Biology subjects

Hulleman, J.

Publications and source records attributed to Hulleman, J..

7 recordsLinked to original sources

bioRxiv2026

An Inducible Model of RPE-Associated Hydroxyapatite Mineralization with Relevance to Drusen Formation in Age-Related Macular Degeneration

A cardinal feature of nonexudative age-related macular degeneration (AMD) is the accumulation of drusen between the retinal pigment epithelium (RPE) and Bruch's membrane, yet the mechanisms that initiate and promote drusen formation remain to be fully understood. Hydroxyapatite (HAP), a calcium-phosphate mineral identified within human drusen, has been proposed to contribute to drusen nucleation and is associated with increased likelihood of RPE atrophy. However, mechanistic studies providing insight into RPE-associated mineralization have been limited by a lack of easy-to-use and manipulatable culture models. Here, we established a rapid, inducible ARPE-19-based model of HAP mineralization. We found that ARPE-19 cells cultured in minimum essential media (MEM) supplemented with nicotinamide (NIC), sodium phosphate, and ascorbic acid (NaPAA) reproducibly formed HAP positive deposits, whereas mineralization was not observed while using standard DMEM/F12 medium, DMEM/F12 with NaPAA, MEM-NIC medium, or MEM-NIC medium with alternative osteogenic supplements (such as beta-glycerophosphate, ascorbic acid, and dexamethasone). Scanning electron microscopy with energy dispersive X ray spectroscopy demonstrated that the formed deposits were enriched in calcium (Ca) and phosphorus (P) with Ca/P ratios comparable to drusen-associated HAP deposits from AMD donor tissue. ARPE-19-based HAP deposits were also closely associated with neutral lipid-rich material, staining positive for BODIPY around their core structure. Bulk RNA sequencing of mineralized ARPE-19 cells revealed extracellular matrix, angiogenic, inflammatory, and metabolic transcriptional changes in the absence of strong enrichment of canonical osteogenic pathways. Co-treatment of mineralizing cells with either pyrophosphate, EDTA, or sodium citrate significantly reduced mineral deposition, but these approaches were not able to reverse it. Together, these findings establish a tractable RPE mineralization model that recapitulates key features of AMD-associated HAP and provides a platform for investigating mechanisms of drusen-associated mineral formation.

cell biology↗

bioRxiv2025

Select azo compounds post-translationally modulate HTRA1 abundance and activity potentially through interactions at the trimer interface

High-temperature requirement protein A1 (HTRA1) is a secreted serine protease with diverse substrates, including extracellular matrix proteins, proteins involved in amyloid deposition, and growth factors. Accordingly, HTRA1 has been implicated in a variety of neurodegenerative diseases including a leading cause of blindness in the elderly, age-related macular degeneration (AMD). In fact, genome wide association studies have identified that the 10q26 locus which contains HTRA1 confers the strongest genetic risk factor for AMD. A recent study has suggested that AMD-associated risk alleles in HTRA1 correlate with a significant age-related defect in HTRA1 synthesis in the retinal pigmented epithelium (RPE) within the eye, possibly accounting for AMD susceptibility. Thus, we sought to identify small molecule enhancers of HTRA1 transcription and/or protein abundance using an unbiased high-throughput screening approach. To accomplish this goal, we used CRISPR/Sp.Cas9 engineering to introduce an 11 amino acid luminescent peptide tag (HiBiT) onto the C-terminus of HTRA1 in immortalized ARPE-19 cells. Editing was very efficient ([~]88%), verified by genomic DNA analysis, short interfering RNA (siRNA), and HiBiT blotting. Nineteen-hundred and twenty compounds from two libraries were screened. An azo compound with reported anti-amyloidogenic and cardioprotective activity, Chicago Sky Blue 6B (CSB), was identified as an enhancer of endogenous HTRA1 secretion (2.0 {+/-} 0.3 fold) and intracellular levels (1.7 {+/-} 0.2 fold). These results were counter-screened using HiBiT complement factor H (CFH) edited ARPE-19 cells, verified using HiBiT blotting, and were not due to HTRA1 transcriptional changes. Importantly, serine hydrolase activity-based protein profiling (SH-ABPP) demonstrated that CSB does not affect HTRA1s specific activity. However, interestingly, in follow-up studies, Congo Red, another azo compound structurally similar to CSB, also substantially increased intracellular HTRA1 levels (up to 3.6 {+/-} 0.3 fold) but was found to significantly impair HTRA1 enzymatic reactivity (0.45 {+/-} 0.07 fold). Computational modeling of potential azo dye interaction with HTRA1 suggests that CSB and Congo Red can bind to the non-catalytic face of the trimer interface but with different orientation tolerances and interaction energies. These studies identify select azo dyes as HTRA1 chemical probes which may serve as starting points for future HTRA1-centered small molecule therapeutics.

