SPOC1 (PHF13) is required for spermatogonial stem cell differentiation and sustained spermatogenesis.

SPOC1 (PHF13) is a recently identified protein that has been shown to dynamically associate with somatic chromatin, to modulate chromatin compaction and to be important for proper cell division. Here, we report on the expression of SPOC1 in promyelocytic leukaemia zinc finger (PLZF)-positive undifferentiated spermatogonial stem cells (SSCs) of the mouse testis. To investigate further the biological function of SPOC1 in germ cells we generated Spoc1 mutant mice from a gene-trap embryonic stem cell clone. Postpubertal homozygous Spoc1(-/-) animals displayed a pronounced progressive loss of germ cells from an initially normal germ epithelium of the testis tubules leading to testis hypoplasia. This loss first affected non-SSC stages of germ cells and then, at a later time point, the undifferentiated spermatogonia. Remarkably, successive loss of all germ cells (at >20 weeks of age) was preceded by a transient increase in the number of undifferentiated A(aligned) (A(al)) spermatogonia in younger mice (at >10 weeks of age). The number of primary Spoc1(-/-) gonocytes, the proliferation of germ cells, and the initiation and progression of meiosis was normal, but we noted a significantly elevated level of apoptosis in the Spoc1(-/-) testis. Taken together, the data argue that SPOC1 is indispensable for stem cell differentiation in the testis and for sustained spermatogenesis.

Fluphenazine reduces proteotoxicity in C. elegans and mammalian models of alpha-1-antitrypsin deficiency.

The classical form of α1-antitrypsin deficiency (ATD) is associated with hepatic fibrosis and hepatocellular carcinoma. It is caused by the proteotoxic effect of a mutant secretory protein that aberrantly accumulates in the endoplasmic reticulum of liver cells. Recently we developed a model of this deficiency in C. elegans and adapted it for high-content drug screening using an automated, image-based array scanning. Screening of the Library of Pharmacologically Active Compounds identified fluphenazine (Flu) among several other compounds as a drug which reduced intracellular accumulation of mutant α1-antitrypsin Z (ATZ). Because it is representative of the phenothiazine drug class that appears to have autophagy enhancer properties in addition to mood stabilizing activity, and can be relatively easily re-purposed, we further investigated its effects on mutant ATZ. The results indicate that Flu reverses the phenotypic effects of ATZ accumulation in the C. elegans model of ATD at doses which increase the number of autophagosomes in vivo. Furthermore, in nanomolar concentrations, Flu enhances the rate of intracellular degradation of ATZ and reduces the cellular ATZ load in mammalian cell line models. In the PiZ mouse model Flu reduces the accumulation of ATZ in the liver and mediates a decrease in hepatic fibrosis. These results show that Flu can reduce the proteotoxicity of ATZ accumulation in vivo and, because it has been used safely in humans, this drug can be moved rapidly into trials for liver disease due to ATD. The results also provide further validation for drug discovery using C. elegans models that can be adapted to high-content drug screening platforms and used together with mammalian cell line and animal models.

An autophagy-enhancing drug promotes degradation of mutant alpha1-antitrypsin Z and reduces hepatic fibrosis.

In the classical form of alpha1-antitrypsin (AT) deficiency, a point mutation in AT alters the folding of a liver-derived secretory glycoprotein and renders it aggregation-prone. In addition to decreased serum concentrations of AT, the disorder is characterized by accumulation of the mutant alpha1-antitrypsin Z (ATZ) variant inside cells, causing hepatic fibrosis and/or carcinogenesis by a gain-of-toxic function mechanism. The proteasomal and autophagic pathways are known to mediate degradation of ATZ. Here we show that the autophagy-enhancing drug carbamazepine (CBZ) decreased the hepatic load of ATZ and hepatic fibrosis in a mouse model of AT deficiency-associated liver disease. These results provide a basis for testing CBZ, which has an extensive clinical safety profile, in patients with AT deficiency and also provide a proof of principle for therapeutic use of autophagy enhancers.