Biology subjects

Pham, D. H.

Publications and source records attributed to Pham, D. H..

3 recordsLinked to original sources

bioRxiv2025

Modification of Non-photochemical Quenching Pathways in the C4 Model Plant Setaria viridis Revealed Shared and Unique Photoprotection Mechanisms as Compared to C3 Plants

Light is essential for photosynthesis; however, excess light can increase the accumulation of photoinhibitory reactive oxygen species that reduce photosynthetic efficiency. Plants have evolved photoprotective non-photochemical quenching (NPQ) pathways to dissipate excess light energy. In tobacco and soybean (C3 plants), overexpression of three NPQ genes, violaxanthin de-epoxidase (VDE), Photosystem II Subunit S (PsbS), and zeaxanthin epoxidase (ZEP), hereafter VPZ, resulted in faster NPQ induction and relaxation kinetics, and increased crop yields in field conditions. NPQ is well-studied in C3 plants; however, NPQ and the translatability of the VPZ approach in C4 plants is poorly understood. The green foxtail Setaria viridis is an excellent model to study photosynthesis and photoprotection in C4 plants. To understand the regulation of NPQ and photosynthesis in C4 plants, we performed transient overexpression in Setaria protoplasts and generated (and employed) stable transgenic Setaria plants overexpressing one of the three Arabidopsis NPQ genes or all three NPQ genes (AtVPZ lines). Overexpressing (OE) AtVDE and AtZEP in Setaria produced similar results as in C3 plants, with increased or reduced zeaxanthin (thus NPQ), respectively. However, overexpressing AtPsbS appeared to be challenging in Setaria, with largely reduced NPQ in protoplasts and under-represented homozygous AtPsbS-OE lines, potentially due to competitive and tight heterodimerization of AtPsbS and SvPsbS proteins. Furthermore, Setaria AtVPZ lines had increased zeaxanthin, faster NPQ induction, higher NPQ level, but slower NPQ relaxation. Despite this, AtVPZ lines had improved growth as compared to wildtype under several conditions, especially high temperatures, which is not related to the faster relaxation of NPQ but may be attributable to increased zeaxanthin and NPQ in C4 plants. Our results identified shared and unique characteristics of the NPQ pathway in C4 model Setaria as compared to C3 plants and provide insights to improve C4 crop yields under fluctuating environmental conditions.

plant biology↗

bioRxiv2024

Long-term Tolerance to Islet Transplantation via Targeted Reduction of beta cell-specific T cells.

Type 1 diabetes (T1D) results from insulin insufficiency due to the loss or dysfunction of pancreatic beta cells following T cell-mediated autoimmune attack. Currently the only long-term therapy is daily exogenous insulin replacement. The ideal curative approach is the durable restoration of functional islets via transplantation. To date the limiting factors impeding realization of this goal is the lack of a cost effective and limitless source of high-quality islets suitable for transplantation and the ability to provide long-term islet graft acceptance without prolonged need for deleterious immunosuppression. Ongoing clinical trials are testing islets derived from human induced pluripotent stem cells (iPSC); however, long-term acceptance of islet graft will require a effective therapeutic strategy to prevent engrafted islet destruction by pre-existing islet-antigen specific T cells. Here we demonstrate in the NOD mouse model for T1D that autologous islet graft acceptance can be achieved by the targeted elimination of (re)-activated islet-reactive CD4+ and CD8+ T effector (Teff) cells in the initial post-transplantation period by using a short-acting, combination therapy that results in the elimination of islet-reactive Teff cells by exacerbation of their natural DNA damage response (DDR) to drive apoptosis while at the same time maintaining endogenous Treg cells. Article HighlightsO_LIActivated beta-cell reactive CD4+ and CD8+ T effector cells undergo a profound DNA-damage response which is targetable by small molecule inhibitors of the p53 and cell cycle pathways that lead to apoptosis. C_LIO_LIThe use of a combination of MDM2 and WEE1 inhibitors, which termed "p53 potentiation with checkpoint abrogation" (PPCA), conferred significant therapeutic efficacy in treating mouse models of new onset T1D. C_LIO_LISpecific targeting of these T effector cells by PPCA results in a loss of inflammatory T cell subsets, notably proliferation CD4+ Th0 and Th1 subsets and CD8+ T effector memory cells, as determined by single cell RNA-seq studies with the preservation of T regulatory cells. C_LIO_LIWhen autologous islet grafts are given to established diabetic NOD mice, a single course of PPCA results in long-term islet graft acceptance, restoration of normoglycemia and loss of beta cell specific CD4+ and CD8+ T cells. C_LIO_LIPPCA shows promise as a potential means of estimating islet graft tolerance in T1D recipients of islet graft transplantation. C_LI

immunology↗

bioRxiv2024

Programmable Editing of Primary MicroRNA Switches Stem Cell Differentiation and Improves Tissue Regeneration

Programmable RNA editing is harnessed for modifying mRNA. Besides mRNA, miRNA also regulates numerous biological activities, but current RNA editors have yet to be exploited for miRNA manipulation. To engineer primary miRNA (pri-miRNA), the miRNA precursor, we present a customizable editor REPRESS (RNA Editing of Pri-miRNA for Efficient Suppression of miRNA) and characterize critical parameters. The optimized REPRESS is distinct from other mRNA editing tools in design rationale, hence enabling editing of pri-miRNAs that are not editable by other RNA editing systems. We edited various pri-miRNAs in different cells including adipose-derived stem cells (ASCs), hence attenuating mature miRNA levels without disturbing host gene expression. We further developed an improved REPRESS (iREPRESS) that enhances and prolongs pri-miR-21 editing for at least 10 days, with minimal perturbation of transcriptome and miRNAome. iREPRESS reprograms ASCs differentiation, promotes in vitro cartilage formation and augments calvarial bone regeneration in rats, thus implicating its potentials for engineering miRNA for many applications such as stem cell engineering and tissue regeneration.

bioengineering↗