biochemistry↗

bioRxiv2025

Monitoring mutant myocilin secretion and localization in trabecular meshwork cell cultures using a protein complementation-based luminescence assay

Approximately 2-4% of adult onset and 10% of juvenile onset cases of primary open angle glaucoma can be attributed to non-synonymous coding mutations in MYOC. One of the key characteristics of a pathogenic MYOC mutant is the inability of the resulting protein to be secreted from trabecular meshwork cells. Instead, pathogenic myocilin variants accumulate in the endoplasmic reticulum. Typically, localization of MYOC mutants is compared to wild-type myocilin in cellular secretion assays that use immunoblot to detect myocilin in extracellular media, alongside intracellular soluble and insoluble (aggregated) fractions. Here, we implement a new method that utilizes a complement-based luminescence method in which an 11-residue HiBiT tag is appended to myocilin and complements a truncated nanoluciferase. The method allows for highly sensitive luminescence detection and does not require immunoblot. We tested non-synonymous coding variants T377R, D384G, D395ins, C433Y, T455K, and L486F, in an established immortalized trabecular meshwork cell line. Secretion was tested in 96-well plate format, revealing poor secretion for these mutants compared to wild-type myocilin. For assays conducted in 6-well plates, myocilin mutants were accumulated in intracellular fractions. HiBiT luminescence signals correlated well with immunofluorescence as well as immunoblot but is more sensitive than the latter. Overall, our study demonstrates that complement-based detection of mutant myocilin using luminescence allows for facile and sensitive detection of myocilin localization and has confirmed secretion defects for seven variants. HighlightsO_LIMutations in myocilin are causal for early onset open angle glaucoma C_LIO_LIIn the lab pathogenic myocilin mutations are characterized by secretion defects C_LIO_LIWe validate a complement luminescence assay for detection of myocilin localization C_LIO_LIThe luminescence-based assay is more sensitive than traditional immunoblot C_LIO_LIWe confirm secretion defects for several mutants not previously characterized C_LI TOC Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=71 SRC="FIGDIR/small/640780v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@1647a7aorg.highwire.dtl.DTLVardef@1a4e56dorg.highwire.dtl.DTLVardef@d29165org.highwire.dtl.DTLVardef@477e4f_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2024

A spectrum of clinically-identified cysteine mutations in fibulin-3 (EFEMP1) highlight its disulfide bonding complexity and potential to induce stress response activation

Fibulin-3 (FBLN3), also known as EFEMP1, is a secreted extracellular matrix (ECM) glycoprotein that contains forty cysteine residues. These cysteines, which are distributed across one atypical and five canonical calcium-binding epidermal growth factor (EGF) domains, are important for regulating FBLN3 structure, secretion, and presumably function. As evidence of this importance, a rare homozygous p.C55R mutation in FBLN3 negates its function, alters disulfide bonding, and causes marfanoid syndrome. Additional studies suggest that heterozygous premature stop codon mutations in FBLN3 may also cause similar, albeit less severe, connective tissue disorders. Interestingly, a series of twenty-four cysteine mutations in FBLN3 have been identified in the human population and published in the Clinical Variation (ClinVar) and gnomAD databases. We tested how seven of these cysteine mutants (five loss-of-cysteine variants: C42Y, C190R, C218R, C252F, and C365S, two gain-of-cysteine variants: R358C, Y369C) and two newly developed mutations (G57C and Y397C) altered FBLN3 secretion, disulfide bonding, MMP2 zymography, and stress response activation Surprisingly, we found a wide variety of biochemical behaviors: i) loss-of-cysteine variants correlated with an increased likelihood of disulfide dimer formation, ii) N-terminal mutations were less likely to disrupt secretion, and were less prone to aggregation, iii) in contrast to wild-type FBLN3, multiple, but not all variants failed to induce MMP2 levels in cell culture, and iv) C-terminal mutations (either loss or gain of cysteines) were more prone to significant secretion defects, intracellular accumulation/misfolding, and stress response activation. These results provide molecular and biochemical insight into FBLN3 folding, secretion, and function for many cysteine mutations found in the human population, some of which may increase the likelihood of subclinical connective tissue or other FBLN3-associated haploinsufficiency diseases.

biochemistry↗

bioRxiv2022

Important anatomical, age-related, and species considerations regarding ocular fibulin-3 (EFEMP1) analysis

