Biology subjects

Haq, W.

Publications and source records attributed to Haq, W..

8 recordsLinked to original sources

bioRxiv2026

Evidence for a rod-to-cone lactate shuttle in the mammalian retina

In his seminal 1920s studies, Otto Warburg found the retina to generate large amounts of lactate. However, it was unclear what retinal cells produced lactate and whether it was a metabolic waste product or used further. Here, we show that lactate produced by rod photoreceptors fuels the energy-intensive function and viability of cone photoreceptors. In an initial expression analysis, we found monocarboxylate transporter-1 (MCT1), lactate-producing lactate-dehydrogenase-A (LDHA), and pyruvate carboxykinase-1 (PCK1) localized to rod photoreceptors, while high-affinity MCT2, pyruvate-producing LDHB, and PCK2 were expressed in cones. We then exposed retina to defined media containing either glucose or lactate as caloric component, and applied specific MCT inhibitors. In glucose-containing medium, 1H-NMR metabolomics showed rod MCT1 inhibition to increase retinal lactate, suggesting rods as a major source of lactate. In lactate-only medium, functional recordings using micro-electroretinography showed decreased rod function, while cone function was maintained. In glucose-containing medium, blocking rod MCT1 abolished cone function. Long-term treatment with MCT inhibitors selectively decreased photoreceptor viability. Conversely, supplementing the defined medium with lactate preserved cone viability in the rd1 mouse model for Retinitis Pigmentosa. Together, our data suggest that lactate shuttling from rods is crucial for cone function and viability. This may explain cone degeneration seen in various retinal diseases and provides an entirely new avenue for metabolism-based treatment development. The discovery of a lactate-shuttle between two functionally similar, yet distinct types of neurons may have far-reaching implications for our understanding of the central nervous system in general.

neuroscience↗

bioRxiv2024

Protein kinase G inhibition preserves photoreceptor viability and function in a new mouse model for autosomal dominant retinitis pigmentosa

Retinitis Pigmentosa (RP) is the most common inherited retinal degeneration, characterized by an initial loss of rod photoreceptor cells. Photoreceptor cell death has been associated with high levels of cyclic guanosine-3', 5'-monophosphate (cGMP) in animal models of autosomal recessive RP (ARRP) and autosomal dominant RP (ADRP). cGMP analogues inhibiting protein kinase G (PKG) have been found to prevent rod degeneration in ARRP disease models, but their effects on ADRP are unknown. Here, we used the recently generated rhodopsin-mutant RhoI255d/+ ADRP mouse model to investigate cGMP-signaling and the effects of cGMP analogues targeting PKG. cGMP accumulation was investigated by retinal immunostaining in wild-type (WT), RhoI255d/+, and RhoI255d/I255d mice. The therapeutic efficacy of the cGMP analogues CN03 and CN238 was evaluated on organotypic retinal explant cultures derived from WT and RhoI255d/+ mice. Readouts included the TUNEL assay and immunostaining for cone arrestin-3. Downstream effectors of cell death were visualized using calpain, poly-ADP-ribose polymerase (PARP), and histone deacetylase (HDAC) in situ assays, as well as caspase-3 immunostaining. Photoreceptor function was assessed using micro-electroretinogram ({micro}ERG) recordings. When compared with WT, RhoI255d photoreceptors displayed cGMP accumulation in outer segments. In the RhoI255d/+ ADRP model, CN03 and CN238 significantly reduced the number of dying photoreceptors. However, the relatively small number of photoreceptors exhibiting caspase-3 activity was not changed by the treatment. Remarkably, CN238 effectively provided long-lasting neuroprotection of cone photoreceptors and preserved retinal light responsiveness of RhoI255d/+ retina. Overall, this study suggests caspase-independent but cGMP-dependent cell death as a dominant degenerative mechanism in the RhoI255d/+ ADRP mouse model. PKG inhibition demonstrated robust neuroprotection of both rod and cone photoreceptors, while the marked preservation of retinal function, especially with the compound CN238, highlighted cGMP analogues for the treatment of ADRP.

neuroscience↗

bioRxiv2022

Using cGMP analogues to modulate photoreceptor light sensitivity: Perspectives for the treatment of retinal degeneration.

