Update on "Cell Therapy" Clinics Offering Treatments of Ocular Conditions Using Direct-To-Consumer Marketing Websites in the U.S.

PURPOSE: To assess the scope of U.S.-based companies advertising and administering non-Federal Drug Administration (FDA) approved cell-based therapy (herein called NFACT) for ocular conditions based on information from companies' public websites after the FDA's legal actions against specific NFACT clinics in 2018 and 2019. Current findings are compared to previously published data from 2017. DESIGN: Trend study looking at U.S.-based companies that use direct-to-consumer marketing and have websites advertising therapy for ocular conditions. METHODS: A systematic and extensive keyword-based Internet search was utilized to identify, document, and analyze U.S. business websites offering NFACT for ocular conditions as of August 2022. Main outcomes measured include, clinic locations, marketed ocular conditions, types of NFACT offered, source of stem cells used, routes of administration, and treatment costs. RESULTS: From the prior analysis in 2017 to the 2019 analysis, there was a decrease in the number of NFACT clinics from 76 to 62 and companies from 40 to 39. Given the concerning persistence of NFACTs in August 2019 an additional analysis was performed in 2022 which showed a drastic decrease in NFACT clinics from 62 in 2019 to 18 in 2023 and from 39 companies to 13 in 2023. In both 2019 and 2022, the most commonly referenced ocular condition was age-related macular degeneration (2019 - 72%, 2022 - 92%). The state with the most clinics was in Texas (2019 - 12; 2022 - 5). Autologous adipose-derived stem cells were the most common cell type used in both analyses. CONCLUSIONS: In 2019 U.S.-based direct-to-consumer companies marketing NFACT persisted despite (1) a lack of high-quality clinical evidence supporting the efficacy of these procedures, (2) the association of some of these treatments with severe vision loss, and (3) increasing FDA oversight and recent legal action. In 2022 the number of clinics and companies decreased, but their persistence is a reminder that continued concern is necessary and ophthalmic associations need to continue advocacy efforts to protect patients from these potentially predatory organizations.

McCannel Suture Technique Resolves Persistent Dysphotopsia Following Laser Peripheral Iridotomy in Phakic Eyes.

A 57-year-old woman presented with photophobia and complaint of a persistent white light in the inferior field of her left eye for 18 months following laser peripheral iridotomy both eyes. In primary gaze, the upper lid margin was noted to bisect the iridotomy at 2 o'clock left eye (OS). She relates that the light moves with her eyelid OS only and resolves by lifting the lid. A 54-year-old male presented with complaint of seeing 2 horizontal lines in his field of vision immediately following laser iridotomy OS that have persisted for a duration of 7 years. He notes they are constant and resolve by lifting up the eyelid. In primary position, the left upper lid margin was noted to bisect the iridotomy at 12 o'clock OS. Given the presence of nonresolving symptomatic dysphotopsia, each patient underwent surgical repair of the iridotomy using a McCannel suture technique with complete resolution of their symptoms. Dysphotopsias are an uncommon complication that can occur following laser peripheral iridotomy. If they persist and conservative measures are ineffective, iris suture repair can provide a definitive intervention in resolving them. Laser iridotomies located in the far periphery pose a surgical challenge with respect to accessibility. A McCannel suture technique provides a feasible approach in suturing them with minimal iris manipulation. Furthermore, it is prudent to assess the upper lid position in primary gaze before creating an iridotomy in order to avoid interference with the lid margin tear film meniscus that can lead to the formation of symptomatic dysphotopsia.

Corneal neovascularization.

The optical clarity of the cornea is essential for maintaining good visual acuity. Corneal neovascularization, which is a major cause of vision loss worldwide, leads to corneal opacification and often contributes to a cycle of chronic inflammation. While numerous factors prevent angiogenesis within the cornea, infection, inflammation, hypoxia, trauma, corneal degeneration, and corneal transplantation can all disrupt these homeostatic safeguards to promote neovascularization. Here, we summarize its etiopathogenesis and discuss the molecular biology of angiogenesis within the cornea. We then review the clinical assessment and diagnostic evaluation of corneal neovascularization. Finally, we describe current and emerging therapies.

Force production of human cytoplasmic dynein is limited by its processivity.

