on bone.

嗯，在你知道的，经过各种尝试后，比如建立标准生化测定实验，没成功；做质谱分析，没成功。我已经不记得我们还尝试了什么。我们尝试了我们能想到的几乎一切。但实际上，当Muriel Babey来实验室时，她决定将这些突变小鼠置于高脂饮食中。我们知道高脂饮食可能会改变这些神经元的活动，但没想到它会有什么影响。结果是，当我们让这些小鼠吃高脂饮食时，我们失去了骨骼表型，这给了我们一个线索，让我们能找到突变小鼠体内发生了哪些基因变化。我们发现了一组基因发生了改变，并将范围缩小到两个基因。最终，负责这一表型的基因编码的是一种叫做CCN-3（细胞通信网络-3）的蛋白质。然后我们通过多种方式证明了这确实是对骨骼有巨大影响的蛋白质。

Nick Petrić Howe

And could you describe for me a couple of the ways that you showed this? Did you reduce the amount of this that the mice had? Increase it? That sort of thing, to sort of show the effects.

你能描述一下你们是如何证明这一点的吗？是减少小鼠体内的这种蛋白质还是增加它的表达，以此展示它（蛋白质）的作用？

Holly Ingraham

Right. So, we did sort of that classic, let's get rid of it in this mutant mice, which we did, and we saw that the bone was lost. Or let's take wild type control mice, and let's over express this. And then when we did that, we found that bone formation, bone volume, bone strength, all increased. So we– we came at this multiple ways. And then we also worked with my co-lead, which is Tom Ambrosi he did an experiment with his collaborators where they took two-year-old male mice. So, these are pretty feeble ‘old gentlemen’, as we would call them, and they do a fracture on these femurs. And then what he did is he took CCN-3 in a slow-release gel, so it just releases slowly over time, and then he looks at fracture repair. So what was amazing is that the fracture repair was accelerated and improved in these two-year-old mice. And really, when you look at it, they look like a fracture repair of a two-month-old mouse. So, you're really rejuvenating this whole system. So when I saw that data, I said, this is real. I believe it.

好的。我们采用了经典的方式，在突变小鼠中去除这种蛋白质，结果发现骨量减少。然后我们在正常小鼠中过表达这种蛋白质，结果发现骨形成、骨量和骨强度都增加了。我们用了多种方法来验证。此外，我的合作者Tom Ambrosi与他的合作团队也进行了实验，他们在两岁的雄性小鼠身上做了股骨骨折实验。然后他们将CCN-3加入缓释凝胶中，让它缓慢释放，观察骨折修复情况。令人惊讶的是，这些两岁小鼠的骨折修复加速且明显改善，修复效果接近两个月大小鼠的骨折修复。所以，当我看到这些数据时，我相信这是真的。

Nick Petrić Howe

It's interesting though as well, because, like you say, this was in male mice, and you won't have thought that this hormone, this protein, would be something that they would really, you know, be dealing with.

这很有意思，因为你提到这是在雄性小鼠身上进行的实验，而你原本不会想到这种蛋白质会在雄性中起作用。

Holly Ingraham

Well, okay, so that's the other beautiful thing about this project is that this is a female specific hormone, and we'll talk about when it comes on in normal females during lactation but what is really beautiful about this is it works on both male and female bone. So, the female specificity is just where it's being made and when it's being made by the female brain. But it's an equal opportunity hormone, so it works on both males and females, which is fantastic.

对，这也是这个项目的另一个亮点。这是一个雌性特异性激素，我们谈到它在雌性哺乳期的作用，但它对雄性和雌性骨骼都有作用。雌性特异性仅仅在于它在何时何地由雌性大脑产生。但它是一个平等的激素，对雄性和雌性骨骼都有效，这非常棒。

Nick Petrić Howe

So yeah, maybe that– we can talk about that, though. So what do you think this hormone is doing? Like, how does it play out in normal lactation cycle?

那么，这个激素在正常的哺乳周期中是如何起作用的呢？

Holly Ingraham

Right. So, after identifying CCN-3 as the hormone that was responsible for the this bone phenotype in these mutant mice, we then asked, well, is this relevant? Is this relevant to any physiology? Normally in phenomena. So, we– we looked at every stage possible, and again, thinking, oh, well, maybe it comes on after weaning, because we know that bone builds up after weaning, and we were really surprised that this hormone comes on right during lactation. So, a little bit right after birth, this hormone appears in the brain. It comes on like gangbusters. And so then, you know, you go back to the literature. This is where I tell young people, read, read the old literature. You're not the first to have discovered something. And so that's what we ended up doing. And we found some amazing literature from 20 years ago and even longer that, it's been known that during lactation bone formation is up but the net result is bone loss because you're resorbing it to strip calcium off. 

