Chaperone therapy for molecular pathology in lysosomal diseases

In lysosomal diseases, enzyme deficiency is caused by misfolding of mutant enzyme protein with abnormal steric structure that is expressed by gene mutation. Chaperone therapy is a new molecular therapeutic approach primarily for lysosomal diseases. The misfolded mutant enzyme is digested rapidly or aggregated to induce endoplasmic reticulum stress. As a result, the catalytic activity is lost. The following sequence of events results in chaperone therapy to achieve correction of molecular pathology. An orally administered low molecular competitive inhibitor (chaperone) is absorbed into the bloodstream and reaches the target cells and tissues. The mutant enzyme is stabilized by the chaperone and subjected to normal enzyme proteinfolding (proteostasis). The first chaperone drug was developed for Fabry disease and is currently available in medical practice. At present three types of chaperones are available: competitive chaperone with enzyme inhibitory bioactivity (exogenous), non-competitive (or allosteric) chaperone without inhibitory bioactivity (exogenous), and molecular chaperone (heat shock protein; endogenous). The third endogenous chaperone would be directed to overexpression or activated by an exogenous low-molecular inducer. This new molecular therapeutic approach, utilizing the three types of chaperone, is expected to apply to a variety of diseases, genetic or non-genetic, and neurological or non-neurological, in addition to lysosomal diseases.

Delivery of genome-editing biomacromolecules for treatment of lung genetic disorders

Genome-editing systems based on clustered, regularly interspaced, short palindromic repeat (CRISPR)/associated protein (CRISPR/Cas), are emerging as a revolutionary technology for the treatment of various genetic diseases. To date, the delivery of genome-editing biomacromolecules by viral or non-viral vectors have been proposed as new therapeutic options for lung genetic disorders, such as cystic fibrosis (CF) and α-1 antitrypsin deficiency (AATD), and it has been accepted that these delivery vectors can introduce CRISPR/Cas9 machineries into target cells or tissues in vitro, ex vivo and in vivo. However, the efficient local or systemic delivery of CRISPR/Cas9 elements to the lung, enabled by either viral or by non-viral carriers, still remains elusive. Herein, we first introduce lung genetic disorders and their current treatment options, and then summarize CRISPR/Cas9-based strategies for the therapeutic genome editing of these disorders. We further summarize the pros and cons of different routes of administration for lung genetic disorders. In particular, the potentials of aerosol delivery for therapeutic CRISPR/Cas9 biomacromolecules for lung genome editing are discussed and highlighted. Finally, current challenges and future outlooks in this emerging area are briefly discussed.

Small-molecule modulators of serine protease inhibitor proteins (serpins)

Serine protease inhibitors (serpins) are a large family of proteins that regulate and control crucial physiological processes, such as inflammation, coagulation, thrombosis and thrombolysis, and immune responses. The extraordinary impact that these proteins have on numerous crucial pathways makes them an attractive target for drug discovery. In this review, we discuss recent advances in research on small-molecule modulators of serpins, examine their mode of action, analyse the structural data from crystallised protein-ligand complexes, and highlight the potential obstacles and possible therapeutic perspectives. The application of in silico methods for rational drug discovery is also summarised. In addition, we stress the need for continued research in this field.

The Multifaceted Effects of Alpha1-Antitrypsin on Neutrophil Functions

Neutrophils are the predominant immune cells in human blood possessing heterogeneity, plasticity and functional diversity. The activation and recruitment of neutrophils into inflamed tissue in response to stimuli are tightly regulated processes. Alpha1-Antitrypsin (AAT), an acute phase protein, is one of the potent regulators of neutrophil activation via both -protease inhibitory and non-inhibitory functions. This review summarizes our current understanding of the effects of AAT on neutrophils, illustrating the interplay between AAT and the key effector functions of neutrophils.

Reactive Center Loop Insertion in α-1-Antitrypsin Captured by Accelerated Molecular Dynamics Simulation

Protease inhibition by metastable serine protease inhibitors (serpins) is mediated by one of the largest functional intradomain conformational changes known in biology. In this extensive structural rearrangement, protease-serpin complex formation triggers cleavage of the serpin reactive center loop (RCL), its subsequent insertion into central β-sheet A, and covalent trapping of the target protease. In this study, we present the first detailed accelerated molecular dynamics simulation of the insertion of the fully cleaved RCL in α-1-antitrypsin (α₁AT), the archetypal member of the family of human serpins. Our results reveal internal water pathways that allow the initial incorporation of side chains of RCL residues into the protein interior. We observed structural plasticity of the helix F (hF) element that blocks the RCL path in the native state, which is in excellent agreement with previous experimental reports. Furthermore, the simulation suggested a novel role of hF and the connected turn (thFs3A) as chaperones that support the insertion process by reducing the conformational space available to the RCL. Transient electrostatic interactions of RCL residues potentially fine-tune the serpin inhibitory activity. On the basis of our simulation, we generated the α₁AT mutants K168E, E346K, and K168E/E346K and analyzed their inhibitory activity along with their intrinsic stability and heat-induced polymerization. Remarkably, the E346K mutation exhibited enhanced inhibitory activity along with an increased rate of premature structural collapse (polymerization), suggesting a significant role of E346 in the gatekeeping of the strain in the metastable native state.