PurposeFibulin-3 (F3) or EFEMP1 is a secreted extracellular matrix glycoprotein implicated in several ocular diseases. Little is known about the native biology of this protein. Thus, our study aims to determine expression and localization characteristics of F3 utilizing a range of mammalian species as well as F3-associated changes with age. MethodsGene expression analyses for fibulins as well as immunohistochemistry for F3 were conducted in ocular tissue from mice, pigs, non-human primates (NHPs), and humans (n = 3-5). Age-based F3 expression study along with changes in ECM remodeling enzymes was also evaluated in mice. ResultsWithin the mouse retina, F3 staining was consistent throughout the entirety of the retina (far-periphery, mid-periphery, and central), being enriched in the ganglion cell layer and inner nuclear layer (INL). However, in humans, the F3 staining pattern was quite unique; enriched in the RPE, INL, and outer nuclear layer (ONL) in the peripheral retina, but then shifting to predominantly outer plexiform layer (OPL) staining in the central retina and macula with waning RPE immunoreactivity approaching the fovea. We demonstrate that F3 expression in the mouse retina significantly increases with age, and the levels of extracellular F3 degrading enzymes produced by the RPE and retina (e.g., Mmp2 and Htra1) decrease with age. ConclusionsThese findings demonstrate that F3 has distinct species-dependent as well as ocular region-specific expression and localization patterns. We also show that F3 and ECM enzyme dynamics favor F3 accumulation in the retina and RPE with increasing age.

neuroscience↗

bioRxiv2021

A simple secretion assay for assessing new and existing myocilin variants

With the increasing use of molecular genetics approaches for determination of potential disease-causing mutations, it is becoming more important to be able to interpret and act upon the provided results. As an example of such an instance, nearly 300 mutations have been identified in the myocilin (MYOC) gene, which is the most commonly mutated gene causing primary open angle glaucoma. Yet a lack of sufficient information exists for many of these variants, hindering their definitive classification. While the function of MYOC is unclear, biochemically, the vast majority of glaucoma-causing MYOC mutations result in protein non-secretion and intracellular insoluble aggregate formation in cultured cells. Previously we generated a Gaussia luciferase-based MYOC fusion protein to sensitively track secretion of the protein. Herein we applied this same assay to fourteen clinically-derived MYOC variants with varying degrees of predicted pathogenicity and compared the luciferase secretion results with the better established MYOC assay of western blotting. Eight of the variants (G12R, V53A, T204T, P254L, T325T, D380H, D395_E396insDP, and P481S) had not been biochemically assessed previously. Of these, P254L and D395_E396insDP demonstrated significant secretion defects from human embryonic kidney (HEK-293A) cells reminiscent of glaucoma-causing mutations. Overall, we found that the luciferase assay results agreed with western blotting for thirteen of the fourteen variants (93%), suggesting a strong concordance. These results suggest that the Gaussia luciferase assay may be used as a complementary or standalone assay for quickly assessing MYOC variant behavior, and anticipate that these results will be useful in MYOC variant curation and reclassification.

biochemistry↗

bioRxiv2021

SUFFICIENT ACTIVITY OF THE UBIQUITIN PROTEASOME SYSTEM IN AGED MICE AND DURING RETINAL DEGENERATION SUPPORTS DHFR-BASED CONDITIONAL CONTROL OF PROTEIN ABUNDANCE IN THE RETINA

The Escherichia coli dihydrofolate reductase (DHFR) destabilizing domain (DD) serves as a promising approach to conditionally regulate protein abundance in a variety of tissues. In the absence of TMP, a DHFR stabilizer, the DD is degraded by the ubiquitin proteasome system (UPS). To test whether this approach could be effectively applied to a wide variety of aged and disease-related ocular mouse models, which may have a compromised UPS, we evaluated the DHFR DD system in aged mice (up to 24 mo), a light-induced retinal degeneration (LIRD) model, and two genetic models of retinal degeneration (rd2 and Abca4-/- mice). Aged, LIRD, and Abca4-/- mice all had similar proteasomal activities and high-molecular weight ubiquitin levels compared to control mice. However, rd2 mice displayed compromised chymotrypsin activity compared to control mice. Nonetheless, the DHFR DD was effectively degraded in all model systems, including rd2 mice. Moreover, TMP increased DHFR DD-dependent retinal bioluminescence in all mouse models, however the fold induction was slightly, albeit significantly, lower in Abca4-/- mice. Thus, the destabilized DHFR DD-based approach allows for efficient control of protein abundance in aged mice and retinal degeneration mouse models, laying the foundation to use this strategy in a wide variety of mice for the conditional control of gene therapies to potentially treat multiple eye diseases.

physiology↗