Identification of interaction sites between human betaA3- and alphaA/alphaB-crystallins by mammalian two-hybrid and fluorescence resonance energy transfer acceptor photobleaching methods

Dynamic imaging of the effect of mesenchymal stem cells on osteoclast precursor cell chemotaxis for bone defects in the mouse skull

Background/purpose

Mesenchymal stem cells (MSCs) transplantation has previously been used in the field of regenerative medicine. Although bone regeneration is known to occur through the interaction between osteoblasts and osteoclasts, the effect of MSCs on osteoclasts is unknown. Therefore, the purpose of this study was to investigate the effect of MSCs on the chemotaxis of osteoclast precursor cells (RAW264 macrophage cells).

Materials and methods

Bone defects were created in mice skulls, and MSCs and a scaffold of carbonated hydroxyapatite were transplanted into the bone defects. RAW264 cells were then transplanted into the mouse tail vein, and their dynamics were observed by an in vivo imaging system.

Results

The fluorescent intensity of the MSCs transplant group at the bone defect region was significantly higher on days 3, 5, and 7 compared with the MSCs non-transplant group.

Conclusion

Increased RAW264 chemotaxis to the bone defect region occurred following the simultaneous implantation of MSCs in the skull defect.

Interaction of βA3-Crystallin with Deamidated Mutants of αA- and αB-Crystallins

Interaction among crystallins is required for the maintenance of lens transparency. Deamidation is one of the most common post-translational modifications in crystallins, which results in incorrect interaction and leads to aggregate formation. Various studies have established interaction among the α- and β-crystallins. Here, we investigated the effects of the deamidation of αA- and αB-crystallins on their interaction with βA3-crystallin using surface plasmon resonance (SPR) and fluorescence lifetime imaging microscopy-fluorescence resonance energy transfer (FLIM-FRET) methods. SPR analysis confirmed adherence of WT αA- and WT αB-crystallins and their deamidated mutants with βA3-crystallin. The deamidated mutants of αA–crystallin (αA N101D and αA N123D) displayed lower adherence propensity for βA3-crystallin relative to the binding affinity shown by WT αA-crystallin. Among αB-crystallin mutants, αB N78D displayed higher adherence propensity whereas αB N146D mutant showed slightly lower binding affinity for βA3-crystallin relative to that shown by WT αB-crystallin. Under the in vivo condition (FLIM-FRET), both αA-deamidated mutants (αA N101D and αA N123D) exhibited strong interaction with βA3-crystallin (32±4% and 36±4% FRET efficiencies, respectively) compared to WT αA-crystallin (18±4%). Similarly, the αB N78D and αB N146D mutants showed strong interaction (36±4% and 22±4% FRET efficiencies, respectively) with βA3-crystallin compared to 18±4% FRET efficiency of WT αB-crystallin. Further, FLIM-FRET analysis of the C-terminal domain (CTE), N-terminal domain (NTD), and core domain (CD) of αA- and αB-crystallins with βA3-crystallin suggested that interaction sites most likely reside in the αA CTE and αB NTD regions, respectively, as these domains showed the highest FRET efficiencies. Overall, results suggest that similar to WT αA- and WTαB-crystallins, the deamidated mutants showed strong interactionfor βA3-crystallin. Variable in vitro and in vivo interactions are most likely due to the mutant’s large size oligomers, reduced hydrophobicity, and altered structures. Together, the results suggest that deamidation of α-crystallin may facilitate greater interaction and the formation of large oligomers with other crystallins, and this may contribute to the cataractogenic mechanism.

Multidimensional significance of crystallin protein-protein interactions and their implications in various human diseases

BACKGROUND

Crystallins are the important structural and functional proteins in the eye lens responsible for refractive index. Post-translational modifications (PTMs) and mutations are major causative factors that affect crystallin structural conformation and functional characteristics thus playing a vital role in the etiology of cataractogenesis.

SCOPE OF REVIEW

The significance of crystallin protein-protein interactions (PPIs) in the lens and non-lenticular tissues is summarized.

MAJOR CONCLUSIONS

Aberrancy of PPIs between crystallin, its associated protein and metal ions has been accomplished in various human diseases including cataract. A detailed account on multidimensional structural and functional significance of crystallin PPI in humans must be brought into limelight, in order to understand the biochemical and molecular basis augmenting the aberrancies of such interaction. In this scenario, the present review is focused to shed light on studies which will aid to expand our present understanding on disease pathogenesis related to loss of PPI thereby paving the way for putative future therapeutic targets to curb such diseases.