Cyclic nucleotide-gated (CNG) channels play an essential role within the phototransduction cascade in vertebrates. Although rod and cone light responses are mediated through similar pathways, each photoreceptor type relies on a specific CNG-channel isoform. In many forms of retinal degeneration, increased cGMP levels initiate a pathophysiological rollercoaster, which starts with an enhanced CNG-channel activation, often in rod photoreceptors. This causes cell death of both rods and cones, and eventually leads to complete blindness. Unfortunately, the targeting of the desired channel isoform still constitutes the bottleneck for many therapeutic schemes. Here, we present a novel strategy, based on cGMP analogues with opposite types of action, which allows for the selective modulation of either rod or cone photoreceptors. A combined treatment with a weak rod-selective CNG-channel inhibitor (Rp-8-Br-PET-cGMPS) and a cone-selective CNG-channel activator (8-pCPT-cGMP) preserved the normal CNG-channel function at physiological and pathological cGMP levels. The effectiveness of this approach was tested and confirmed in explanted mouse retina. Under physiological conditions, the inhibitor silenced the rods selectively and decreased the dependency of cone responses on light intensity. Remarkably, the activator, when applied together with the inhibitor, reinstated only the light responsiveness of cones. Yet, when applied alone, the activator dampened rod responses more strongly than those of cones. Hence, combinations of cGMP analogues with desired properties may elegantly address the isoform-specificity problem in future pharmacological therapies. Beyond therapies for retinal degeneration diseases, treatments based on this strategy may allow modulation of visual performance in certain light environments or disease conditions. One Sentence SummaryA combination of cGMP analogues with opposite types of action can selectively modulate either rod or cone photoreceptor function.

physiology↗

bioRxiv2021

Retinal degeneration: Multilevel protection of photoreceptor and ganglion cell viability and function with the novel PKG inhibitor CN238.

Hereditary retinal degeneration (RD) is often associated with excessive cGMP-signaling in photoreceptors. Previous research has shown that inhibition of cGMP-dependent protein kinase G (PKG) can slow down the loss of photoreceptors in different RD animal models. In this study, we identified a novel PKG inhibitor, the cGMP analogue CN238, with strong protective effects on photoreceptors in retinal degeneration rd1 and rd10 mutant mice. In long-term organotypic retinal explants, CN238 preserved rd1 and rd10 photoreceptor viability and function. Surprisingly, in explanted retinae CN238 also protected retinal ganglion cells from axotomy induced retrograde degeneration and preserved their functionality. Together, these results confirm the strong neuroprotective capacity of PKG inhibitors for both photoreceptors and retinal ganglion cells, thereby significantly broadening their potential applications for the treatment of retinal diseases and possibly neurodegenerative diseases in general.

neuroscience↗

bioRxiv2020

Inhibition of VCP preserves retinal structure and function in autosomal dominant retinal degeneration

Due to continuously high production rates of rhodopsin (RHO) and high metabolic activity, photoreceptor neurons are especially vulnerable to defects in proteostasis. A proline to histidine substitution at position 23 (P23H) leads to production of structurally misfolded RHO, causing the most common form of autosomal dominant Retinitis Pigmentosa (adRP) in North America. The AAA-ATPase valosin-containing protein (VCP) extracts misfolded proteins from the ER membrane for cytosolic degradation. Here, we provide the first evidence that inhibition of VCP activity rescues degenerating P23H rod cells and improves their functional properties in P23H transgenic rat and P23H knock-in mouse retinae, both in vitro and in vivo. This improvement correlates with the restoration of the physiological RHO localization to rod outer segments (OS) and properly-assembled OS disks. As a single intravitreal injection suffices to deliver a long-lasting benefit in vivo, we suggest VCP inhibition as a potential therapeutic strategy for adRP patients carrying mutations in the RHO gene.

