Germline loss of PKM2 promotes metabolic distress and hepatocellular carcinoma

Alternative splicing of the Pkm gene product generates the PKM1 and PKM2 isoforms of pyruvate kinase, and PKM2 expression is closely linked to embryogenesis, tissue regeneration, and cancer. To interrogate the functional requirement for PKM2 during development and tissue homeostasis, we generated germline PKM2 null mice (Pkm2-/-). Unexpectedly, despite being the primary isoform expressed in most wild-type adult tissues, we found that Pkm2-/- mice are viable and fertile. Thus, PKM2 is not required for embryonic or postnatal development. Loss of PKM2 leads to compensatory expression of PKM1 in the tissues that normally express PKM2. Strikingly, PKM2 loss leads to spontaneous development of hepatocellular carcinoma (HCC) with high penetrance that is accompanied by progressive changes in systemic metabolism characterized by altered systemic glucose homeostasis, inflammation, and hepatic steatosis. Therefore, in addition to its role in cancer metabolism, PKM2 plays a role in controlling systemic metabolic homeostasis and inflammation, thereby preventing HCC by a non-cell-autonomous mechanism. RNA was isolated from flash frozen ground whole liver tissue of 35 week old PKM2 KO and WT mice. Three independent mice from each condition were used as biological replicates.Pkm基因产物通过可变剪接生成丙酮酸激酶（pyruvate kinase）的PKM1与PKM2两种同工型，PKM2的表达与胚胎发生、组织再生及肿瘤发生密切相关。为探究PKM2在发育与组织稳态中的功能需求，我们构建了生殖系PKM2敲除小鼠（Pkm2-/-）。令人意外的是，尽管PKM2是多数野生型成年组织中的主要表达同工型，但Pkm2-/-小鼠仍可正常存活并繁育。由此可见，PKM2并非胚胎发育或出生后发育所必需。PKM2缺失会导致原本表达PKM2的组织中出现PKM1的代偿性表达。值得注意的是，PKM2缺失会以高外显率诱导自发性肝细胞癌（hepatocellular carcinoma, HCC）发生，同时伴随以全身葡萄糖稳态紊乱、炎症反应及肝脂肪变性为特征的进行性全身代谢改变。因此，除参与肿瘤代谢过程外，PKM2还可通过调控全身代谢稳态与炎症反应，以非细胞自主机制预防肝细胞癌的发生。本研究从35周龄的PKM2敲除（KO）与野生型（WT）小鼠的速冻研磨全肝组织中提取总RNA，每组各使用3只独立小鼠作为生物学重复。