Biology subjects

Fisher, J. J.

Publications and source records attributed to Fisher, J. J..

3 recordsLinked to original sources

bioRxiv2025

The genetic origin of fetal growth restriction and mitochondrial complex I dysregulation

BackgroundMitochondria are organelles required for bioenergetic homeostasis, providing energy in the form of ATP to support cellular function, growth, and proliferation. Mitochondria synthesise ATP using the electron transport chain (ETC) to produce an electrochemical gradient that facilitates the conversion of ADP to ATP by ATP synthase. Mitochondrial function is governed by an intricate bidirectional relationship between the mitochondrial genome encoding 1-2% of proteins and the nuclear genome which encodes 98-99% of mitochondrial proteins. Pregnancy creates a unique environment whereby the mitochondrial genome of the placenta is maternally inherited, while the nuclear genome is comprised of both maternal and paternal contributions. Thus, mitochondrial structure and function are largely dependent on the adaptability of mitochondria to conform to the new mixed nuclear genome. In pregnancy, fetal growth restriction (FGR) is characterised by poor placental development, underlying trophoblast insufficiencies, and is associated with mitochondrial dysfunction within the placenta, although the mechanisms which underpin these changes remain unclear. This study investigated if mitochondrial dysfunction in FGR is programmed by genetic incompatibility arising from single nucleotide polymorphisms (SNPs). Methods and findingsWe performed a targeted meta-analysis of over 100 genome wide association studies within the early growth genetics (EGG) consortium, assessing 289 genes encoding mitochondrial function across the ETC and ATP synthase. This study identified 37 SNPs across 32 genes associated with low birthweight. Sanger sequencing was performed to validate the presence of 10 SNPs of interest located within the nuclear genome in a cohort of fetal growth restricted placentas. Of the 10 SNPs assessed we confirmed the presence of 6 in FGR, and identified an additional previously unidentified SNP, and detected 3 nucleotide deletions across numerous components of the electron transport chain. This analysis identified 5 mutations within genes that encode complex I. Subsequent analysis of the gene and proteins that correspond to complex I mutations was performed using PCR, proteomics, and western blotting. Notably, we identified significant downregulation of NDUFA6 at the gene and protein level in FGR, lower protein levels of NDUFS3 and NDUFS6, and confirmed the largest log2 fold change identified in NDUFS6 by western blot. Subsequent investigation of mitochondrial respiratory capacity identified decreased ATP-linked respiration in FGR using Seahorse XF Analysis. ConclusionOur results identify that there is an inheritable contribution of SNPs within the maternal and paternal nuclear genome in fetal growth restriction. These SNPs alter gene expression and protein abundance of mitochondrial complex I components, impacting structural assembly and subsequent bioenergetic function within the placenta. Collectively these findings suggest that SNPs that affect mitochondrial assembly and function are associated with low birthweight and fetal growth restriction.

developmental biology↗

bioRxiv2025

Placental Iron Utilisation in Fetal Growth Restriction: Alterations in Mitochondrial Heme Synthesis and Iron-Sulfur Cluster Assembly Pathways

Fetal growth restriction (FGR) affects [~]10% of pregnancies worldwide and is often associated with placental insufficiency. Iron is essential for maternal haematopoietic adaptations and placental processes such as mitochondrial iron-sulfur (Fe-S) cluster assembly, heme synthesis, and erythropoiesis. This study aimed to characterise iron transport and downstream utilisation in FGR. Placental tissues from term uncomplicated (n=19) and FGR (n=18) pregnancies were analysed. Maternal iron status was retrospectively assessed from clinical records. Placental mRNA and protein expression of iron-dependent pathways were analysed via RT-qPCR, LC-MS, and western blotting. Placental iron content was assessed histologically, and heme levels were measured by activity assay. FGR pregnancies showed significantly elevated maternal serum ferritin and lower red cell distribution width, although remained within normal clinical values. Placental iron uptake transporters TFRC and DMT1 were significantly upregulated, while the iron exporter to the fetus, ferroportin, was reduced, indicating increased iron retention in the FGR placenta. Despite altered transporter expression, Fe3 iron levels were unchanged, suggesting iron utilisation over storage. Subsequent investigations identified reduced mitochondrial Fe-S synthesis components (FDXR, FDX2, NDUFAB1, HSPA9), and a prioritisation of mitochondrial and cytosolic heme synthesis enzymes in FGR. Protein levels of haemoglobin subunits (HBG1, HBG2, HBB, HBA1) and erythrocyte membrane markers (EPB41, EPB42, SPTA1, SPTB, ANK1) were decreased. These findings reveal a compensatory response in FGR placentae, with increased iron uptake and utilisation favouring heme synthesis over Fe-S cluster formation, possibly to support oxygen handling under poor placental vascularisation and reduced fetal oxygenation, with potential consequences for mitochondrial energy metabolism. Key PointsO_LIIron plays a critical role in placental function, while iron-dependent pathway components are well-characterised, their integrated response and adaptive reprogramming in fetal growth restriction (FGR) remain poorly understood. C_LIO_LIIn FGR, maternal iron status was unchanged, however, placental iron uptake proteins were increased and ferroportin reduced, suggesting that the placenta retains iron. C_LIO_LIFGR placentae showed altered de novo mitochondrial iron-sulfur cluster (Fe-S) formation and a bottleneck in late-stage Fe-S cluster assembly. C_LIO_LIThis shift in Fe-S synthesis prioritises mitochondrial and cytosolic heme synthesis pathways, consistent with increased heme utilisation and breakdown. C_LIO_LIGlobin subunits were lower in protein abundance and impaired placental erythrocyte structure in FGR. C_LIO_LIDysregulation of erythrocyte membrane proteins in FGR placentae suggests altered erythrocyte structure, potentially representing an adaptive response to inadequate vascularisation, attempting to optimise oxygen delivery to the fetus. C_LI

physiology↗

bioRxiv2025

Electron tomography reveals mitochondrial network and cristae remodelling during cell differentiation in the human placenta

Mitochondria adapt their structure through fusion and fission, yet how their morphology and cristae architecture alter as cells differentiate remains unclear. The human placenta is an ideal model for studying mitochondrial diversity within a single tissue. As epithelial trophoblast cells of the placenta differentiate, their accompanying mitochondria morphologically and functionally transform. We used array tomography to characterise mitochondrial volume and network complexity. Cryo-electron tomography revealed two distinct subpopulations of mitochondria within progenitor cytotrophoblasts, and a singular, homogeneous population in the differentiated syncytiotrophoblast. We showcased the 3D topology of individual cristae through a standardised metric of "curvedness". Proteomic analysis of isolated mitochondria identified reduced dynamics proteins and cristae organisation complexes, accompanied by subunit variations within the electron transport chain, ATP synthase, and altered supercomplex abundance. This study highlights the advantages of combining multimodal imaging with mechanistic insights, to elucidate the process of mitochondrial morphology and cristae architecture remodelling as cells differentiate.

cell biology↗