Possible Existence of Lysosome-Like Organella within Mitochondria and Its Role in Mitochondrial Quality Control

The accumulation of unhealthy mitochondria results in mitochondrial dysfunction, which has been implicated in aging, cancer, and a variety of degenerative diseases. However, the mechanism by which mitochondrial quality is regulated remains unclear. Here, we show that Mieap, a novel p53-inducible protein, induces intramitochondrial lysosome-like organella that plays a critical role in mitochondrial quality control. Mieap expression is directly regulated by p53 and is frequently lost in human cancer as result of DNA methylation. Mieap dramatically induces the accumulation of lysosomal proteins within mitochondria and mitochondrial acidic condition without destroying the mitochondrial structure (designated MALM, for Mieap-induced accumulation of lysosome-like organelles within mitochondria) in response to mitochondrial damage. MALM was not related to canonical autophagy. MALM is involved in the degradation of oxidized mitochondrial proteins, leading to increased ATP synthesis and decreased reactive oxygen species generation. These results suggest that Mieap induces intramitochondrial lysosome-like organella that plays a critical role in mitochondrial quality control by eliminating oxidized mitochondrial proteins. Cancer cells might accumulate unhealthy mitochondria due to p53 mutations and/or Mieap methylation, representing a potential cause of the Warburg effect

Apilimod Inhibits the Production of IL-12 and IL-23 and Reduces Dendritic Cell Infiltration in Psoriasis

Psoriasis is characterized by hyperplasia of the epidermis and infiltration of leukocytes into both the dermis and epidermis. IL-23, a key cytokine that induces TH17 cells, has been found to play a critical role in the pathogenesis of psoriasis. Apilimod is a small-molecule compound that selectively suppresses synthesis of IL-12 and IL-23. An open-label clinical study of oral administration of apilimod was conducted in patients with psoriasis. Substantial improvements in histology and clinical measurements were observed in patients receiving 70mg QD. The expression of IL-23p19 and IL-12/IL-23p40 in skin lesions was significantly reduced in this dose group, with a simultaneous increase in IL-10 observed. A decrease in the levels of TH1 and TH17 cytokines/chemokines in skin lesions followed these p19 and p40 changes. In parallel, a reduction in skin-infiltrating CD11c+ dendritic cells and CD3+ T cells was seen, with a greater decrease in the CD11c+ population. This was accompanied by increases in T and B cells, and decreases in neutrophils and eosinophils in the periphery. This study demonstrates the immunomodulatory activity of apilimod and provides clinical evidence supporting the inhibition of IL-12/IL-23 synthesis for the treatment of TH1- and TH17-mediated inflammatory diseases

Mieap, a p53-Inducible Protein, Controls Mitochondrial Quality by Repairing or Eliminating Unhealthy Mitochondria

Maintenance of healthy mitochondria prevents aging, cancer, and a variety of degenerative diseases that are due to the result of defective mitochondrial quality control (MQC). Recently, we discovered a novel mechanism for MQC, in which Mieap induces intramitochondrial lysosome-like organella that plays a critical role in the elimination of oxidized mitochondrial proteins (designated MALM for Mieap-induced accumulation of lysosome-like organelles within mitochondria). However, a large part of the mechanisms for MQC remains unknown. Here, we report additional mechanisms for Mieap-regulated MQC. Reactive oxygen species (ROS) scavengers completely inhibited MALM. A mitochondrial outer membrane protein NIX interacted with Mieap in a ROS-dependent manner via the BH3 domain of NIX and the coiled-coil domain of Mieap. Deficiency of NIX also completely impaired MALM. When MALM was inhibited, Mieap induced vacuole-like structures (designated as MIV for Mieap-induced vacuole), which engulfed and degraded the unhealthy mitochondria by accumulating lysosomes. The inactivation of p53 severely impaired both MALM and MIV generation, leading to accumulation of unhealthy mitochondria. These results suggest that (1) mitochondrial ROS and NIX are essential factors for MALM, (2) MIV is a novel mechanism for lysosomal degradation of mitochondria, and (3) the p53-Mieap pathway plays a pivotal role in MQC by repairing or eliminating unhealthy mitochondria via MALM or MIV generation, respectively

Cellular phenotype in normal controls and psoriasis patients before and after 70mg QD treatment.

<p>Whole blood cells from normal controls and psoriasis patients were analyzed by cytometry for the cellular phenotype. Results shown are the percentile ranges based on cell counts (cells/µL) of peripheral CD4⁺ T cells, CD8⁺ T cells, B cells, monocytes, eosinophils and neutrophils from normal controls (<i>n</i>  =  16) and psoriasis patients in 70mg QD cohort (<i>n</i>  =  12) at baseline (week 0) and week 12. Plot: bottom line, 10^th%; bottom box, 25^th%; top box, 75^th%; top line, 90^th%. *, <i>p</i> < 0.05; **, <i>p</i> <0.01; statistically significant differences between before (week 0) and after (week 12) 70mg QD apilimod treatment in psoriasis patients.</p

Histological improvement by apilimod treatment.

<p>Histology and immunohistochemistry of one patient (1046) showing improved histology and clinical measures (58%reduction in PASI score) at week 12 in the 70mg QD apilimod treated group. Skin biopsies from non-lesions (left) and lesions (middle) at baseline and lesion at week 12 (right) were stained with H&E, K16, anti-CD3 Ab, anti-CD11c Ab, or anti- IL-12p40 Ab. Cells staining positive for CD3, CD11c and IL-12p40 are indicated (arrows).</p

Clinical response based on assessment of skin biopsies and PASI and PGA.

<p>Clinical response based on assessment of skin biopsies and PASI and PGA.</p

Mean skin-infiltrating T cell and dendritic cell numbers.

1<p>Mean cell numbers of epidermal CD3⁺ (T cell) cells, dermal CD3⁺ cells, epidermal CD11c⁺ (dendritic cell) cells, and dermal CD11c⁺ cells per low-power field during treatment, with patients classified by response. There were 17 responders and 30 non-responders in the analysis.</p