bims-smemid 2025-06-22 papers

Cell Metab. 2025 Jun 12. pii: S1550-4131(25)00266-9. [Epub ahead of print]

The integrated stress response fine-tunes stem cell fate decisions upon serine deprivation and tissue injury.

Epidermal stem cells produce the skin's barrier that excludes pathogens and prevents dehydration. Hair follicle stem cells (HFSCs) are dedicated to bursts of hair regeneration, but upon injury, they can also reconstruct, and thereafter maintain, the overlying epidermis. How HFSCs balance these fate choices to restore physiologic function to damaged tissue remains poorly understood. Here, we uncover serine as an unconventional, non-essential amino acid that impacts this process. When dietary serine dips, endogenous biosynthesis in HFSCs fails to meet demands (and vice versa), slowing hair cycle entry. Serine deprivation also alters wound repair, further delaying hair regeneration while accelerating re-epithelialization kinetics. Mechanistically, we show that HFSCs sense each fitness challenge by triggering the integrated stress response, which acts as a rheostat of epidermal-HF identity. As stress levels rise, skin barrier restoration kinetics accelerate while hair growth is delayed. Our findings offer potential for dietary and pharmacological intervention to accelerate wound healing.

Keywords: dietary intervention; epidermal stem cells; fate selection; hair follicle stem cells; hair regrowth; integrated stress response; serine metabolism; tissue regeneration; tissue repair; wound healing

DOI: https://doi.org/10.1016/j.cmet.2025.05.010

Redox Biol. 2025 Jun 09. pii: S2213-2317(25)00228-9. [Epub ahead of print]85 103715

Regulation of redox homeostasis by ATF4-MTHFD2 axis during white adipose tissue browning.

Rehna Paula Ginting, Hoang-Anh Pham-Bui, Choijamts Munkhzul, Siti Aisyah Fuad, Ahyeon Son, Jong-Seok Moon, Jaeseok Han, Mihye Lee, Min-Woo Lee.

Maintaining redox balance is crucial for mitochondrial homeostasis. During browning of white adipocytes, both the quality and quantity of mitochondria undergo dramatic changes. However, the mechanisms controlling the redox balance in the mitochondria during this process remain unclear. In this study, we demonstrate that thermogenic activation occurs before mitochondrial biogenesis during cold-induced browning of inguinal white adipose tissue (iWAT) and is accompanied by increased mitochondrial stress and integrated stress response (ISR) signaling. Specifically, cold exposure enhances the expression of ATF4, an ISR effector. Adipocyte-specific deletion of ATF4 results in increased energy expenditure, but paradoxically leads to a lower core body temperature, and heightened pro-inflammation in iWAT after cold exposure, which is restored by the antioxidant, MitoQ. Mechanistically, ATF4 regulates the redox balance through MTHFD2, an enzyme involved in mitochondrial redox homeostasis by NADPH generation. Cold exposure upregulates MTHFD2 expression in an ATF4-dependent manner, and its inhibition by DS18561882 in vivo leads to impaired cold-induced mitochondrial respiration similar to the effects of ATF4 loss. These findings suggest that ATF4 is essential for redox balance via MTHFD2, thereby affecting tissue homeostasis during iWAT browning.

DOI: https://doi.org/10.1016/j.redox.2025.103715

EMBO J. 2025 Jun 16.

Dysfunctional mitochondria trap proteins in the intermembrane space.

Tamara Flohr, Markus Räschle, Johannes M Herrmann.

The accumulation of mitochondrial precursor proteins in the cytosol due to mitochondrial dysfunction compromises cellular proteostasis and is a hallmark of diseases. Why non-imported precursors are toxic and how eukaryotic cells prevent their accumulation in the cytosol is still poorly understood. Using a proximity labeling-based assay to globally monitor the intramitochondrial location of proteins, we show that, upon mitochondrial dysfunction, many mitochondrial matrix proteins are sequestered in the intermembrane space (IMS); something we refer to as "mitochondrial triage of precursor proteins" (MitoTraP). MitoTraP is not simply the result of a general translocation block at the level of the inner membrane, but specifically directs a subgroup of matrix proteins into the IMS, many of which are constituents of the mitochondrial ribosome. Using the mitoribosomal protein Mrp17 (bS6m) as a model, we found that IMS sequestration prevents its mistargeting to the nucleus, potentially averting interference with assembly of cytosolic ribosomes. Thus, MitoTraP represents a novel, so far unknown mechanism of the eukaryotic quality control system that protects the cellular proteome against the toxic effects of non-imported mitochondrial precursor proteins.

Keywords: Intermembrane Space; Mitochondria; Nucleolus; Protein Targeting; Ribosome

DOI: https://doi.org/10.1038/s44318-025-00486-1

Cell Rep. 2025 Jun 19. pii: S2211-1247(25)00659-X. [Epub ahead of print]44(7): 115888

Cold-inducible GOT1 activates the malate-aspartate shuttle in brown adipose tissue to support fuel preference for fatty acids.

Chul-Hong Park, Minsung Park, Miranda E Kelly, Helia Cheng, Sang Ryeul Lee, Cholsoon Jang, Ji Suk Chang.

Brown adipose tissue (BAT) simultaneously metabolizes fatty acids (FAs) and glucose under cold stress but favors FAs as the primary fuel for heat production. It remains unclear how BAT steers fuel preference toward FAs over glucose. Here, we show that the malate-aspartate shuttle (MAS) is activated by cold in BAT and plays a crucial role in promoting mitochondrial FA utilization. Mechanistically, cold stress selectively induces glutamic-oxaloacetic transaminase (GOT1), a key MAS enzyme, via the β-adrenergic receptor-PKA-PGC-1α axis. The increase in GOT1 activates MAS, transferring reducing equivalents from the cytosol to mitochondria. This process enhances FA oxidation in mitochondria while limiting glucose oxidation. In contrast, loss of MAS activity by GOT1 deficiency reduces FA oxidation, leading to increased glucose oxidation. Together, our work uncovers a unique regulatory mechanism and role for MAS in mitochondrial fuel selection and advances our understanding of how BAT maintains fuel preference for FAs under cold conditions.

Keywords: CP: Metabolism; GOT1; NADH shuttle; PGC-1α; brown adipocytes; fatty acid oxidation; glucose oxidation; glutamic oxaloacetic transaminase 1; glycolysis; malate-aspartate shuttle; mitochondrial thermogenesis

DOI: https://doi.org/10.1016/j.celrep.2025.115888