Human induced pluripotent stem cells (hIPSCs) represent a unique opportunity for regenerative medicine since they offer the prospect of generating unlimited quantities of cells for autologous transplantation as a novel treatment for a broad range of disorders1,2,3,4. However, the use of hIPSCs in the context of genetically inherited human disease will require correction of disease-causing mutations in a manner that is fully compatible with clinical applications3,5. The methods currently available, such as homologous recombination, lack the necessary efficiency and also leave residual sequences in the targeted genome6. Therefore, the development of new approaches to edit the mammalian genome is a prerequisite to delivering the clinical promise of hIPSCs. Here, we show that a combination of zinc finger nucleases (ZFNs)7 and piggyBac8,9 technology in hIPSCs can achieve bi-allelic correction of a point mutation (Glu342Lys) in the α1-antitrypsin (A1AT, also called SERPINA1) gene that is responsible for α1-antitrypsin deficiency (A1ATD). Genetic correction of hIPSCs restored the structure and function of A1AT in subsequently derived liver cells in vitro and in vivo. This approach is significantly more efficient than any other gene targeting technology that is currently available and crucially prevents contamination of the host genome with residual non-human sequences. Our results provide the first proof of principle for the potential of combining hIPSCs with genetic correction to generate clinically relevant cells for autologous cell-based therapies.

. Here, we examined the use of human iPS cells for modeling inherited metabolic disorders of the liver. Dermal fibroblasts from patients with various inherited metabolic diseases of the liver were used to generate a library of patient-specific human iPS cell lines. Each line was differentiated into hepatocytes using what we believe to be a novel 3-step differentiation protocol in chemically defined conditions. The resulting cells exhibited properties of mature hepatocytes, such as albumin secretion and cytochrome P450 metabolism. Moreover, cells generated from patients with 3 of the inherited metabolic conditions studied in further detail (α 1 -antitrypsin deficiency, familial hypercholesterolemia, and glycogen storage disease type 1a) were found to recapitulate key pathological features of the diseases affecting the patients from which they were derived, such as aggregation of misfolded α 1 -antitrypsin in the endoplasmic reticulum, deficient LDL receptor-mediated cholesterol uptake, and elevated lipid and glycogen accumulation. Therefore, we report a simple and effective platform for hepatocyte generation from patient-specific human iPS cells. These patient-derived hepatocytes demonstrate that it is possible to model diseases whose phenotypes are caused by pathological dysregulation of key processes within adult cells.

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Endoplasmic reticulum (ER) dysfunction is important in the pathogenesis of many neurological diseases. In this review, we examine the evidence for ER dysfunction in a range of neurological conditions including cerebral ischaemia, sleep apnoea, Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, the prion diseases and Familial Encephalopathy with Neuroserpin Inclusion Bodies (FENIB). Protein misfolding in the endoplasmic reticulum initiates a well-studied 'Unfolded Protein Response' in energy-starved neurones during stroke that is relevant to the toxicity of reperfusion. The toxic peptide Aβ induces 'ER stress' in Alzheimer's disease leading to activation of similar pathways, while the accumulation of polymeric neuroserpin in the neuronal ER triggers a poorly understood 'ER overload response'. In other neurological disorders such as Parkinson's and Huntington's diseases ER dysfunction is well recognised but the mechanisms for this are less clear. By targeting components of these signalling responses, it may prove possible to ameliorate their toxic effects and treat a range of neurodegenerative conditions. 1 IMPLICATIONS OF ENDOPLASMIC RETICULUM DYSFUNCTION

Alpha 1 -antitrypsin is the most abundant circulating protease inhibitor. The severe Z deficiency allele (Glu342Lys) causes the protein to undergo a conformational transition and form ordered polymers that are retained within hepatocytes. This causes neonatal hepatitis, cirrhosis, and hepatocellular carcinoma. We have developed a conformation-specific monoclonal antibody (2C1) that recognizes the pathological polymers formed by a 1 -antitrypsin. This antibody was used to characterize the Z variant and a novel shutter domain mutant (His334Asp; a 1 -antitrypsin King's) identified in a 6-week-old boy who presented with prolonged jaundice. His334Asp a 1 -antitrypsin rapidly forms polymers that accumulate within the endoplasmic reticulum and show delayed secretion when compared to the wild-type M a 1 -antitrypsin. The 2C1 antibody recognizes polymers formed by Z and His334Asp a 1 -antitrypsin despite the mutations directing their effects on different parts of the protein. This antibody also recognized polymers formed by the Siiyama (Ser53Phe) and Brescia (Gly225Arg) mutants, which also mediate their effects on the shutter region of a 1 -antitrypsin. Conclusion: Z and shutter domain mutants of a 1 -antitrypsin form polymers with a shared epitope and so are likely to have a similar structure. (HEPATOLOGY 2010;52:1078-1088 T he serpinopathies are conformational diseases characterized by the polymerization and intracellular retention of members of the serine protease inhibitor or serpin superfamily of proteins.1 The best known is a 1 -antitrypsin deficiency, with the most common severe deficiency allele being the Z mutation (Glu342Lys). This mutation results in the retention of ordered polymers of a 1 -antitrypsin as periodic acid Schiff positive inclusion bodies within the endoplasmic reticulum (ER) of hepatocytes.2 These inclusions predispose the individual homozygous for the Z variant of the a 1 -antitrypsin protease inhibitor (PI*Z) to neonatal hepatitis, cirrhosis, and rarely, hepatocellular carcinoma.3 Deficiency of circulating a 1 -antitrypsin results in early onset panlobular emphysema.