在确认CCN-3是导致突变小鼠骨骼表型的激素后，我们想知道这是否与正常的生理现象有关。我们查看了每一个可能的阶段，原本以为它可能在断奶后出现，因为我们知道断奶后骨骼会再生。但令人惊讶的是，这种激素在哺乳期就出现了，大约在分娩后不久，这种激素就会大量出现在大脑中。所以我们回顾了文献，发现20年前甚至更早的研究已经知道，哺乳期骨骼生成增加，但因为钙质被剥离，最终导致骨质流失。

Nick Petrić Howe

Right? So, during lactation, bones are being stripped for calcium and without oestrogen you'd expect them to be completely broken down, but this hormone is kind of stepping up to the plate and preventing this from happening.

对，哺乳期间骨骼中的钙质被剥离，按理说在没有雌激素的情况下骨骼会完全崩解，但这个激素起到了防止这一现象的作用。

Holly Ingraham

Exactly. And so you need a way of ensuring that you don't just crumble into nothingness when you're breastfeeding.

没错，你需要一个机制来确保哺乳时骨骼不会完全崩解。

Nick Petrić Howe

And I guess the other thing I was wondering as well is, your study was obviously focused on these mouse models. You have done a bit of work with human cells as well, but do you think the same thing happens in humans?

我还想知道，你们的研究主要是在小鼠模型上进行的，但你们也做了一些关于人类细胞的研究。你认为人类体内也有类似的情况吗？

Holly Ingraham

Well, that's a wonderful question. And Muriel Babey, who is an adult endocrinologist, I think, is going to be working with some clinical people, once we can get samples. And– and this stuff is really hard to detect in the blood because there's not really good reagents right now, which is the other thing we're trying to do. But I think once we get those reagents, that's one of the first questions. Is this relevant to humans? I'm going to guess, yes, but that has yet to be proved.

这是个好问题。Muriel Babey是成人内分泌学家，我认为她将与一些临床专家合作，一旦我们能获得样本就会开始研究。这种物质在血液中难以检测，因为目前没有好的检测试剂，这是我们正在努力解决的问题之一。但我认为，一旦我们有了这些试剂，这将是我们首先要探讨的问题之一。这在人体中是否相关？我猜测是的，但还没有证据证明。

Nick Petrić Howe

So you've got an idea of what role this hormone plays during breastfeeding, but I wonder what you think are the broader implications of this finding. There are a lot of diseases that affect bones, things like osteoporosis, where bones become weaker. Could this hormone be potentially something that people could look to.

你们已经了解了这个激素在哺乳期间的作用，我想知道它在更广泛的方面会有什么影响。很多骨骼疾病，例如骨质疏松症，都会导致骨骼变弱。你认为这种激素有可能成为治疗的靶点吗？

Holly Ingraham

Right, so I think that in terms of the translational aspects of this, I do think hopefully we'll get there someday. We hope that we can, because this is a natural hormone, very much like a GLP one that has now been used for obesity. And, you know, I'm hoping with new technology, we could really see if this can be translated. And I do think that the fracture repair data suggests that it looks promising. And I also think that it– there was just an article in the Washington Post describing a woman that had lactational osteoporosis, which can be really severe. And so, one wonders whether part of this whole pathway is disturbed in women like that, so that they're fine until they get challenged with this pregnancy and lactation. And so, the question is, are we going to find variants of this pathway in women like that that are susceptible to lactational osteoporosis?

我认为，在转化应用方面，我们希望有朝一日能够实现。这是一种天然激素，类似于目前用于治疗肥胖的GLP-1激素。我希望借助新技术，我们能够看到这种激素的应用潜力。骨折修复数据表明它很有前景。最近《华盛顿邮报》上有一篇文章提到了一位患有哺乳期骨质疏松症的女性，这种情况可能非常严重。所以我们也在想，是否有部分女性在怀孕和哺乳期间由于这种激素通路受损而导致骨骼问题。我们会研究这些女性是否有这种通路的变异，使她们更容易患上哺乳期骨质疏松症。

Nick Petrić Howe

That was Holly Ingraham, of the University of California, San Francisco, in the US. For more on that story, check out the show notes for some links.

这就是来自美国加州大学旧金山分校的Holly Ingraham。想了解更多相关信息，请查看节目笔记中的链接。