GENERAL SIGNIFICANCE

The interactions with α-crystallins always aid to protect their structural and functional characteristics. The up-regulation of αB-crystallin in the non-lenticular tissues always decodes as biomarker for various stress related disorders. For better understanding and treatment of various diseases, PPI studies provide overall outline about the structural and functional characteristics of the proteins. This information not only helps to find out the route of cataractogenesis but also aid to identify potential molecules to inhibit/prevent the further development of such complicated phenomenon. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.

Therapeutic potential of α-crystallin

BACKGROUND

The findings that α-crystallins are multi-functional proteins with diverse biological functions have generated considerable interest in understanding their role in health and disease. Recent studies have shown that chaperone peptides of α-crystallin could be delivered into cultured cells and in experimental animals with beneficial effects against protein aggregation, oxidation, inflammation and apoptosis.

SCOPE OF REVIEW

In this review, we will summarize the latest developments on the therapeutic potential of α-crystallins and their functional peptides.

MAJOR CONCLUSIONS

α-Crystallins and their functional peptides have shown significant favorable effects against several diseases. Their targeted delivery to tissues would be of great therapeutic benefit. However, α-crystallins can also function as disease-causing proteins. These seemingly contradictory functions must be carefully considered prior to their therapeutic use.

GENERAL SIGNIFICANCE

αA and αB-Crystallin are members of the small heat shock protein family. These proteins exhibit molecular chaperone and anti-apoptotic activities. The core crystallin domain within these proteins is largely responsible for these prosperities. Recent studies have identified peptides within the crystallin domain of both α- and αB-crystallins with remarkable chaperone and anti-apoptotic activities. Administration of α-crystallin or their functional peptides has shown substantial inhibition of pathologies in several diseases. However, α-crystallins have been shown to promote disease-causing pathways. These two sides of the proteins are discussed in this review. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.

Changes in solvent accessibility of wild-type and deamidated βB2-crystallin following complex formation with αA-crystallin

Aberrant protein interactions can lead to aggregation and insolubilization, such as occurs during cataract formation. Deamidation, a prevalent age-related modification in the lens of the eye, decreases stability of the major lens proteins, crystallins. The mechanism of deamidation altering interactions between αA-crystallin and βB2-crystallin was investigated by detecting changes in solvent accessibility upon complex formation during heating. Solvent accessibility was determined by measuring hydrogen/deuterium exchange levels of backbone amides by high-resolution mass spectrometry. Deuterium levels in wild type βB2-crystallin increased 50-60% in both domains following complex formation with αA-crystallin. This increased solvent accessibility indicated a general loosening along the backbone amides. Peptides with the greatest deuterium increases were located at the buried monomer-monomer interface, suggesting that the βB2 dimer was disrupted. The only region where the deuterium levels decreased was in βB2 peptide 123-139, containing an outside loop, and may be a potential site of interaction with αA. Mimicking deamidation at the βB2 dimer interface prevented complex formation with αA. When temperatures were lowered, an αA/βB2 Q70E/Q162E complex formed with similar solvent accessibilities as αA/WT βB2. Deamidation did not disrupt specific αA/βB2 interactions but favored aggregation before complex formation with αA. We conclude that deamidation contributes to cataract formation through destabilization of crystallins before they can be rescued by α-crystallin.

Novel roles for α-crystallins in retinal function and disease

α-Crystallins are key members of the superfamily of small heat shock proteins that have been studied in detail in the ocular lens. Recently, novel functions for α-crystallins have been identified in the retina and in the retinal pigmented epithelium (RPE). αB-Crystallin has been localized to multiple compartments and organelles including mitochondria, golgi apparatus, endoplasmic reticulum and nucleus. α-Crystallins are regulated by oxidative and endoplasmic reticulum stress, and inhibit apoptosis-induced cell death. α-Crystallins interact with a large number of proteins that include other crystallins, and apoptotic, cytoskeletal, inflammatory, signaling, angiogenic, and growth factor molecules. Studies with RPE from αB-crystallin deficient mice have shown that αB-crystallin supports retinal and choroidal angiogenesis through its interaction with vascular endothelial growth factor. αB-Crystallin has also been shown to have novel functions in the extracellular space. In RPE, αB-crystallin is released from the apical surface in exosomes where it accumulates in the interphotoreceptor matrix and may function to protect neighboring cells. In other systems administration of exogenous recombinant αB-crystallin has been shown to be anti-inflammatory. Another newly described function of αB-crystallin is its ability to inhibit β-amyloid fibril formation. α-Crystallin minichaperone peptides have been identified that elicit anti-apoptotic function in addition to being efficient chaperones. Generation of liposomal particles and other modes of nanoencapsulation of these minipeptides could offer great therapeutic advantage in ocular delivery for a wide variety of retinal degenerative, inflammatory and vascular diseases including age-related macular degeneration and diabetic retinopathy.