Measuring the Effect of Histone Deacetylase Inhibitors (HDACi) on the Secretion and Activity of Alpha-1 Antitrypsin

Alpha-1 antitrypsin deficiency (AATD) is a protein conformational disease with the most common cause being the Z-variant mutation in alpha-1 antitrypsin (Z-AAT). The misfolded conformation triggered by the Z-variant disrupts cellular proteostasis (protein folding) systems and fails to meet the endoplasmic reticulum (ER) export metrics, leading to decreased circulating AAT and deficient antiprotease activity in the plasma and lung. Here, we describe the methods for measuring the secretion and neutrophil elastase (NE) inhibition activity of AAT/Z-AAT, as well as the response to histone deacetylase inhibitor (HDACi), a major proteostasis modifier that impacts the secretion and function of AATD from the liver to plasma. These methods provide a platform for further therapeutic development of proteostasis regulators for AATD.

Update on alpha-1 antitrypsin deficiency: New therapies

α1-Antitrypsin deficiency is characterised by the misfolding and intracellular polymerisation of mutant α1-antitrypsin within the endoplasmic reticulum of hepatocytes. The retention of mutant protein causes hepatic damage and cirrhosis whilst the lack of an important circulating protease inhibitor predisposes the individuals with severe α1-antitrypsin deficiency to early onset emphysema. Our work over the past 25years has led to new paradigms for the liver and lung disease associated with α1-antitrypsin deficiency. We review here the molecular pathology of the cirrhosis and emphysema associated with α1-antitrypsin deficiency and show how an understanding of this condition provided the paradigm for a wider group of disorders that we have termed the serpinopathies. The detailed understanding of the pathobiology of α1-antitrypsin deficiency has identified important disease mechanisms to target. As a result, several novel parallel and complementary therapeutic approaches are in development with some now in clinical trials. We provide an overview of these new therapies for the liver and lung disease associated with α1-antitrypsin deficiency.

α1-Antitrypsin deficiency

α1-Antitrypsin deficiency (A1ATD) is an inherited disorder caused by mutations in SERPINA1, leading to liver and lung disease. It is not a rare disorder but frequently goes underdiagnosed or misdiagnosed as asthma, chronic obstructive pulmonary disease (COPD) or cryptogenic liver disease. The most frequent disease-associated mutations include the S allele and the Z allele of SERPINA1, which lead to the accumulation of misfolded α1-antitrypsin in hepatocytes, endoplasmic reticulum stress, low circulating levels of α1-antitrypsin and liver disease. Currently, there is no cure for severe liver disease and the only management option is liver transplantation when liver failure is life-threatening. A1ATD-associated lung disease predominately occurs in adults and is caused principally by inadequate protease inhibition. Treatment of A1ATD-associated lung disease includes standard therapies that are also used for the treatment of COPD, in addition to the use of augmentation therapy (that is, infusions of human plasma-derived, purified α1-antitrypsin). New therapies that target the misfolded α1-antitrypsin or attempt to correct the underlying genetic mutation are currently under development.

Aberrant disulphide bonding contributes to the ER retention of alpha1-antitrypsin deficiency variants

Mutations in alpha1-antitrypsin (AAT) can cause the protein to polymerise and be retained in the endoplasmic reticulum (ER) of hepatocytes. The ensuing systemic AAT deficiency leads to pulmonary emphysema, while intracellular polymers are toxic and cause chronic liver disease. The severity of this process varies considerably between individuals, suggesting the involvement of mechanistic co-factors and potential for therapeutically beneficial interventions. We show in Hepa1.6 cells that the mildly polymerogenic I (Arg39Cys) AAT mutant forms aberrant inter- and intra-molecular disulphide bonds involving the acquired Cys39 and the only cysteine residue in the wild-type (M) sequence (Cys232). Substitution of Cys39 to serine partially restores secretion, showing that disulphide bonding contributes to the intracellular retention of I AAT. Covalent homodimers mediated by inter-Cys232 bonding alone are also observed in cells expressing the common Z and other polymerising AAT variants where conformational behaviour is abnormal, but not in those expressing M AAT. Prevention of such disulphide linkage through the introduction of the Cys232Ser mutation or by treatment of cells with reducing agents increases Z AAT secretion. Our results reveal that disulphide interactions enhance intracellular accumulation of AAT mutants and implicate the oxidative ER state as a pathogenic co-factor. Redox modulation, e.g. by anti-oxidant strategies, may therefore be beneficial in AAT deficiency-associated liver disease.

An integrative approach combining ion mobility mass spectrometry, X-ray crystallography, and nuclear magnetic resonance spectroscopy to study the conformational dynamics of α1 -antitrypsin upon ligand binding

Native mass spectrometry (MS) methods permit the study of multiple protein species within solution equilibria, whereas ion mobility (IM)-MS can report on conformational behavior of specific states. We used IM-MS to study a conformationally labile protein (α1 -antitrypsin) that undergoes pathological polymerization in the context of point mutations. The folded, native state of the Z-variant remains highly polymerogenic in physiological conditions despite only minor thermodynamic destabilization relative to the wild-type variant. Various data implicate kinetic instability (conformational lability within a native state ensemble) as the basis of Z α1 -antitrypsin polymerogenicity. We show the ability of IM-MS to track such disease-relevant conformational behavior in detail by studying the effects of peptide binding on α1 -antitrypsin conformation and dynamics. IM-MS is, therefore, an ideal platform for the screening of compounds that result in therapeutically beneficial kinetic stabilization of native α1 -antitrypsin. Our findings are confirmed with high-resolution X-ray crystallographic and nuclear magnetic resonance spectroscopic studies of the same event, which together dissect structural changes from dynamic effects caused by peptide binding at a residue-specific level. IM-MS methods, therefore, have great potential for further study of biologically relevant thermodynamic and kinetic instability of proteins and provide rapid and multidimensional characterization of ligand interactions of therapeutic interest.