neuroscience↗

bioRxiv2020

Interferon-γ signaling synergizes with LRRK2 in human neurons and microglia

Increasing evidence suggests a role for interferons (IFNs) in neurodegeneration. Parkinsons disease (PD) associated kinase LRRK2 has been implicated in IFN type II (IFN) response in infections and nigral neuronal loss. However, whether and how LRRK2 synergizes with IFN-{gamma} still remains unclear. Here, we employed dopaminergic (DA) neurons and microglia differentiated from patient induced pluripotent stem cells to unravel the role of IFN-{gamma} in LRRK2-PD. We show that IFN-{gamma} induces LRRK2 expression in both DA neurons and microglial cells. LRRK2-G2019S, the most common PD-associated mutation, sensitizes DA neurons to IFN-{gamma} by decreasing AKT phosphorylation. IFN-{gamma} suppresses NFAT activity in both neurons and microglia and synergistically enhances LRRK2-induced defects of NFAT activation. Furthermore, LRRK2-G2019S negatively regulates NFAT via calcium and microtubule dynamics. Importantly, we uncover functional consequences of the reduction of NFAT activity in both cell types, namely defects of neurite elongation and alteration of microglial activation profile and motility. We propose that synergistic IFN-{gamma}/LRRK2 activation serves as a direct link between inflammation and neurodegeneration in PD.

neuroscience↗

bioRxiv2019

HDAC inhibition ameliorates cone survival in retinitis pigmentosa mice

Cone photoreceptor cell death in inherited retinal diseases, such as Retinitis Pigmentosa (RP), leads to the loss of high acuity and color vision and ultimately to blindness. In RP, a vast number of mutations perturb the structure and function of rod photoreceptors while cones remain initially unaffected. Cone death follows rod death secondarily due to increased oxidative stress, inflammation, and loss of structural and nutritional support provided by rods. Here, we show that secondary cone cell death in animal models for RP was associated with an increased activity of histone deacetylates (HDACs). A single intravitreal injection of an HDAC inhibitor at a late stage of the disease, when majority of rods have already degenerated, was sufficient to delay cone death and support long-term cone survival. Moreover, the surviving cones remained light sensitive and initiated light-driven ganglion cell responses. RNA-seq analysis of protected cones demonstrated that HDAC inhibition led to multi-level protection via regulation of different pro-survival pathways, including MAPK, PI3K-Akt, and autophagy. This study suggests a unique possibility for a targeted pharmacological protection of both primary degenerating rods and secondary dying cones by HDAC inhibition and creates hope to maintain vision in RP patients independent of the disease stage.

neuroscience↗

bioRxiv2019

Human Retina-on-a-Chip: Merging Organoid and Organ-on-a-Chip Technology to Generate Complex Multi-Layer Tissue Models

The devastating effects and incurable nature of hereditary and sporadic retinal diseases such as Stargardt disease, age-related macular degeneration or retinitis pigmentosa urgently require the development of new therapeutic strategies. Additionally, the prevalence of retinal toxicities is becoming more and more an issue of novel targeted therapeutic agents. To date, (ophthalmologic) drug development largely relies on animal models. Inadequate translatability of results from animal models to humans, however, limits advances in drug development and discovery. Hence, the establishment of more relevant human tissue-based in vitro models is of upmost importance. The discovery of self-forming retinal organoids (ROs) derived from human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hiPSCs) is a promising approach to model the complex stratified retinal tissue. Yet, ROs lack vascularization and cannot recapitulate the important physiological interactions of matured photoreceptors and the retinal pigment epithelium (RPE). In this study, we present the retina-on-a-chip (RoC), a novel microphysiological model of the human retina integrating more than seven different essential retinal cell types derived from hiPSCs in a vasculature-like perfusion and enabling, for the first time, the recapitulation of the interaction of mature photoreceptor segments with RPE in vitro. We show that this interaction enhances the formation of outer segment like-structures and the establishment of in vivo-like physiological processes such as outer segment phagocytosis and calcium dynamics. In addition, we demonstrate the applicability of the RoC for drug testing, by reproducing the retinopathic side effects of the anti-malaria drug chloroquine and the antibiotic gentamicin. The developed hiPSC-based RoC has the potential to promote drug development and provide new insights into the underlying pathology of retinal diseases.

bioengineering↗