Biology subjects

Hakam, S.

Publications and source records attributed to Hakam, S..

3 recordsLinked to original sources

bioRxiv2026

Ca2+ influx through ER-plasma membrane contacts is required for brown fat thermogenesis and metabolic health

Brown adipose tissue (BAT) exhibits exceptional metabolic plasticity, rapidly increasing energy expenditure to sustain thermogenesis during cold exposure. This high metabolic activity imposes substantial demands on cellular systems, requiring robust adaptive mechanisms to maintain homeostasis and prevent cellular stress. Yet, the pathways that support and coordinate these adaptive responses in brown adipocytes remain incompletely understood. Here, we identify a cold-induced adaptive program in BAT characterized by the formation of endoplasmic reticulum-plasma membrane (ER-PM) contact sites and the activation of store-operated calcium entry (SOCE), which is essential for maintaining brown adipocyte health during thermogenic activation. Cold exposure enhances ER-PM contacts and upregulates the expression of STIM and Orai proteins, key mediators of SOCE. Loss of STIM in brown adipocytes disrupts intracellular Ca{superscript 2} homeostasis and induces aberrant aggregation of ER membranes. STIM deficiency also impairs cold-induced mitochondrial fission resulting in hyperfused mitochondria with reduced oxidative capacity, independently of UCP1 abundance. Importantly, mice lacking STIM in BAT exhibit impaired lipid oxidation, are cold intolerant and develop exacerbated peripheral insulin resistance when challenged with a high-fat diet. Together, these findings identify ER-PM remodeling and STIM-mediated SOCE as a central regulator that links organelle architecture to brown adipocyte function and contributes to whole-body metabolic homeostasis.

cell biology↗

bioRxiv2025

Light and sex modify Snord116 genotype effects on metabolism, behavior, and imprinted gene networks following circadian entrainment

Mammals utilize imprinted and X-linked epigenetic mechanisms in development, metabolism, and behavior. Imprinted genes, including Prader-Willi syndrome Snord116 noncoding RNAs, are implicated in the regulation of sleep and circadian rhythms through poorly understood mechanisms. Utilizing mouse models of Snord116 deficiency and overexpression, we performed an integrated, sex-stratified analysis of free running behaviors, indirect calorimetry, and cortical transcriptomes following entrainment to a 22 hour light:dark T-cycle. We observed significant interactions of sex, entrainment, and Snord116 genotype in period length at baseline and after-effects of post-entrainment. Snord116 deletions effect on respiratory exchange ratio was light sensitive, with sex and entrainment effects dominant under total darkness. Snord116 genotype impacted both rhythmic and non-rhythmic cortical gene networks that integrated sex, light, and entrainment effects with genotype-phenotype correlations. A co-expressed gene network enriched for imprinted, Snord116-target, and Xist-proximal long noncoding RNAs was identified as a light-sensitive regulatory hub of sexual dimorphic responses to a dynamic environment.

animal behavior and cognition↗

bioRxiv2024

Females with autism spectrum disorders show stronger DNA methylation signatures than males in perinatal tissues

BackgroundAutism spectrum disorder (ASD) comprises a group of neurodevelopmental conditions currently diagnosed by behavioral assessment in childhood, although neuropathology begins during gestation. A poorly understood male bias for ASD diagnosis is thought to be due to both biological sex differences and cultural biases against female diagnosis of ASD. Identification of molecular biomarkers of ASD likelihood in newborns would provide more objective screening and early intervention. Epigenetic dysregulation has been reported in multiple tissues from newborns who are later diagnosed with ASD, but this is the first study to investigate sex-specific DNA methylation signatures for ASD in newborn blood, an accessible and widely banked tissue. MethodsDNA methylation was assayed from ASD and typically developing (TD) newborn blood (discovery set n = 196, replication set n = 90) using whole genome bisulfite sequencing (WGBS). Sex-stratified differentially methylated regions (DMRs) were assessed for replication, comparisons by sex, overlaps with DMRs from other tissues, and enrichment for biological processes and SFARI ASD-risk genes. ResultsWe found that newborn blood ASD DMRs from both sexes significantly replicated in an independent cohort and were enriched for hypomethylation in ASD compared to TD samples, as well as location in promoters, CpG islands and CpG shores. Comparing females and males, we found that most DMRs with sex differences amongst TD individuals were also found in ASD individuals, plus many additional DMRs with sex differences that were only found in those with ASD. Newborn blood DMRs from females were enriched for the X chromosome and both sexes showed significant overlap with DMRs from umbilical cord blood and placenta but not post-mortem cortex. DMRs from all tissues were enriched for neurodevelopmental processes (females) and SFARI ASD-risk genes (females and males). LimitationsThis study is primarily limited by sample sizes, particularly amongst females. ConclusionsOverall, we found a highly replicated sex-specific DNA methylation signature of ASD in newborn blood that showed support for the female protective effect and convergence with epigenetic and genetic signatures of ASD in newborns. These results demonstrate the utility of newborn blood in ASD screening and emphasizes the importance of sex-stratification in future studies.

genomics↗