Cytoplasmic dynein is a highly complex motor protein that generates forces toward the minus end of microtubules. Using optical tweezers, we demonstrate that the low processivity (ability to take multiple steps before dissociating) of human dynein limits its force generation due to premature microtubule dissociation. Using a high trap stiffness whereby the motor achieves greater force per step, we reveal that the motor's true maximal force ("stall force") is ~2 pN. Furthermore, an average force versus trap stiffness plot yields a hyperbolic curve that plateaus at the stall force. We derive an analytical equation that accurately describes this curve, predicting both stall force and zero-load processivity. This theoretical model describes the behavior of a kinesin motor under low-processivity conditions. Our work clarifies the true stall force and processivity of human dynein and provides a new paradigm for understanding and analyzing molecular motor force generation for weakly processive motors.

Molecular mechanism of cytoplasmic dynein tension sensing.

Cytoplasmic dynein is the most complex cytoskeletal motor protein and is responsible for numerous biological functions. Essential to dynein's function is its capacity to respond anisotropically to tension, so that its microtubule-binding domains bind microtubules more strongly when under backward load than forward load. The structural mechanisms by which dynein senses directional tension, however, are unknown. Using a combination of optical tweezers, mutagenesis, and chemical cross-linking, we show that three structural elements protruding from the motor domain-the linker, buttress, and stalk-together regulate directional tension-sensing. We demonstrate that dynein's anisotropic response to directional tension is mediated by sliding of the coiled-coils of the stalk, and that coordinated conformational changes of dynein's linker and buttress control this process. We also demonstrate that the stalk coiled-coils assume a previously undescribed registry during dynein's stepping cycle. We propose a revised model of dynein's mechanochemical cycle which accounts for our findings.

Cytoplasmic dynein regulates its attachment to microtubules via nucleotide state-switched mechanosensing at multiple AAA domains.

Cytoplasmic dynein is a homodimeric microtubule (MT) motor protein responsible for most MT minus-end-directed motility. Dynein contains four AAA+ ATPases (AAA: ATPase associated with various cellular activities) per motor domain (AAA1-4). The main site of ATP hydrolysis, AAA1, is the only site considered by most dynein motility models. However, it remains unclear how ATPase activity and MT binding are coordinated within and between dynein's motor domains. Using optical tweezers, we characterize the MT-binding strength of recombinant dynein monomers as a function of mechanical tension and nucleotide state. Dynein responds anisotropically to tension, binding tighter to MTs when pulled toward the MT plus end. We provide evidence that this behavior results from an asymmetrical bond that acts as a slip bond under forward tension and a slip-ideal bond under backward tension. ATP weakens MT binding and reduces bond strength anisotropy, and unexpectedly, so does ADP. Using nucleotide binding and hydrolysis mutants, we show that, although ATP exerts its effects via binding AAA1, ADP effects are mediated by AAA3. Finally, we demonstrate "gating" of AAA1 function by AAA3. When tension is absent or applied via dynein's C terminus, ATP binding to AAA1 induces MT release only if AAA3 is in the posthydrolysis state. However, when tension is applied to the linker, ATP binding to AAA3 is sufficient to "open" the gate. These results elucidate the mechanisms of dynein-MT interactions, identify regulatory roles for AAA3, and help define the interplay between mechanical tension and nucleotide state in regulating dynein motility.

Control of cytoplasmic dynein force production and processivity by its C-terminal domain.

Cytoplasmic dynein is a microtubule motor involved in cargo transport, nuclear migration and cell division. Despite structural conservation of the dynein motor domain from yeast to higher eukaryotes, the extensively studied S. cerevisiae dynein behaves distinctly from mammalian dyneins, which produce far less force and travel over shorter distances. However, isolated reports of yeast-like force production by mammalian dynein have called interspecies differences into question. We report that functional differences between yeast and mammalian dynein are real and attributable to a C-terminal motor element absent in yeast, which resembles a 'cap' over the central pore of the mammalian dynein motor domain. Removal of this cap increases the force generation of rat dynein from 1 pN to a yeast-like 6 pN and greatly increases its travel distance. Our findings identify the CT-cap as a novel regulator of dynein function.

Cep192 controls the balance of centrosome and non-centrosomal microtubules during interphase.