Familial encephalopathy with neuroserpin inclusion bodies (FENIB) is an autosomal dominant dementia that is characterized by the retention of polymers of neuroserpin as inclusions within the endoplasmic reticulum (ER) of neurons. We have developed monoclonal antibodies that detect polymerized neuroserpin and have used COS-7 cells, stably transfected PC12 cell lines and transgenic Drosophila melanogaster to characterize the cellular handling of all four mutant forms of neuroserpin that cause FENIB. We show a direct correlation between the severity of the disease-causing mutation and the accumulation of neuroserpin polymers in cell and fly models of the disease. Moreover, mutant neuroserpin causes locomotor deficits in the fly allowing us to demonstrate a direct link between polymer accumulation and neuronal toxicity.

Point mutants of α1-antitrypsin form ordered polymers that are retained as inclusions within the endoplasmic reticulum (ER) of hepatocytes in association with neonatal hepatitis, cirrhosis and hepatocellular carcinoma. These inclusions cause cell damage and predispose to ER stress in the absence of the classical unfolded protein response (UPR). The pathophysiology underlying this ER stress was explored by generating cell models that conditionally express wildtype α1-antitrypsin, two mutants that cause polymer-mediated inclusions and liver disease (E342K [the Z allele] and H334D) and a truncated mutant (Null Hong Kong, NHK) that induces classical ER stress and is removed by ER associated degradation. Expression of the polymeric mutants resulted in gross changes in the ER luminal environment that recapitulated the changes seen in liver sections from individuals with PI*ZZ α1-antitrypsin deficiency. In contrast expression of NHK α1-antitrypsin caused electron lucent dilatation and expansion of the ER throughout the cell. Photobleaching microscopy in live cells demonstrated a decrease in the mobility of soluble luminal proteins in cells that express E342K and H334D α1-antitrypsin when compared to those that express wildtype and NHK α1-antitrypsin (0.34±0.05, 0.22±0.03, 2.83±0.30 and 2.84±0.55 μm2/s respectively). There was no effect on protein mobility within ER membranes indicating that cisternal connectivity was not disrupted. Polymer expression alone was insufficient to induce the UPR but the resulting protein overload rendered cells hypersensitive to ER stress induced by either tunicamycin or glucose depletion. Conclusion Changes in protein diffusion provide an explanation for the cellular consequences of ER protein overload in mutants that cause inclusion body formation and α1-antitrypsin deficiency.

The dementia familial encephalopathy with neuroserpin inclusion bodies (FENIB) is caused by the accumulation of mutant neuroserpin within neurons (Davis, R. L., Shrimpton, A. E., Holohan, P. D., Bradshaw, C., Feiglin, D., Sonderegger, P., Kinter, J., Becker, L. M., Lacbawan, F., Krasnewich, D., Muenke, M., Lawrence, D. A., Yerby, M. S., Shaw, C.-M., Gooptu, B., Elliott, P. R., Finch, J. T., Carrell, R. W., and Lomas, D. A. (1999) Nature 401, 376 -379), but little is known about the trafficking of wild type and mutant neuroserpins. We have established a cell model to study the processing of wild type neuroserpin and the Syracuse (S49P) and Portland (S52R) mutants that cause FENIB. Here we show that Syracuse and Portland neuroserpin are retained soon after their synthesis in the endoplasmic reticulum and that the limiting step in their processing is the transport to the Golgi complex. This is in contrast to the wild type protein, which is secreted into the culture medium. Mutant neuroserpin is retained within the endoplasmic reticulum as polymers, similar to those isolated from the intraneuronal inclusions in the brains of individuals with FENIB. Remarkably, the Portland mutant showed faster accumulation and slower secretion compared with the Syracuse mutant, in keeping with the more severe clinical phenotype found in patients with the Portland variant of neuroserpin. Both mutant and wild type neuroserpin were partially degraded by proteasomes. Taken together, our results provide further understanding of how cells handle defective but ordered mutant proteins and provide strong support for a common mechanism of disease caused by mutants of the serine protease inhibitor superfamily.Neuroserpin is a member of the serpin superfamily and is predominantly expressed by neurons of the developing and adult brain. This serpin is secreted from the axonal growth cones of the central and peripheral nervous system, where it inhibits the enzyme tissue plasminogen activator (1-5). The expression pattern of neuroserpin and its in vitro inhibitory activity implicate this serpin in regulating axonal growth, reducing seizure activity, controlling damage in cerebral infarction, and regulating emotional behavior and memory (6 -10).We have recently described an autosomal dominant dementia, familial encephalopathy with neuroserpin inclusion bodies (FENIB), 1 that is characterized by inclusions of mutant neuroserpin within cortical and subcortical neurons (11-13). This dementia is unusual in that the inclusions result from the retention of ordered polymers of neuroserpin, most likely within the endoplasmic reticulum (ER) of neurons (11). Moreover, the number of inclusions is directly related to the molecular instability caused by the mutation and inversely proportional to the age of onset of dementia (13). For example, the Syracuse mutation (S49P) causes dementia in middle age, whereas the more severe Portland mutant (S52R) causes more inclusions and an onset of dementia in the early 20s. Polymers of the serpins result from the sequential...