Using Diffusion Maps to Analyze Reaction Dynamics for a Hydrogen Combustion Benchmark Dataset.

We use local diffusion maps to assess the quality of two types of collective variables (CVs) for a recently published hydrogen combustion benchmark dataset1 that contains ab initio molecular dynamics (MD) trajectories and normal modes along minimum energy paths. This approach was recently advocated in2 for assessing CVs and analyzing reactions modeled by classical MD simulations. We report the effectiveness of this approach to molecular systems modeled by quantum ab initio MD. In addition to assessing the quality of CVs, we also use global diffusion maps to perform committor analysis as proposed in.2 We show that the committor function obtained from the global diffusion map allows us to identify transition regions of interest in several hydrogen combustion reaction channels.

Using machine learning to go beyond potential energy surface benchmarking for chemical reactivity.

We train an equivariant machine learning (ML) model to predict energies and forces for hydrogen combustion under conditions of finite temperature and pressure. This challenging case for reactive chemistry illustrates that ML potential energy surfaces are difficult to make complete, due to overreliance on chemical intuition of what data are important for training. Instead, a 'negative design' data acquisition strategy using metadynamics as part of an active learning workflow helps to create a ML model that avoids unforeseen high-energy or unphysical energy configurations. This strategy more rapidly converges the potential energy surfaces such that it is now more efficient to make calls to the external ab initio source when query-by-committee models disagree to further molecular dynamics in time without need for ML retraining. With the hybrid ML-physics model we realize two orders of magnitude reduction in cost, allowing for prediction of the free-energy change in the transition-state mechanism for several hydrogen combustion reaction channels.

Glucocorticoids and their receptors: insights into specific roles in mitochondria.

Glucocorticoids (GCs) affect most physiological systems and are the most frequently used drugs for multiple disorders and organ transplantation. GC functions depend on a balance between circulating GC and cytoplasmic glucocorticoid receptor II (GR). Mitochondria individually enclose circular, double-stranded DNA that is expressed and replicated in response to nuclear-encoded factors imported from the cytoplasm. Fine-tuning and response to cellular demands should be coordinately regulated by the nucleus and mitochondria; thus mitochondrial-nuclear interaction is vital to optimal mitochondrial function. Elucidation of the direct and indirect effects of steroids, including GCs, on mitochondria is an important and emerging field of research. Mitochondria may also be under GC control because GRs are present in mitochondria, and glucocorticoid response elements (GREs) reside in the mitochondrial genome. Therefore, mitochondrial gene expression can be regulated by GCs via at least two different mechanisms: direct action on mitochondrial DNA and oxidative phosphorylation (OXPHOS) genes, or by an indirect effect through interaction with nuclear genes. In this review, we outline possible mechanisms of regulation of mitochondrial genes in response to GCs in view of translocation of the GR into mitochondria and the possible regulation of OXPHOS genes by GREs in the mitochondrial genome.

Autophagy deficiency leads to protection from obesity and insulin resistance by inducing Fgf21 as a mitokine.

Despite growing interest and a recent surge in papers, the role of autophagy in glucose and lipid metabolism is unclear. We produced mice with skeletal muscle-specific deletion of Atg7 (encoding autophagy-related 7). Unexpectedly, these mice showed decreased fat mass and were protected from diet-induced obesity and insulin resistance; this phenotype was accompanied by increased fatty acid oxidation and browning of white adipose tissue (WAT) owing to induction of fibroblast growth factor 21 (Fgf21). Mitochondrial dysfunction induced by autophagy deficiency increased Fgf21 expression through induction of Atf4, a master regulator of the integrated stress response. Mitochondrial respiratory chain inhibitors also induced Fgf21 in an Atf4-dependent manner. We also observed induction of Fgf21, resistance to diet-induced obesity and amelioration of insulin resistance in mice with autophagy deficiency in the liver, another insulin target tissue. These findings suggest that autophagy deficiency and subsequent mitochondrial dysfunction promote Fgf21 expression, a hormone we consequently term a 'mitokine', and together these processes promote protection from diet-induced obesity and insulin resistance.