Cep192 is a centrosomal protein that contributes to the formation and function of the mitotic spindle in mammalian cells. Cep192's mitotic activities stem largely from its role in the recruitment to the centrosome of numerous additional proteins such as gamma-tubulin and Pericentrin. Here, we examine Cep192's function in interphase cells. Our data indicate that, as in mitosis, Cep192 stimulates the nucleation of centrosomal microtubules thereby regulating the morphology of interphase microtubule arrays. Interestingly, however, cells lacking Cep192 remain capable of generating normal levels of MTs as the loss of centrosomal microtubules is augmented by MT nucleation from other sites, most notably the Golgi apparatus. The depletion of Cep192 results in a significant decrease in the level of centrosome-associated gamma-tubulin, likely explaining its impact on centrosome microtubule nucleation. However, in stark contrast to mitosis, Cep192 appears to maintain an antagonistic relationship with Pericentrin at interphase centrosomes. Interphase cells depleted of Cep192 display significantly higher levels of centrosome-associated Pericentrin while overexpression of Cep192 reduces the levels of centrosomal Pericentrin. Conversely, depletion of Pericentrin results in elevated levels of centrosomal Cep192 and enhances microtubule nucleation at centrosomes, at least during interphase. Finally, we show that depletion of Cep192 negatively impacts cell motility and alters normal cell polarization. Our current working hypothesis is that the microtubule nucleating capacity of the interphase centrosome is determined by an antagonistic balance of Cep192, which promotes nucleation, and Pericentrin, which inhibits nucleation. This in turn determines the relative abundance of centrosomal and non-centrosomal microtubules that tune cell movement and shape.

Covalent immobilization of microtubules on glass surfaces for molecular motor force measurements and other single-molecule assays.

Rigid attachment of microtubules (MTs) to glass cover slip surfaces is a prerequisite for a variety of microscopy experiments in which MTs are used as substrates for MT-associated proteins, such as the molecular motors kinesin and cytoplasmic dynein. We present an MT-surface coupling protocol in which aminosilanized glass is formylated using the cross-linker glutaraldehyde, fluorescence-labeled MTs are covalently attached, and the surface is passivated with highly pure beta-casein. The technique presented here yields rigid MT immobilization while simultaneously blocking the remaining glass surface against nonspecific binding by polystyrene optical trapping microspheres. This surface chemistry is straightforward and relatively cheap and uses a minimum of specialized equipment or hazardous reagents. These methods provide a foundation for a variety of optical tweezers experiments with MT-associated molecular motors and may also be useful in other assays requiring surface-immobilized proteins.

An improved optical tweezers assay for measuring the force generation of single kinesin molecules.

Numerous microtubule-associated molecular motors, including several kinesins and cytoplasmic dynein, produce opposing forces that regulate spindle and chromosome positioning during mitosis. The motility and force generation of these motors are therefore critical to normal cell division, and dysfunction of these processes may contribute to human disease. Optical tweezers provide a powerful method for studying the nanometer motility and piconewton force generation of single motor proteins in vitro. Using kinesin-1 as a prototype, we present a set of step-by-step, optimized protocols for expressing a kinesin construct (K560-GFP) in Escherichia coli, purifying it, and studying its force generation in an optical tweezers microscope. We also provide detailed instructions on proper alignment and calibration of an optical trapping microscope. These methods provide a foundation for a variety of similar experiments.

The yeast dynein Dyn2-Pac11 complex is a dynein dimerization/processivity factor: structural and single-molecule characterization.

Cytoplasmic dynein is the major microtubule minus end-directed motor. Although studies have probed the mechanism of the C-terminal motor domain, if and how dynein's N-terminal tail and the accessory chains it binds regulate motor activity remain to be determined. Here, we investigate the structure and function of the Saccharomyces cerevisiae dynein light (Dyn2) and intermediate (Pac11) chains in dynein heavy chain (Dyn1) movement. We present the crystal structure of a Dyn2-Pac11 complex, showing Dyn2-mediated Pac11 dimerization. To determine the molecular effects of Dyn2 and Pac11 on Dyn1 function, we generated dyn2Δ and dyn2Δpac11Δ strains and analyzed Dyn1 single-molecule motor activity. We find that the Dyn2-Pac11 complex promotes Dyn1 homodimerization and potentiates processivity. The absence of Dyn2 and Pac11 yields motors with decreased velocity, dramatically reduced processivity, increased monomerization, aggregation, and immobility as determined by single-molecule measurements. Deleting dyn2 significantly reduces Pac11-Dyn1 complex formation, yielding Dyn1 motors with activity similar to Dyn1 from the dyn2Δpac11Δ strain. Of interest, motor phenotypes resulting from Dyn2-Pac11 complex depletion bear similarity to a point mutation in the mammalian dynein N-terminal tail (Loa), highlighting this region as a conserved, regulatory motor element.