A novel CRYAB mutation resulting in multisystemic disease

Mutations in the CRYAB gene, encoding alpha-B crystallin, cause distinct clinical phenotypes including isolated posterior polar cataract, myofibrillar myopathy, cardiomyopathy, or a multisystemic disorder combining all these features. Genotype/phenotype correlations are still unclear. To date, multisystemic involvement has been reported only in kindred harboring the R120G substitution. We report a novel CRYAB mutation, D109H, associated with posterior polar cataract, myofibrillar myopathy and cardiomyopathy in a two-generation family with five affected individuals. Age of onset, clinical presentation, and muscle abnormalities were very similar to those described in the R120G family. Alpha-B crystallin may form dimers and acts as a chaperone for a number of proteins. It has been suggested that the phenotypic diversity could be related to the various interactions between target proteins of individual mutant residues. Molecular modeling indicates that residues D109 and R120 interact with each other during dimerization of alpha-B crystallin; interestingly, the two substitutions affecting these residues (D109H and R120G) are associated with the same clinical phenotype, thus suggesting a similar pathogenic mechanism. We propose that impairment of alpha-B crystallin dimerization may also be relevant to the pathogenesis of these disorders.

A serine-type protease activity of human lens βA3-crystallin is responsible for its autodegradation

PURPOSE

The purpose of the study was to determine whether the autodegradation of human βA3-crystallin is due to its intrinsic protease activity.

METHODS

Recombinant His-tagged human βA3-crystallin was expressed in E. coli and purified by a Ni+2-affinity column chromatographic method. To determine protease activity, the purified crystallin was incubated for 24 h with either sodium deoxycholate, Triton X-100, or CHAPS {3-[(3-Cholamidopropyl) dimethylammonio]-1-propanesulfonate} and with benzoyl DL-arginine p-nitroanilide (BAPNA), a colorimetric protease substrate. The autodegradation of the crystallin at 0 h and 24 h on incubation at 37 °C with and without detergents (CHAPS/Triton X-100) was also determined by sodium dodecylsulfate-PAGE (SDS-PAGE) method. To examine whether the autodegradation of the crystallin was due to its protease activity, the crystallin was incubated with inhibitors of serine-, metallo- and cysteine-proteases. The binding of the intact βA3-crystallin and its autodegradation products to FFCK [5-carboxyfluorescenyl-1-phenylalaninyl-chloromethyl ketone], an analog of TPCK [1-Chloro-3-tosylamido-4-phenyl-2-butanone, a chymotrypsin-type serine protease inhibitor] was also determined by their incubation followed by SDS-PAGE and scanning for fluorescence using a Typhoon 9400 scanner.

RESULTS

βA3-crystallin protease activity showed activation in the presence of CHAPS but not in presence of Triton X-100. Upon incubation of βA3-crystallin for 24 h with CHAPS or sodium deoxycholate and BAPNA as a substrate, a time-dependent increase in the Arg-bond hydrolyzing activity was observed. SDS-PAGE analysis exhibited autodegradation products with Mr of 22, 27 and 30 kDa, which on partial NH2-terminal sequencing showed cleavage of Lys17-Met18, Gln4-Ala5 and Thr-Gly (in the NH2-terminal His-tag region) bonds, respectively. Almost no autodegradation of the βA3-crystallin occurred during its incubation alone or with CHAPS plus serine protease inhibitors (phenylmethylsulfonyl fluoride [PMSF], approtinin, and chymostatin). In contrast, the autodegradation occurred in the presence of metallo-protease inhibitors (EDTA and EGTA) and cysteine protease inhibitors (E-64, N-methylmaleimide and iodoacetamide). The βA3-crystallin also exhibited binding to FFCK, suggesting existence of a chymotrypsin-type active site in the βA3-crystallin protease.

CONCLUSIONS

The results suggested that a serine-type protease activity of βA3-crystalllin was responsible for its autodegradation. The specific bonds cleaved during autodegradation (Gln4-Ala5 and Lys17-Met18), were localized in the NH2-terminal arm of βA3-crystallin.