Clark Patsy, Dziarmaga Alison, Eccles Michael, Goodyer Paul
Department of Human Genetics, McGill University, Montreal, Quebec, Canada.
J Am Soc Nephrol. 2004 Feb;15(2):299-305. doi: 10.1097/01.asn.0000111248.23454.19.
In renal-coloboma syndrome (RCS), null mutations of the PAX2 gene cause renal hypoplasia due to a congenital deficit of nephrons; affected individuals may develop renal insufficiency in childhood. During normal kidney development, PAX2, is expressed at high levels throughout the arborizing ureteric bud (UB); recent observations suggest that one of its key roles is to suppress apoptosis in this collecting duct lineage. The authors hypothesized that increased UB cell apoptosis due to PAX2 haploinsufficiency must directly influence the rate of branching morphogenesis in developing kidney and the number of nephrons that can be formed before birth, when nephrogenesis in humans comes to an end. If so, the authors reasoned that caspase inhibitors might be used to suppress unwanted UB cell apoptosis during kidney development in Pax2(1Neu) mutant mice and rescue the genetic UB branching defect. E17.5 kidneys from Pax2(1Neu) mutant mice had smaller (-25%) longitudinal cross-sectional area and 3.5-fold increase in collecting duct cell apoptosis versus wild-type littermates; mutant E13.5 kidney explants allowed to arborize for 50 h in vitro had 18% fewer terminal branches than wild-types. However, exposure to the caspase inhibitor, Z-VAD-fmk (25 micro M), significantly increased terminal branch number in mutant explants (23%). It also increased branching in wild-type explants, apparently reflecting an effect of Z-VAD-fmk on basal apoptosis induced by ex vivo culture conditions. Similarly, when pregnant mice were injected daily with Z-VAD-fmk (10 micro g/g weight from E10.5 to E17.5), apoptosis of Pax2(1Neu) fetal collecting duct cells was suppressed to 40% of untreated mutants; by E14, terminal branch number was increased to 152% that of untreated litters. These studies support the hypothesis that PAX2 normally optimizes the rate of branching morphogenesis in fetal kidney by suppressing UB apoptosis. Furthermore, it suggests that caspase inhibitors can rescue the branching defect caused by PAX2 mutations.
在肾-眼裂综合征（RCS）中，PAX2基因的无效突变由于肾单位先天性缺陷导致肾发育不全；受影响个体在儿童期可能会出现肾功能不全。在正常肾脏发育过程中，PAX2在整个分支的输尿管芽（UB）中高水平表达；最近的观察表明，其关键作用之一是抑制该集合管谱系中的细胞凋亡。作者推测，由于PAX2单倍体不足导致的UB细胞凋亡增加必然会直接影响发育中肾脏的分支形态发生速率以及出生前（人类肾发生结束时）可形成的肾单位数量。如果是这样，作者推断半胱天冬酶抑制剂可能用于抑制Pax2(1Neu)突变小鼠肾脏发育过程中不必要的UB细胞凋亡，并挽救遗传性UB分支缺陷。与野生型同窝小鼠相比，Pax2(1Neu)突变小鼠E17.5期的肾脏纵向横截面积更小（-25%），集合管细胞凋亡增加3.5倍；在体外培养50小时以使其分支的突变型E13.5期肾脏外植体的终末分支比野生型少18%。然而，用半胱天冬酶抑制剂Z-VAD-fmk（25μM）处理可显著增加突变型外植体的终末分支数量（23%）。它还增加了野生型外植体的分支，这显然反映了Z-VAD-fmk对离体培养条件诱导的基础细胞凋亡的影响。同样，当怀孕小鼠从E10.5到E17.5每天注射Z-VAD-fmk（10μg/g体重）时，Pax2(1Neu)胎儿集合管细胞的凋亡被抑制至未处理突变体的40%；到E14时，终末分支数量增加至未处理同窝小鼠的152%。这些研究支持了PAX2通常通过抑制UB细胞凋亡来优化胎儿肾脏分支形态发生速率的假设。此外，这表明半胱天冬酶抑制剂可以挽救由PAX2突变引起的分支缺陷。
